EEE 34 Electrical Measurements Laboratory
Student Laboratory Manual © v2.0 December 2015
Electrical and Electronics Engineering Institute College of Engineering University of the Philippines – Diliman
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Table of Contents Table of Contents Contents .............................................................................................................................................................i List of Figures Figures .................................................................................................................................................................. iv Introduction Introduction ..................................................................................................................................................................... vi Course Syllabus Syllabus ............................................................................................................................................................. vii Class Policies Policies ................................................................................................................................................................... ix 1 Safety Practices in the Laboratory [1] .............................................................................................................. 1 1.1 Care in handling and use of a multimeter .................................................................................................. 1 1.2 Laboratory Rules and Regulations ................................................................................................................ 2 2 Laboratory Equipment, Tools and Components ....................................................................................... Components ....................................................................................... 3 2.1 Laboratory Equipment ....................................................................................................................................... 3 2.1.1 Power Supply ................................................................................................................................................. 5 2.1.2 Function/Signal Generator ...................................................................................................................... 8 2.1.3 Analog Oscilloscope ................................................................................................................................. 10 2.1.4 Digital Oscilloscope .................................................................................................................................. 12 2.1.5 Equipment Calibration ........................................................................................................................... 13 2.2 Laboratory Components ................................................................................................................................. 14 2.2.1 Passive Components ................................................................................................................................ 14 2.2.1.1 Resistors ............................................................................................................................................... 14 Resistor Value Reading ............................................................................................................................ 15 Potentiometer .............................................................................................................................................. 16 2.2.1.2 Capacitors ............................................................................................................................................ 17 2.2.1.3 Inductors .............................................................................................................................................. 18 2.2.2 Active Components .................................................................................................................................. 19 2.3 Laboratory Tools ............................................................................................................................................... 20 2.3.1 Multimeter ................................................................................................................................................... 20 2.3.1.1 Analog Multimeter ........................................................................................................................... 21 Using the Multimeter to Measure Voltage, Current and Resistance ..................................... 22 Zero-ing the Meter Scale ......................................................................................................................... 24 Connectivity/Continuity Test ................................................................................................................ 24 2.3.1.2
Digital Multimeter ....................................................................................................................... 25
.............................................................................. 27 2.3.2 D’Arsonval Galvanometer or 1mA Movement .............................................................................. 2.3.3 Protoboard/Breadboard ........................................................................................................................ 28 2.3.3.1 Protoboard Wiring ........................................................................................................................... 29 2.3.3.2 Debugging/Troubleshooting Circuits [11] ............................................................................... 30
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Table of Contents Table of Contents Contents .............................................................................................................................................................i List of Figures Figures .................................................................................................................................................................. iv Introduction Introduction ..................................................................................................................................................................... vi Course Syllabus Syllabus ............................................................................................................................................................. vii Class Policies Policies ................................................................................................................................................................... ix 1 Safety Practices in the Laboratory [1] .............................................................................................................. 1 1.1 Care in handling and use of a multimeter .................................................................................................. 1 1.2 Laboratory Rules and Regulations ................................................................................................................ 2 2 Laboratory Equipment, Tools and Components ....................................................................................... Components ....................................................................................... 3 2.1 Laboratory Equipment ....................................................................................................................................... 3 2.1.1 Power Supply ................................................................................................................................................. 5 2.1.2 Function/Signal Generator ...................................................................................................................... 8 2.1.3 Analog Oscilloscope ................................................................................................................................. 10 2.1.4 Digital Oscilloscope .................................................................................................................................. 12 2.1.5 Equipment Calibration ........................................................................................................................... 13 2.2 Laboratory Components ................................................................................................................................. 14 2.2.1 Passive Components ................................................................................................................................ 14 2.2.1.1 Resistors ............................................................................................................................................... 14 Resistor Value Reading ............................................................................................................................ 15 Potentiometer .............................................................................................................................................. 16 2.2.1.2 Capacitors ............................................................................................................................................ 17 2.2.1.3 Inductors .............................................................................................................................................. 18 2.2.2 Active Components .................................................................................................................................. 19 2.3 Laboratory Tools ............................................................................................................................................... 20 2.3.1 Multimeter ................................................................................................................................................... 20 2.3.1.1 Analog Multimeter ........................................................................................................................... 21 Using the Multimeter to Measure Voltage, Current and Resistance ..................................... 22 Zero-ing the Meter Scale ......................................................................................................................... 24 Connectivity/Continuity Test ................................................................................................................ 24 2.3.1.2
Digital Multimeter ....................................................................................................................... 25
.............................................................................. 27 2.3.2 D’Arsonval Galvanometer or 1mA Movement .............................................................................. 2.3.3 Protoboard/Breadboard ........................................................................................................................ 28 2.3.3.1 Protoboard Wiring ........................................................................................................................... 29 2.3.3.2 Debugging/Troubleshooting Circuits [11] ............................................................................... 30
ii 3 Electrical Measurements Measurements .................................................................................................................................... 32 3.1 Theory and Practice ......................................................................................................................................... 33 3.2 Error and Linearity ........................................................................................................................................... 34 3.2.1 Error ............................................................................................................................................................... 34 3.2.2 Linearity........................................................................................................................................................ 34 3.3 Accuracy and Precision ................................................................................................................................... 36 3.4 Circuit-Level Analysis of the Multimeter ................................................................................................. 37 3.4.1 Practical Power Supply ........................................................................................................................... 37 3.4.2 Characteristic of the 1mA movement Galvanometer Scale ..................................................... 38 3.4.3 DC Ammeter ................................................................................................................................................ 39 3.4.4 DC Voltmeter............................................................................................................................................... 41 3.4.5 Ohmmeter .................................................................................................................................................... 43 4 Experiments Experiments ............................................................................................................................................................... 45 Experiment 0: Basic Measurements ................................................................................................................. 47 Experiment 1: Debugging Circuits ..................................................................................................................... 52 Experiment 2: DC Measurements (Current) .................................................................................................. 57 Experiment 3: DC Measurements (Voltage) .................................................................................................. 61 Experiment 4: Resistance Measurements ...................................................................................................... 66 Experiment 5-a: Introduction to Oscilloscopes (Analog) ........................................... ..................... ........................................... .............................. ......... 71 Experiment 5-d: Introduction to Oscilloscopes (Digital) ......................................................................... 79 Experiment 6: AC Detection – Diodes .............................................................................................................. 87 Experiment 7: AC Analysis – RLC Circuits ...................................................................................................... 94 Experiment 8: Transducers and Operational Amplifiers ......................................................................... 98 5 Documentation ....................................................................................................................................................... Documentation ....................................................................................................................................................... 101 5.1 Documentation Guidelines .......................................................................................................................... 101 5.1.1 Technical Development ........................................................................................................................ 101 5.1.2 Paper Format and Appearance ......................................................................................................... 101 5.2 Online Submission Guidelines.................................................................................................................... 102 6 Project ......................................................................................................................................................................... 103 6.1 Project Guidelines ........................................................................................................................................... 103 6.1.1 Project Proposal ...................................................................................................................................... 103 6.1.2 Project Testing and Construction ............................................ ...................... ............................................ ............................................ ................................... ............. 104 6.1.3 Project Documentation ......................................................................................................................... 104 6.1.4 Project Presentation .............................................................................................................................. 104 6.1.5 Criteria for Grading ................................................................................................................................ 105 6.2 Frequently Asked Questions (FAQs) ....................................................................................................... 105 References References .................................................................................................................................................................... 107
iii Appendix A: Sample IEEE Paper for A4 Page Size ......................................................................................... 109 Appendix B: Some Notes from Transducer Datasheets ............................................................................... 110 Appendix C: Some Notes from Operational Amplifier (Op-Amp) Datasheets .................................... 112 Appendix D: Available Components in Instruments Room*...................................................................... 113
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List of Figures Figure 1. Connecting wires ........................................................................................................................................... 3 Figure 2. Alligator clips .................................................................................................................................................. 4 Figure 3. Controlled-voltage supply (left) and controlled-current supply (right) modes. ........... ..... 5 Figure 4. Controlled-voltage supply mode with 8.8V used to power-up a simple circuit. ................. 6 Figure 5. Triple output power supply unit (PSU). ............................................................................................... 6 Figure 6. Programmable DC Power Supply (Triple Output)........................................................................... 7 Figure 7. Sig-gen set at 1.0001kHz and 10Vpeak-to-peak (Vpp) level. ...................................................... 8 Figure 8. Sig-gen probe. The circuit-end are red and black alligator clips while the sig-gen end is a BNC connector. ............................................................................................................................................................... 8 Figure 9. Analog oscilloscope self-calibration using built-in 2Vpp 1kHz square-wave signal. ..... 10 Figure 10. Oscilloscope probes. ............................................................................................................................... 11 Figure 11. Digital Oscilloscope ................................................................................................................................. 12 Figure 12. Resistor types based on composition material and tolerance level. [5] ....................... .... 14 Figure 13. Resistor Color Code. [5] ........................................................................................................................ 15 Figure 14. Potentiometer: actual (left), electrical model (middle) and usual electrical symbols (right). [6] ......................................................................................................................................................................... 16 Figure 15. Different types of capacitors, both non-polar and polar. [7] ................................................. 17 Figure 16. . Ceramic capacitor value reading. [8] ............................................................................................. 18 Figure 17. Different types of inductors. [9] ........................................................................................................ 18 Figure 18. Analog multimeters. ............................................................................................................................... 21 Figure 19. Analog multimeter selector knob. [2] ............................................................................................. 22 Figure 20. Analog multimeter calibration scale. [3] ........................................................................................ 23 Figure 21. Zero-ing the meter scale. [4] ............................................................................................................... 24 Figure 22. Hand-held digital multimeters. .......................................................................................................... 25 Figure 23. Bench digital multimeter. ..................................................................................................................... 26 Figure 24. 1mA movement. ....................................................................................................................................... 27 Figure 25. Protoboard. [10] ....................................................................................................................................... 28 Figure 26. Protoboard wiring of two complex circuits: messy wiring (left) and clean wiring (right). [10] ...................................................................................................................................................................... 29 Figure 27. PHD Comics: Debugging. [12] ............................................................................................................. 31 Figure 28. (a) Simple resistive circuit, (b) ideal voltmeter, and (c) practical voltmeter ................. 33 Figure 29. Input-output relationship showing linearity. .............................................................................. 34 Figure 30. Difference between accuracy and precision. [13] ...................................................................... 36 Figure 31. Practical voltage source (left) and practical current source (right). [14] ........................ 37 Figure 32. 1mA movement inside structure (left) and its electrical symbol (right). [15] ............... 38 Figure 33. Measuring current using the galvanometer as the ammeter. ............................................... 39 Figure 34. Extending the range of the ammeter. .............................................................................................. 40 Figure 35. DC Voltmeter structure using 1mA movement. .......................................................................... 41 Figure 36. Measuring voltage using the galvanometer with a series resistor as the voltmeter. .. 41 Figure 37. Ohmmeter structure using 1mA movement. ................................................................................ 43 Figure 38. Measuring the resistance of an unknown resistor using analog ohmmeter. .................. 44 Figure B. 1. Typical response curve – temperature versus resistance of UEI447 NTC Thermistor. ............................................................................................................................................................................................. 110 Figure B. 2. Basic Centigrade temperature sensor . ................................................ 111 Figure B. 3. Resistance as a function of illumination. ................................................................................... 111
2℃ 150℃
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Figure C. 1. LM741 operational amplifier pin-outs. ...................................................................................... 112 Figure C. 2. LF353 operational amplifier pin-outs......................................................................................... 112
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Introduction Taking electrical measurements is an essential skill that every engineer must learn and master. Without it, we will not know how to evaluate and improve thi ngs. This is an essential part that somehow shapes the kind of technology we have today – further on what it would be like tomorrow. However, taking electrical measurements is not a simple read-and-record task. This skill requires that a student must be able to determine (and hence apply): a. what kind of measurements or experiments are best suited for a particular application; b. which tool or set of tools are essential to accomplish such task; c. how to analyze, verify, and interpret or ‘make-sense’ of the acquired data, and; d. how to properly report data such that others can understand them without vagueness, ambiguity and/or confusion. EEE 34 (Electrical Measurements Laboratory) is the gateway of students in familiarizing with the common equipment, components, and tools being used in EEE instructional laboratories – while observing safety practices. The main goal of the course is to provide students a further understanding of the theoretical concepts gained in EEE 31 (Introduction to Electrical and Electronics Engineering) and currently learning in EEE 33 (Electric Circuit Theory) by implementing actual circuits and investigating the practical issues in measurements through hands-on experiments. This student laboratory manual aims to provide the students (as well as laboratory instructors) a complete, uniform and coherent document in achieving the course goals and objectives. This will also give laboratory instructors more time to focus in teaching and guiding the students with the hands-on rather than providing the “offline” knowledge. The delivery of the content, however, still depends on the prerogative of the instructor. In summary, this manual aims to present EEE 34 in an efficient and effective way. My sincerest gratitude to Siegfred Balon, Adrian Salces, and previous & current EEE 34 instructors whose work built the foundation of, and hence further improved, this course; to Jaybie de Guzman for bringing up the concept of writing this laboratory manual – and in his contribution in providing some of the content. Finally, I wish to thank my past EEE 34 students for inspiring me to write this laboratory manual.
Engr. Patth Rick L. Ramirez Electrical and Electronics Engineering Institute University of the Philippines – Diliman
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Course Syllabus EEE 34 – Electrical Measurements Laboratory I.
Credits 1.0 unit laboratory
II.
Prerequisites / Co-requisites EEE 31 (prerequisite), EEE 33 (co-requisite)
III.
Schedule 1 meeting/week, 3 hours/meeting
IV.
Course Description Laboratory procedures and practice, data collection and analysis, laboratory documentation, standard electric instruments and circuits, basic electric circuit behaviour, transducers.
V.
Course Goals a. b. c. d.
VI.
Course Objectives a. b. c. d.
VII.
1
2-3
4
Set-up and characterize simple electrical circuits and electrical measurement systems. Describe the behaviour of a circuit as electrical characteristics of an electrical component or transducer are changed. Demonstrate safe and proper laboratory skills and create properly formatted and meaningful laboratory documentation Incorporate the use of electrical measurement equipment in the analysis and characterization of simple electrical circuits.
Course Schedule and Content
Session #
0
To understand concepts and practical issues in electrical measurement To gain knowledge of the operation and interaction of various electric components and transducers in electrical circuits and measurement systems. To develop skills in proper laboratory procedures and practice, data collection and analysis, and laboratory documentation To familiarize the use of analog and digital electrical measurement equipment such as oscilloscopes, multimeters and signal generators
Session objectives Clarify class policies and note important ideas about the course; demonstrate proper use of laboratory facilities and equipment; Emphasize safety practice in the laboratory Introduce passive components used in EEE – resistors, capacitors and inductors. Perform basic electrical measurements Perform different methods of making DC voltage and current measurement; identify when each method is applicable; specify the degree of accuracy of any measurement made and identify the main causes of error. Perform different methods of measuring resistance; identify when each method is applicable; S pecify the degree of accuracy of any measurement made and identify the main causes of error.
Topic Syllabus Discussion, Laboratory equipment procedures and practice, Safety Quiz Electronic component value reading, Basic Electrical Measurements DC Measurements
Resistance Measurements
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Assess basic laboratory, instrumentation and measurement skills; review and apply learned concepts and skills from the first two experiments. Describe the operation of a triggered sweep oscilloscope; make basic measurements using an oscilloscope; specify the degree of accuracy of any measurement made and identify the main causes of error. Experimentally determine the voltage across a conducting diode; explain concepts involved in making peak and RMS voltage measurements of AC signals; account errors introduced by non- ideal characteristics of the diode on the measurements made. Review and apply learned concepts and skills from the experiments 3 and 4. Perform measurements using the basic and advanced features of digital instrumentation and measurement equipment; enumerate the benefits and drawbacks of digital measurement equipment as compared to analog measurement equipment. Determine the inductance or capacitance of a device using input-output time-domain waveforms; specify the degree of accuracy of identify the main causes of error. Describe the operation and electrical characteristics of commonly-used transducers and sensors; perform measurements using transducers, sensors and electrical measurement circuits; account errors introduced by non-ideal characteristics of the transducers and sensors on the measurements made.
6-7
8-9
10 11
12
13
14-15 16
VIII.
AC Measurements (Power, RMS, Peak-to-peak Voltage, Phasor, Power factor)
2nd Practical Exam (for topics covered in meetings 6-9) Digital Instrumentation (Signal Generator, Digital Multimeter)
Inductance and Capacitance Measurements
Transducers and sensors
References
Larry D. Jones & A. Foster Chin, Electronic Instruments and Measurements, 2nd Edition, Prentice-Hall, 1991. Joseph Carr, Elements of Electronic Instrumentation and Measurements, 3rd Edition, Prentice-Hall, 1996. Albert D. Helfrick and William D. Cooper. Modern Electronic Instrumentation and Measurement Techniques, 2nd Edition, Prentice-Hall, 1990. Alan S. Morris, Principles of Measurement and Instrumentation, 2nd Edition, PrenticeHall, 1993.
Requirements Safety and Work Ethics Laboratory Reports Practical Exams Project
X.
Oscilloscope Fundamentals
Transducer Project Project Presentation
IX.
1st Practical Exam (For topics covered in meetings 1 to 4)
10% 45% 30% 15%
Grading System [100,92] (92,88] (88,84] (84,80] (80,76]
1.00 1.25 1.50 1.75 2.00
(72,68] (68,64] (64,60] (60,0]
2.50 2.75 3.00 5.00 No 4.00 nor INC.
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Class Policies Laboratory Instructor Name: Office Room: Email Address: Consultation Hours:
The following may change depending on the prerogative of respective laboratory instructor: a. For every laboratory task, a student must form/join a group (maximum of 3 depending on available workstations). Groupings (either random or choose-your-own) may vary from task to task. It is the responsibility of the student to acquaint with his/her group-mates at the start of every experiment. UP students are expected to be versatile and thus can work with all kind of team-mates. b. Pre-Laboratory (“Pre-Lab” ) report must be submitted in class before any corresponding experiment. Separate Pre-Lab sheets are available in this manual. A student will NOT be allowed to do the experiment in failure to submit the Pre-Lab report. Copied work is intellectual dishonesty and will never be accepted. c. Each group* must submit a laboratory report ( “Post-Lab” ) that summarizes the experiment and answers the guide questions in the experiment through the results obtained. Further observation and in-depth analysis will earn additional merit. The laboratory report must be submitted ‘in-print’ (not necessarily coloured) two weeks after the experiment (due 30 minutes from official start of class). Late papers will automatically receive a zero grade. The Post-Lab report must be in IEEE paper format (a sample template is given in Appendix B). d. For any submitted report, never forget to cite reference/s if there is/are any. Failure to properly document and acknowledge an existing work is co nsidered intellectual malpractice. e. Student/s arriving 30 minutes late will be considered absent and will receive no grade for the laboratory reports on the experiment for that day. However, for the love of learning, he/she/they can still join his/her/their group-mates in performing the experiment. No make-up class for unexcused absence/s. f. Student/s incurring more than three (3) absences will be advised to drop the course or will be given a failing grade if the dropping period has lapsed. g. Work ethics inside the laboratory must be observed. No phones or gadgets. However, they can be used shortly for documentation purposes. Clean up your workplace when don e. Make sure to turn off all equipment and measuring tools/devices before leaving. Components used must be returned properly. h. Class standing will be available online at the middle of the semester. i. In case of a class suspension, wait for announcements from the laboratory instructor regarding deadlines and how the schedule of activities will be changed. Also, inform the laboratory instructor for schedule conflicts (esp. Monday classes) with scheduled departmental exams as early as possible. j. All students should be aware of the safety practices, as well as the rules and regulations, imposed in the laboratory. These are available in the succeeding sections. Initial requirements: 1. Join our Facebook group/UVLe section with name _____________ and passkey ______________. Announcements and other broadcast message will be posted here. 2. Accomplish a softcopy version of the traditional student index card – the Student Information Card (SIC). A sample template with guidelines can be found in our online group. *Grading of course requirements to be submitted by group is INDEPENDENT of any issue internal to the group concerned (e.g. student A did not participate preparing this/that, student B is going to be late but the final report is with him/her, etc.). Although a portion of grade is evaluated per group, the majority still is individual assessment.
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1 Safety Practices in the Laboratory [1] Safety is always the biggest concern when working in a laboratory, particularly when dealing with electricity. This concern covers not only valuable research work and equipment, but extends to the lives of the people as well. More often than not, accidents happen due to carelessness and improper handling or use of equipment. Most accidents can be avoided through proper safety precautions and common sense. Here are a few of them. 1. 2. 3. 4.
