FAKULTI PENDIDIKAN TEKNIKAL DAN VOKASIONAL
DBK 11802 ELECTROMECHANICAL LAB REPORT 01 ( MULTIMETER) PREPARED BY :
ZAINAB HANNAN BT RAMLI
LB110265
WATI BT AMBO AWE
LB110322
SITI FATIMAH BT MEGAT FAUZI
LB110354
HASMALAILIE BT YUSOFF
LB110280
DPLI KEMAHIRAN TEKNIKAL (SECTION 13)
LECTURER : PUAN ROSNEE BT AHAD
Title
: Analog multimeter measurement and application
Objectives :
At the end of this experiment, students should be able to i)
Do the measurement by using analog multimeter
Theory
ii)
Give knowledge about the usage of analog multimeter and its functions.
iii)
Practice how to read the scale and set the range of multimeter
:
Multimeter is a device used for the measurement of AC or DC voltages, currents and also resistances. Some meters are also capable of measuring temperatures, conductivities and frequencies. Multimeter are available in two types according to the way of reading is presented; an anlog multimeter uses a pointer to indicate a value and a digital multimeter gives a numeric value. The main parts of an analog multimeter are briefly described below. 1. Meter section Meter section consists of scales and pointer. The degree of deflection of the pointer enables the voltage value, current value and resistance value to be read. There are various kinds of scales. Check the position of the range selector described below and read the scale tha t matches the position of the range selector. DC V : Direct current voltage AC V : Alternating current voltage DC A : Direct current : Resistance Ω 2. Range selector Select one of the measuring ranges of DC voltage (DC V). AC voltage (AC V), DC current (DC A) or resistance ( ) by rotating this selector. In each of the range a finer range more suitable for measuring the desired value can be selected. 3. Zero position adjuster If the pointer is not at the zero position before a measurement it can be adjusted to the zero position using the zero position adjuster. 4. Measuring terminal The measuring terminals are the + and – (COM) terminals. Connect the red test lead to the + terminal and connect black test lead to the – (COM) terminal. 5. Ohm Adjuster
After selection any of the position (x1, x100, x1K, etc) of the resistance range by the range selector for measurement of a resistance, put both test leads in contact with each other and adjust the pointer to the 0 ohm position at this time.
Analog multimeter description panel
Figure 1 1 .Case with protective bumper 2 .Analog display 3 .Resistance zero adjustment knob 4 .Resistance range 5 .Battery test range 6 .DC current range 7 .Pin cover 8 .Attachable test leads with probes 9 .Power off 10.Range switch 11.DC voltage range 12.AC voltage range
Measurement method of Analogue multimeters Analogue meters take a little power from the circuit under test to operate their pointer. They must have a high sensitivity of at least 20k /V or they may upset the circuit under test and give an incorrect reading. Batteries inside the meter provide power for the resistance ranges, they will last several years but you should avoid leaving the meter set to a resistance range in case the leads touch accidentally and run the battery flat. Typical ranges for analogue multimeters like the one illustrated: (the voltage and current values given are the maximum reading on each range) • • • • •
DC Voltage: 0.5V, 2.5V, 10V, 50V, 250V, 1000V. AC Voltage: 10V, 50V, 250V, 1000V. DC Current: 50µA, 2.5mA, 25mA, 250mA. A high current range is often missing from this type of meter. AC Current: None. (You are unlikely to need to measure this). Resistance: 20 , 200 , 2k , 20k , 200k . These resistance values are in the middle of the scale for each range.
It is a good idea to leave an analogue multimeter set to a DC voltage range such as 10V when not in use. It is less likely to be damaged by careless use on this range, and there is a good chance that it will be the range you need to use next anyway!
