Lab Manual of Pneumatics control

ELECTRO PNEUMATICS PNEUMATICS (Model No : VMPT - 302 LC)

Technical Reference

Version 1.0

Technical Clarification /Suggestion : / Technical Support Division,

Vi Microsystems Pvt. Ltd., Plot No :75,Electronics Estate, Perungudi,Chennai - 600 096,INDIA. Ph: 91- 44-24961852, 91-44-24963142 Mail : service@vimicrosystem [email protected], s.com, Web : www.vimicrosystems.com 01 - 12 - 04 - 20

ELECTRO PNEUMATICS

VMPT-302 LC

CHAPTER - 1 INTRODUCTION OF PNEUMATICS SYSTEM

Vi Microsystems Pvt. Ltd.,

[1]

ELECTRO PNEUMATICS

VMPT-302 LC

CHAPTER - 1 INTRODUCTION OF PNEUMATICS SYSTEM


[1]

ELECTRO PNEUMATICS 1.1 1.1

VMPT-302 LC

APPLICATIONS OF OF PN PNEUMAT MATICS

Pneumatics Pneumatics deals the use of compressed air, Most commonly commonly,, compressed co mpressed air is used to to do mechanical mechanical work-that is to produce motion and to generate forces. Pneumatic Pneumatic drives have have the task of o f converting the energy stored in compressed air into motion. Cylinders Cylinders are most most commonly used for pneumatic pneumatic drives. They The y are character charac terized ized by by robust construct const ruction, ion, a large larg e range of types, simple simple insta installation llation and favorable favorable price/performance. price/per formance. As a result of these benefits, pneumatics is used in a wide range of applications.

Pneumatic linear cylinder and pneumatic swivel cylinder cy linder

Some of the many applications of pneumatics are * * * * * *

Handling of work pieces (such as clampin clamping, g, positioni po sitioning, ng, separating separat ing,, stacking, rotating) rot ating) Packaging Filling Open Openiing and and clos closiing of door doorss (suc (such h as buses uses and and trai trains) Metal tal-for -form ming (e (emboss ossing an and pre presssing) Stamping

1 .2

Signal and information

A signal is the representation of information the representation is by means of the value or value pattern of the physical physical variable. variable.


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ELECTRO PNEUMATICS

VMPT-302 LC

Signal/physical variable Pressure 7 bar 5 4 3 2 1

Time

0

Information a) Analog Pointer position 7 6 5 4

3

4

2

5

1

3

6

0

7 8

2 1

Time

0

b) Digital Display 7 6 5

3

Pressure bar

4 3 2 1 0

Time

c) Binary Pressure

Supply Pressure Yes 1

No 0


Time

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ELECTRO PNEUMATICS

VMPT-302 LC

Analog signal

An analog signal is a signal in which information information is assigned point po int by point to a continuous cont inuous value range of the signal parameter parameter (DIN 19226. Part Par t 5). Application example

In the case of a pressure gauge, each pressure value (information parameter) is assigned a particular display value ( = information). information). If the signal signal rises r ises o r falls, the information information changes continuously. Digital signal

A digital digital signal is is a signal with a finite finite number of value ranges of the information parameter . Each value range is assigned a specific item of information (DIN 19226). Application example

A pressure measuring system with a digital display shows the pressure in increments of 1 bar. There are 8 possible possible display display values values ( 0 to t o 7 bar) for a pressure range of o f 7 bar. That is, there eight possible possible value ranges for for the t he information information parameter. If the signal rises or falls, falls, the information information changes in increments. Binary Signal

A binary binary signal is a digital digital signal with only two value ranges for the t he informat information ion parameter. parameter . If the signal rises or falls, the information changes in increments. Application example

A control contr ol lamp indicates indicates whether whet her a pneumatic system is is being being correct corr ectly ly supplied with compressed air. If the supply pressure pres sure ( = signal is below below 5 bar, the control lamp lamp is off off (0 status). status). If the pressure is above 5 bar, bar, the control contro l lamp lamp is is on ( 1status). 1.3 1.3

Sign ignal fl flow in in a control trol system tem

A controller can be divided into the functions signal input, signal processing signal output and command execution. The mutual influence influence of these functions is shown by the signal flow diagram. * Sign Signal alss from from the sign signal al input nput are logi logical cally ly associ associated ated (sign (signal al process processin ing). g). Sign Signal alss for signal input and signal process are low power signals. Both functions are part of the signal signal control sect ion. * At the the sign signal al outpu outputt stage stage,, sign signal alss are are ampl ampliified fied from low powe powerr to hi high powe power. r. Signal output forms the link between the signal control section and the power section.


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ELECTRO PNEUMATICS

*

VMPT-302 LC

Com Command and execu executi tion on take take plac placee at at a hi high power power level evel-th -that at is, is, in order order to reac reach ha high high speed (such as for fast rejection of a workpiece form a machine) machine) or to exert a high high force force (such as for for a press). Command Command execut execution ion belongs to the power section of a control co ntrol system.

Command execution

r n o e i w t o c P e s

Signal output

Signal Processing

l o r t n n o o i c t l c a e n s g i S

Signal input

Signal flow in a control system

The components in the circuit circuit diagram of a purely pneumatic pneumatic controller are arranged so that t hat the t he signal flow flow is clear. Bottom Botto m up: input input elements elements (such as manuall manually y operated valves), valves), logical logica l association elements elements (such ( such as two-pressure valves), valves), signal signal output elements (power valves, valves, such as 5/2 - way valves) and finally command execution (such as cylinders). 1.4 1.4

Pneu Pneum matic atic and and Ele Elect ctrro pneu pneuma mati ticc cont contrrol sys syste tem ms

Both pneumatic and electro pneumatic pneumatic controllers contr ollers have have a pneumatic pneumatic power section (see fig 1.4). The signal control section varies according to type. *

In a pn pneum eumatic atic con control trol pneu pneum matic atic com compon ponen ents ts are are use used, d, tha thatt is, is, vari various ous type typess of valves, valves, sequences, air barriers, etc.