Do NOT touch anything that you are unfamiliar with. Follow instructions. They are there for a reason. Be careful and do NOT hurry. Always watch where you are going and what you come into contact with. Do NOT eat or drink in the laboratory. (NO FOOD or DRINKS allowed inside the lab) You do not want to ingest small parts, potentially hazardous chemicals, and other materials. Spills can also cause equipment and electrical wiring to short circuit and catch fire. 5. Wear proper clothing. It is advisable to wear closed rubber shoes to avoid body contact to ground when dealing with electricity. Those who wear contact lenses may be more sensitive to the fumes and heat. 6. Do NOT work on electrical equipment when you are completely alone and never work on “live” equipment when you are tired. 7. Unless it is impossible to avoid, do not work on live circuits. Always unplug/turn off devices before working on them. If you are working on wiring, turn off all power. Turn off the circuit breaker or fuse - or master switch, if necessary - and make sure power cannot be restored accidentally. 8. Never touch electrical equipment while standing on a damp or metal floor. Also, never handle electrical equipment when you or the equipment is wet or damp. 9. Ground all high-voltage points - remember, a capacitor can store a charge that can kill you. Do NOT handle electrical equipment that is not grounded and never remove equipment grounds. 10. Above all, communicate. Do not be afraid to ask questions if you are not sure about what you are doing. A lot of damage can result from incorrect procedures. Also, report anything out of the ordinary, particularly frayed wires, excessive heating, sparks, and smoke that can lead to a potentially dangerous situation. Remember, it is better to be safe than sorry. Additional Precautions: 1. 2.
3. 4. 5.
DO NOT TOUCH the power plugs connecting the table outlets to the floor outlets – doing so risks being subjected to an electric shock, and possibly death. Take note of the limitations of the instruments and components (power, current, or voltage). Make sure that you do not subject components and instruments to values of voltage and currents that can destroy them. When measuring voltage, it is good practice to use just one hand. Just clip one terminal to one node and hold the other at the insulated part of the test probe, NEVER on the metal tip. In measuring current, shut power off before breaking the circuit. Insert the ammeter before turning the power on. Report damages as soon as possible.
1.1 Care in handling and use of a multimeter Before inserting the meter into the circuit be certain that: The meter switch or switches have been set to the proper measurement function. The meter switch or switches have been first set to the highest voltage or current range in measuring an unknown voltage or current. This will reduce the possibility of meter overload and damage. The meter test leads have been plugged into the proper test jacks. The polarity is being observed in measuring voltage or current. Power is disconnected before resistance is measured in the circuit In measuring current, the circuit has been broken so that the meter may be inserted in series with the circuit The voltage or current to be measured does not exceed the range or capabilities of the meter. WARNING: Do not allow the meter to be connected for a prolonged time when the needle goes to the left of zero or beyond the full-scale deflection.
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1.2 Laboratory Rules and Regulations (Approved by the UP-EEEI Faculty-in-charge of ALab/BELab as of December 2015 ) 1. Students are expected to conduct themselves in a professional and courteous manner when inside the laboratory. 2. DO NOT BRING IN any fluid or flammable/explosive materials inside the laboratory. 3. Food and drinks are not allowed inside the laboratory. 4. Bags and other personal items must be placed in designated areas during laboratory classes. 5. Floor, wall and table electrical outlets in the laboratory should be used and handled carefully. Report any damaged or broken utility outlets. 6. Be aware of power ratings, current and voltage requirements, warnings, and special instructions on each laboratory exercises. 7. VANDALISM is not tolerated. This includes removal of equipment tags & labels, writing on walls, cabinets, tables, chairs etc. 8. A student shall be held liable for equipment or damaged due to abuse, misuse, negligence, or disregard of basic electronics know-how. Ignorance of proper equipment handling shall not be accepted as an excuse. Replacement or repair expenses shall be demanded to liable student who inflicted damaged to UP Property. 9. As in the case of loss or broken electronic components, students are held responsible to replace the items. 10. Equipment that is not yet/anymore in use should be turned off and/or unplugged. 11. Laboratory equipment may not be taken elsewhere. All laboratory work done with ALab/BELab equipment should be done inside the ALab/BELab. 12. CLEANLINESS and ORDERLINESS of the laboratory should always be maintained. Students are expected to clean up their work areas after the class and throw away waste materials in the trash bins provided. 13. Non-students and other students not enrolled in a class are not allowed inside the laboratory 14. Students with laboratory classes at other time slots may join a laboratory class with the consent of the instructor holding the class. The first priority to use the Laboratory is given to students who are in regularly scheduled class. 15. Students may not use the laboratory equipment/room without the supervision of his/her instructor or permission from the laboratory faculty-in-charge/technician. 16. Only UP ID will be accepted in borrowing laboratory equipment and components. Students who fail to return the equipment /components on time will not be allowed to borrow again.
Violation of the aforementioned rules and regulations shall be met with punishments ranging from, but not limited to grade deductions, a failing grade, suspension or expulsion from the university or a combination thereof. Replacement of damaged equipment or other properties shall also be demanded of the violator.
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2 Laboratory Equipment, Tools and Components This chapter gives the student a quick overview on the common equipment, tools, and components being used in EEE laboratories. The goal of this chapter is for students to gain familiarity on how these things work and look like. However, the operation and proper usage should be demonstrated in class. The tools and equipment include the multimeters, power supplies, function or signal generator, oscilloscope, 1mA movement and the protoboard. Note however that the images shown here might not be the same actual tools or equipment that we are going to use in our laboratory (a different brand or version might be available). Nonetheless, their usage and operation should be similar.
2.1 Laboratory Equipment Laboratory equipment are electronic apparatus which are intended for specific purpose or application. These are bench-type apparatus that should stay on the station where these are designated. The cost for each ranges from tens to hundreds of thousand PHP that is why safe and proper usage must always be observed. In EEE laboratories, we can find various laboratory equipment depending on the work or needs of such respective laboratories. For EEE 34, we will use the (a) power supply, (b) function/signal generator, and (c) oscilloscopes. The power supply, as the name implies, generates or supplies power (usually DC) to the circuit to be connected to it. The function/signal generator, on the other hand, also supplies power but in AC form. Lastly, oscilloscopes are used to capture and display signals, usually AC signals and in ti me-domain analysis. Before we proceed with the discussion, it is useful to become clear on the types of connectors we will commonly use. Shown in Figure 1 are connecting wires – the simplest and quickest way to connect components and circuits. These are basically conducting wires, usually of made up of cheap metal, wrapped with coloured insulator. The use of colors helps in defining nodes, as it conveniently applies to all, in co nstructing circuits.
Figure 1. Connecting wires
4 Another common connectors are called alligator clips, shown in Figure 2, as the conducting clip resembles the mouth of an alligator. The terminologies here are quite intuitive – because the thinking/analysis ‘difficulty’ must not depend on the identification of each tools or equipment.
Figure 2. Alligator clips
Alligator clips are just like connecting wires except that the end/s is/are of the form of alligator clip/s (ugh… cannot find another term for it). Connecting wires, alligator clips, and other types of connectors represent the solid lines that we use to construct our circuits in theory. From this point on, the reader must be able to distinguish alligator clips easily from other types of tobe-discussed connectors.
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2.1.1 Power Supply In most EEE laboratory courses, we will only deal with voltage supplies. Current supplies, on the other hand, is seldom used unless the work is on power electronics. Let us examine the single output DC power supply shown in the figu re below.
Figure 3. Controlled-voltage supply (left) and controlled-current supply (right) modes.
The adjust knobs set the desired level of voltage or current. The major knobs are for coarse adjustments while the ‘FINE’ tunes in finer granularity useful in setting supply with high accuracy. Shown on left of Figure 3 is the controlled-voltage supply mode (look closely – green LED is lit on “CV”) while on the right it is in controlled-current supply (green LED is lit on “CC”). Throughout the course, we will only use voltage supplies so it is necessary that our power supply is in CV mode. To achieve this, turn the ‘current adjust knob’ fully clockwi se and the CV LED should be lit. While on this mode, be extra careful that the red and black alligator clips do not get shorted. Otherwise, the supply will force itself to go in CC mode (with a ‘ticking’ sound). Such short-circuit event is harmful not only to your circuit components but also to one’s personal health. Remember that it is not the voltage but the current that could be fatal. The color code again is intuitive and we can see, is also uniform – red for positive and black for negative. Note that the GND port in the equipment is NOT the ground of the to-beconstructed-circuit but the ground of the equipment itself. The students are the ones deciding/designing which node is the ground for their circuits. For example, suppose we have set 5.0V as shown on the left of Figure 3. This voltage level indicates a potential difference of 5.0V between the positive and negative ports (i.e., from the negative port, there is a voltage rise of 5.0V going to the positive port). We can therefore use either port as the “reference” or the ground of the to-be-constructed circuit . If the black clip is used as ground/reference, then the red clip serves as positive (+) 5.0V. If the red clip is used as ground/reference instead, then the black clip serves as negative (-) 5.0V. The students should not be confused with this concept especially if we go into applications requiring bipolar voltage supplies (e.g. +/-5V for operational amplifiers).
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Figure 4. Controlled-voltage supply mode with 8.8V used to power-up a simple circuit.
In Figure 4, the power supply is providing the circuit with 8.8V. However, while the power supply is in CV mode, it also indicates a current of 0.01A. Is there something wrong here? Actually, there is none. The power supply also indicates how much current, with the set voltage level at CV mode, the circuit is drawing. If we have set to 8.8V and the circuit is drawing 0.01A, how much power (in Watts) does the circuit consume? Lastly, notice the position of the decimal point both in current and voltage. Suppose we target to get a voltage level of 0.1V. Since the supply only displays up to tenths digit, if it displays 0.1V, then we are not certain if we have 0.1000V or 0.1999V. Therefore, perhaps we can adjust from 0.0999V and stop turning the knob just before it displays 0.1000V. Does that make sense? Looking forward, imagine if all groups in one class uses single output DC supply and a group needs at least 2 voltage levels each. Then, the workstations will be filled with a bunch of DC supplies. With that, the laboratory also has triple output power supply units (PSU). An actual photo is shown in Figure 5 .
Figure 5. Triple output power supply unit (PSU).
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In this DC supply (see Figure 5), Output A has fixed 5.0V supply (1000mA overload limit) while Outputs B and C (250mA overload limit) are adjustable from 0V to 20V. The galvanometer scale indicates the voltage/current level of Output B or C depending on the selection switch found at the bottom. The interface ports here however is a bit different with that of the single output DC supply. Alligator clips (for both ends) can be ‘clipped’ on the metallic ports on one end and the other to your circuit. In any case, it is always a safe practice to set the desired voltage level first in ISOLATION before using them to power-up your circuit (i.e. before turning the supply ON). Imagine if the supply is already connected to your circuit and you suddenly turned it on not knowing that the previous setting might be as high as 30V! Will the experience from what is going to happen be worth it? Fortunately, our laboratories are now equipped with more advanced equipment. Shown in Figure 6 is a programmable DC power supply. It is similar to the one in Figure 5 but the settings and controls are now digital (keyword programmable). Usage of this equipment is not difficult once the operation of previously discussed power supplies are well understood. One evident advantage of this one is the circuit does not need to be disco nnected physically to “isolate” from the supply. An ON/OFF button is available to switch these supplies. DC supply #1 is ON as shown in Figure 6.
Figure 6. Programmable DC Power Supply (Triple Output)
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2.1.2 Function/Signal Generator The function or signal generator (simply called as sig-gen) is an equipment that is basically an AC signal source. The DC power supply is also a signal source but gives only DC voltage.
50Ω BNC Connector Female Figure 7. Sig-gen set at 1.0001kHz and 10Vpeak-to-peak (Vpp) level.
Students from their physics courses should already be familiar with waveform concepts such as amplitude, frequency, period, as well as the differences between a sinusoidal, square, and triangular waveforms. Shown in Figure 7, as an example, is the sig-gen set at 1.0001kHz with 10Vpeak-to-peak (Vpp) level. Note that although it displays 10Vpp, the sig-gen might not necessarily be able to supply the exact 10Vpp (e.g. it might be attenuated to, say, 8Vpp). If that is the case, how do we determine if we are using a true 10Vpp? One way to test is to use the oscilloscope and ASSUME that, as a measuring tool, it is well-calibrated (see Section 2.1.5 Equipment Calibration) and working properly. The same case might hold for frequency setting but for most basic circuits, accuracy deviation of about 100Hz is tolerable (e.g. 0.900kHz or 1.100kHz can most likely represent the true 1.000kHz).
50Ω BNC Connector Male
Figure 8. Sig-gen probe. The circuit-end are red and black alligator clips while the sig gen end is a BNC connector.
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The only proper probe that must be used for sig-gen is the one shown in Figure 8. Notice that one end uses red and black alligator clips (used for the positive and negative respectively). Proper polarity should always be observed. The clips are to be connected to the circuit (similar to the usage when dealing with DC power supply). In other words, the color-coding is NOT a suggestion. At the other end, the connector is a male 50Ω BNC connector. The female 50Ω BNC port is shown in Figure 7. BNC is used for a secured/locked match and is not a straight-forward plugand-play connector. The laboratory instructor must demonstrate the proper mating and unmating of this type of connector. Of course, these are technical terms.
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2.1.3 Analog Oscilloscope Oscilloscope is a basic measuring tool used to display amplitude variation of a signal over time. The functionalities and extended capabilities of digital oscilloscopes can be easily understood with the understanding of the analog ones. Analog oscilloscopes are basically bulky compared to digital ones mainly due to the cathode-ray tube used for display (green phosphor grid shown in Figure 9).
Figure 9. Analog oscilloscope self-calibration using built-in 2Vpp 1kHz square-wave signal.
An example of oscilloscope probe is shown in Figure 10. One end is also a male BNC connector type while the other end is DIFFERENT with that used for sig-gen. In order to display a stable signal, it should be referenced/grounded properly (i.e., signal is not floating). The probe pin is suitable for inserting to a protoboard/breadboard. The probe cap with hook is an accessory that can be used for clamping/probing on one leg (lead wire) of a circuit component, say, of a resistor. These same probes can be used for digital oscilloscopes.
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Probe Cap with Hook
Probe Pin (exposed when Probe Cap is removed)
Ground or reference (“negative”) clamped with an alligator clip BNC connector
Probe Compensation (attenuation setting slide switch)
Figure 10. Oscilloscope probes.
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2.1.4 Digital Oscilloscope Digital oscilloscopes are more ‘user - friendly’ than analog ones (CAUTION: no equipment is designed as fool-proof). Since it is digital, extended functionalities such as storage, acquisition, filtering, etc. are easily employed. As mentioned in the previous section, working with this one (see Figure 11) is relatively intuitive once the operation of analog oscilloscopes are observed. However, our laboratories now are equipped with digital ones, even for introductory courses such as EEE 34. Thus, a dedicated experiment was designed to explore the functionalities of this digital oscilloscope. In any case, if a relatively new equipment comes available, whatever it may be, it is a good practice to read the user manual / guide first. Non-engineering individuals usually take their new equipment out of the box to use it right away. They often disregard the user manual enclosed with it (e.g. got a new mobile phone?). In doing so, they will not be able to explore the full capabilities of their equipment and worse, to troubleshoot even when basic problems arise.
Figure 11. Digital Oscilloscope
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2.1.5 Equipment Calibration Un-packing new equipment assumes that it functions as expected. For example, a power supply set to generate 5.0Vdc (as displayed/read) must read an exact 5.0Vdc when measured by a voltmeter (as also displayed/read), just as we expect it to be. In fact, there are four possible scenario for interpreting the values displayed. Let us stick with the example given above, these are: i. Power supply is correct, voltmeter is correct ii. Power supply is wrong, voltmeter is correct iii. Power supply is correct, voltmeter is wrong iv. Power supply is wrong, voltmeter is wrong In fact there is a fifth case and it is too widespread that it is worth mentioning here. v. The interpreter/student is wrong all along How do we determine which one is the true “correct ”? This is where calibration comes in. Equipment must undergo periodic evaluation to determine if they are still functioning the way they are expected to be. The mechanisms inside these equipment degrade with time (e.g. magnets inside a multimeter) and with frequent use. Thus, re-tuning is necessary, just like how a musician re-tunes a guitar. This is what we call calibration and is only performed by skilled electronics technicians. How will this affect our work or experiment? What if we do not know if the equipment we are using are well-calibrated? Or it is already many years after the equipment was last calibrated? For the sake of performing instructional experiments, it is safe to assume that the measuring tool/equipment is the one that is well-calibrated (like scenario [ii] above, but hopefully we have [i]). Doing research experiments however requires all tools and equipment to be wellcalibrated. Going back to our example, even if the power supply displays 5.0Vdc but say the voltmeter reads a different one, then we will ASSUME that the voltmeter, as the measuring tool, reading is the true value – then adjusting the power supply might be necessary to achieve a specific target value.
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2.2 Laboratory Components Laboratory components are the components we see in our schematic/circuit diagrams. Here we will discuss two basic types of electronic components: (a) passive, and (b) active components. The former, being passive, dissipates energy and hence introduce losses. These components do not require a source of energy to perform their intended operation. On the other hand, active components require a source of energy. Most active components are non-linear and can amplify a signal. For example, if the input is 5V, then it is possible for the output to reach a voltage greater than the 5V input (a form of amplification).
2.2.1 Passive Components This section will familiarize the students on the basic components used in EEE instructional laboratories. It is expected that students already know the principles behind their operation and the underlying circuit analysis (EEE 31/33).
2.2.1.1 Resistors Resistors are the most fundamental and commonly used of all the electronic components. Resistors basically resist or regulate the flow of current running through the circuit. There are several types of resistor based on composition material, tolerance accuracy, and wattage. Each is suitable for a specific application. For example, high wattage resistors are used in power electronics while film resistors (known for low-noise characteristic) are used for radio communication electronics. For instructional purposes, we are only interested with the resistance value and hence a typical 4-band resistor (can handle up to 0.25 Watts) is sufficient (see Figure 12).
Figure 12. Resistor types based on composition material and tolerance level. [5]
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Resistor Value Reading Determining the value of a resistor with four (4) color bands is straightforward. Although the color-coding is intuitive (i.e., visible spectrum), the student is encouraged to develop their own mnemonics to help them identify the resistance more easily. For example, black suggests darkness or absence of something so it represents zero (0). This helps rather than using B-B-RO-Y-G-B-V-G-W (G-S-None). Furthermore, the said mnemonics has 3 Bs & 3 Gs which might result to confusion. The additional bands on 5- and 6-band resistors provide better tolerance accuracy and additional information about temperature coefficient. These are high-grade resistors and are too much to be used for instructional purposes. For resistor with 4 color-bands: 1st band = 1st digit 2nd band = 2nd digit 3rd band = Multiplier 4th band = Tolerance (Gold-5%, Silver-10% and None-20%) For example, if we have Yellow-VioletRed-Gold, then we have,
410 ± 5% ℎ or basically 4.7kΩ. How can we be so sure that we are reading the color band in the correct sequence and not the other way around? Well, did we just mention that the 4th band can only take on gold, silver or none? Equivalently, the first band cannot take on these colors.
Figure 13. Resistor Color Code. [5]
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Potentiometer Two wire-lead resistors have fixed resistance value but often times, we need a specific and/or out-of-fixed-standard resistance value in our circuit design and implementation. This makes variable resistor or potentiometer (dubbed as pot ) a useful tool. Potentiometer is a threeterminal component with variable or adjustable resistance. It can be thought of as two resistors in series that simultaneously change values with movement of the wiper (see Figure 14).
Figure 14. Potentiometer: actual (left), electrical model (middle) and usual electrical symbols (right). [6]
A potentiometer is identified with its value (usually printed on its casing). Suppose that we have a 10kΩ potentiometer. Using an ohmmeter, the 10kΩ or a close value can be measured on end-to-end (in the diagram, it is 3-1 or 1-3 since resistors are passive components and do not have polarity). We can get the variable resistance by tapping the terminal 2 and using either terminal 1 or 3 for the other end. Adjusting the wiper (corresponds to terminal 2) changes the resistances of 1-2 and 2-3 “resistors” simultaneously. To assess our understanding, suppos e again that we have a 10kΩ potentiometer and 1 -2 measures 4kΩ, then the expected value to be measured on 2-3 would be?
= 0 1
CAUTION: Adjusting the wiper on extreme positions (i.e., , see Figure 14) can result in a technical short on either leg which will draw overload current from the power supply if the circuit is not properly designed.