Resistance Measurement Multimeter with selector set to "Ohms". This meter only has a single Ohms range. Set the multimeter to Ohms or Resistance (turn meter on if it has a separate power switch). Understand that resistance and continuity are opposites. The multimeter measures resistance in ohms, it can not measure continuity. When there is little resistance there is a great deal of continuity. Conversely, when there is a great deal of resistance, there is little continuity. With this in mind, when we measure resistance we can make assumptions about continuity based on the resistance values measured. Observe the meter indication. If the test leads are not in contact with anything, the needle or pointer of an analog meter will be resting at the left most position. This is represents an infinite amount of resistance, or an "open circuit"; it is also safe to say there is the no continuity, or path between the black and red probes. Careful inspection of the dial should reveal the OHM scale. It is usually the topmost scale and has values that are highest on the left of the dial (a sideways "8" for infinity) and gradually reduce to 0 on the right. This is opposite of the other scales; they have the lowest values on the left and increase going right. Connect the black test lead to the jack marked "Common" or "-" Connect the red test lead to the jack marked with the Omega (Ohm symbol) or letter "R" near it. Set the range (if provided) to R x 100. Hold the probes at the end of the test leads together. The meter pointer should move fully to the right. Locate the "Zero Adjust" knob and rotate so t hat the the meter indicates "0" (or as close to "0" as possible). Note that this position is the "short circuit" or "zero ohms" indication for this R x 1 range of this meter. Always remember to "zero" the meter immediately after changing resistance ranges. Replace batteries if needed. If unable to obtain a zero ohm indication, this may mean the batteries are weak and should be replaced. Retry the zeroing step above again with fresh batteries. Measure resistance of something like a known-good lightbulb. Locate the two electrical contact points of the bulb. They will be the threaded base and the center of the bottom of the base. Have a helper hold the bulb by the glass only. Press the black probe against the threaded base and the red probe against the center tab on the bottom of the base. Watch the needle move from resting at the left and move quickly to 0 on the right. Change the range of the meter to R x 1. Zero the meter again for this range. Repeat the step above. Observe how the meter did not go as far to the right as before. The scale of resistance has been changed so that each number on the R scale can be read directly. In
the previous step, each number represented a value that was 100 times greater. Thus, 150 really was 15,000 before. Now, 150 is just 150. Had the R x 10 scale been selected, 150 would have been 1,500. The scale selected is very important for accurate measurements. With this understanding, study the R scale. It is not linear like the other scales. Values at the left side are harder to accurately read than those on the right. Trying to read 5 ohms on the meter while in the R x 100 range would look like 0. It would be much easier at the R x 1 scale instead. This is why when testing resistance, adjust the range so that t he readings may be taken from the middle rather than the extreme left or right sides. Test resistance between hands. Set the meter to the highest R x value possible. Zero the meter. Loosely hold a probe in each hand and read the meter. Squeeze both probes tightly. Notice the resistance is reduced. Let go of the probes and wet your hands. Hold the probes again. Notice that the resistance is lower still. For these reasons, it is very important that the probes not touch anything other than the device under test. A device that has burned out will not show "open" on the meter when testing if your fingers provide an alternate path around the device, like when they are touching the probes. T esting round cartridge type and older style glass automotive fuses will indicate low values of resistance if the fuse is lying on a metal surface when under test. The meter indicates the resistance of the metal surface that the fuse is resting upon (providing an alternate path between the red and black probe around the fuse) instead of trying to determine resistance through the fuse. Every fuse, good or bad, will indicate "good". Voltage Measurement Set the meter for the highest range provided for AC Volts. Many times, the voltage to be measured has a value that is unknown. For this reason, the highest range possible is selected so that the meter circuitry and movement will not be damaged by voltage greater than expected. If the meter were set to the 50 volt range and a common U.S. electrical outlet were to be tested, the 120 volts present could irreparably damage the meter. Start high, and work downward to the lowest range that can be safely displayed. Insert the black probe in the "COM" or "-" jack. Insert the red probe in the "V" or "+" jack. Locate the Voltage scales. There may be several Volt scales with different maximum values. The range chosen the selector knob determines which voltage scale to read. The maximum value scale should coincide with selector knob ranges. T he voltage scales, unlike the Ohm scales, are linear. The scale is accurate anywhere along its length. It will of course be much easier accurately reading 24 volts on a 50 volt scale than on a 250 volt scale, where it might look like it is anywhere between 20 and 30 volts. Test a common electrical outlet. In the U.S. you might expect 120 volts or even 240 volts. In other places, 240 or 380 volts might be expected. Press the black probe into one of the straight slots. It should be possible to let go of the black probe, as the contacts behind the face of the outlet should grip the probe, much like it does when a plug is inserted. Insert the red probe into the other straight slot. The meter should indicate a voltage very close to 120 or 240 volts (depending on type outlet tested). Remove the probes, and rotate the selector knob to the lowest range offered, that is greater than the voltage indicated (120 or 240).