*

In an elect electroro-pn pneu eum matic atic con control the the sign signal al control control secti section on is is mad madee up of a elect electri rica call components, components , for example example with electrical electr ical input input buttons, butt ons, proxim pro ximity ity switches, relays, or a programm progr ammabl ablee logic controll contro ller. er.

The directional control valves form the interface between the signal control section and the pneumatic pneumatic power section in both both types of controller.


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VMPT-302 LC

Power Components Cylinder COMMAND EXECUTION

Swivel cylinder Pneumatic motors Optical displays

Final control elements SIGNAL OUTPUT

r e w o p n c o i t t i a c e m s u e n P

Electropneumatically operated directional control valves

Processing Elements Relays SIGNAL PROCESSING

SIGNAL INPUT

SIGNAL FLOW

Contactors Programmable logic controllers (PLCs)

Input Elements Pushbuttons Control switches Limit switches Reed switches Ind.proximity sensors Cap.proximity switches Light barriers Pressure-actuated Switches

n o i t c e s l o r t n o c l a n g i s l a c i r t c e l E

Electropneumatic components

Fig. 1.4 Signal flow and components of a pneumatic control system.


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VMPT-302 LC

1.5

The structure and mode of operation of an electro pneumatic controller

*

The electrical signal control section switches the electrically actuated directional control valves.

*

The directional control valves cause the piston rods to extend and retract.

*

The position of the piston rods is reported to the electrical signal control section by proximity switches.

Fig.1.5 Structure of a modern electro pneumatic controller.


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ELECTRO PNEUMATICS 1.6

VMPT-302 LC

Advantages of electro pneumatic controllers

Electro pneumatic controllers have the following advantages over pneumatic control systems: *

Higher reliability (fewer moving parts subject to wear)

*

Lower planning and commissioning effort. Particularly for complex controls

*

Lower installation effort, particularly when modern components such as valve terminals are used

*

Simpler exchange of information between several controllers.

Electro pneumatic controllers have asserted themselves in modern industrial practice and the application of purely pneumatic control systems is a limited to a few special applications


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ELECTRO PNEUMATICS

VMPT-302 LC

CHAPTER - 2 FUNDAMENTALS OF ELECTRICAL TECHNOLOGY


[9]


VMPT-302 LC

Direct current and alternating current

A simple electrical circuit consists of a voltage source, a load, and connection lines. Physically, charge carriers electrons move through the electrical circuit via the electrical conductors from the negative pole of the voltage source to the positive pole. This motion of charge carriers is called electrical current. Current can only flow if the circuit is closed. There are two types of current - direct current and alternating current: *

If the electromotive force in an electrical circuit is always in the same direction, the current also always flows in the same direction. This is called direct current (DC) or a DC circuit.

*

In the case of alternating current or an AC circuit, the voltage and current change direction and strength in a certain cycle.

Direct current

1 t n e r r u C


Alternating current

Time t

1 t n e r r u C

Time t

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I

3 S 4 V=12V

+ H

Fig. 2.1: DC circuit

Fig 2.1 shows a simple DC circuit consisting of a voltage source, electrical lines, a control switch, and a load (here a lamp). Technical direction of flow

When the control switch is closed, current I flows via the load. The electrons move from the negative pole to the positive pole of the voltage source. The direction of flow from quotes “positive” to” negative” was laid down before electrons were discovered. This definition is still used in practice today. It is called the technical direction of flow. 2.2

Ohm’s Law

Electrical conductors

Electrical current is the flow of charge carriers in one direction. A current only flow in a material if a sufficient number of free electrons are available. Materials that meet this criterion are called electrical conductors. The metals copper, aluminum and sliver are particularly good conductors. Copper is normally used for conductors in control technology. Electrical resistance

Every material offers resistance to electrical current. This results when the free-moving electrons collide with the atoms of the conductor material, inhibiting their motion. Resistance is low in electrical conductors. Materials with particularly high resistance are called insulators. Rubber and plastic-based materials are used for insulation of electrical wires and cables.


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ELECTRO PNEUMATICS

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Source emf

The negative pole of a voltage source has a surplus of electrons. The positive pole has a deficit. This difference results in source emf (electromotive force). Ohm’s law

Ohm’s law expresses the relationship between voltage, current and resistance. It states that in a circuit of given resistance, the current is proportional to the voltage, that is * *

If the voltage increases, the current increases. If the voltage decreases, the current decreases.