Short circuit events can cause fire. Thus, as a good practice, a 100Ω resistor or near-value is usually place in series with a potentiometer. In the event that an unintentional short was set in potentiometer, the 100Ω will still be able to regulate the flowing current. However, diagrams in our experiments do not include this ‘safety’ resistor. This is for student to evaluate mistakes on their own. The smell of a burnt potentiometer is not an inviting experience nor memory. Also, it is for students to develop critical thinking in circuit design considerations. In summary, it is essential that students understand the operation of each tool before they can realize its limitations and possible precautions. Some potentiometers available in our instructional laboratories are packaged in a potentiometer box (combination of 100Ω, 1kΩ, 10kΩ, 100kΩ and 1MΩ pots). However, some of them might have already been damaged/burnt/shorted by previous curious students. Thus, it is also a good practice to check potentiometers individually using ohmmeter before using them. Singular potentiometers are also available in the laboratory. The metal casing and the wiper knob, although made up of metallic conductors, are isolated with the pins. Thus, it is safe to adjust the wiper while holding the metal casing even if the circuit is powered-up. The size of pins of an actual potentiometer may vary. The actual one shown in Figure 14 can be inserted in a protoboard. In other cases, alligator clips can be used. Just be aware that adjacent clips may get shorted since potentiometer pins are spaced closely together.
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2.2.1.2 Capacitors Another essential component in electronics is the capacitor. This device stores charges and maintains energy in its electric field. The SI unit for capacitance is Farad (in honour of Michael Faraday for his major contributions in the field of electromagnetism) Although considered a passive component, there are polar and non-polar types of capacitors. This depends on the materials used as dielectric inside the capacitor. Some materials permit only one direction for the flow of displacement current while others permit bidirectionality. Non-polars include ceramic, mylar and film capacitors. Electrolytic and tantalum capacitors are polarized. Most blown-up/burnt (usually the first affected in fault conditions) components in a circuit are capacitors.
Figure 15. Different types of capacitors, both non-polar and polar. [7]
Extra care should be observed before powering-up circuit with polar capacitors. How do we determine which leg is the positive/negative? If the component is brand new, the longer leg should be the positive. In other cases (e.g. legs are cut at same length), markings should be available on the body of the capacitor. As shown in Figure 15, electrolytic capacitor indicates negative band while tantalum capacitor shows the positive mark. Capacitance values are printed either as-is (see electrolytic type) or by code (see ceramic type). Let us examine the electrolytic capacitor in Figure 15. The absolute maximum voltage it can handle is 16V. If charged above that value, then the capacitor will explode. The capacitance is 4700uF which is equivalent to 4.7mF. For the human brain, it is easier or convenient to process the information 4.7mF. Why do you think that manufacturers prefer the label 4700uF as compared to 4.7mF given the fact that they are just the same? Well, while you are thinking the reason behind that logic, let us share a story of buying components in an electronics shop… EEE Student: (To sales assistant ) “10 pieces of 4.7mF 16V electrolytic capacitor please.” Sales Assistant: “Sorry but we do not have 4.7mF.” EEE Student: (Saddened because his long trip to the shop will be useless. Thinks for a moment. Asked the sales assistant again.) “Can I have 10 pieces of 4 700uF electrolytic capacitor please?” Sales Assistant: “Okay, Sir. What voltage rating?” EEE Student: ($#@@#$!$@$^* deep inside.) ”16V. Thanks!” Sales Assistant: “ Okay. Wait for a moment.”
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Haha! What a funny story! Students might encounter a similar experience. Anyway, the main reason why the dot marking is highly discouraged is that it might get erased easily. Mistaking 47mF for a 4.7mF can greatly affect the circuit operation by design. On another note, ceramic and mylar capacitors usually use 3- or 4-character code to indicate the capacitance value. The reading is similar with the resistor color bands only that the value is already printed here. Note however that the resulting value is not Farad but pico-Farad (pF or − ). Capacitance values are usually in the pico-, nano-, micro- and milli- range so it would be easier to refer to the smallest unit. An example is shown in Figure 16, with value,
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10 = 47000 = 47 = 0.047 The last character usually denotes the temperature coefficient and can be disregarded for instructional purposes. Figure 16. . Ceramic capacitor value reading. [8]
2.2.1.3 Inductors Lastly, we consider inductors as an essential component in electronics. This device keeps magnetic flux and stores energy in its magnetic field. The SI unit for inductance is Henry (in honour of Joseph Henry for his work on electromagnetic induction). We will not discuss inductors in detail but shown in Figure 17 are common types of inductors.
Figure 17. Different types of inductors. [9]
Some inductors look like resistors but in a closer view, inductors are more “curvy”. The reason is that inside it is a wound coil of magnetic wires as compared to the typical resistor manufactured using carbon. Transformers (a magnet core with wires wound around) can serve as inductors.
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2.2.2 Active Components Active components are electronic components that require a source of energy to operate. Most of them are non-linear and can provide signal amplification. EEE 34 is not focused on active components but we introduce them here anyway. Examples of active components are: 1. Diodes 2. Special-purpose diodes (e.g. Light-emitting Diodes or LEDs) 3. Bipolar Junction Transistors (BJTs) 4. Field Effect Transistors (FETs) 5. Analog Integrated Circuits (e.g. operational amplifiers or op-amps) 6. Digital Integrated Circuits 7. Detectors and emitters
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2.3 Laboratory Tools We will define laboratory tools as light-weight portable things that we use in the laboratory. Included here are the multimeters, galvanometers, and protoboard. The in-depth discussion on multimeter is reserved in a later section (see Section 3.4 Circuit-Level Analysis of the Multimeter)
2.3.1 Multimeter Multimeter, as the name implies, measures multiple electrical quantities including resistance, voltage, and current. Some advanced multimeters can measure capacitance and even inductance but for basic electronics using multimeters, we will only deal with the three fundamental quantities provided by the Ohm’s Law. The multimeter, or meter shorthand, can be therefore referred to depending on the intended function: voltmeter – if measuring voltage; ammeter – if measuring current; ohmmeter – if measuring resistance. From this early point, let us always remind ourselves that in using multimeter to measure current and voltage:
→ = ℎ → = ℎ Multimeters, both analog and digital, easily get damaged through misuse by students who do not understand the two statements above. The words above are in fact already redundant. For EEE 34, it is OKAY to make this kind of mistake at first but repeating the same mistake is NOT justifiable – it is somehow unwise. The most common damage done to multimeters is a blown-up fuse caused by overcurrent. Students forcefully connect the meter in parallel to measure current – which is totally wrong! If you still do not understand what is being discussed here, then think of it again and again.
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2.3.1.1 Analog Multimeter For EEE 34, we will first use analog multimeters and learn about their capabilities and limitations in early experiments. Analog multimeters available in the laboratory are sho wn in the figure below.
Figure 18. Analog multimeters.
Notice that the multimeter on the left has fixed probes while the one on the right has detachable probes but that is not really important. They also have t he same set of selection knobs since they use the same galvanometer scale (the calibration with the needle pointer). We will discuss an in-depth analysis of analog multimeter in the next chapter under Section 3.4 CircuitLevel Analysis of the Multimeter. Inquisitive readers are advised to jump to that section before proceeding with next sections in this chapter. The color coding of the probes is intuitive – red for positive and black for negative. Basically, both probes are just conductor wires so they serve the same purpose. That is, they can be technically interchanged. However, to avoid confusion, we follow the color code especially that we are dealing with analog multimeter where proper polarity is a must.
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Using the Multimeter to Measure Voltage, Current and Resistance Let us take a closer look on the selector knob (see Figure 19) and the calibration scale (see Figure 20). Figure 20 is just similar to the 1mA movement galvanometer scale only that it indicates lot of markings. Nonetheless, the operation is the same. To measure voltage, turn the selector knob to the appropriate DCV level. For safety, always choose the range with the nearest higher level than the expected value to be measured. For example, if expecting to measure 8V, set the meter to 10V instead of 50V. This will give us better accuracy in gathering data while protecting the multimeter from ‘over -voltage’ . The same practice goes when measuring current (DCmA). In reading the measured DCV or DCmA value, use the calibration scale (the line with markers) just below the reflector strip. The reflector strip is used to avoid parallax error . The needle pointer will cast a shadow somewhere along this strip. The shadow therefore is on the same surface plane with the calibration scale. Thus, reading the value would be easier. The corresponding reading scales (the numbers) to use for voltage and current readings are below the reflector strip. Observe the range of the reading scales and the range on the selector knob. What do you notice? Is there a pattern? Yes, there is. The full-scale readings are 10, 50 and 250. All of which are multiples of the range on the selector knob. Let us explain this more closely. If expecting to measure 8V, it would be easier (and safe) to set the multimeter knob to 10V and use the 0 to 10V reading scale since the proportionality constant or factor to use is 1. The needle pointer will fall on (or near) the column of 8, 40 and 200. But of course, the reading would be most convenient if read on the calibration scale with 8. Using 40 requires a factor of 5, while using 200 requires a factor of 25. As a test of understanding, if expecting to measure for instance a voltage level of 2.3V, where should we set the selector knob? What reading scale is the most convenient to use? This is just a matter of ratio and proportion.
Figure 19. Analog multimeter selector knob. [2]
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Measuring resistance using analog multimeter is a bit different from measuring voltage and current. The calibration and reading scale are located above the reflector strip – obviously with the Ω symbol ( see Figure 20) 20). The extreme ends are and 0Ω representing open and short conditions respectively. The ohmmeter selector knob, instead of a range, is a set of multipliers. The resistance calibration scale is NOT linear as compared to that of DCV/DCmA. The distances between markings with smaller value are large and they decrease as the value tends to Why is that so? Of course there is an engineering reason behind it and we will learn about it in future experiment/s. Obviously, we can get higher accuracy if the needle pointer falls on values with smaller resistance number. This is why it is preferred to use the highest possible multiplier depending on the expected resistance value when measuring.
∞Ω
∞.
The current markings in light blue on o n each multiplier (see Figure 19) 19) signifies the amount of current that is running on ohmmeter leads when shorted. Energy is available since ohmmeter operates with a battery. This implies a precaution in using an ohmmeter. ohmmeter. In measuring resistance, the circuit or resistor under test should not be powered-up. If it is, then the power supplied to the circuit under test and the power given by the ohmmeter might affect the reading. Also, there are components such as integrated circuits (ICs) that cannot handle current as high as 150mA (1x setting). Care should be observed before measuring resistance on these kinds of electronic components. On the other hand, the ohmmeter is also useful especially in testing other electronic components if working or not (e.g. light-emitting diodes or LEDs – how?). Reflector Strip
Figure 20. Analog multimeter calibration scale. [3]
If the analog multimeter is not in use, turn it OFF by switching the selector knob to OFF to conserve its battery! Digital multimeters automatically switch off when idle for a certain time.
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Zero-ing the Meter Meter Scale
∞Ω
For ohmmeter however, the default position of the needle falls on the left-most with representing open circuit. Before making any resistance measurement using analog multimeter, it is necessary to always zero the scale. It makes sense since any reading should always start with zero as reference. Each multiplier setting might have different initial zero position.
Figure 21. Zero-ing the meter scale. [4]
To zero the scale, short the leads together and turn the zero adjust knob (see Figure 19) 19) until the needle pointer falls exactly on 0Ω mark as shown in Figure 21. 21. There might be some settings where the scale could not be zero-ed. Note that human body can be thought of as a single wire conductor. Putting hands in contact with the leads as shown in the figure above is fine only when zero-ing the scale. If already measuring resistance of a resistor for example, then do not clip the legs of the resistor to the ohmmeter leads using hands. The reading might be the combined resistance of the resistor and human body. Better place the resistor on the insulated table or on the protoboard before taking measurements. Zero-ing the meter scale is essentially reaching the full-scale current. That is why the 0Ω scale in Figure 20 is aligned with the full-scale current (right-most mark) on the calibration scale.
Connectivity/Continuity Test Performing connectivity or continuity test is essential for basic debugging/troubleshooting. In analog multimeters at ohmmeter mode, a shorted , connected or continuous condition must display 0Ω. A good wire conductor ideally has a resistance of 0Ω. This is most useful in checking continuity of connecting wires, alligator clips, connectors, etc. Determining which holes are connected and which are not in a protoboard can also be checked easily using connectivity test. Digital and other analog multimeters have advanced indicator for connectivity test. Most are of the form of a buzzer. It will sound once the device under test is checked to be connected.
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Note that some connecting wires or clips are connected if placed in a certain position (e.g. twisted), while at other orientation may appear to be not connected. Wires are covered with plastic insulation so visual inspection might not be possible. Just be aware that this scenario is not impossible happen. Most students get lost if their circuit is not functioning as expected – only to find out that one of their connecting wires is “open”.
2.3.1.2
Digital Multimeter
A “user-friendly” type of multimeter is the digital version. However, just like socially, we should not take the friendliness of others for granted. These multimeters, although contains protective circuits, still have their limits. So the “user-friendly” term might be a misleading one for us. For example, some digital multimeters can detect over-voltage even if the selector knob setting is unintentionally unchanged to the proper setting. If set on such condition for some specific long time, the internal protection circuitry might eventually fail thus damaging the tool. In summary, proper care should ALWAYS ALWAYS be observed in handling ANY laboratory tool or equipment.
Figure 22. Hand-held digital multimeters.
The digital display would be the most obvious distinction of a digital to that of an analog multimeter as shown in Figure 22. 22. The black probe probe is always placed on the COM (common) COM (common) port and the red red probe probe on VDΩ port. Other ports are used for high-current applications and those are not in the scope of this course. We also have bench digital multimeters as shown in Figure 23. 23. This type of multimeter is more robust than the hand-held version (the size and weight can explain why). Its proper use is no puzzle once the student is well-familiarized with analog and digital multimeters.
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Figure 23. Bench digital multimeter.
So if the students were to ask, which is better to use, the analog or the digital multimeter? Whatever the answer may be, engineers should develop a way of thinking on how to reason out for the choices that they make (especially when defending, say, an engineering design). Engineers do not make decisions right away. They first think of options and alternatives, then they weigh them. After all, there should be a reason for everything.
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2.3.2 D’Arsonval Galvanometer or 1mA Movement The D’Arsonval galvanometer or 1mA movement is basically a permanent magnet moving-coil transducer that uses the principle of electromagnetism in determining the magnitude of passing current. The needle deflection indicates the magnitude of current. The galvanometer is calibrated with full-scale of 1mA – hence the name 1mA movement.
Figure 24. 1mA movement.
There are two ports to connect in order to use this 1mA movement (see Figure 24). For proper polarity, the color code is here once again. But wait, do currents have polarity? Of course the answer is no, they do not have polarity. Rather, the red and black color code here represents the direction of the current. Note that we are using analog device and proper “polarity” must always be observed. The current must enter the positive (red) port and exit the negative (black) port. If interchanged, then the needle will try to deflect more to the left (i.e., on the “negative” of the scale) and this might damage the tool. Since this tool measures current (up to 1mA only), what should be the best way to check if this measuring tool is working properly or not?
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2.3.3 Protoboard/Breadboard Translating circuits from diagrams on paper to actual implementation is an essential skill one needs to master in this course. The “paper” that we will use in laying -out our circuits is the protoboard (short for prototyping board). It is sometimes called breadboard since the holes resemble that of a bread (working in the laboratory can get one really hungry). For discussion purposes, let us stick using the term protoboard. The protoboard conveniently provides connected holes in a row. Since the holes are arranged in a matrix fashion (see Figure 25), the question now is which rows are connected, and equivalently, which are not. Let us begin by describing a short row and a long row.
Long row
Short rows
Connecting wires
Canal
Figure 25. Protoboard. [10]
Basically, the holes in a short row are internally connected. Adjacent short rows, as well as short rows across the canal , are NOT connected. The holes in a long row are internally connected but depending on the brand, the other half may or may not be connected. The example in Figure 25 shows a discontinuous red (+) and blue (-) lines. This indicates that long rows do not continue on the entire length the protoboard. That is why we can see connecting wires ‘jumping’ from one long row to another on the other half. Long rows have (+) and (–) labels since these lines are usually used as power ports (e.g. the + and – of a 5.0V supply). But why do we reserve longer lines for the power ports? It is fairly simple. If the circuit has a lot of components, it will consume the whole protoboard space and most likely, all components will require power. Thus, power ports can be easily accessed anywhere on the protoboard. The protoboard canal serves a purpose especially when using dual in-line package ICs such as operational amplifiers (see Appendix C: Some Notes from Operational Amplifier (Op-Amp) Datasheets or Figure 26). Try to look closely on Figure 26 on how ICs are placed on the protoboard. Engineers do not really need to memorize which holes are connected and which are not. Remember that we have the tools. When in doubt, we can insert connecting wires in a pair of holes and use a multimeter to do a connectivity test. On a side note, true engineering education will not teach its students by making them memorize stuff (e.g. formulas, here-and-there, this-and-that, etc.). Instead, it will teach its students by guiding them in learning how to solve problems and overcome obstacles.
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2.3.3.1 Protoboard Wiring Setting-up a circuit on a protoboard needs patience especially for first-timers. If one does not know what a short and open, connected and not connected mean, then he/she will surely get snowballed in constructing a circuit. It might take more time and practice for others depending on the learning curve of the student. Nonetheless, constructing a circuit on a protoboard should be an easy task.
Figure 26. Protoboard wiring of two complex circuits: messy wiring (left) and clean wiring (right). [10]
Let us compare the wiring of two complex circuits shown in Figure 26. Both use a bunch of components but the wiring on the left is a bit messy compared to the one on the right. Both are working as intended so functionality will not be an issue. This scenario is somehow similar to writing computer programs. As long as the code is working, students tend not to care because it is already working. However, what will be the possible disadvantage of the circuit wiring on the left compared to the one on the right (HINT: This also applies to computer programming)? Obviously, the one on the left is prone to errors. Consequently, whenever there is error, it will be hard to trace where the error arises. This leads us to our next section – which is one of the most important skills every EEE student must possess.
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2.3.3.2 Debugging/Troubleshooting Circuits [11] After constructing a complicated circuit, it is not uncommon for it to be non-functional. This may be due to wiring/connection errors, faulty parts and/or incorrect equipment settings (e.g. wrong power supply setting). The process of finding and correcting these problems is called debugging. It is very easy to get lost in the myriad of possible sources of error. Also, thinking of possible solutions for an unknown problem is an overwhelming task. Debugging circuits (just like debugging programs) might be a highly frustrating task for EEE students, especially if one does not know the causes of such unwanted errors. However, even if the nature of the problem is not identified beforehand (existence does not necessarily imply its nature), debugging circuit would be easy if approached in a systematic manner. Imagine if a student will debug a circuit that looks like the one presented in Figure 26(left). He/she might save more time if he/she will just reconstruct the entire circuit instead of finding where the error is. Thus, it is advisable to practice neat wiring at the very first time. Debugging is a skill that requires continuous practice and experience. One must fully understand the operation of his/her circuit as a whole and per-component (or sub-circuit) basis before he/she can identify the possible causes of error. One cannot solve something that he/she does not acknowledge as a problem in the first place. If the circuit is not functioning the way it is designed to, then there must be problem/s. Here are some tips on debugging/troubleshooting circuits: Make sure that the tool used for debugging is working properly. For example, test first a voltmeter on a battery or DC power supply. Make sure that the tools are on their proper setting. The circuit might be working properly but the measuring tool is not set correctly giving you “incorrect” information. Before checking the response of your circuit, have the intuition to compare it with the theoretical response (e.g. “I expect to measure 2.5V here” ). Practical results, most of the time, are close to the theoretical ones. This is one proper way to validate results. Always try to ask yourself, “ Do the data that I have make sense?” Learn the functions of various parts of the circuit. Knowing them can help you devise tests to determine whether or not each part is functioning properly. Test all connections. Most problems come from faulty wires, alligator clips, probes and even shorted components. Check the actual wiring against the circuit schematic. A simple method is verifying which nodes are connected and which are not. Double check yo ur wiring. Students tend to insert wires on unintended adjacent holes on the protoboard. Double check if you are using the correct component values (e.g. 1kΩ was used instead of 10kΩ). Make sure that all parts and components are working properly (e.g. might be using a broken potentiometer). If you think you have pinpointed a possible source of problem, then devise a quick and easy experiment to test your hypothesis (e.g. connectivity test for a suspected faulty wire). Make sure that the power supply is ON and has the correct setting. Debug by following the signal path (e.g. from input to output). Start checking from the supply down to the output component in the ci rcuit (e.g. voltage measurements). If the circuit can be divided into stages or modules, then check them separately. Isolation is a good approach in tracing the source of error. Always remember that very simple errors are a lso very common errors.