Reinsert the probes again as described earlier. The meter may indicate between 110 and as much as 125 volts this time. The range of the meter is important to obtain accurate measurements. If the pointer did not move, it is likely that DC was chosen instead of AC. The AC and DC modes are not compatible. The correct mode MUST be set. If not set correctly, the user would mistakenly believe there was no voltage present. This could be deadly. Be sure to try BOTH modes if the pointer does not move. Set meter to AC volts mode, and try again. Whenever possible, try to connect at least one probe in such a way that it will not be required to hold both while making tests. Some meters have accessories that include alligator clips or other types of clamps that will assist doing this. Minimizing your contact with electrical circuits drastically reduces that chances of sustaining burns or injury.
Current Amperes Measurement Determine if AC or DC by measuring the voltage of the circuit as outlined above. Set the meter to the highest AC or DC Amp range supported. If the circuit to be tested is AC but the meter will only measure DC amps (or vice-versa), stop. The meter must be able to measure the same mode (AC or DC) Amps as the voltage in the circuit, otherwise it will indicate 0. Be aware that most multimeters will only measure extremely small amounts of current, in the uA and mA ranges. 1 uA is .000001 amp and 1 mA is .001 amp. These are values of current that flow only in the most delicate electronic circuits, and are literally thousands (and even millions) of times smaller than values seen in the home and automotive circuits that most homeowners would be interested testing. Just for reference, a typical 100W / 120V light bulb will draw .833 Amps. This amount of current would likely damage the meter beyond repair. A "clamp-on" type ammeter would be ideal for the typical homeowner requirements, and does not require opening the circuit to take measurements (see below). If this meter were to be used to measure current through a 4700 ohm resistor across 9 Volts DC, it would be done as outlined below: Insert the black probe into the "COM" or "-" jack. Insert the red probe into the "A" jack. Shut off power to the circuit. Open the portion of the circuit that is to be tested (one lead or the other of the resistor). Insert the meter in series with the circuit such that it completes the circuit. An ammeter is placed IN SERIES with the circuit to measure current. It cannot be placed "across" the circuit the way a voltmeter is used (otherwise the meter will probably be damaged). Polarity must be observed. Current flows from the positive side to the negative side. Set the range of current to the highest value. Apply power and adjust range of meter downward to allow accurate reading of pointer on the dial. Do not exceed the range of the meter, otherwise it may be damaged. A reading of about 2 milliamps should be indicated since from Ohm's law I = V / R = (9 volts)/(4700 Ω) = . 00191 amps = 1.91 mA.
If you're measuring the current consumed by the device itself, be aware of any filter capacitors or any element that requires an inrush (surge) current when switched on. Even if the operating current is low and within the range of the meter fuse, the surge can be MANY times higher than the operating current (as the empty filter capacitors are almost like a short circuit). Blowing the meter fuse is almost certain if the DUT's (device under test) inrush current is many times higher than the fuses rating. In any case, always use the higher range measurement protected by the higher fuse rating (if your meter has two fuses), or just be careful.
Procedures : 1. DC Voltage Readings (unit volt) i) ii) iii)
iv)
The positive prove (red) was ensured in positive (+) terminal and the negative prove (black) was ensured in negative (-) terminal. Selector DCV was selected to range 50 DVC. The black colour scale was observed to find the maximum scale. The maximum scale at 50 based on selector value 50 DVC. The reading was taken.
2. Resistor value reading (unit
i) ii)
iii) iv) v)
)
The positive prove (red) was ensured in positive (+) terminal and the negative prove (black) was ensured in negative (-) terminal. Before make reading the resistor measurement at the selector switch of analog multimeter, the two probe positive and negative were touch and make 0 adjustment for resistor The selector was selected to range at x1 and x1K. The top of the black colour scale was observed to find the number in based from the right at 0 . The reading of scale was taken and multiplied the value at the scale 1 and 1000 .
3. AC volt reading (unit volt)
i)
The red test lead was plug into the OUTPUT socket and the black one into the –COM.
ii)
The range selecter was set at the selected range position (range 1000)
iii)
The black colour scale was observed to find the maximum scale. The maximum scale at 10 based on selector value 1000 AVC. The reading was taken.
iv)
4. DC Ampere reading (unit mA)
i)
The red test lead was placed into + socket and the black one into the –COM for DCA range at 50µA – 250 mA.
ii)
The red test lead was placed into the DC 10A MAX socket and the black one into the –COM for DCA range at 250 mA-10A.