V

=

R.I

V R I

= = =

Voltage; Resistance; Current;

Unit : Volt (V) Unit : Ohm () Unit : Ampere (A)

Electrical Power

In mechanics, power can be defined by means of work. The faster work is done, the greater t he power needed. So power is “ work divided by time”. In the case of a load in an electrical circuit, electrical energy is converted into kinetic energy (for example electrical motor), light (electrical lamp), or heat energy (such as electrical heater, electrical lamp). The faster the energy is converted, the higher the electrical power so here, to power means converted energy divided by time. Power increases with current and voltage. The electrical power of a load is also called its electrical power input. P P V I

= = = =

V.I Power; Voltage; Current;

Unit Unit Unit

: : :

Watt (W) Volt (V) Ampere (A)

Application example

Power of a coil The solenoid coil of a pneumatic 5/2 - way valve is supplied with 24V DC. The resistance of the coil is 60ohm. What is the power? The current is calculated by means of ohm’s law:


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ELECTRO PNEUMATICS

VMPT-302 LC I



V R



24V 60



0.4 A

The electrical power is the product of current and voltage: P 2.3

=

V.I = 24V. 0.4 A = 9.6 W

Function of a solenoid

A magnetic field is induced when a current is passed through an electrical conductor. The strength of the magnetic field is proportional to the current. Magnetic fields attract iron, nickel and cobalt. The attraction increases with the strength of the magnetic field. Air-core coil

Coil with iron core and air gap

Fig. 2.3: Electrical coil and magnetic lines of force Structure of a solenoid

The solenoid has the following structure: *

The current-bearing conductor is wound around a coil. The overlapping of the lines of force of all loops increases the strength of the magnetic field resulting in a main direction of the field.

*

An iron core is placed in the centre. When current flows, the iron is also magnetized. This allows a significantly higher magnetic field to be induced with the same current (compared to an air-core coil)


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ELECTRO PNEUMATICS

VMPT-302 LC

These two measures ensure that an solenoid exerts a strong force on ferrous (=containing iron) materials. Applications of solenoids

In electro pneumatic controls, solenoids are primarily used to control the switching of valves, relays or contractor. This can be demonstrated using the example of the spring-return directional control valve: *

If current flows through the solenoid coil, the piston of the valve is actuated.

*

If the current is interrupted, a spring pushes the piston back into its initial position.

Reactance in AC circuits

If a AC voltage is applied to a coil, an alternating current flows. This means that the current and magnetic field are constantly changing. The change in the magnetic field induces a current in the coil. The induced current opposes the current that induced the magnetic field. For this reason, a coil offers “resistance” to an alternating current. This is called reactance. The reactance increases with the frequency of the voltage and t he inductance of the coil. Inductance is measured in Henry (H) 1 H



1

VS A

 1S

Reactance in DC circuits

In the case of DC circuits, the current, voltage and magnetic field only change when the current is switched on. For this reason reactance only applies when the circuit is closed (switching on the current) In addition to reactance, t he coil has ohmic resistance. This resistance applies both to AC circuits and DC circuits. 2.4

Function of a capacitor

A capacitor consists of two metal plates with an insulating layer (dielectric) between them. If the capacitor is connected to a DC voltage source closing the switch S1 in by this. If the circuit is then interrupted, the charge remains stored in the capacitor. The larger the capacitance of a capacitor, the greater the electrical charge it can store for a given voltage.


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ELECTRO PNEUMATICS

VMPT-302 LC

Capacitance is measured in Farad (F):

1F  1

AS V

If the charged capacitor is now connected t o a load (closing switch S2 in Fig. 2.6), the capacitor discharges. Current flows through the load until the capacitor is fully.

Air-core coil

Coil with iron core and air gap

mA

mA

S1

S2

V + + + + + + -

- - - - -

Fig. 2.4: Function of a capacitor 2.5

Function of a diode

Diodes are electrical components that only allows current to flow in one direction *

In the flow direction, the resistance is so low that the current can flow unhindered.

*

In the reverse direction, the resistance is so high that no current flows.

If a diode is inserted into a AC circuit, the current can only flow in one direction. The current is rectified. The effect of a diode on an electrical circuit is comparable to the effect of a non-return valve on a pneumatic circuit.


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ELECTRO PNEUMATICS

VMPT-302 LC

I

V

~

R

Voltage V

Time t

Current I

Time t

Fig. 2.5: Function a diode 2.6

Measurement in Electrical Circuits

Measurement

Measurement means comparing an unknown variable (such as the length of a pneumatic cylinder) with a known variable (such as the scale of a measuring tape). A measuring device (such as a ruler) allows such measurements to be made. The (such as 30.4 cm)


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ELECTRO PNEUMATICS

VMPT-302 LC

Measurement in electrical circuits

Electrical current, voltages and resistance are normally measured with multimeters. These devices can be switched between various modes: *

DC current and voltage, AC current and voltage

*

Current, voltage and resistance.

The multimeter can only measure correctly if the correct mode is set. Devices for measuring voltage are also called voltmeters. Devices for measuring current are also called ammeters.

V DC +

0

10

20

30

40

DC

DATA/HOLD

AUTO

AC

PEAK HOLD

RANGE

TTL 

A mA

mV

V

A

OFF

F nF

+ Cx 10A ! A

A mA

TTL V 

COM ! 400 mA MAX

5 00 V M AX

1 00 0V 750V

Fig. 2.6: Multimeter


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ELECTRO PNEUMATICS

VMPT-302 LC

Danger

*

Before carrying out a measurement, ensure that voltage of the controller on which you are working does not exceed 24V!

*

Measurements on parts of a controller operating at higher voltages (such as 230V) may only be carried out by persons with appropriate training or instruction.

*

Incorrect measurement methods can result in danger to life.

*

Please read the safety precautions in chapters 3 and 7!

Procedure for measurements on electrical circuits

Follow the following steps when making measurements of electrical circuits.

2.7

*

Switch off voltage source of circuit.

*

Set multimeter to desired mode. (Voltmeter or ammeter, AC or DC, resistance)

*

When measuring DC voltage or current, check for correct polarity. (“+” probe of device to positive pole of voltage source).

*

Select largest range.

*

Switch on voltage source.

*

Observe pointer or display and step down to smaller range.

*

Record measurement for greatest pointer deflection (smallest measuring range).

*

For pointer instruments, always view from vertically above display in order to avoid parallax error.