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Engineering is the art of solving problems. In debugging circuits, we want to find and correct errors. We develop algorithms and methods to achieve proper debugging. However, there is no fixed way of using these debugging techniques. We figure them out through experiments. Debugging circuit requires skills and experience, and as an art, it also requires creativity.
Figure 27. PHD Comics: Debugging. [12]
Revisit this section until the student develops the skill of debugging by him/herself. In case of hopelessness, ask the help of the laboratory instructor. The instructor will probably throw the question asked by students back to them. Present to the instructor how the tried solutions did not work.
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3 Electrical Measurements Performing experiments is essential, but gathering data and analysing & interpreting them are more valuable. This chapter briefly introduces basic concepts of measurement – error & linearity and accuracy & precision. In order to recognize or define error, we must first draw the difference between theory and practice. To put some sense on empirical results to be obtained from the experiments, the students should have a good understanding of the ideal and practical conditions of power supplies, the characteristic of a 1mA movement, and finally the differences between the modes of an analog multimeter using the galvanometer scale.
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3.1 Theory and Practice EEE 31 and EEE 33 teach us the fundamentals of circuit theory. What we write and solve in paper there assumes ideal conditions both for the equipment and components used. For example, a 1kΩ resistor in paper has no tolerance and hence the value will stay as 1kΩ , and a 5.0Vdc supply will stay as 5.0Vdc, no more no less. We refer to these values as theoretical values. In practice however, this is usually not the case. Let us take a simple circuit as an example (see Figure 28). For simplicity and as an example, we will only examine the difference between an ideal and practical voltmeter. Thus, values of R1, R2 and the 5Vdc stay as they are.
Figure 28. (a) Simple resistive circuit, (b) ideal voltmeter, and (c) practical voltmeter
Suppose we are going to measure the voltage output Vout of the simple resistive circuit at R2. Using the ideal voltmeter (see Figure 28b), by voltage division, we should be able to measure 2.5Vdc – theoretical value. However, practical voltmeters have some internal resistance in parallel with them. The parallel resistance is usually high but for exaggeration, we will assume a value of 1kΩ (see Figure 28c). Using the practical voltmeter, we can measure about 1.67Vdc at the output. The deviation comes from the unwanted internal resistance of the practical voltmeter. The measured value is far (or near?) from the theoretical value. If we are not aware that a practical voltmeter has this internal resistance, then we can interpret the measured value as erroneous. So how do we develop the right intuition to determine if our measurements make sense or not? This is where we should bridge theory and practice. An inquisitive and clever student will not settle on reading measurements – he/she will make sense out of it. That is, he/she can defend why such results were gathered. The error or deviation in measured value depends on how our practical approach deviates from ideal case. In our example, if the internal resistance approaches infinity (ideal), then the measured value should also approach a value of 2.5Vdc (ideal). Getting ‘ high’ deviation value in what we measure in practice does not mean that the theories are wrong. In fact, the measurements we make should be guided by the principles set by circuit theory.
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3.2 Error and Linearity
3.2.1 Error Let us begin by differentiating theoretical value (TV) with the measured value (MV). Theoretical value is simply the ideal, nominal or target value while measured value is the actual value pertaining to real-world measurement. Thus, error (e) can be defined as the difference between the measured value and theoretical value.
= || Error value is always positive so we take the absolute value of the difference. Further, for a specific measurement, the theoretical value is constant. Evaluating error in terms of percentage by referencing to the theoretical value is more meaningful. Thus we have,
%= % 3.2.2 Linearity For now, let us not consider time variation on our data. This simplifies our analysis into one dimension only. Consider a system that has input and output. Let us take a headphone amplifier for example where the electrical signals (input) are converted and amplified to produce sound (output). There will be a certain range on the amplitude of electrical signals where the headphone amplifier can convert in a proportional manner. However, as the input electrical signal increases further, the headphone amplifier may saturate and produce an almost constant high sound level. This scenario is depicted in Figure 29.
Figure 29. Input-output relationship showing linearity.
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The linear region of a system, assuming voltages as input and output quantities, can be described by,
=
where is the proportionality constant. In this region, an increase in the input will produce an increase (or a decrease in some systems) with a certain proportionality factor. At the non-linear region however, the relationship between the input and output can be described by higher order equation such as,
= ⋯ where
,,…, are the weights per degree of input.
The input can be thought of as the independent variable while the output as the dependent variable. Students are encouraged to think of other examples of system that exhibit linear and nonlinear input-output relationship.
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3.3 Accuracy and Precision Compared to the expected or theoretical value, how do we determine the closeness of gathered actual data? Can we call it accurate, precise, or both? Accuracy and precision are two different things and one must observe care when using either of these terms. To understand these basic concepts, let us examine Figure 30.
Figure 30. Difference between accuracy and precision. [13]
Four (4) target boards with different levels of accuracy and precision are shown. Let the bullseye be the expected or theoretical value and the trial shots as the gathered data. The x-axis is increasing with accuracy while the y-axis with precision. Clearly, higher accuracy means that the gathered data, no matter how sparse the data is, have minimal error. That is, data are close to the theoretical value. On the other hand, precision suggests how gathered data are close to each other (i.e., consistency) regardless of the amount of error. The best condition is undoubtedly Figure 30d. However, it is important to recognize that analysis is done after gathering the data. Performing an experiment is not targeting the theoretical data. Some “researchers” tend to bias the process of (i.e., before or during the experiment) gathering data just to conclude that they got an accurate and precise data. This is not a good research practice. One must report what are actually collected. After all, there are no correct nor incorrect data – only improper execution of experiments.
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3.4 Circuit-Level Analysis of the Multimeter The physical appearance and overview of the operation of multimeter was discussed in the previous chapter. Before we proceed, let us again remind ourselves on how to measure current and voltage using multimeters.
→ = ℎ → = ℎ In this chapter, we will dig deeper on how multimeters work in a circuit-level point of view – the ammeter, voltmeter and ohmmeter. Before that, we should be able to understand voltage source, current source, and the characteristic of the 1mA movement. The galvanometer scale is the primary component used to indicate current, voltage and resistance in an analog sense.
3.4.1 Practical Power Supply The power supply is the source and hence, the circuit to be connected (called sink ) will draw energy from it. The redundancy of terms used here will help us understand and remember the concepts and later on, to develop intuition. In circuit theory (EEE 31/33), we always assume that voltage and current sources are ideal. However, in a real-world scenario (e.g. EEE 34), some non-ideal conditions exist.
Figure 31. Practical voltage source (left) and practical current source (right). [14]
A practical voltage source is represented with a series resistance while a practical current source has a parallel resistance as shown in Figure 31. How do these resistances make the sources non-ideal? If we connect a resistive network/circuit at nodes a and b of the voltage source with e Volts, the circuit will draw energy or current i . There will be a voltage drop across the series resistance r . Thus, instead of supplying the full voltage e to the circuit, a lower level of (e – ir) Volts is supplied. The reason why a parallel resistance on a current source makes it a practical one is left for the students to analyze.
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Nowadays, power supplies are designed such that these non-idealities are, if not eliminated, minimized. We can assume that the power supplies in the laboratory are close to ideal ones. This section only opens to us that such practicality exists.
3.4.2 Characteristic of the 1mA movement Galvanometer Scale We have seen how the 1mA movement looks like. Inside it are permanent magnet, coils, the needle pointer, and the calibration scale for the reading as shown in Figure 32. The electrical symbol used is a circle with a letter ‘A’ (signifying Ampere) since it senses current.
Figure 32. 1mA movement inside structure (left) and its electrical symbol (right). [15]
The 1mA movement is characterized by its internal resistance (meter resistance) and the full-scale current it can measure safely, . In this case, the full-scale current is obviously 1mA. The internal resistance varies from one galvanometer to another. Typical value ranges from to .
50Ω 300Ω
Note that the following discussions will use the galvanometer scale to measure not only current but also voltage and resistance. Is that really possible? Using circuit analysis, the answer is definitely a yes. We will limit our discussion on DC analysis. AC analysis will be tackled in later experiments where digital multimeters will be used.
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3.4.3 DC Ammeter Using the 1mA movement to measure DC current is pretty straightforward. We only need to insert the 1mA movement to the line where we want to determine the current. Suppose we have a resistive circuit where we want to measure the current (call it circuit under test ). In this chapter, we denote the circuit under test in red while the circuit under discussion in black for uniformity in circuit diagrams. For simpler analysis, we represent the circuit under test by its Thevenin equivalent with a voltage source and series resistance as shown in Figure 33. Nodes a and b are initially connected.
Figure 33. Measuring current using the galvanometer as the ammeter.
Next we want to identify the current flowing through the circuit . Break the circuit to split a and b and insert the 1mA movement as suggested in Figure 33. The 1mA movement is now part of the circuit and it is then re-closed. The current will now flow through the meter and the needle will deflect to display a reading. This scheme is fairly simple. However, let us remember the physical limitations of the 1mA movement.
First is that the 1mA movement has a finite internal resistance . One should be able to recognize that the reading will be affected since there is an additional series resistance to the
= while the current with meter inserted . Let us define ammeter accuracy as the ratio of two values, is, = + circuit. The current without the meter is simply,
= = =
Clearly, if then the accuracy would be unity (or 100%). depends on the circuit under test and thus our ammeter should work with any circuit’s equivalent Thevenin resistance value. For an ideal ammeter, what should be the value of ? What is the worst case scenario relating and ? Lastly, is it possible to achieve > 1?
Given the quantified ammeter accuracy, the amount of error will be,
=
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The term insertion error is used since we get this error by literally inserting the ammeter to the circuit. The importance of giving a specific name will be evident as we discussed the error for the voltmeter case.
The second and last limitation of the 1mA movement is its full-scale limit. is constant and the ammeter can only measure values less than or equal to this value. Is there a way to extend the measurement range? For example if the needle deflects to full-scale 1mA position, the extended-ammeter actually “measures” a higher value of say , 10mA? This is possible through current division. Since the 1mA movement can only handle up to 1mA, the remaining 9mA current (real measured current is 10mA) should flow somewhere else.
Let the target current (i.e., extended range) be . To extend the range of the ammeter, we need a lower resistance value compared to that is connected in parallel with the 1mA movement. This is a shunt (another term for ‘parallel’) resistor, where the majority of the current will flow (see Figure 34). Remember that current tends to flow in a path with least resistance.
Figure 34. Extending the range of the ammeter.
Figure 34 shows how to extend the range of the 1mA movement. Simply connect a shunt resistor across the 1mA movement. The question now is how do we determine the value of to extend from to ? We must know the value of first. Then by KCL we have,
= With maximum current
Thus, the value of
, the voltage across the nodes is, =
should be,
= = ( − ) Since
< , then indeed, < . (− )
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3.4.4 DC Voltmeter In the previous section, we have seen how simple it is to use the 1mA movement to act as an ammeter. In this section, we will use the 1mA movement to measure voltage instead. By Ohm’s Law, . Since the 1mA movement measures current, we only need a resistor in series to make it act as a voltmeter as shown in Figure 35.
=
Figure 35. DC Voltmeter structure using 1mA movement.
=
Let us define input resistance of the voltmeter as . This is the resistance looking into the voltmeter. and are the measured current and voltage respectively of this constructed voltmeter. For clarity, the 1mA movement displays current reading. We are taking advantage of the fact that we have the knowledge of to indicate a voltage reading as provided by Ohm’s Law. Instead of a full -scale current , the full-scale voltage that our constructed voltmeter can measure is, .
= =
Next we define the voltmeter accuracy. Suppose again that we have a resistive circuit but this time, we use a Norton equivalent instead (see Figure 36).
Figure 36. Measuring voltage using the galvanometer with a series resis tor as the voltmeter.
= . Connecting the voltmeter . It can be shown that the voltmeter +
Without the voltmeter, the voltage is in parallel, the voltage is accuracy is,
=
= =
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=
Again, if then the accuracy would be unity (or 100%). depends on the circuit under test and thus our voltmeter should work with any circuit’s equivalent No rton resistance value. For an ideal voltmeter, what should be the value of ? One might think an outright answer of infinity. If is also very large or of about infinite value, then we have,
= = ∞ ∞ ∞ ≡ ?
The above equation does not make sense in the very first place. Math tells us that this case is ‘indeterminate’. To achieve maximum accuracy, ideally we want such that,
≫
= ≈ = Similar to the DC ammeter, is it possible to have accuracy, the amount of error will be,
> 1? Given the quantified voltmeter
= For voltmeter, the error is termed as loading error due to the ‘loading effect ’ caused by connecting the meter with finite resistance to a circuit. Ideally, all current in Figure 36 should stay within the circuit under test even if we connect the voltmeter in parallel. This was not the case since we have read a current reading translating to our voltage reading .
Accuracy and error values represented above are dimensionless. Values in percentage are preferred however when reporting data. There should be no confusion between the ideal conditions of voltage source and voltmeter, as well as between current source and the ammeter. For each combination, the former is a source and the latter can be thought of as a sink .
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3.4.5 Ohmmeter Ohmmeter is the mode of multimeter that measures resistance. We have learned that both the ammeter and voltmeter draw current from the circuit under test in order to get a reading. For an ohmmeter, the case is different. In fact, ohmmeters have their own voltage supply. In actual, this voltage supply is of the form of a battery. The voltage being supplied by a battery is not constant over time. Will this affect the resistance reading? How to correct or re-calibrate the ohmmeter for such changes? Analog ohmmeters always have the zero adjust knob. It is basically a potentiometer used to “zero” the ohmmeter (see Figure 37). The reader is encouraged to look back at the physical structure of the analog multimeter in the previous chapter. This will help in interconnecting the concepts discussed in this section. The ohmmeter circuitry constructed using the 1mA movement is shown in the figure below.
a
b Figure 37. Ohmmeter structure using 1mA movement.
Let us define the resistance seen looking into the ohmmeter structure as,
= Shorting the leads a and b, we can ‘zero’ the ohmmeter such that,
→ =
Suppose that we are to measure a resistor with unknown value, as shown in Figure 38. We connect the ohmmeter leads to the legs of the resistor. The measured or displayed current will now be,
=
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Figure 38. Measuring the resistance of an unknown resistor using analog ohmmeter.
. This is a measure of ∈[,]. It can be easily
Here we define a parameter called meter deflection denoted by how the needle deflects in reference to the full-scale position. Thus, shown that,
= =
The 1mA movement displays the position of the needle, hence the value of . If we know the value of , then we can determine the resistance value of the unknown resistor using the equation above.
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4 Experiments The concepts presented in the previous chapters serve as a strong foundation in performing the required experiments, as well as developing critical analysis on the data to be gathered. This chapter contains the inventory o f required experiments for EEE 34. A pre-lab sheet is available for students to answer and submit in class before each actual experiment either inprint or handwritten on a pad paper. The in-lab sheets however are not to be submitted. These serve as guide for students throughout each experiment. After gathering data and analysing them, some required discussion questions are to be answered. The complete, concise and coherent documentation in IEEE format should be submitted per group – two (2) weeks after the experiment is finished. Note that some experiments might take up two (2) meetings depending on available schedule. All experiments for EEE 34 should be performed throughout the semester. The experiments presented here are in chronological order but the delivery still depends on the laboratory instructor. A SAFETY QUIZ must be passed by a student before he/she proceeds with any experiment. If the student fails the quiz, then he/she will be marked absent for the experiment scheduled for that day. In other words, he/she can only perform an experiment until he/she passed the safety quiz. The format and administration of the quiz again depend on the laboratory instructor.
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Electrical Measurements Laboratory – EEE 34 Name: Student Number: Section: Date:
__________________________________________________________ __________________________ __________________________ __________________________ Experiment 0a (Pre-Lab) Basic Measurements
Put a check on the box if the corresponding task is accomplished. A. Join the class section’s online group.
Found in EEE 34 Student Laboratory Manual… B. Read and understand Class Policies , Chapter 1 Safety Practices in the Laboratory [1], Section 1.1 Care in handling and use of a multimeter, and Section 1.2 Laboratory Rules and Regulations – with all their sub-section/s, if applicable.
C. Read and understand Section 2.3.1 Multimeter, Section 2.1.1 Power Supply, Section 2.2.1.1 Resistors, Section 2.3.3 Protoboard/Breadboard, Section 3.1 Theory and Practice, and Section 3.2.1 Error – with all their sub-section/s, if applicable. Do/answer the following (indicate all references used): 1. List the advantages/disadvantages of using analog meters over digital meters. Which is better to use and why?
2. Draw two separate diagrams showing a multimeter measuring (a) voltage across and (b) current through a resistor in a simple one-loop circuit.
3. (This item is NOT required.) What are the different types of resistors, capacitors and inductors? Why these components are manufactured using different types of material?
REFERENCE/S:
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Electrical Measurements Laboratory – EEE 34 Group Number/Letter: _______ Members: _______________________________ _______________________________ _______________________________
Date: Section:
__________________ __________________
Experiment 0: Basic Measurements I.
OBJECTIVES a) Learn to use the power supply, protoboard, and analog multimeter. b) Learn to measure voltage, current and resistance in simple circuits.
II.
MATERIALS & EQUIPMENT (3) different value resistors (different with other resistors below; for Part A) (1) 1kΩ resistor (1) 100Ω resistor (1) 5.1kΩ resistor (1) 50Ω resistor (1) digital multimeter (DMM) (1) single power supply (1) analog multimeter (AMM) protoboard, connectors and clips
III. PROCEDURE NOTE: You can use a digital multimeter (DMM) to counter-check your measurements using analog multimeter (AMM). A. Measuring Resistance using Ohmmeter 1. Zeroing the meter scale. Choose a resistance range. Short the two meter leads by touching the metallic points together. Use the zero knob on the front of the meter to adjust the pointer so it is aligned with the zero printed on the Ohms scale. On which resistance range the sensitivity of the scale is the least (i.e., cannot be zeroed)? Explain why . 2. Determine the nominal value of the three resistors issued to your group by reading the color code. Record this nominal value in the table below. 3. Using the analog multimeter (AMM) as ohmmeter, select a resistance range/multiplier that, for this resistor, will place the needle somewhere in the middle or right-side of the scale. Zero the meter on this scale, then measure the resistor value. Remember to re-zero if you change scales. You will be able to accurately read the resistance to two significant places, why? Interpolate the third digit. Record the measured value of the resistors using Table I.
Resistors Ra Rb Rc
TABLE I RESISTANCE OF DIFFERENT RESISTORS Color Code Resistance (Ω) (indicate 4-band colors) based on Color Code
Resistance (Ω) based on AMM
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B. Measuring Voltage using Voltmeter 1. Set the function switch on the front of the AMM to DC voltage (V DC), and the range switch on the highest scale. 2. Turn on the power supply and turn the output voltage all the way up. Be careful to observe the proper polarity. Touch the AMM leads to the output jacks on the power supply as shown in Fig. 1. If the needle deflects the wrong way, i.e. to the left instead of to the right, the meter lead positions need to be reversed. Select a scale that places the needle as high as possible on the scale, without pegging the needle. Measure and record the maximum output voltage of the supply.
Figure 1. Connection between power supply and analog multimeter set to VDC.
3. Turn the output voltage all the way down and measure and record the minimum voltage this power supply can produce. If a FINE knob is available on your power supply unit, turn this also to minimum. 4. Repeat steps 2 and 3 to another power supply (borrow from the group beside you). Record your results in the table below. Did you achieve the ideal minimum and maximum voltages? If not, explain why. TABLE II POWER SUPPLY VOLTAGES Power Supply PS1 PS2
Minimum Voltage (mV)
Maximum Voltage (V)
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C. Determining Resistance Using Voltage and Current Measurements 1. Set the power supply to 10V then turn it off. Set up the circuit shown below on a protoboard using R1 = 1kΩ and R2 = 5.1kΩ.
Figure 2. Simple circuit setup.
Draw the circuit including the multimeter which you will use to measure the voltage across R2 and explain why you think this will work. 2. Set the function switch on the AMM to read DC voltage (DCV), and the scale switch to the range appropriate for measuring 10V. Turn on the power supply and then measure the voltage across the resistor R2. Take note of the voltage polarity before taking your measurement. If you don’t get a reading, check your connections carefully. Record the actual voltage to three significant figu res. Draw the circuit including the multimeter which you will use to measure the current through R2 and explain why you think this will work. 3. Set the function controls on the AMM to read DC amperes (DCmA). Start with the scale switch set to the highest scale. One step at a time, change the range switch so that more sensitive current scales are selected. If the needle “pegs” at the upper end of the scale, quickly switch back to the next higher scale. Read the current indicated on the meter and record this value. 4. Using the measured values for the voltage across and the current through this resistor, compute the power dissipated by the resistor R2. Show your solution.