iii)
The range selector was set at a selected DCA range position (0.25A or 250mA)
iv)
The black colour scale was observed to find the maximum scale. The maximum scale at 250 based on selector value 250 DCV.A The reading was taken.
v)
Figure 2
Result :
i) ii) iii) iv) v) vi)
Selector DCV DCV DCA Resistor Resistor ACV
Range 50 2.5 0.25 X1 X1K 1000 Table 1
Reading 9 0.45 0.045 92.5 92500 180
Unit VDC VDC A
V AC
Calculation: i)
Selector DCV, Range 50 1 division = 50-40 10 =1 Therefore, the reading on the scale is, = 9 VDC 9 x1
ii) Selector DCV, Range 2.5 1 division = 2.5-2.0 10 = 0.05 Therefore, the reading on the scale is, 9 x 0.05 = 0.45 VDC
iii) Selector DCA, Range 0.25 1 division = 0.25-0.20 10 = 0.05 10 =0.005 Therefore, the reading on the scale is, = 0.045 VAC 9 x 0.005 iv) Selector Resistor, Range x1
1 division = 100-50 10 =5 ½ division = 5 2 = 2.5 Therefore, the reading on the scale is, 50 + (8x5) + 2.5 = 92.5 = 92.5 92.5 x 1
v) Selector Resistor, Range x1K
1 division = 100-50 10 =5 ½ division = 5
2 = 2.5 Therefore, the reading on the scale is, 50 + (8x5) + 2.5 = 92.5 92.5 x 1K = 92.5 K
= 92500 vi) Selector ACV, Range 1000 1 division = 1000 – 800 10 = 200 10 = 20 Therefore, the reading on the scale is, 9 x 20 = 180 VAC
Discussion There is a general measuring sequences that we have to considered before a DC voltage, AC voltage, DC current and resistance were measured; 1. Adjustment of zero position
Before using the multimeter, we placed in it’s the level position and checked that the pointer is in the ‘0’ position at the extreme left of the scales. We adjusted ii by used the zero position adjuster if the pointer is not at the zero position.
2. Selection of measuring range
Measuring range (voltage, current or resistance) a selected and the range selector is set to the position that matched the type and anticipated magnitude of the measurement valued.
3. Connection of test leads
The red and black test leads are connected to the + and - terminal of the multimeter respectively.
Then the probe connected at the other ends of the test leads to the circuit to be measured.
4. Reading of Indication
Indication of the scale corresponding to the measuring range selected was read by the range selector.
Based on the result of the reading value experiment above; 1. DC Voltage reading
The selector are DCV in 50V range and the reading shown at 9 VDC.
The selector are DCV in 2.5V range and the reading shown at 0.45 VCD
2. DC Ampere reading
The selector are DCA in 0.25mA and the reading shown at 0.045A.
3. Resistor Value reading
The selector are Resistor in X1Ω and the reading shown at 92.5 Ω.
The selector are Resistor in X1 KΩ and t he reading shown at 92500 Ω
4. AC volt reading
The selector are ACV in 1000V and the reading shown at 180 VAC
Conclusion Based on the experiment that we have done, we can concluded that, Analog multimeters are electrical test instruments which are used to measure voltage, current, resistance, frequency and signal power. The basic functionality of an analog multimeter will include measurement of electrical potential in volts, resistance in ohms, and current in amps. Analog multimeters can be used to find electronic and electrical short circuit problems. Advanced analog multimeters come with more features such as capacitor, diode and IC testing modes. Specific measurements made by analog multimeters include DC voltage, AC voltage, DC current, AC current, frequency range for AC currents, and decibel measurement. Analog multimeters that measure current may have a current clamp built-in or configured as a probe. A current clamp is a sensor that clamps around the wire. When searching for analog multimeters it is important to consider the measurement range for whichever value is being measured. An analog multimeter displays these values via a dial, typically a moving pointer or needle.
Misconseption
1. There are misconception about joint the terminal meter where red color for negative terminal (+) and black color for positive terminal (-).
2. There are misconception about reading the resistance scale where think that it is
usual scale and reads onwards. Besides, when resistance s to be measured, an 0 Ω adjustment is necessary each time the range is changed.
3. There is misconception when taking accurate reading because it always confuse with the reflection visible affected by looking at an angle from the left or right. Affected that, in certain ranges the indicated value may differ widely from the actual value.
4. There is misconception about the measurement both of DC Voltage and DC Current is similar. Moreover, the use of many scale on the same instrument can cause confusion.