Voltage Measurement

For voltage measurement, the measuring device (voltmeter) is connected in parallel to the load. The voltage drop across the load corresponds to the voltage drop across the measuring device. A voltmeter has an internal resistance. In order to avoid an inaccurate measurement, the current flowing thought the voltmeter must be as small as possible, so the internal resistance of the voltmeter must be as high as possible.


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V

H

V Voltmeter

Fig. 2.7. Voltage measurement 2.8

Current Measurement

For current measurement, the measuring device (ammeter) is connected in series to the load. The entire current flows through the device Each ammeter has an internal resistance. In order to minimize the measuring error, t he resistance of the ammeter must be as small as possible.

A

Ammeter

H

V

Fig. 2.8 Current measurement


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ELECTRO PNEUMATICS

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Resistance Measurement

The resistance of a load in a DC circuit can either be measured directly or indirectly. *

Indirect measurement measures the current through the load and the voltage across the load (Fig.2.9a). The two measurements can either be carried out simultaneously or one after the other. The resistance is then measured using ohm’s law.

*

For direct measurement the load is separated from the rest of the circuit (Fig.2.9b). The measuring device (ohmmeter) is set to resistance measurement mode and connected to the terminals of the load. The value of the resistance is displayed.

If the load defective (for example, the magnetic coil of a valve is burned out), the measurement of resistance either results in a value of zero (short-circuit) or an infinitely high value (open circuit). Warning

The direct method must be used for measuring the resistance of a load in AC circuits.

Current I A

V

Voltage V

H

V

H

R=V I

Fig. 2.9. Measuring Resistance


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ELECTRO PNEUMATICS

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Sources of error

Measuring device cannot measure voltage, current and resistance to any desired degree of accuracy. The measuring device itself influences the circuit it is measuring, and no measuring device can display a value precisely. The permissible display error of a measuring device is given as a percentage of the upper limit of the effective range. For example, for a measuring device with an accuracy of 05, the display error must not exceed 0.5% of the upper limit of the effective range. Application example Display Error

A class 1.5 measuring device is used to the measure the voltage of a 9V battery. The range is set once to 10V and once to 100V. How large is the maximum permissible display error for the two effective ranges? Range

Permissible display error

10V

15 .

10V .

100

100V

100V .

1.5 100



0.15V



15 . V

Percentage error 0.15

.100



1.66%

. 100



16.6%

9V

15 . 9V

Table 2.1 : Calculating the display error

The example shows clearly that the permissible error is less for the smaller range. Also, the device can be read more accurately. For this reason, you should always set the smallest possible range.


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ELECTRO PNEUMATICS

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CHAPTER - 3 COMPONENTS AND ASSEMBLIES IN THE ELECTRICAL SIGNAL CONTROL SECTION


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VMPT-302 LC

Power supply unit

The signal control section of an electro pneumatic controller is supplied with power via the electrical mains. The controller has a power supply unit for this purpose (see Fig. 3.1). The individual assemblies of the power supply unit have the following tasks: *

The transformer reduces the operating voltage. The mains voltage (i.e. 230V) is applied to the input of the transformer. A lower voltage (i.e.24V) is available at the input.

*

The rectifier converts the AC voltage into DC voltage. The capacitor at the rectifier output smooths the voltage.

*

The voltage regulator at the output of the power supply unit is required to ensure that the electrical voltage remains constant regardless of the current flowing. Fig. 3.1 : Component parts of a power supply unit for an electro pneumatic controller.

~

Rectifier Transformer

Stabilization Powersupply unit

Safety Precaution

*

Because of the high input voltage, power supply units are part of the power installation (DIN /VDE 100).

*

Safety regulations for power installations must be observed.

*

Only authorized personnel any work on power supply units.


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VMPT-302 LC

Push Button and control switches

Switches are installed in circuits to apply a current to a load or to interrupt the circuit. These switches are divided into pushbuttons and control switches. *

Control switches are mechanically detented in the selected position. The switch position remains unchanged until a new switch position is selected. Example; Light switches in the home.

*

Push button switches only maintain the selected position as long as the switch is actuated (pressed). Example : Bell push.

Normally open contact (make)

In the case of a normally open contact, the circuit is open if the switch is in its initial position (not actuated). The circuit is closed by pressing the push button - current flows to the load. When the plunger is released, the spring returns the switch to its initial position, interrupting the circuit.


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ELECTRO PNEUMATICS

1.Actuator type (push button)

VMPT-302 LC

2.Switch element

3.Contact

Fig. 3.2: Normally open contact (make) - section and symbol 3.3

Normally closed contact (break)

In this case, the circuit is closed when the switch is in its initial position. The circuit is interrupted by pressing the pushbutton.

1.

Actuator type (push button)

2.

Contact

3. Switch element

Fig. 3.3: Normally open contact (break) - section and symbol


[ 25 ]


VMPT-302 LC

Changeover contact

The changeover contact combines the functions of the normally open and normally closed contacts in one device. Changeover contacts are used to close one circuit and open another in one switching operation. The circuits are momentarily interrupted during changeover.

1. 2.

Actuator type (push button) Contact (Normally closed contact)

3. 4.

Switching element Contact (Normally open contact)

Fig. 3.4 Changeover contact - section and symbol 3.5

Sensors for measuring displacement and pressure

Sensors have the task of measuring information and passing this on to the signal processing part in a form that can easily be processed. In electropnematic controllers, sensors are primarily used for the following purposes: * * *

No to detect the advanced and retracted end position of the piston rod in cylinder drives To detect the presence and position of work pieces To measure and monitor pressure

Limit switches

A limit switch is actuated when a machine part or workpiece is in certain position. Normally, actuation is effected by a cam. Limit switches are normally changeover contacts. They can then


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be connected - as required - as normally open contact, normally closed contact or changeover contact.