D. Computing Resistance and Error In previous sections of this exercise, you determined the value of the resistor by direct measurement using the ohmmeter and by reading the color code. In this section you will compute the actual resistance using Ohm’s law and compare the results. Show all solutions. 1. Replace R2 with each resistor used in Part A one at a time. With the measured values of the voltage and current obtained using steps C.2 and C.3, solve for the resistance R2 using Ohm’s law. Record the measured and computed values in Table III.
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TABLE III USING OHM’S LAW TO MEASURE RESISTANCE Resistors Resistance of R2 (Ω) computed using Ohm’s Law Ra Rb Rc
2. For the following error calculations, assume that the resistance value determined using the ohmmeter in Part A is the actual value of the resistor R2. Compute error between the measured and nominal/true (color code) value, using the equation,
100% %= 3. Repeat these error calculations for the computed resistance of D.1 as the actual value. Record these values and tabulate the results by creating Table IV.
Resistors
Resistance (Ω) Color Code
TABLE IV ERROR CALCULATIONS Resistance (Ω) Ohmmeter
%
Resistance (Ω) Ohm’s Law
%
Ra Rb Rc 4. Explain the possible origins of any error in these resistance values.
E. Power Ratings 1. Using the Fig. 2 but this time using R1 = 100Ω and R2 = 50Ω, compute for the voltage across, current through, and the power dissipated by each of the resistors. Show solutions. 2. Replace R1 with 1kΩ resistor. Compare with the previous case in terms of power ratings. Explain using circuit analysis.
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Electrical Measurements Laboratory – EEE 34 Name: Student Number: Section: Date:
__________________________________________________________ __________________________ __________________________ __________________________ Experiment 1 (Pre-Lab) Debugging Circuits
Put a check on the box if the corresponding task is accomplished. A. Accomplish and submit the Student Information Card (SIC) Found in EEE 34 Student Laboratory Manual… B. Read and understand Section Connectivity/Continuity Test , Section Potentiometer , Section 2.3.3 Protoboard/Breadboard, Section 3.1 Theory and Practice, Section 2.1.5 Equipment Calibration, and Section 2.3.3.2 Debugging/Troubleshooting Circuits [11] – with all their sub-section/s, if applicable. Do/answer the following (indicate all references used): 1. What is a light-emitting diode (LED)? Briefly discuss its operation. Include diagrams.
2. Some students fear to vary or tweak the circuit against to what is provided in the instructional schematic diagram. This fear originates from possible corresponding costs and consequences to damage to components and equipment properties. However, this fear serves as a barrier why many students cannot learn how to debug circuits. In your own opinion, explain how you will overcome this fear?
REFERENCE/S:
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Electrical Measurements Laboratory – EEE 34 Group Number/Letter: _______ Members: _______________________________ _______________________________ _______________________________
Date: Section:
__________________ __________________
Experiment 1: Debugging Circuits I.
OBJECTIVES a) To recognize the existence of a problem in a non-working circuit. b) To determine the nature of the said problem. c) To debug circuits in a systematic manner.
II.
MATERIALS & EQUIPMENT (1) protoboard (1) single power supply (1) analog multimeter (AMM) (1) 555 IC connectors, clips and probes
III.
(3) 1kΩ resistor (1) 470k Ω resistor (1) red LED (1) green LED (1) 1uF capacitor
PROCEDURE
A. Connectivity/Continuity Test Most, if not all, problems encountered in a non-working circuit are due to points that no longer form electrically continuous connections. The causes may not be observable or easily identifiable when the problem arises. Some of the possible causes include: a blown-up fuse or component, corroded connectors, disconnected or faulty wires, loose connections or simply an unintended open circuit. Constructing circuits usually overlooks a very important assumption – that all wires and connectors are good . Using a bad wire can be troublesome especially if used in a complex circuit. Thus, it is a good practice to check all wires and connectors first before using them in constructing circuits. 1. Set the analog multimeter (AMM) in ohmmeter mode. The multiplier setting is immaterial. Get five (5) connecting wires, five (5) connector clips, two (2) power supply clips, one (1) oscilloscope probe, and one (1) signal generator probe. Label each connector. 2. Use connectivity/continuity test to check if each connector is either good or bad. A 0Ω reading (or even if the needle deflects to the 0Ω direction) indicates a good or connected condition. Construct a table and record the status of each connector. 3. Use connecting wires and connectivity test to verify the connected ports on a protoboard. Draw the protoboard and indicate which group of ports (e.g. row, column) are connected.
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B. Theoretical and Practical Measurements 1. Set the power supply to 10V then turn it off. Set up the circuit shown below on a protoboard using R1 = R2 = 1kΩ.
Figure 1. Theoretical and practical measurements.
2. It is very useful to determine first the theoretical signal values in a circuit before interpreting if acquired measurements are erroneous or not. In other words, the actual values should guide the experimenter if the data being gathered are valid or not. From the circuit, what are the theoretical voltages across the power supply, R1, and R2? 3. Using a voltmeter Vdc, measure the voltage across the power supply, R1, and R2. Tabulate your results. Did you get measurement values close to the actual ones? If not, explain why. 4. Put another resistor R3 = 1kΩ in parallel with R2. Repeat steps B.2 and B.3.
C. Simple Circuit to Test if a Component is Working Properly 1. Construct the circuit shown in Figure 2. Use R = 1kΩ, Vs = 10V, and two differentlycolored LEDs for D1 and D2. The diagram for LED is also provided.
Figure 2. Simple circuit. [0b-1]
2. Assuming your wiring is correct and all LEDs are in good condition, only one LED should be lit. Which one (D1 or D2)? Measure the voltages Vin and Vout using a voltmeter Vdc. 3. Now, reverse the position of both D1 and D2. Which LED is lit at this moment? Note that this procedure tests if an LED is working or not. However, there are easier and more creative ways to check the condition of an LED. This is just one way to demonstrate testing of components using a simple circuit.
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D. Complex Circuit 1. Construct the circuit shown in Figure 3. The 555 IC pin-outs is shown in Figure 4. This circuit emulates the traffic lights we see in the streets. Make the circuit work and call the attention of your instructor once done. The dots indicate connected nodes and jumps are not connected nodes.
Figure 3. Flashing LED circuit. [0b-2]
Figure 4. 555 IC pin-outs. [0b-3]
2. Setup your circuit supposing that you “carelessly” constructed it (i.e., it should not function properly). It might be wrong wiring, different components, faulty wires, faulty components, etc. 3. Find a partner group that is also finished with D.1 and D.2. Exchange circuit/protoboard. Debug the circuit. Document how your group debugged the circuit in a systematic manner. It would be easier to provid e a step-by-step process.
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IV.
REQUIRED DISCUSSION 1. There are some scenarios wherein connectors are continuous only in a certain orientation or position, or when held tightly/loosely, or left hanging. What might this suggest? 2. Suppose the battery and light bulb circuit shown in Figure 5 failed to work, explain how you will use the divide-and-conquer approach approach to debug the circuit. At which pair of nodes will you start st art checking for voltage measurement? Explain.
Figure 5. Battery and light bulb circuit. [0b-4]
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Electrical Measurements Laboratory – EEE 34 Name: Student Number: Section: Date:
__________________________________________________________ __________________________ __________________________ __________________________
Experiment 2 (Pre-Lab) DC Measurements (Current) Put a check on the box if the corresponding task is accomplished.
Found in EEE 34 Student Laboratory Manual… Read and understand Section 2.3.2 D’Arsonval Galvanometer or 1mA Movement , Section 3.4 Circuit-Level Analysis of the Multimeter, Multimeter, Section 3.4.3 DC Ammeter, Ammeter, Section 3.4.4 DC Voltmeter, Voltmeter, Section 3.4.5 Ohmmeter, Ohmmeter, Section 2.1.5 Equipment Calibration, Calibration, and Section Potentiometer – with all their subsection/s, if applicable. Do/answer the following (indicate all references used): 1. What is/are the IDEAL characteristic/s of a voltage source? Of a current source? Voltage Source
Current Source
2. What is/are the IDEAL characteristic/s of an ammeter, voltmeter and ohmmeter? Ammeter
Voltmeter
Ohmmeter
3. Which of the meters (ammeter, voltmeter, or ohmmeter) need/s an internal power source to operate? Which do/does not and why?
REFERENCE/S:
57
Electrical Measurements Laboratory – EEE 34 Group Number/Letter: _______ Members: _______________________________ _______________________________ _______________________________
Date: Section:
__________________ __________________
Experiment 2: DC Measurement Measurementss (Current) I.
OBJECTIVES a) To know the different methods of making analog DC current measurements and to know when each method is applicable b) To be able to specify the degree of accuracy of any measurements made
II.
MATERIALS & EQUIPMENT (2) Variable DC Voltage Supplies (1) 1mA Movement (1) Potentiometer Box (1) Digital Multimeter
III.
(1) Analog Multimeter (3 per value) Resistors 100, 1 k , 10 k (1) Resistor 10-20 Protoboard, Connecting Wires, Alligator Clips
PROCEDURE
A. Determining the Internal Resistance of the 1mA Movement 1. Connect the circuit shown in Figure 1 with R2 disconnected and the power supply turned off. The voltage adjustment knob of the power supply should be set to minimum (fully counter-clockwise). 2. Turn the power supply on. Slowly increase Vs using the voltag e adjustment knob. The 1mA movement needle should start to move upscale. Continue increasing Vs until the needle indicates full-scale (1 mA). 3. Connect R2. Use a 200 or 500 potentiometer. Its initial setting is immaterial. Nevertheless, once inserted, the 1mA movement reading should decrease. Adjust the shaft of R2 until the 1mA movement indicates half-scale (0.5 mA). (If the current through the ammeter does not reach half-scale using the 200 potentiometer, try a larger valued potentiometer.) 4. Disconnect R2. Measure its resistance using an ohmmeter. The value measured will be approximately equal to the internal resistance of the 1mA movement, Rm. B. Errors in Current Measurements Due to Insertion Effects 1. Refer to the circuit in Figure 2. For each combination of Vs and R in Table I, compute for the value of the current, I , that should flow. Make sure that you are using the correct value for Vs! Use a digital voltmeter if necessary. Fill out Table I correspondingly. TABLE I CURRENT MEASUREMENTS Vs (V) I , Ideal (mA) I , Measured using 1mA movement (mA) R (Ω) 0.1 200 1 2k 10 20 k
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2. For each of these same combinations, set up the circuit of Figure 2 and measure the current that flows by replacing the short circuit between a and b with your 1mA movement. Complete Table I with your measured values. C. Extending the Range of the 1mA Movement 1. The full-scale range of a 1mA movement can be extended by connecting a shunt resistor across it, as shown in Figure 3. Given knowledge on the value of your Rm, compute for the value of the shunt resistor, Rsh that will extend the range of your ammeter from 1 mA to 10 mA. 2. Use the scheme of Figure 4 to obtain a resistance with a value equal to that computed in Procedure A above (use a 10-20 resistor). This setup will act as your shunt resistance in Figure 3. Or you can just use a resistor with a value near to the one you computed in Procedure C.1. 3. Setup the newly-constructed 10mA movement. Check its operation with the three calibration values indicated in Table II. As shown in Figure 3, neglecting the internal resistance of the newly-constructed 10mA movement, you can vary the voltage supply instead to obtain the calibration current values. For example, if Vs = 2V and R = 1k in series, then a 2mA current should flow through the circuit. Fill up the table correspondingly. TABLE II CHECKING THE OPERATION OF THE 10mA MOVEMENT Calibration 1mA movement Corresponding Current (mA) Reading (Deflection) Reading of Iu (mA)
Measured
Computed
2 4 6 8 10
Figure 1
Figure 1. Determining the internal resistance of the 1mA movement.
Figure 3. Newly-constructed 10mA movement.
Figure 2. Investigating insertion error in current measurements.
Figure 4. Obtaining the required shunt resistor.
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IV.
REQUIRED DISCUSSION Try to answer the following while you are inside the laboratory. Some questions can be answered by further investigating the procedure stated above. 1. If we are to measure the internal resistance of the 1mA movement, why not use an ohmmeter right away? State possible reasons. 2. Show that the method used in determining the internal resistance of the 1mA movement is just an approximation. What is the internal resistance of your ammeter based on the procedure? Assuming that the internal resistance you obtained is typical of an ammeter, show that for the resistor R1 used in the procedure, the approximation has high accuracy. 3. Based on the meter resistance of your 1mA movement, predict the accuracy that you should obtain for each of the measurements made in Procedure B. Compare these figures with the actual accuracy of your measurements. Account for any differences. Extend Table I (or create a new table) to show these figures. 4. Show how you computed for the value of Rsh to be used to convert your 1mA movement into a 10mA movement. What is the combined meter resistance of your 10mA movement? 5. Discuss the linearity and accuracy of the 10mA movement you constructed based on the calibration points given to you in Table II. What are the possible sources of error, (if there is any)?
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Electrical Measurements Laboratory – EEE 34 Name: Student Number: Section: Date:
__________________________________________________________ __________________________ __________________________ __________________________
Experiment 3 (Pre-Lab) DC Measurements (Voltage) Put a check on the box if the corresponding task is accomplished.
Found in EEE 34 Student Laboratory Manual… Read and understand again Section 2.3.2 D’Arsonval Galvanometer or 1mA Movement , Section 3.4 Circuit-Level Analysis of the Multimeter, Section 3.4.3 DC Ammeter, Section 3.4.4 DC Voltmeter, Section 3.4.5 Ohmmeter, Section 2.1.5 Equipment Calibration, and Section Potentiometer – with all their subsection/s, if applicable. Do/answer the following (indicate all references used): 1. Given the knowledge on the operation of 1mA movement (i.e., galvanometer), explain how it can be used to measure voltage. Explain loading error in using this method.
2. Explain the principle behind (voltage/current) source transformation.
3. Explain how a potentiometer can be used as a vo ltage divider. Provide a circuit diagram.
REFERENCE/S:
61
Electrical Measurements Laboratory – EEE 34 Group Number/Letter: _______ Members: _______________________________ _______________________________ _______________________________
Date: Section:
__________________ __________________
Experiment 3: DC Measurements (Voltage) I.
OBJECTIVES a) To know the different methods of making analog DC voltage measurements and to know when each method is applicable b) To be able to specify the degree of accuracy of any measurements made
II.
MATERIALS & EQUIPMENT (2) Variable DC Voltage Supplies (1) 1mA Movement (1) Potentiometer Box (1) Protoboard
III.
(1) Analog Multimeter [AMM] (1) Digital Multimeter [DMM] (3 per value) Resistors 1 k , 10 k , 100 k Connecting Wires, Alligator Clips
PROCEDURE
A. Determining the Internal Resistance of the 1mA Movement Use a digital multimeter set to ohmmeter and measure the internal resistance of your 1mA movement. Record its value. B. The DC Voltmeter using 1mA Movement 1. A DC ammeter can be used to measure voltage by simply connecting a resistor in series with it, as shown in Figure 2. Compute the value of the series resistance Rs that will enable your 1mA movement to measure DC voltages up to 10 volts. 2. Use the potentiometer to obtain the resistance computed in step 1 above. Set up your 10V full-scale voltmeter. Check its operation with the three calibration values indicated in Table I. Use the power supply for each calibration voltage value. Fill out Table I correspondingly. NOTE: You can use a standard resistor value if the internal resistance of 1mA movement is very low. TABLE I DC VOLTMETER USING 1mA MOVEMENT Calibration 1mA Movement Corresponding Voltage (V) Reading (Deflection) Reading of Vu (V) 2 4 6 8 10
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C.
Errors in Voltage Measurements Due to Loading Effects 1. Refer to the circuit in Figure 3. For each of the values of R given in Table II, compute for the value of Vx that should be obtained. Fill out Table II correspondingly. 2. For each of the values of R in Table II, set up Figure 3 and measure the voltage Vx using your just constructed voltmeter (see Figure 2). Fill the measured values into Table II. TABLE II LOADING EFFECTS IN VOLTAGE MEASUREMENTS Theoretical Vx (V) Measured Vx (V) R (Ω) 1k 10 k 100 k
D.
The Potentiometer Bridge Method of Measuring Voltage 1. The potentiometer bridge method can be used to make voltage measurements with absolutely no loading effect on the measured circuit. A potentiometer bridge ‘voltmeter’ is shown in Figure 4. The DC supply should be set to the desired full -scale voltage. The potentiometer is adjusted such that the resistance between points X and Y is initially zero to avoid a reverse reading in your multimeter. A voltage measurement is made by: a. connecting terminals a & b to the unknown voltage to be measured, making sure that proper polarities are observed b. adjusting the potentiometer until the 1mA movement reads zero, then c. disconnecting a & b and removing the potentiometer from the circuit. d. measuring the resistance RXY . Also, measure the resistances RWX and RWY. The measured voltage should correspond to the value determined by voltage division. 2. Repeat Procedure C using the potentiometer bridge method. Fill out Table III with your measurements. NOTE: Since Figures 3 and 4 use the same voltage level (10Vdc), you can in fact use a single DC supply and implement them in parallel.
R (Ω) 1k 10 k 100 k
TABLE III LOADING EFFECTS IN VOLTAGE MEASUREMENTS Theoretical Vx (V) RXY (Ω) RWY (Ω) Corresponding Vx (V)
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Figure 1. Determining the internal resistance of the 1mA movement.
Figure 2. DC Voltmeter to measure an unknown voltage using the 1mA movement.
Figure 3. Investigating loading effects in voltage measurements.
Figure 4. Measuring an unknown voltage using potentiometer bridge technique.
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IV.
REQUIRED DISCUSSION Try to answer the following while you are inside the laboratory. Some questions can be answered by further investigating the procedure stated above. 1. Show how you computed for the value of Rs to be used to convert your 1mA movement into a 10 V voltmeter. What is the internal resistance of your 10 V voltmeter? 2. Using a graph, plot the measured voltage Vreading (y-axis) vs. calibration voltage Vcalibration (x-axis) in Table I. In the same graph, also plot the ideal function Vreading = Vcalibration. Compare the two plots. Discuss the linearity and accuracy of the 10V voltmeter you constructed based on the calibration. What are the possible sources of error (if there is any)? 3. Based on the internal resistance of your 10V voltmeter, predict the accuracy that you should obtain for each of the measurements made in Procedure C. Compare these figures with the actual accuracy of your measurements. Account for any differences. Extend Table II (or create a new table) to show these figures. 4. Prove that the measured voltage across a & b in Procedure D is equal to the unknown voltage being measured. Why is there no loading effect when this technique is used to measure voltages? Is this consistent with your results? Account for any errors. 5. What are the advantages and disadvantages associated with each technique used to measure voltage in this exercise?
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Electrical Measurements Laboratory – EEE 34 Name: Student Number: Section: Date:
__________________________________________________________ __________________________ __________________________ __________________________
Experiment 4 (Pre-Lab) Resistance Measurements Put a check on the box if the corresponding task is accomplished.
Found in EEE 34 Student Laboratory Manual… Read and understand again Section 2.3.2 D’Arsonval Galvanometer or 1mA Movement , Section 3.4 Circuit-Level Analysis of the Multimeter, Section 3.4.3 DC Ammeter, Section 3.4.4 DC Voltmeter, Section 3.4.5 Ohmmeter, Section 2.1.5 Equipment Calibration, and Section Potentiometer – with all their subsection/s, if applicable. Do/answer the following (indicate all references used): 1. From the previous experiments, what practical issues have you learned so far?
2. Do these change the way you view theories in circuit analysis? If yes, how? Otherwise, why?
3. State possible precautions in using an ohmmeter.
REFERENCE/S:
66
Electrical Measurements Laboratory – EEE 34 Group Number/Letter: _______ Members: _______________________________ _______________________________ _______________________________
Date: Section:
__________________ __________________
Experiment 4: Resistance Measurements I.
OBJECTIVES a) To know the different methods of measuring resistance b) To know when each method can be applied c) To be able to specify the accuracy of any measurements made
II.
MATERIALS & EQUIPMENT (1) Variable DC Supply (1) 1 mA Movement (1) Digital Multimeter (1) Analog Multimeter
III.
(1) Potentiometer Box (1 each) Resistors Ra, Rb, Rc and 10kΩ, 20kΩ (1) 10k Ω potentiometer Protoboard, Connecting Wires, Alligator Clips
PROCEDURE
A. The Series Ohmmeter Method 1. Set up the circuit of Figure 1. Set the power supply to 10V and use a 10K potentiometer for R2. Make sure that the potentiometer is set to maximum and it reaches the indicated value (or more). 2. Short together terminals a & b and adjust R2 until the 1mA movement indicates full scale. Leave R2 at this setting. 3. Your instructor will have available three resistors Ra, Rb and Rc whose resistances you are supposed to determine. Record into Table I the deflection D produced by each resistance in the 1mA movement when the resistance is connected to the circuit at terminals a & b.
; ∈ [0,1] = 1 TABLE I
Resistor Ra Rb Rc
SERIES OHMMETER METHOD Deflection (D) Corresponding Resistance Reading (Ω)
Using the equation Ru = Ro (1 - D)/D, where Ro = Rm + R2, compute the corresponding resistance readings and record these in Table I. B. The Voltmeter - Ammeter Method 1. The same resistances Ra, Rb and Rc are to be determined using the circuit in Figure 2. Use an analog multimeter as the voltmeter and the 1mA movement as the ammeter. Do not use the digital voltmeter (DVM) as the intended loading effects will not be observed. Vs may be set to any reasonable value provided that the 1mA movement does not go beyond
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full-scale and the maximum power rating of Ru (unknown resistor) is not exceeded. In other words, Ru should not get too hot while in the powered circuit. For each of the unknown resistances connected in place of Ru, record the readings of the voltmeter and the ammeter. Fill the readings into Table II.
Resistor Ru Ra Rb Rc
Vs (V)
TABLE II VOLTMETER-AMMETER METHOD A Voltmeter Ammeter reading Corresponding Resistance reading (V) (mA) Reading* (Ω)
*neglecting loading effects from meters 2. Repeat the above procedure using the circuit of Figure 3 to fill in Table III.
Resistor Ru Ra Rb Rc
Vs (V)
TABLE III VOLTMETER-AMMETER METHOD B Voltmeter Ammeter reading Corresponding Resistance reading (V) (mA) Reading* (Ω)
*neglecting loading effects from meters C. The Wheatstone Bridge Method 1. The Wheatstone bridge method is a popular method of measuring resistance particularly in the field of instrumentation. Figure 4 shows a Wheatstone bridge circuit. Set up the circuit in Figure 4. Use a potentiometer for R3. Let R1 = 10kΩ and R2 = 20kΩ. Verify that the power rating (0.25 W) of R1 and R2 are not exceeded even with a source voltage of 20V. Use the voltmeter mode of the analog multimeter. Make sure of the polarity. 2. Before turning the power on, the potentiometer R3 should first be set to maximum (for minimum power dissipation). Choose the potentiometer with the greatest resistance value. Two measurements will be made for each unknown resistance, one with Vs = 5 volts and another with Vs = 10 volts. The voltmeter should be initially set to be able to read the maximum imbalance of the bridge, which is Vs. Powering up the circuit, the voltmeter must be able to read a POSITIVE voltage. 3. The value of Ru can be determined from the values of R1, R2 and R3 if the bridge is balanced. The objective, therefore, is to get the bridge balanced by adjusting the potentiometer until the voltmeter reads zero (or the lowest you can get since the potentiometer has limited adjustment resolution). Decrease the effective resistance of R3 until you get a zero. If you are having a hard time obtaining a null, use the next lower value of the potentiometer. Remember to set first the effective R3 to the highest resistance setting before adjusting the knob. 4. For each of the resistances Ra, Rb and Rc, take note of the resistance R3 that balances the bridge for each of the power supply settings specified in C.2 above. This can be done by disconnecting R3 from the circuit and measuring the resistance on the potentiometer. Fill the obtained values into Table IV. Use a digital multimeter.
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TABLE IV WHEATSTONE BRIDGE METHOD Resistor Ru Ra Rb Rc
R3 (Ω) at Vs = 5V
R3 (Ω) at Vs = 10V
5. Answer the required discussion question #6 before asking the actual values Ra, Rb, and Rc from your instructor. Do the values obtained make sense?
Figure 1. Series ohmmeter method
Figure 3. Voltmeter-ammeter method B
Figure 2. Voltmeter-ammeter method A
Figure 4. Wheatstone bridge method
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IV.
REQUIRED DISCUSSION Try to answer the following while you are inside the laboratory. Some questions can be answered by further investigating the procedure stated above. 1. Show that the relationship between unknown resistance Ru and deflection D for the series ohmmeter circuit of Figure 1 is given by: Ru = Ro (1 - D)/D, where Ro = Rm + R2 ; D = (I mA)/(1mA) In our case, what is the value of Ro? Why was it not necessary to measure the value of R2 to be able to determine the value of Ro? 2. Use the equation given in IV.1 above to determine the values of Ra, Rb and Rc. Treat these as your experimental results. Compare these with the actual values of Ra, Rb, and Rc given by your instructor. NOTE: Let the color codes correspond to their theoretical values. Account for any differences. Extend Table I (or create a new table) to show your results. 3. From the voltage and current readings obtained in Procedure B, compute the corresponding resistance values of Ra, Rb, and Rc both for the circuit of Figure 2 and the circuit of Figure 3. Neglect the loading effect of the meters. Compare these with the actual values of Ra, Rb and Rc. Tabulate your results. Account for any differences obtained. 4. From the voltage and current readings obtained in Procedure B, re-compute the corresponding resistance values of Ra, Rb and Rc taking i nto account the loading effect of the meters. How do these compare with the previously computed values and with the actual values of Ra, Rb and Rc? 5. Given the two possible arrangements for making resistance measurements using the voltmeter-ammeter method, when should one method be used instead of the other if the resistance is to be taken as the voltage reading divided by the current reading? 6. Derive the relationship between R1, R2, R3 and Ru for the Wheatstone bridge circuit of Figure 4 under balanced conditions. 7. Taking into account the tolerances of the resistances used in the bridge, compute for the range of possible values of Ra, Rb and Rc from the values of R3 obtained in Procedure C. Do the actual values of Ra, Rb and Rc fall within the computed ranges? 8. What was the actual effect of varying the power supply voltage on the resistance measurements made using the Wheatstone bridge method? What should the actual effects have been? 9. Compare the three methods of making resistance measurements taking into consideration simplicity, cost, speed, accuracy of measuring equipment, tolerance of resistances used, and any other points that may be of interest.
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Electrical Measurements Laboratory – EEE 34 Name: Student Number: Section: Date:
__________________________________________________________ __________________________ __________________________ __________________________
Experiment 5-a/d (Pre-Lab) Introduction to Oscilloscopes Put a check on the box if the corresponding task is accomplished. Familiarize with different parts of an analog oscilloscope. You can use http://en.wikibooks.org/wiki/Practical_Electronics/Oscilloscopes as a guide or start but not as a reference.
Found in EEE 34 Student Laboratory Manual… Read and understand Section 2.1.2 Function/Signal Generator, Section 2.1.3 Analog Oscilloscope, and Section 2.1.4 Digital Oscilloscope. Do/answer the following (indicate all references used): 1. What is an oscilloscope?
2. What are the uses of an oscilloscope?
3. Tell the difference between analog and digital oscilloscope.
4. Given a sinusoidal signal, explain the amplitude, frequency and period through illustration.
REFERENCE/S:
71
Electrical Measurements Laboratory – EEE 34 Group Number/Letter: _______ Members: _______________________________ _______________________________ _______________________________
Date: Section:
__________________ __________________
Experiment 5-a: Introduction to Oscilloscopes (Analog) I.
OBJECTIVES a) To familiarize the student with the operation of a triggered sweep oscilloscope. b) To be able to make basic measurements using an oscilloscope
II.
MATERIALS & EQUIPMENT (1) Dual Trace Triggered Sweep Oscilloscope (1) Signal Generator
III.
PROCEDURE
NOTE: Not all oscilloscopes in the laboratory are of the same brand/version. Varying a setting may vary from one to another (e.g. pulling a knob instead of rotating, etc.). Nonetheless, the basic knobs (and functionalities) should be present on the front panel of any oscilloscope. The student is expected to familiarize him/herself with different oscilloscope interfaces in the laboratory.
Part 1: Initial Settings for Single Trace Operation Before turning the power on, set the oscilloscope as instructed below. Display System Controls: Set the INTENSITY approximately halfway between extremes. Vertical System Controls: Set the vertical mode to Channel 1. Set the Channel 1 VOLTS/DIV selector switch to the least sensitive position (fully counterclockwise). The VAR control knob of the VOLTS/DIV switch (usually at the center of the VOLTS/DIV selector switch) should be in its calibrated detent position [fully pressed, fully counterclockwise (or clockwise) until it locksdirection depends on the location of “ CAL”, the calibrated position] Set the Channel 1 input coupling to GND. Note: Some oscilloscopes label their vertical channels Channel A & B or Channel X & Y instead of Channel 1 & 2. Horizontal System Controls: Set the SEC/DIV (or MAIN TIME/DIV) switch to 0.5 ms. The VAR control knob of the SEC/DIV switch (usually at the center of the SEC/DIV selector switch) should be in its calibrated x 1 detent position. Trigger System Controls: Set the trigger mode to AUTO. Set the trigger source to Channel 1 (internal). Set the trigger slope to '+'.
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Part 2: The Display System Controls Make sure the line voltage setting on the oscilloscope is correct before turning on the power. Turn the oscilloscope on and allow it to warm up for approximately 30 seconds. Locating the Beam: A horizontal line should appear on the screen. You may have to use the Channel 1 vertical POSITION control knob to locate the line. Position the line at the center of the screen. Use the horizontal POSITION control knob to horizontally center the trace. Try to explore the extreme positions using these knobs. Return the beam back to the center of the screen. Focus: The trace you have on the screen may be out of fo cus. Make it as sharp as possible with the FOCUS control.
Intensity: Set the brightness or illumination to a level comfortable to you. Refrain from setting the screen too bright to preserve the screen (i.e. make it last longer). Trace Rotation: A trace rotation screw is sometimes available for adjusting the display should the trace not be perfectly horizontal.
Part 3: The Vertical System Controls Connect the base of a probe to the Channel 1 vertical input connector. If the probe has an adjustable attenuation, set it to x 10. Compensating the Probe: Set the Channel 1 VOLTS/DIV switch so that the oscilloscope displays 0.2 volts/division. Make sure the VAR control knob is in its calibrated detent position. Remember that you are using a x10 probe. (Generally, you would have to multiply the VOLTS/DIV indication by 10 to get the correct calibration.) Set the channel 1 input coupling to AC. Connect the probe tip to the PROBE ADJ terminal (on some oscilloscopes, this is the CAL terminal) provided on the oscilloscope. If the signal is too small, adjust the VOLTS/DIV knob such that your signal is at least 1 major division peak-to-peak (i.e. from minimum to maximum). If the signal on the screen is not steady, adjust the trigger LEVEL control until the signal stabilizes. If the signal still does not stabilize, adjust the SEC/DIV knob and then the trigger LEVEL control until you stabilize your signal. Display 2-3 cycles of the signal. 1. Draw the exact wave shape that appears on the screen. Show how the display appears in relation to the graticule markings on the oscilloscope face. (The wave that appears on the screen should be perfectly square. If it is not, a screwdriver adjustment should be made on the compensation box at th e base of the probe until a square waveform is obtained.)
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2. Set the probe to x1. Choose an appropriate VOLTS/DIV setting such that the whole waveform is visible. Draw the exact waveform and indicate the VOLTS/DIV and SEC/DIV used. What is the difference between a x1 and a x10 probe? What is the advantage of one over the other?
3. Why is compensation needed? What do you actually do when you compensate a probe? Does an x1 probe have to be compensated?
Controlling Vertical Sensitivity: Set the probe attenuation back to x10, VOLTS/DIV setting to 0.2 volts/div and SEC/DIV to 0.5 ms/div. Adjust the Channel 1 vertical POSITION control knob to line up the lower edge of the PROBE ADJ waveform with the center graticule line. 4. How many major divisions is the height of the displayed waveform? What is the corresponding peak-to-peak voltage of the PROBE ADJ signal?
5. Turn the Channel 1 VOLTS/DIV switch two click stops to the right (clockwise). What is the new Channel 1 scale factor?
6. How many major divisions is the height of the displayed waveform now? Is this consistent with the measurement made in 4 above?
7. What is the effect of turning the VAR control knob of the VOLTS/DIV switch out of its detent position? What possible use could this knob have?
Return the VAR knob to its detent position.
Coupling the Signal: Set the Channel 1 input coupling to GND and position the trace on the center graticule line.
74 8. With the probe connected to the PROBE ADJ terminal, switch the Channel 1 input coupling to AC. What is the eventual position of the waveform on the screen?
9. Is this true for all settings of the VOLTS/DIV switch?
10. Now switch Channel 1 input coupling to DC. What happens to the displayed signal?
11. What is the difference between AC and DC coupling? When should one be used in place of the other? (Use the trigger level to stabilize the waveform in case it is unstable).
The Vertical Mode Controls: Connect a probe to the channel 2-input connector. Do not forget to set the probe to x10 if it is adjustable. Set the Channel 2 VOLTS/DIV switch to 0.2 volts and the Channel 2 VOLTS/DIV VAR control knob to its calibrated detent position. Set the channel 2 input coupling to GND. Set the vertical mode to CH 2(channel 2). The displayed signal will now come from the channel 2 connector. Vertically position the channel 2 trace to the center of the screen with the channel 2 vertical POSITION control. Set the channel 2 coupling to AC and check the compensation of the channel 2 probe as you did with the channel 1 probe. Play around with the channel 2 controls as you did with the channel 1 controls to give you a feel for using channel 2. With both the channel 1 and channel 2 probes connected to the PROBE ADJ terminal, set their corresponding input coupling to AC and set also the vertical mode to DUAL TRACE (this corresponds to either the CHOP or ALT mode on other oscilloscopes). The signals from both probes will simultaneously appear on the screen. Use the vertical POSITION control of either channel to separate the traces. You may have to readjust the INTENSITY control to get the desired intensity. Try both the ALT and CHOP modes. For each mode, adjust the SEC/DIV to a very slow setting (counter-clockwise) and observe how the traces are made. Try to observe how the 2 modes are different.
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Part 4: The Horizontal System Control Making Time Measurements: Switch the vertical mode back to CH 1 and display the PROBE ADJ signal at the center of the screen. Use the horizontal POSITION control knob to adjust the display until one rising edge of the displayed waveform is aligned with the center vertical graticule. 12. How many major and minor horizontal graticule markings is it to the next rising edge of the waveform? How many seconds does this correspond to?
13. Change the sweep SEC/DIV setting to 0.2 ms. How many graticule markings is one period of the displayed waveform now? Are your two measurements consistent?
14. Set the SEC/DIV switch back to 0.5 ms. Turn the VAR control knob of the SEC/DIV switch out of its calibrated x1 detent position. How does this affect the display? What are the possible uses of this knob?
Return the VAR control knob to its calibrated x1 detent position. 15. Pull the horizontal position control knob (on other oscilloscopes, this corresponds to pulling the VAR control knob) to magnify the sweep SEC/DIV (x5 on some scopes, x10 on other scopes). What is the new horizontal scale factor (SEC/DIV)?
16. How many graticule markings is the period of the displayed waveform now? Is this consistent with your previous measurements?
Part 5: The Trigger System Slope Control: Restore the sweep SEC/DIV to x1 (unmagnified, i.e. VAR returned to x1 detent). Use the oscilloscope to display, through channel 1, a 15 KHz, 2 volt peak-to-peak sinusoidal voltage with no DC offset. Adjust the sweep speed (SEC/DIV) so that two to three cycles of the waveform are displayed. Move the trace to the right with the horizontal POSITION control until you can see the beginning of the trace. 17. Draw the resulting traces as you vary the SLOPE control from '+' to '-'. How does each setting affect the display? Explain why.
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Trigger Level and Trigger Mode: NOTE: Trigger mode is in AUTO 18. Move the trigger LEVEL control back and forth through all of its travel. How does this affect the start of the trace? Why?
Notice that while the signal might lose synchronism at some level control settings, the trace never disappears. 19. Set the Trigger Mode switch to NORMAL. Now when you use the trigger LEVEL control to move the triggering point, you'll find places where the trace disappears. Explain this difference in behaviour between normal and auto triggering.
Reset the trigger mode to AUTO. Increase the VOLTS/DIV setting to the next more sensitive position (clockwise). 20. Move the trigger point using the trigger LEVEL control as you did in 18 above. Which VOLTS/DIV setting allows the trigger level control knob to have a larger range of motion before the waveform becomes unstable? If you do not perceive any difference, try an even more sensitive VOLTS/DIV setting.
21. Is the trigger level a voltage level or a 'number of divisions' level? Exp lain.
Dual Trace Triggering: Set the vertical mode to DUAL TRACE (ALT or CHOP on other oscilloscopes). Simultaneously display the signal generator output and the PROBE ADJ signal. 22. Only one of the signals can be made stable using the trigger LEVEL control? Which one and why? Does your scope have the capability of making the other trace appear stable? Explain.
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External Trigger: Reset the scope for single trace Channel 1 operation and redisplay the signal generator output. Now set the trigger source to EXT. 23. Can the trace be stabilized using the trigger LEVEL control knob? Why or why not?
24. Transfer the channel 2 probe to the EXT TRIGGER input connector (this means that the 2 probes are in parallel with the signal source). The display can now stabilize when the external trigger input is connected to the signal source? Why?
25. Does the trigger LEVEL control behave in the same manner as with internal triggering when the vertical sensitivity is increased? (observed in 19)
26. In this case, is the trigger level a voltage level or a 'number of divisions' level?
27. Do the SLOPE control and the mode AUTO and NORMAL setting still behave in the same way?
Line Triggering: 28. Set the trigger source to LINE. The display should destabilize. Why?
29. Lower the signal generator output frequency (around 500 Hz) until the display stabilizes. At what frequency is a stable display achieved?
Continue lowering the signal generator output. Obtain four to five frequencies at which a stable display is obtained. 30. What signal frequencies can be displayed with stability with the trigger source set to line? Why? What possible use could this feature have?
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The following are empty grid scales that you can use in sketching waveforms.
Volts Div: _________ Time Div: _________
Volts Div: _________ Time Div: _________
Volts Div: _________ Time Div: _________
Volts Div: _________ Time Div: _________
Volts Div: _________ Time Div: _________
Volts Div: _________ Time Div: _________
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Electrical Measurements Laboratory – EEE 34 Group Number/Letter: _______ Members: _______________________________ _______________________________ _______________________________
Date: Section:
__________________ __________________
Experiment 5-d: Introduction to Oscilloscopes (Digital) I.
OBJECTIVES c) To familiarize the student with the operation of a triggered sweep oscilloscope. d) To be able to make basic measurements using an oscilloscope
II.
MATERIALS & EQUIPMENT (1) Dual Trace Triggered Sweep Oscilloscope (1) Signal Generator
III.
PROCEDURE
NOTE: Not all oscilloscopes in the laboratory are of the same brand/version. Varying a setting may vary from one to another (e.g. pulling a knob instead of rotating, etc.). Nonetheless, the basic knobs (and functionalities) should be present on the front panel of any oscilloscope. The student is expected to familiarize him/herself with different oscilloscope interfaces in the laboratory.
Part 1: Initial Settings for Single Trace Operation Like all complex measuring equipment, necessary settings have to be configured: On the Display Menu, set the Grid setting so that the grid appears on the display On the Channel Menu, i.e. CH1 and CH2, set the Volts/Div setting to Coarse. Still on the Channel Menu set the Probe setting to x1 by default.
Some convention on this document: Major divisions indicates the large graduations on the grid on the oscilloscope screen while minor divisions indicate the smaller graduations on the grid. The division pertained on VOLTS/DIV or SEC/DIV are the major divisions. Vertical System Controls: Find the vertical controls on the scope. Set the vertical mode to Channel 1 by pressing CH1. Pressing it again shows the menu for Channel 1. It might also indicate which channels are active by lighting up the button. Set the Channel 1 VOLTS/DIV (it is the vertical SCALE knob on most digital scopes) selector switch to the least sensitive position (fully counterclockwise). Set the Channel 1 input coupling to GND. Channel 1 input Coupling can be accessed in the Channel 1 menu. Note: Some oscilloscopes label their vertical channels Channel A & B or Channel X & Y instead of Channel 1 & 2. Horizontal System Controls: Find the horizontal controls on the scope.
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Set the SEC/DIV (or MAIN TIME/DIV; it is the horizontal SCALE knob in most scopes) switch to 0.5 ms.