1.

Guide pin

4.

2. 3.

Positive opening lever5. Housing 6.

Compressing spring

7.

Bent leaf spring Contact pressure spring

8. 9.

Contact (Normally open contact) Contact blade Contact (normally closed contact)

Fig. 3.5: Mechanical limit switch: construction and connection possibilities 3.6

Proximity switches

In contrast to limit switches, proximity switches operated contactlessly (non-contact switching reliability). The following types of proximity switch are differentiated:


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ELECTRO PNEUMATICS

* * * *

VMPT-302 LC

Reed switch Inductive proximity switch Capacitive proximity switch. Optical proximity switch.

Reed switch

Reed switches are magnetically actuated proximity switches. They consist of two contact reeds in a glass tube filled with inert gas. The field of a magnet causes the two reeds to close. Allowing current to flow. In reed switches that act as normally closed contacts, the contact reeds are closed by small magnets. This magnetic field is overcome by the considerably stronger magnet ic field of the switching magnets. Reed switches have a long service life and a very short switching time (approx.0.2 ms). They are maintenance-free, but must not be used in environments subject to strong magnetic fields (for example in the vicinity of resistance welders).

Fig. 3.6. Reed switch (normally open contact) 3.7

Electronic sensors

Inductive, optical and capacitive proximity switches are electronic sensors. They normally have three electrical contacts. * * *

Contact for supply voltage Contact for ground. Contact for output signal


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In these sensors, no movable contact is switched instead, the output is either electrically connected to the supply voltage or to ground (= output voltage 0V). Positive and negative switching sensors

There are two types of electronic sensor with regard to the polarity of the output voltage. *

*

In positive switching sensors, the output voltage is zero if no part is detected in the proximity. The approach of a workpiece or machine part leads to switch over of the output, applying the supply voltage. In negative switching sensors, the supply voltage is applied to the output if no part is detected in the proximity. The approach of a workpiece or machine part leads to switch over of the output, switching the output voltage to 0V.

Inductive proximity sensors

An inductive proximity sensor consists of an electrical oscillator (1), a flip-flop (2) and an amplifier (3). When a voltage is applied, the oscillator generates a high-frequency alternating magnetic field that is emitted form the front of the sensor. If an electrical circuit is introduced into this field, the oscillator is attenuated. The downstream circuitry, consisting of a flip-flop and an amplifier, evaluates the behavior of the oscillator and actuates the output. Inductive proximity sensors can be used for the detection of all good electrical conductors (materials). In addition to metals, these include, for example, graphite.


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Symbol

Metal Schematic diagram

Function circuit diagram

1

2

Oscillator (1

Fli -flo (2

3 Am lifier (3

Fig. 3.7 : Inductive proximity sensor


[ 30 ]


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Capacitive proximity sensor

A capacitive proximity sensor consists of a capacitor and an electrical resistance that together form an RC oscillator, and a circuit for evaluation of the frequency. An electrostatic field is generated between the anode and the cathode of the capacitor. A stray field forms at the front of the sensor. If an object is introduced into this stray field forms at the front of the sensor. If an object is introduced into this stray field, the capacitance of the capacitor changes. The oscillator is attenuated. The circuitry switches the output. Capacitive proximity sensors not only react to highly conductive materials ( such as metal) but also to insulators of high dielectric strength (such as plastics, glass, ceramics, fluids and wood). Symbol Schematic diagram

Function circuit diagram

1

2

Oscillator (1)

Flip-flop (2)

3 Amplifier (3)

Fig. 3.8: Capacitive proximity sensor

Optical proximity sensors use optical and electronic means for object detection. Red or infrared light is used. Semiconductor light-emitting diodes (LEDs) are particularly reliable sources of red or infrared light. They are small and rugged, have a long service life and can be simply modulated. Photo diodes or photo transistors are used as a receiver. Red light has the advantage that the light beam can be seen during adjustment of the optical axes of the proximity switch. Polymer optical fibers can also be used because of their low attenuation of light of this wavelength.

Optical Proximity sensor


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Three different types of optical proximity switch are differentiated; *

One-way light barrier

*

Reflective light barrier

*

Diffuse reflective optical sensor.

3.9

Mechanical Pressure switch

In the mechanically actuated pressur e switch, the pressure acts on a cylinder surface. If the pressure exerted exceeds the spring force of the return spring, the piston moves and operates the contact set.

Fig. 3.9:

piston-actuated pressure switch

Diaphragm pressure switches are of increasing importance. Instead of actuating a mechanical contact, the output is switched electronically. Pressure or force sensitive sensors are attached to the diaphragm. The sensor signal is evaluated by an electronic circuit. As soon as the pressure exceeds a certain value, the output is switched.


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VMPT-302 LC

Relays and contactors

Construction of a relay

A relay is an electromagnetically actuated switch. When a voltage is applied to the solenoid coil, an electromagnet field results. This causes the armature to be attract ed to the coil core. The armature actuates the relay contacts, either closing or opening them, depending on the design. A return spring returns the armature to its initial position when the current to the coil is interrupted.

1. 2.

Coil core Return spring

3. 4.

Relay coil Amature

5. 6.

Insulation Contact

Fig. 3.10 : Construction of a relay

A relay coil can switch one or more contacts. In addition to the type of relay described above, there are other types of electromagnetically actuated switch, such as the retentive relay, the time relay, and the contactor.