Trigger System Controls: Find the trigger controls on the scope. On the trigger menu, do the following: Set the trigger mode to EDGE. o Set the trigger sweep to AUTO. o Set the trigger source to Channel 1 (internal). o Set the trigger slope to ' ↑'. o Part 2: The Display System Controls Locating the Beam: A horizontal line should appear on the screen. You may have to use the Channel 1 vertical POSITION control knob to locate the line. Position the line at the center of the screen (For digital scopes, it is centered by default). Use the horizontal POSITION control knob to horizontally center the trace. Try to explore the extreme positions using these knobs. You will notice that the position label POS in the screen varies. Return the beam back to the center of the screen. Part 3: The Vertical System Controls Connect the base of a probe to the Channel 1 vertical input connector. If the probe has an adjustable attenuation, set it to x 10. On digital oscilloscopes, you can adjust the probe attenuation on the probe setting in the Channel 1 menu as you initially set. Some probes don't have an attenuation switch but has default attenuations such as x100, etc. Check the label/s on your probe. Compensating the Probe: Set the Channel 1 VOLTS/DIV switch so that the oscilloscope displays 0.2 volts/division. The volts/div setting can be checked via the CH1 label on the screen. Remember that you are using a x10 probe. Set the channel 1 input coupling to AC. Connect the probe tip to the PROBE ADJ terminal (on some oscilloscopes, this is the CAL terminal; mostly it is labeled by a square wave or pulse with 2Vpp) provided on the oscilloscope. If the signal is too small, adjust the VOLTS/DIV knob such that your signal is at least 1 major division peak-to-peak (i.e. from minimum to maximum). If the signal on the screen is not steady, adjust the trigger LEVEL control until the signal stabilizes. Display 2-3 cycles of the signal by adjusting the SEC/DIV knob. 1. Draw the exact wave shape that appears on the screen. Show how the display appears in relation to the graticule markings on the oscilloscope face. (The wave that appears on the screen should be perfectly square. If it is not, a screwdriver adjustment should be made on the compensation box at th e base of the probe until a square waveform is obtained.) 2. Set the probe to x1. Choose an appropriate VOLTS/DIV setting such that the whole waveform is visible. Draw the exact waveform and indicate the VOLTS/DIV and SEC/DIV used. What is the difference between a x1 and a x10 probe? What is the advantage of one over the other? (If your probe doesn't have a x10 attenuation switch, borrow from other groups. Then, return it after trying it out.) 3. Why is compensation needed? What do you actually do when you compensate a probe? Does an x1 probe have to be compensated?
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Controlling Vertical Sensitivity: Set the probe attenuation back to x10, VOLTS/DIV setting to 0.2 volts/div and SEC/DIV to 0.5 ms/div. If you do not have an attenuation switch, you can use the probe attenuation setting on the Channel 1 menu to make it x10. If your probe has an attenuation switch, make sure that the probe setting in the scope is at x1 so that you can use the x10 attenuation on your probe. Adjust the Channel 1 vertical POSITION control knob to line up the lower edge of the PROBE ADJ waveform with the center graticule line. 4. How many major divisions is the height of the displayed waveform? What is the corresponding peak-to-peak voltage of the PROBE ADJ signal?
Confirm your estimate peak-to-peak voltage by using the measure function. Choose Measure → Voltage → Peak -to-peak. 5. Turn the Channel 1 VOLTS/DIV switch two click stops to the right (clockwise). What is the new Channel 1 scale factor?
6. How many major divisions is the height of the displayed waveform now? Is this consistent with the measurement made in 4 above?
Coupling the Signal: Set the Channel 1 input coupling to GND and position the trace on the center graticule line. 7. With the probe connected to the PROBE ADJ terminal, switch the Channel 1 input coupling to AC. What is the eventual position of the waveform on the screen?
8. Is this true for all settings of the VOLTS/DIV switch?
9. Now switch Channel 1 input coupling to DC. What happens to the displayed signal? 10. What is the difference between AC and DC coupling? When should one be used in place of the other? (Use the trigger level to stabilize the waveform in case it is unstable).
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The Vertical Mode Controls: Connect a probe to the channel 2-input connector. Do not forget to set the probe to x10 if it is adjustable. Set the Channel 2 VOLTS/DIV switch to 0.2 volts. Set the channel 2 input coupling to GND. Set the vertical mode to CH 2(channel 2) only by turning off Channel 1. The displayed signal will now come from the channel 2 connector. Vertically position the channel 2 trace to the center of the screen with the vertical POSITION control. Set the channel 2 coupling to AC and check the compensation of the channel 2 probe as you did with the channel 1 probe. Play around with the channel 2 controls as you did with the channel 1 controls to give you a feel for using channel 2. With both the channel 1 and channel 2 probes connected to the PROBE ADJ terminal, set their corresponding input coupling to AC and tu rn on both channels. The signals from both probes will simultaneously appear on the screen. Use the vertical POSITION control to separate the traces by pressing the corresponding channel you want to move and move it using the position knob.
Part 4: The Horizontal System Control Making Time Measurements: Switch the vertical mode back to CH 1 (turn off Channel 2) and dis play the PROBE ADJ signal at the center of the screen. Use the horizontal POSITION control knob to adjust the display until one rising edge of the displayed waveform is aligned with the center vertical graticule (For digital scopes, it is aligned by default). 11. How many major and minor horizontal graticule markings is it to the next rising edge of the waveform? How many seconds does this correspond to?
Confirm your estimate by using the measure function for Time → Period. 12. Change the sweep SEC/DIV setting to 0.2 ms. How many graticule markings is one period of the displayed waveform now? Are your two measurements consistent?
Part 5: The Trigger System Slope Control: Use the oscilloscope to display, through channel 1, a 12 KHz, 2 volt peak-to-peak sinusoidal voltage with no DC offset produced by the function generator. Adjust the SEC/DIV so that two to three cycles of the waveform are displayed.
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13. Move the Trigger LEVEL control knob back and forth through all of its travel. How does this affect the start of the trace? Why?
14. Draw the resulting traces as you vary the SLOPE control from '↑' to '↓'. How does each setting affect the display? Explain why.
Notice that while the signal might lose synchronism at some level control settings, the trace never disappears. 15. Set the Trigger Sweep switch to NORMAL. Now when you use the trigger LEVEL control to move the triggering point, you'll find places where the trace disappears or freezes. Explain this difference in behaviour between normal and auto triggering.
Reset the trigger mode to AUTO. Increase the VOLTS/DIV setting to the next more sensitive position (clockwise). 16. Move the trigger point using the trigger LEVEL control as you did in 13 above. Which VOLTS/DIV setting allows the trigger level control knob to have a larger range of motion before the waveform becomes unstable? If you do not perceive any difference, try an even more sensitive VOLTS/DIV setting.
17. Is the trigger level a voltage level or a 'number of divisions' level? Explain.
Dual Trace Triggering: Set the vertical mode to DUAL TRACE by turning on both channels. Simultaneously display the signal generator output and the CAL signal. 18. Only one of the signals can be made stable using the T rigger control knob? Which one and why? Does your scope have the capability of making the other trace appear stable? Explain.
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External Trigger: Reset the scope for single trace Channel 1 operation and redisplay the signal generator output. Now set the trigger source to EXT. 19. Can the trace be stabilized using the trigger LEVEL control knob? Why or why not?
20. Transfer the channel 2 probe to the EXT TRIGGER input connector on the scope (this means that the 2 probes are in parallel with the signal source) and connect the probe tip to the signal generator output as well. The display can now stabilize when the external trigger input is connected to the signal source. Why? If not, try adjusting the trigger knob to find a stable signal.
21. Does the trigger LEVEL control behave in the same manner as with internal triggering when the vertical sensitivity is increased? (observed in 1 6)
22. Do the SLOPE ('↑' , ' ↓') control and the mode AUTO and NORMAL setting still behave in the same way?
Line Triggering: 23. Set the trigger source to LINE. The display should destabilize. Why?
24. Lower the signal generator output frequency (around 500 Hz) until the display stabilizes. (Adjust the SEC/DIV as well to display 3-4 periods of the trace). At what frequency is a stable display achieved? 25. Continue lowering the signal generator output. Obtain four to five frequencies at which a stable display is obtained. 26. What signal frequencies can be displayed with stability with the trigger source set to line? Why? What possible use could this feature have?
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The following are empty grid scales that you can use in sketching waveforms.
Volts Div: _________ Time Div: _________
Volts Div: _________ Time Div: _________
Volts Div: _________ Time Div: _________
Volts Div: _________ Time Div: _________
Volts Div: _________ Time Div: _________
Volts Div: _________ Time Div: _________
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Electrical Measurements Laboratory – EEE 34 Name: Student Number: Section: Date:
__________________________________________________________ __________________________ __________________________ __________________________
Experiment 6 (Pre-Lab) AC Detection – Diodes Do/answer the following (indicate all references used): 1. What is a diode? Explain diode operation using its V-I characteristic.
2. What are the common uses/applications of diodes?
3. Given a sinusoidal signal, v(t) with amplitude Vs, derive its average (Vave) and RMS (Vrms) value.
REFERENCE/S:
87
Electrical Measurements Laboratory – EEE 34 Group Number/Letter: _______ Members: _______________________________ _______________________________ _______________________________
Date: Section:
__________________ __________________
Experiment 6: AC Detection – Diodes I.
OBJECTIVE To maximize the oscilloscope's function as a tool i n AC analysis
II.
MATERIALS & EQUIPMENT (1) Oscilloscope (3 to 4) alligator clips (2 each) 1kΩ and 10kΩ resistors (1) Signal Generator (1) Digital Multimeter [DMM] (1) 1N4001 diode (1) Potentiometer box (1) Protoboard (1) 0.1uF ceramic capacitor (1) 1mA movement (1) Full wave bridge rectifier
III.
PROCEDURE
A. V-I Characteristic of a Diode 1. Using a digital multimeter at diode mode, measure the effective forward voltage (Vf ) of a conducting diode. Connect the positive terminal to the anode and the negative terminal to cathode. DMMs usually display the diode voltage in mV. Vf = ___________ mV
Figure 1. Exploring the V-I characteristic of a diode. [4-1] 2. Refer on the figure above. Display both Vr and Vd in the oscilloscope by using the dual display capability. To display the correct voltage polarity, let probe A measure Vd and probe B measure Vr. Place the negative terminals of probe A and probe B to point n. This is a requirement of the oscilloscope dual display to have the probes share the same ground in order to achieve stable and synchronized display. Place the positive terminal of probe A to the (+) side of Vd while the positive terminal of probe B at (-) side of Vr. You can insert the probe pins to holes of the breadboard. Pull the CH B position knob to INVert the signal
Diode V-I Characteristic
88 (push/latch button in some oscilloscopes). This effectively follows the polarity based on the Figure 1.
To view the diode’s V -I characteristics, set the oscilloscope coupling to X-Y and set the vertical mode to DUAL with both at 1V/div. Sketch the Id (y-axis) vs Vd (x-axis) characteristics of the diode. Note that Vr is used to represent Id (series configuration) since the current through the resistor is proportional to the voltage across it. Use Vs = 10Vpp sinusoid 1kHz.
B. Some Diode Circuits Four circuits shown in Figure 2 are diode-resistor and diode-capacitor combinations that demonstrate clipping, rectification, level shifting and filtering. NOTE: Ask your instructor to discuss the differences between these four. Use the sine wave from the signal generator with frequency of 1 kHz as the AC voltage source (input), and adjust the amplitude to 4 volts peak-to-peak, no offset. Use R = 1 kΩ and C = 0.1 uF. Assuming an ideal input voltage, sketch the output voltage for each circuit (the signal here now should NOT be inverted). Use 3-4 cycles of the output waveform. Make sure to set the coupling to DC so that you will be able to view if there are any voltage offsets in the output signals. This is essential so that you cannot mistake clipping with rectification. Explain what the circuit does (i.e., its operation). In addition, observe what happens when you reverse the diode (no sketches required for the reversed-diode setup). Discuss your observations.
Figure 2. Diode circuits
Circuit No. 1
Circuit No. 1 Operation
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Circuit No. 2
Circuit No. 2 Operation
Circuit No. 3
Circuit No. 3 Operation
Circuit No. 4
Circuit No. 4 Operation
NOTE: Before proceeding with the succeeding sections, ask your instructor to discuss the difference between Vave and Vrms. C. The Half – Wave Detector 1. Compute for the value of Rs in the circuit of Figure 3 that will allow the 1mA movement to indicate a full scale reading when the supply voltage Vs is 10 Vpeak (this is equivalent to 20 V-peak-to-peak or 20Vpp). Assume a sinusoidal input voltage waveform. NOTE: The 1mA movement measures the average current passing through it.
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2. Set up the circuit using 1 kHz input. Obtain Rs from a potentiometer. The current reading in the 1mA movement should correspond to the level of peak voltage from the input, hence, a half(full)-wave detector! Check the operation of your detector by comparing its reading with the reading of the multimeter (average voltage or Vdc at the output) for the different AC input voltages from your signal generator. Tabulate your results.
Peak Voltage Vs (V) 10 8 5 2
TABLE I HALF-WAVE DETECTOR 1mA movement Voltmeter Reading Reading (mA) at the Output (Vdc)
Computer Vs – from Im
3. Using the oscilloscope, display Vout with 3-4 cycles. Draw the waveform. Indicate the volts/div and time/div settings used.
D. The Full – Wave Detector 1. Repeat Procedure C with the circuit in Figure 4. Use the full-wave bridge rectifier. NOTE: Be careful in handling the full-wave bridge rectifier. The lead legs are fragile and bending/twisting too much can easily snap a leg off. The full-wave bridge rectifier has 4 diodes inside. TABLE II FULL-WAVE DETECTOR Peak Voltage 1mA movement Voltmeter Reading Computer Vs – Vs (V) Reading (mA) at the Output (Vdc) from Im 10 8 5 2 E. Peak Detection 1. Compute for the theoretical value of Rs in the circuit of Figure 5 that will allow the 1mA movement to indicate the peak value of Vs with full scale range of 10 V. HINT: What is the theoretical value of Vout? 2. Set up the circuit using 1 kHz input. Obtain Rs from potentiometer. Check the operation of your detector by using it to measure the peak values of the different AC input voltages from your signal generator. For each reading, record the RMS value of the input signal from the function generator as measured by a multimeter. Tabulate your results.
Peak Voltage Vs (V) 10 8 5 2
RMS Voltage of Input using Voltmeter
TABLE III PEAK DETECTOR 1mA Voltmeter movement Reading at the Reading (mA) Output (Vdc)
Computer Vs – from Im
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3. Using the oscilloscope, display Vout with 3-4 cycles. Draw the waveform. Indicate the volts/div and time/div settings used.
Figure 3. Half-wave detector circuit.
Figure 4. Full-wave detector circuit.
Figure 5. Peak-detector circuit.
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REQUIRED DISCUSSION Try to answer the following while you are inside the laboratory. Some questions can be answered by further investigating the procedure stated above. 1. Discuss how a digital multimeter measures the voltage of a conducting diode. 2. How do the voltage you obtained in Procedure A compare with those typical for silicon diodes (about 0.7V)? 3. Derive the relationship between the ammeter reading and the amplitude of the input for sinusoidal inputs to the circuit of Figure 3. From the relationship, derive derive the equation that recalibrates the ammeter reading to indicate input RMS voltage. 4. How do the readings obtained by your half-wave detector compare with those readings obtained by the multimeter? What is the basic source of difference between between the two? Is this consistent with your data? Suggest how the relationship derived in #3 above can be modified to achieve more accurate accurate readings. What would your ammeter scale look like? 5. Derive the equation that recalibrates the ammeter reading to indicate input RMS voltage for the full-wave detector circuit of Figure 4. 6. How do the readings obtained by your full-wave detector compare with those readings obtained from the multimeter? What is the basic source of difference between the two? Is this consistent with your data? 7. What equation was used to compute for the value value of Rs in Procedure E? Justify using this equation. 8. What are the advantages and disadvantages of full-wave detection versus half-wave detection? 9. For each of the input voltage in Procedure E, compute for the theoretical value of peak voltage. Incorporate these these computed values in to your tabulated data. How do these values compare with with the values you measured using using your peak detector? What is the basic source of error? 10. For the peak detector circuit of Figure 5, what is the maximum possible decay of the voltage across the capacitor taking into account the capacitance value and values of Rs and Rm? Is this decay insignificant when compared with the full scale range of the peak detector?
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Electrical Measurements Laboratory – EEE 34 Name: Student Number: Section: Date:
__________________________________________________________ __________________________ __________________________ __________________________
Experiment 7 (Pre-Lab) AC Analysis – RLC Circuits Put a check on the box if the corresponding task is accomplished. Review phasor analysis for circuit networks involving R, L and C.
Found in EEE 34 Student Laboratory Manual… Read and familiarize with passive components in Sections 2.2.1.2 Capacitors and 2.2.1.3 Inductors. Inductors.
Do/answer the following (indicate all references used):
= cos into its complex frequency domain using phasor
1. Express transformation.
2. Discuss how to compute for impedances ZR, ZL, ZC. What is the relationship between Z L, ZC and XL, XC respectively?
REFERENCE/S:
94
Electrical Measurements Laboratory – EEE 34 Group Number/Letter: _______ Members: _______________________________ _______________________________ _______________________________
Date: Section:
__________________ __________________
Experiment 7: AC Analysis – RLC Circuits I.
OBJECTIVE To familiarize the student with the basics of AC circuit analysis.
II.
MATERIALS & EQUIPMENT (1) Digital Multimeter [DMM] (1) Ceramic capacitor (0.1uF) (1) Oscilloscope (1) Resistor (1KΩ) (1) Signal generator (1) Protoboard (1) Transformer (secondary will serve as inductor) Alligator clips and connecting wires
III.
PROCEDURE
A. Impedance of a Practical Inductor 1. With the function generator and with the aid of the oscilloscope, produce a 10 volt (p-p), 60 Hz sine wave without DC offset (this will serve as your supply voltage, VS, in Figure 1). 2. Use the secondary of the transformer as your inductor (e.g. one end at 0V and another end at 12V). Measure the resistance RL of this inductor using using the DMM. Wire up Figure 1 using R = 1KΩ . Measure RMS voltages values VT, VR and VZ using the Vac of the multimeter. Verify using the oscilloscope (the Vpeak and Vrms are related – note that we have a sinusoidal signal) 3. Compute for the values of current I, the inductance L and the inductive reactance XL. TABLE I IMPEDANCE OF PRACTICAL INDUCTOR Measured Values Computed Values RL = I = VT = L = VR = XL = VZ = B. Making RMS Measurements 1. Set the function generator to 60 Hz sinusoidal waveform. Connect it to the multimeter. Set the multimeter to AC volts. 2. Adjust the amplitude knob of the function generator until you get a multimeter reading of 5 V. Use the oscilloscope to display the generated signal. Measure the amplitude of the voltage and the period of the waveform. What is the relationship of the voltage from the multimeter reading to the voltage measured using the oscilloscope?
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C. K.V.L. in AC circuits C.1. Inductive Circuits Connect the oscilloscope probe as shown in Figure 2 using the same source as in PART A. Use CHOP mode and invert the signal in CHANNEL 2. Adjust your VOLTS/DIV and TIME/DIV settings to obtain a fairly large and wide (at least one to two periods) waveform. Draw the traces indicating the significant points. Include volts/div and ti me/div settings. By how much does VR lag VZ? In degrees, how much is this equivalent to? Add the two traces using the ADD function of the oscilloscope. Draw the trace indicating the significant points. Take note of the amplitudes of the traces. With the use of a phasor diagram, show that the sum of VR and VZ equals VT.
C.2. Capacitive Circuits Wire up Figure 3 using R=1KΩ and C=0.1uF. For VS, use 7 volt (p -p), 1500 Hz sine wave without DC offset. Use the VERTICAL mode in ALT mode and invert the signal in CHANNEL 2. Adjust your VOLTS/DIV and TIME/DIV settings to obtain a fairly large and wide waveform. Draw the traces indicating the significant points. By how much time does VR lead VC? In degrees, how much is this equivalent to? Add the two traces using the ADD function of the oscilloscope. Draw the trace indicating the significant points, taking note of the amplitudes of the traces. Again, using phasor diagrams, show that the sum of VR and VC equals VT.
IV.