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Applications of relays

In electro pneumatic control systems, relays are used for the following functions: *

Signal multiplication

*

Delaying and conversion of signals

*

Association of information

*

Isolation of control circuit from main circuit

In purely electrical controllers, the relay is also used for isolation of DC and AC circuits. Retentive relay

The retentive relay responds to current pulses: *

The armature is energized when a positive pulse is applied.

*

The armature is de-energized when a negative pulse is applied.

*

If no input signal is applied, the previously set switch position is retained (retention).

The behavior of a retentive relay is analogous to that of a pneumatic double pilot valve, which responds to pressure pulses. Construction and mode of operation

Electrically actuated directional control valves are switched with the aid of solenoids. They can be divided into two groups: *

Spring-return valves only remain in the actuated position as long as current flows through the solenoid.

*

Double solenoid valves retain the last switched position even when no current flows through the solenoid.


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Initial position

In the initial position all solenoids of an electrically actuated directional control valve are deenergized and the solenoids are inactive. A double solenoid valve has no clear initial position, as it does not have a return spring. Port Designation

Directional control valves are also differentiated by the number of ports and the number of switching position. The valve designation results from the number of ports and positions, for example: *

Spring-return 3/2-way valve

*

5/2-way double solenoid valve

The following section explains the construction and mode of operation of the major types of valve. 3.11

Directly controlled 3/2-way valve

Fig. 3.11 shows two cross-sections of a directly controlled electrically actuated 3/2-way valve. *

In its initial position, the working port 2 is linked to the exhaust port 3 by the slot in the armature (see detail) (fig. 3.11a).

*

If the solenoid is energized, the magnetic field forces the armature up against the pressure of the spring (Fig.3.11b). The lower sealing seat opens and the path is free for flow from pressure port 1 to working port 2. The upper sealing seat closes, shutting off the path between port 1 and port 3.

*

If the solenoid coil is de-energized, the armature is retracted to its initial position by the return spring (Fig. 3.11a). The path between port 2 and port 3 is opened and the path between port 1 and port 2 closed. The compressed air is vented via the armature tube at port 3.


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Manual override

The manual override a allows the path between port 1 and port 2 to be opened even if the solenoid is not energized. When the screw is turned, the eccentric cam actuates the armature. Turning the screw back returns the armature to its initial position.

3.11a 3.12

3.11a

3/2 Way valve normally open

Fig. 3.12 shows an electrically actuated 3/2-way valve, normally open. Fig.3.12a shows the valve in its initial position, Fig. 3.12b actuat ed. Compared to the initial position of the closed valve (fig. 3.12) the pressure and exhaust ports are reversed.


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Fig 3.12 : 3/2-way valve with manual override (normally open) 3.13

Pilot controlled directional

In pilot controlled directional control valves, the valve piston is indirectly actuated. *

The armature of a solenoid opens or closes an air duct from port 1.

*

If the armature is open, compressed air form port 1 actuates the valve piston.

*

If the coil is de-energized, the armature is pressed against the lower sealing seat by the spring. The chamber of the upper side of the piston is vented(Fig. 3.13a).

*

If the coil is energized, the solenoid pulls the armature down. The chamber on the upper side of the piston is pressurized (Fig. 3.13b)


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Fig. 3.13 explains the mode of operation of the pilot control. 3.14

Pilot controlled 3/2-way valve

Fig. 3.14 shows two cross-sections of an electrically actuated pilot controlled 3/2-way valve. * *

*

In its initial position, the piston surface is only subject to atmospheric pressure, so the return spring pushes the piston up (Fig. 3.14a, b) Ports 2 and 3 are connected. If the solenoid coil is energized, the chamber below the valve piton is connected to pressure port 1. The force on the upper surface of the valve piston increases, pressing the piston down. The connection between ports 2 and 3 is closed, the connection between ports 1 and 2 opened. The valve remains in this position as long as the solenoid coil is energized. If the solenoid coil is de-energized, the valve switches back to its initial position.

A minimum supply pressure (control pressure) is required to actuate the pilot controlled valve against the spring pressure. This pressure is given in the valve specifications and lies-depending on type - in the range of about 2 t o 3 bar.


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Comparison of pilot controlled and directly actuated valves

The greater the flow rate of a directional control valve, the higher the flow. In the case of a directly actuated valve, flow to the consuming device is released by the armature (see Fig. 4.2). In order to ensure a sufficiently large opening and sufficient flow rate, a relatively large armature is required. This in turn requires a large return spring - against which the solenoid must exert a large force. This results in relatively large component size and high power consumption. In a pilot controlled valve, flow to the consuming device is switched by the main stage (Fig.4.5). The valve piston is pressurized via the air duct. A relatively small airflow is sufficient, so the armature can be comparatively small with low actuat ion force. The solenoid can also be smaller than for a directly actuated valve. Power consumption and heat dissipation are lower. The advantages with regard to power consumption, size of solenoids and heat dissipation have led to almost exclusive use being made of pilot controlled directional control valve in electro pneumatic control systems. 3.15

Pilot controlled 5/2-way valve

Fig. 3.15 shows the two switching positions of an electrically actuated pilot controlled 5/2-way valve. *

In its initial position, the piston is at the left stop (fig.3.15a). Port 1 and 2 and ports 4 and 5 are connected.

*

If the solenoid coil is energized, the valve spool moves to the right stop (Fig. 3.15b). In this position, ports 1 and 4 and 2 and 3 are connected.

*

If the solenoid is de-energized, the return spring returns the valve spool to its initial position.

*

Pilot air is supplied via port 84.

2

1


3

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Fig. 3.15


VMPT-302 LC

Pilot controlled 5/2-way solenoid valve

[ 40 ]


VMPT-302 LC

5/3-way valve with exhausted initial position

Fig. 4.8 shows the three switching positions of an electrically actuated, pilot controlled 5/3-way valve.

*

In its initial position, the solenoid coils are de-energized and the piston spool is held in the mid-position by the two springs (Fig4.8a). Ports 2 and 3 and 4 and 5 are connected. Port 1 is closed.

*

If the left solenoid coil is energized, the piston moves to its right stop (Fig.4.8b). Ports 1 and 4 and 2 and 3 are connected.

*

If the right solenoid coil is energized, the piston moves to its left stop (Fig.4.8c). In this position, ports 1 and 2 and 4 and 5are connected.

*

Each position is held as long as the appropriate coil is energized.

If neither coil is

energized, the valve returns to the initial mid-position.


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Fig 3.16 Pilot-actuated 5/3-way double solenoid valve (mid-position exhausted)


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CHAPTER - 4 COMPONENTS LIST OF PNEUMATIC PANEL


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Types of compressor 4.1

Air Compressor

The selection from the various types compressors available in dependent upon quality of air, pressure, quality and cleanliness and how dry the air should be. There are varying levels of these criteria depending on the types of compressor.

Types of compressor

Reciprocating piston compressor

Piston compressor

Rotary piston compressor

Diaphragm compressor

Sliding vane compressor

Flow compressor

Radial-flow compressor

Twin-shaft screw compressor

Axial-flow compressor

Roots compressor

Reciprocating piston compressors

A piston compresses the air drawn in via an inlet valve. The air is passed on via an outlet valve. Reciprocating compressors are very common and provide a wide range of pressures and delivery rates. For higher pressures multistage compression is used with intercooling between each stage of compression. The optimum range of pressures for reciprocating compressors are approximately: up to 400 kPa


(4 bar)

Single stage

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up to 1500 kPa

(15 bar)

Double stage

over 1500 kPa

(> 15 bar)

Treble or multi stage

Also, it is possible but not necessarily economic to operate in the following ranges: up to 1200 kPa

(12 bar)

Single stage

up to 3000 kPa

(30 bar)

Double stage

over 3000 kPa

(> 30 bar)

Treble or multi stage

Diaphragm Compressor

The diaphragm compressor belongs to the reciprocating piston compressor group. The compressor chamber is separated from the piston by a diaphragm. The advantage of this is that no oil can enter into the air flow from the compressor. The diaphragm compressor is therefore used where oil is to be excluded from the air supply, for example in the food, pharmaceutical and chemical industries. Rotary piston compressor

The rotary group of compressors use rotating elements to compress and increase the pressure of the air. During the compression process, the compression chamber is continually reduced. Screw compressor

Two screw-shaped shafts (rotors) turn in opposite directions. The meshed profile of the two shafts causes the air to flow which is then compressed. Flow compressor

These are particularly suitable for large delivery quantities. Flow compressors are made in axial or radial form. The air is made to flow by means of one or several turbine wheels. The kinetic energy is converted into pressure energy. In the case of an axial compressor, t he air is axial compressor, the air is accelerated in the axial direction of flow by means of blades.


[ 45 ]


VMPT-302 LC

List of components

Air service unit

The air service unit is a combination of the following:   

Compressed air filter (with water separated) Compressed air regulator Compressed air lubricator

However, the use of a lubricator does not need to be provided for in the power section of a control system unless necessary, since the compressed air in the control section does not necessarily need to be lubricated. The correct combination, size and type of these elements are determined by the application and the control system demand. An air service unit is fitted at each control system in the network to ensure the quality of air for each individual task. Compressed air filter

The compressed air filter has the job of removing all contaminants from the compressed air flowing through it as well as water which has already condensed. The compressed air enters the filter bowl through guide slots. Liquid particles and larger particles of dirty are separated centrifugally collection in the lower part of the filter bowl. The collected condensate must be drained before the level exceeds the maximum condensate mark, as it will otherwise be reentrained in the air stream. The purpose of the regulator is to keep the operating pressure of the system (secondary pressure) virtually constant regardless of fluctuations in the line pressure (primary pressure) and the air consumption. Compressed air lubricator

The purpose of the lubricator is to deliver a metered quantity of oil mist into a leg of the distribution system when necessary for the operation of the pneumatic system.


[ 46 ]


VMPT-302 LC

3/2 PUSH BUTTON VALVE

This valve consists of three ports and two states. The valve is controlled by a push button and spring force. When the push button is depressed, the internal piston moves, allowing pressurized air to pass from ports P to A. At this stage the valve is active. Upon release of the push button, the spring force moves the internal piston, there by terminating the air flow from ports P to A, and returns to the initial position. Air from port A is exhausted through port R.

3/2 NC ROLLER VALVE

This valve consists of three ports and two states. The valve is controlled by a roller head and spring force. When an external force activates the roller head, the piston moves, compacting the spring force and allowing the flow of pressurized air from ports P to A. When the roller head is de-activated, the spring force causes the valve to return to the initial position. Air flow from ports P to A will terminated and Air is exhausted to atmosphere via the exhaust port R

5/2 Single Pilot Operated Spring Return Valve

This valve consists of five ports and two states. The valve is controlled by pilot air and a spring. Pressurized air enters the valve through port P. If the controller at port X is active, the piston will move and air flow will be established between ports P and B. When the controller at port X is deactivated, the spring expands, terminating the air flow between ports P and B, there by establishing air flow between Ports P and A.