REQUIRED DISCUSSION 1. Discuss the calculations you performed in part A.3. 2. In part B.2, discuss the relationship between the voltage reading in DMM (in AC mode) and the voltage measured using oscilloscope. Are the actual measurements consistent with what you expect theoretically? 3. What is the relationship of the voltage from the multimeter reading to the voltage measured using the oscilloscope? 4. Analyze and discuss your results in part C.1 using the concepts you learned about the voltage and current relationships in an inductive (RL) circuit. 5. Analyze and discuss your results in part C.2 using the concepts you learned about the voltage and current relationships in capacitive (RC) circuit.
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Electrical Measurements Laboratory – EEE 34 Name: Student Number: Section: Date:
__________________________________________________________ __________________________ __________________________ __________________________
Experiment 8 (Pre-Lab) Transducers and Operational Amplifiers Do/answer the following (indicate all references used): 1. What are transducers? What are the types of transducer?
2. What are sensors and actuators? Give examples each.
3. What is an operational amplifier? Describe its basic operation using ideal condition.
4. What are the basic circuit topologies using o perational amplifiers and their uses?
REFERENCE/S:
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Electrical Measurements Laboratory – EEE 34 Group Number/Letter: _______ Members: _______________________________ _______________________________ _______________________________
Date: Section:
__________________ __________________
Experiment 8: Transducers and Operational Amplifiers I. a) b) c) d)
II.
OBJECTIVES Describe the operation and electrical characteristics of commonly-used transducers and sensors. Perform measurements using transducers, sensors and electrical measurement circuits. Account errors introduced by non-ideal characteristics of the transducers and sensors on the measurements made. Use operational amplifier to condition the signal produced by transducers and output corresponding signal/indicators.
MATERIALS & EQUIPMENT (1) Oscilloscope (1) LM35 Centigrade Temperature Sensor (1) Signal generator (1) UEI447 NTC Thermistor (1) Digital multimeter (1) Light Dependent Resistor (LDR) (2) Variable DC supply (1) LF353 Operational Amplifier
III.
wires and clips soldering iron (5) 1kΩ resistors (1) 10kΩ pot
PROCEDURE
A. Thermistor 1. Expose the thermistor to ambient temperature (about 25°C). Do not touch the body of the thermistor itself. 2. Record the time it takes for the resistance reading to stabilize from the instant of point of contact. Stable reading is when the measured value varies insignificantly. Measure and record the resistance of the thermistor. 3. Place the thermistor in contact with the human body (average normal body temperature is 37°C). Placing it between the hands/fingers is usually most convenient. Repeat A.2. 4. Plug-in the soldering iron and wait for about 2-3 minutes until it reaches its heating temperature (about 120°C)*. Place the tip of the iron in contact with the body of the thermistor. Be extra careful that the tip touches ONLY the thermistor. Repeat A.2 then unplug the soldering iron. 5. Tabulate your resistance measurements and plot them against temperature. 6. Compare with datasheet values (see Appendix B: Some Notes from Transducer Datasheets).
* CAUTION: Be EXTRA careful such that the soldering iron does not come into contact with anything not intended including yourself!
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B. LM35 Centigrade Temperature Sensor 1. Connect the LM35 sensor to a +5V DC single power supply and voltmeter to measure Vout as shown on the right. DOUBLE CHECK YOUR CONNECTIONS BEFORE TURNING ON THE POWER. Make sure the clips are not shorted with adjacent pin/clips! Set the voltmeter, if not automatic, to 2V DC scale. 2. Repeat Steps A.1-A.6 but this time measuring the output voltage of LM35 instead of resistance.
C. Light Dependent Resistor (LDR) 1. Connect the LDR to a digital ohmmeter. Expose the LDR to room or ambient lighting on your table and record its “room-light ” resistance. 2. Partially cover the LDR to prevent some light f rom reaching it. Record its “shadow” resistance. 3. Cover the LDR completely. It will help to use any black material so as to prevent all light from reaching the LDR. Record its “dark” resistance. 4. Place the LDR near the room lights and record its “light” resistance. 5. Plot your results. Use intensity of light on the x-axis and the resistance on the y-axis. D. Operational Amplifier used as Voltage Comparator
RECALL: How to use negative DC supply? Who sets the “GND”? 1. Wire-up the circuit as shown on the left. Power up using, Vcc+ = +5 Vdc and Vcc- = - 5 Vdc
NOTE: Only 1 op-amp will be used – choose. Let Vcompare/ref be connected to ground (essentially 0 Vdc) and Vin = 3Vpp 0Vdc offset, 1kHz sinusoidal signal. The schematic of LF353 is as shown below (you can use either of the two opamps inside). The length-wise center of the protoboard (the canal-like) is designed to fit component packages such as LF353. 2. Probe both input and output signals with their zero-levels overlapped. Use DC coupling. Make sure the probes have ground connection. Display the output with two to three periods. Draw the waveforms and state your observations. 3. Vary the DC offset of the input signal in increment/decrement of 0.1Vdc but not exceeding +/-1.5Vdc. Observe what happens to the output waveform. 4. From your observations, explain how the circuit operates as a voltage c omparator.
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IV.
REQUIRED DISCUSSION Try to answer the following while you are inside the laboratory. Some questions can be answered by further investigating the procedure stated above. 1. Briefly explain the theory involved in the operation of each transducer used in this experiment. 2. Compare the thermistor and the LDR in terms of linearity, sensitivity and response time. What type of applications is each suited to and why? 3. Think of and list down other applications of the transducers used in this exercise. 4. Research on three (3) transducers not used in this experiment and briefly discuss the theory behind their operation and cite their applications. 5. In Part D., what are the peak levels of output voltage? How is this related to the supply voltages VCC+ and VCC-?
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5 Documentation As mentioned in the previous chapter, and for emphasis, we can say that performing experiments is essential. Gathering data and analysing & interpreting them however are more valuable. Documenting reports is one of the major objective of EEE 34. One must learn how to report data in an academic perspective. In the field of EEE, the most accepted format is the one provided by the largest professional organization in the world – IEEE. A sample format to be used for Post-Lab documentation can be found in Appendix A: Sample IEEE Paper for A4 Page Size.
5.1 Documentation Guidelines The following guidelines will help the students in producing a complete, readable, and coherent report. These criteria are the keys to an effective report.
5.1.1 Technical Development 1. If the experiment asks for possible explanations (e.g. sources of error), it is expecting the students to think and not just enumerate. All procedure covered in these experiments are governed by circuit theory. Simply put, all explanations should be backed-up with a certain level of circuit theory and analysis. 2. Following #1, explaining, proving and establishing claims through circuit analysis must be presented with guiding equations and/or formulas whenever necessary. 3. In reporting, the procedures done in the experiment should not be repeated word for word. It would help to summarize it. The important things are the measurement results and discussion following it. 4. Tabulating data is not equivalent to presenting data. Tables would not speak for themselves. Consequently, mirroring the tabulated data into paragraph form is still not presenting data. Tabulating data is for organization of measurement values and easier comparison. Presenting data, on the other hand, is explaining the sense or the analysis behind those tabulated data. 5. In-depth and further analysis in Post-Lab reports can earn additional merit.
5.1.2 Paper Format and Appearance 1. Follow the recommended format (see Appendix A: Sample IEEE Paper for A4 Page Size ). Do not include email addresses. 2. Include group letter/number at the first page on upper left corner. This helps the instructor for better tracking and easier grade recording. 3. If you want to re-create or modify the circuit diagrams, there are lots of circuit editor available for free online. One good example is the Dia Diagram Editor (see http://diainstaller.de). 4. Present computations, solutions and equations in a logical and presentable way. Learn to use equation tools in your document processor. Make the final equations in bold-type. 5. Presenting the question from ‘Required Discussion’ and then followed by the answer is allowed. Provide number and italicized the questions for better readability. 6. Do NOT use Wikipedia and other forum websites as reference for academic papers! This is like digging your own grave. 7. It is NOT necessary to include the materials and equipment used in the report.
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8. Avoid hanging title, subtitle or header. (e.g. the title of a section and its first paragraph are cut through next column/next page). 9. Do not include the 'Acknowledgment' part. It is NOT necessary for laboratory reports. 10. Some are printing their reports not from their original machine. Thus, to avoid compatibility between document processors of your own machine (where you edited your report) and the machine printing the final paper, it is a good practice to convert the file first to a PDF format. This will preserve your intended format.
5.2 Online Submission Guidelines The Post-Lab report should be submitted in-print. However, if there are certain events (e.g. class suspensions, etc.) where the instructor wished to check softcopies instead, then certain guidelines submitting the report online should be followed. To be fair with students, deadline should be at least a week once the announcement for an online submission has been made. 1. Email Subject Format Use the following format as the email subject: [ ] by Example: [EEE 34 MCDE] Post-Lab 5 by Bernardo, Ramirez, Salces It is important to follow this format since some emails may be treated as spam and hence filtered. 2. Attachment File Type By default, use: i. Compressed file – if more than 2 files. ii. PDF – documents, spreadsheets, presentations, etc. iii. Or the file type as directed by the instructor. 3. Attachment Size Limit The attachment file size should not exceed 5MB. Compress the files and images as necessary. 4. Sender Address Only one member in a group should be the sender per requirement. The first email sent with valid email subject will be considered as the submission. No sending of version 2.0, modifications, and the like so make sure that what you submit is final. It is assumed that a group is well-coordinated. No questions directed to the instructor by groupmate A if groupmate B already submitted this and that. 5. Recipient Address Use only the email address provided by the instructor. 6. Deadline If deadline is 11:59:00 PM PST, then late is 11:59:01 PM PST. Late reports will never be accepted so better send as early as possible. Deadline extension is never an option. 7. Questions Any question about the requirement should ONLY be done in class or during consultation hours prior to submission deadline.
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6 Project The project is the capstone requirement for EEE 34. After applying the concepts learned in circuit theory into actual setups, it is then time for students to showcase their ability and skills in building and constructing something, and finally make it work. This requirement aims to give the students a fun and fulfilling experience with electronics. This chapter will discuss the project guidelines and will enumerate most common questions stud ents ask during project development.
6.1 Project Guidelines This section will guide the students in developing their desired project from proposal stage up to final presentation. As an emphasis, the project is to be accomplished by group. The number of students in a group is defined at the start of the semester (please see Class Policies). You have the freedom to choose your group-mates for this task.
6.1.1 Project Proposal Students cannot start building their desired project without the consent of the laboratory instructor. From the middle of the semester up to a certain date about three to four weeks before Finals week , the students can propose their desired project topic. The project proposal does not have to be formal. Just prepare a detailed print-out of the circuit diagram for the desired project. It may help to prepare multiple proposals to increase the chance of getting an approved topic. The difficulty of the desired project is to be assessed by the instructor. Students can in fact implement microcontroller-based projects if they can. However, the level of difficulty should be just enough to achieve the objective of this project.
Request for approval can be done through instructor’s consultation hours or during class hours. Take note that a certain topic can only be approved once for the current EEE 34 batch. Therefore, topics are on a “first approve first reserve” basis. Failure to get an approved project topic until deadline may mean an automatic zero for the project grade. Please know the date and time for the deadline of project proposal from the laboratory instructor. No need to submit a formal proposal paper once an approval is acquired. As a reference, the following are some notable works from previous EEE 34 batches (current students can implement similar but not the same project):
Electronic Stethoscope LED Voltmeter Simple FM Transmitter Air Flow Control
Game Show Buttons Music to Light Modulator Electronic Die w/ 'Slow Down' 10-level noise indicator
Students can visit the library to look for books with interesting electronics project or from reliable sources in the internet.
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6.1.2 Project Testing and Construction The project should be implemented on protoboard only. Construction and testing can be done during class hours if the main agenda for the day is over. If there is no extra time, then the class schedule should allot 2-3 weeks to give students time to construct their projects before having the project presentation. Students can always check the availability of needed components with the Instruments Room (see Appendix D). Take note that buying of materials for this project requirement is highly discouraged . Students may be required by the instructor to show up in the laboratory during project construction (e.g. for milestone checking).
6.1.3 Project Documentation Before the actual start of presentation of a group, they should submit a printed (not necessarily in coloured-print) documentation of their project. In simple terms: no documentation, no project grade. Follow IEEE format for A4 size paper. The main parts of the documentation must include:
I. II.
III. IV.
Abstract Introduction Project Development A. Circuit Description B. Circuit Operation C. Project Construction D. Problems Encountered E. Delegation of Tasks F. List of Materials Project Applications Conclusion References
6.1.4 Project Presentation All proponents should be present at the date and time of presentation. The group may opt to present even before their assigned schedule once done with the requirements (e.g. students might want to focus more on major subjects near end of semester). Presentation slides should not be fancy-themed and content should be as concise as possible. Time allowed per group to present is 8-10 minutes only. This includes the demonstration, followed by Q&A for defense – maximum total of 15 minutes per group. No-show group on the day of project presentation will receive an automatic zero (0%) grade for project.
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6.1.5 Criteria for Grading The criteria for 100% project grading is: 60% Demonstration Functionality Wiring Setup [TBA] 20% 20%
Documentation Defense Presentation Slides Question & Answer
(45%) (10%) (5%)
(10%) (10%)
6.2 Frequently Asked Questions (FAQs) 1. What are the available components we have in the Instruments Room? Students can borrow (and return afterwards) their needed components from the Instruments Room. Available components can be checked in Appendix D: Available Components in Instruments Room*. 2. Do we need to borrow again every time we will test our circuit? Yes. Or maybe not. It depends on the administrative rule implemented by the Instruments Lab technician. 3. The specific component we need is not available in the Instruments Room nor in any electronics shop locally. What shall we do? Know the function of the needed component in the circuit. Look for its datasheet online. Find for equivalent component that can serve as a substitute. For example, 2N3904 is equivalent to BC547 for a transistor. Note that importing for a component (i.e., purchasing online) is not necessary. Aside from being costly, it will take time to arrive. If that is the case, better change the project as advised by the instructor. 4. We want to buy components in an electronics shop. (Not a question) OK. It is up to the students. Just a piece of advice – know first all the information you need before you go to any electronics shop. Plan ahead. Check the datasheets of your needed components. There might be equivalent components. Check if the store you are heading to have the components you need. You can check their list online or you can contact them. Otherwise, you will just waste your time and effort. Work smart, not hard. 5. How to determine the corresponding pin-outs of the IC/transistor? Check the datasheet. 6. Is it safe to use a DC supply voltage in place of a battery? Of course.
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7. Is it safe to use a larger supply voltage for our circuit? Check the datasheets of all components on absolute maximum ratings (especially power ratings). 8. Can we improve the design for our project implementation? If you think it will improve your work, then feel free to do so. 9. We are done with our project (with documentation and presentation slides). Can we present on an earlier date? Yes. Anytime within the official class hours. Consult with your instructor for the specific schedule. 10. Is the datasheet for a component “universal ”? Yes. Even if the manufacturers are different, the characteristics of a certain component should be standardized. For example, the 2N3904 from Texas Instruments should have the same characteristics with the 2N3904 produced by Analog Devices. 11. Can we sit-in to other class schedules? Yes. Provided that there are extra stations/equipment. Please refer back to Section 1.2 Laboratory Rules and Regulations. 12. Our circuit is not working and date of presentation is drawing near. What shall we do? Do not be disheartened. Quitters do not have a place here in EEE. You still need to present even if your project is not working. However, you need to justify and explain the causes why your project is not working at the very least. Include in your presentation all the debugging tasks you did to troubleshoot your circuit. It is better to present something than get a grade of 0%. On the contrary, do not be relaxed. 13. Can we present once we are done? Please refer to FAQ #9. The instructor will not accept “ambush” presentations. Students should at least reserve a schedule prior to project presentation. 14. We are paying high laboratory fees in our tuition. Why do we experience lack of components in the Instruments Room? Procuring materials in the government takes a long process. The faculty and the admin are doing their best to address this situation. Also, EEE 34 is not the only laboratory course in EEE. 15. Ahmmm…? Check the datasheet.
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Analog multimeter selector knob. Image adapted from www.pochefamily.org. Last accessed: January 2015.
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Analog multimeter reading scale. Image adapted http://www.dreamstime.com/photos-images/analog-multimeter.html. accessed: January 2015.
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How to use a Multimeter. Image adapted from http://www.wikihow.com/Use-aMultimeter. Last accessed: January 2015.
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Resistors. Image adapted from http://www.electronicstutorials.ws/resistor/res_2.html. Last accessed: January 2015.
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Structure & circuit symbols for variable resistor/'pot'. Image adapted from www.st-andrews.ac.uk . Last accessed: January 2015.
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Capacitor value reading. Image adapted from http://www.electronicstutorials.ws/capacitor/cap_1.html. Last accessed: January 2015.
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Inductor images. Image adapted from http://www.coilws.com/. Last accessed: January 2015.
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Debugging circuits. Article file from http://wwwinst.eecs.berkeley.edu/~ee43/sp03/labs/. Last accessed: January 2015.
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PHD Comics Debugging. Image adapted from http://www.phdcomics.com/comics/archive.php?comicid=673. Last accessed: January 2015.
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Accuracy and Precision. Image adapted from www.extremetech.com. Last accessed: January 2015.
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Voltage and Current Sources. Image adapted from http://hyperphysics.phyastr.gsu.edu/hbase/electric/visource.html. Last accessed: January 2015.
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Galvanometer. Image adapted from http://en.wikipedia.org/wiki/Galvanometer. Last accessed: January 2015.
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LED anode and cathode. Image adapted from www.eng.utah.edu. Last accessed: January 2015.
[0b-2]
Flashing LED circuit. Image adapted from http://www.555-timercircuits.com/flashing-led.html . Last accessed: August 2015.
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555 Timer IC Pinouts. Image adapted http://www.instructables.com/id/Flashing-LED-using-555-Timer/. accessed: January 2015.
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Appendix A: Sample IEEE Paper for A4 Page Size Please see the following links for the sample format. 1. *.doc = https://www.dropbox.com/s/d1ibaghl8f86t7m/IEEE_Paper_Word_Template_A4_V3.do c?dl=0 2. *.pdf = https://www.dropbox.com/s/wp3ax0gghjqdcga/IEEE_Paper_Word_Template_A4_V3.p df?dl=0 Also, sharing here with permission a sample of Post-Lab report from EEE 34 s tudents (AY 1415)… 3. *.pdf = https://www.dropbox.com/s/a49zhel34zncteh/Expt%200%20by%20Quinquito_Jaland oni_Valencia.pdf?dl=0 It is interesting to note here that this is their first Post-Lab report and yet they managed to produce a complete, readable, and coherent work. It is not a perfect report of course but it is fairly great as a first report. Students can use this as a model or guide. This should NOT be copied for Post-Lab 0. At the end of the semester, all students of EEE 34 are expected to produce reports with quality better than this one.
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Appendix B: Some Notes from Transducer Datasheets UEI Series NTC Thermistor For the complete UEI Series NTC Thermistor datasheet, kindly access the PDF at: https://www.dropbox.com/s/kiqbqfscvzlqfw2/UEI%20Series%20NTC%20Thermistor. pdf?dl=0
Figure B. 1. Typical response curve – temperature versus resistance of UEI447 NTC Thermistor .
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Appendix B: Some Notes from Transducer Datasheets LM35 Precision Centigrade Temperature Sensor For a sample of complete LM35 Precision Centigrade Temperature Sensor datasheet, kindly access the PDF at: https://www.dropbox.com/s/67x7f9b7n1f1vff/LM35%20Centigrade%20Temp%20Se nsor.pdf?dl=0
Figure B. 2. Basic Centigrade temperature sensor
2℃ 150℃.
Light Dependent Resistor (LDR) For a sample of complete Light Dependent Resistor (LDR) datasheet, kindly access the PDF at: https://www.dropbox.com/s/y9t1gcdrgprvxde/Light%20Dependent%20Resistor.pdf? dl=0
Figure B. 3 . Resistance as a function of illumination.
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Appendix C: Some Notes from Operational Amplifier (Op-Amp) Datasheets LM741 General Purpose Operational Amplifier For a sample of complete LM741 datasheet, kindly access the PDF at: http://www.ti.com/lit/ds/symlink/lm741.pdf
Figure C. 1 . LM741 operational amplifier pin-outs.
LF353 High-speed Dual Operational Amplifier For a sample of complete LF353 datasheet, kindly access the PDF at: http://www.ti.com/lit/ds/symlink/lf353-n.pdf
Figure C. 2 . LF353 operational amplifier pin-outs.
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Appendix D: Available Components in Instruments Room*
The list above is a good reference to what components are available in the Instruments Room. However, EEE supports various instructional laboratories aside from EEE 34. The list availability or supply might change without prior notice. *Kindly take note the version (and hence revision date) o f this laboratory manual.
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Appendix D: Available Components in Instruments Room*
*Kindly take note the version (and hence revision date) o f this laboratory manual.