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5/2 Double Pilot Operated Valve

This valve consists of five ports and two states. The valve is controlled at both ends by pilot air, which are controlled by some controller Pressurized air enters the valve through port P. If the controller at port X is active, the piston will move and air flow will be established between ports P and B. If the controller at port Y is active, the piston will move and airflow will be established between Ports P and A.

Shuttle valve (or gate)

This component is a control unit, which has two input ports, and one output port. Either of the input ports must be active for the output port to operate. The output Port A is active (has pressure) when pressure is applied to one or both P input ports.

Flow Control Valve

These valves are used to regulate air flow in a pneumatic systems (example to control the piston speeds of the cylinders). As pneumatic pressure as well as the velocity of the piston are directly proportional to the amount of flow of air, so we can control all these parameter by just controlling the flow The air can flow only via the cross section which is adjustable by means of the throttle screw.


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One-way flow control valve

In the case of the one-way flow control valve, the air flow is throttled in one direction only. A check valve blocks the flow of air in the bypass leg and the air can flow only through the regulated cross-section. In the opposite direction, the air can flow freely through the opened check valve. These valves are used for speed regulation of actuators and if possible, should be mounted directly on the cylinder.

Quick Exhaust Valve

Quick Exhaust Valves are used when lengthy return times is to be avoided, particularly with single acting cylinder. The simple idea behind it, is to allow cylinder to return in its maximum speed by reducing resistance to flow of the exhausting air, by expelling the air to atmosphere near to cylinder via a large orifice opening.


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Manifold

The manifold conducts pressurized air flow from the main pressure line and distributes it to the various components connected to it. Generally Port A is the port used for the inlet of pressurized air flow from the input component. The rest Ports B, C, D, and E are used to direct pressurized air to the components. There is no restriction on the component that certain port should act as inlet, it is user choice that any port can be used as inlet and rest as outlets. A

B

C

D

E

A

B

C

D

E

Two pressure valve

The two pressure valve is switched based on the compressed air entering into both input connections 1 and leaving via an output connection 2. Should both input connections being receiving compressed air, the connection with the lower pressure takes precedence and is put out (AND function). 2


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CHAPTER - 5 APPLICATION AND SYMBOLS FOR DIRECTIONAL CONTROL VALVES


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Symbol

Valve type

Applications 2

Pilot controlled spring

Shut-off function

12

return 2/2-way valve

1 2

Pilot controlled spring return 3/2-way valve, normally closed

Single-acting cylinders

12 3

1

Pilot controlled spring return 3/2-way valve, normally open

2

Switching compressed air on and off

10 3

1

4

Pilot controlled spring return 4/2-way valve

2

14 3

1 4

Pilot controlled spring return 5/2-way valve

Double-acting linear or swivel cylinders

2

14 5

3 1

4

2

14

12 5

1 3

4

Pilot controlled spring return 5/2-way valve (normally closed,

2

14

12 5

exhausted or pressurized)

1

4

3 2

14

12 5

1 3

4

Pilot controlled 4/2-way double solenoid valve

Double-acting linear or swivel cylinders with intermediate stop, with special requirements regarding behavior in event of power failure.

2

14

3

1

12

Double-acting linear or swivel cylinders 4

Pilot controlled 5/2-way double solenoid valve

2 12

14 3

5 1


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CHAPTER - 6 PERFORMANCE DATA OF SOLENOID COILS


[ 53 ]


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Performance data of solenoid coils

An electrically actuated directional control valve can be equipped with various different solenoid coils. The valve manufacturer usually offers one or more series of solenoid coils for each type of directional control valve, with connection dimensions to match the valve. The choice of solenoid coil is made on the basis of the electrical performance data (Table 4.4) Coil type

DC Voltage

AC Voltage

Voltages Normal Special

12V,24V,42V,48V on request

24V, 42V, 110V, 230V, 50Hz on request

Voltage fluctuation

Max.±10%

Max.±10%

Frequency fluctuation

-

Max.±5% at nominal voltage

Power consumption for normal voltages

4.1 Wat 12V 4.5 Wat 24V

Pickup : 7.5VA Hold : 6VA

Power factor

-

0.7

Duty cycle

100%

100%

Degree of protection

IP65

IP 65

Cable conduit fitting

PG9

PG9

Ambient temperature

5 - 40°C

Medium temperature

10 - 60°C

10 - 60° C

Average pickup time

10ms

10ms

Table 4.4 Performance data of DC and AC solenoid calls (Festo) 6.2

Specification of operating voltage

The voltage specification in Table 4.4 relates to the voltage supplied to the solenoid coils. The solenoid coils are chosen to match the signal control section of the electro pneumatic control system. If the signal control section operates with a DC voltage of 24V, for example, the corresponding type of coil should be chosen. To ensure proper operation of the solenoid coil, the voltage supplied to it from the signal control section must be within certain limits for the 24V coil type, the limits are as follows: Minimum Voltage : Vmin = 24V. (100% - 10%) = 24V.0.9 = 21.6V Maximum Voltage : Vmax = 24V. (100% + 10%) = 24V.1.1 = 26.4V If the signal control section operates with Ac voltage and there fore AC solenoid coils are used,


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the frequency of the AC voltage must be within a specified range. For the AC coils described in the table, frequencies up to 5% above or below 50Hz are permissible; in other words the permitted frequency range is between 47.5 and 52.5 Hz. 6.3

Electrical connection of solenoid coils

The solenoid coil of a directional control valve if connected to the signal control section of an electro pneumatic control system via a two-core cable. There is a removable plug connector between the cable and the solenoid. When the connector is inserted it is screwed down to protect the plug contacts against the ingress of dust and water. The type of plug connector and cable conduit fitting are specified in the technical documentation for the solenoid coil (such as PG9 in table 4.4) 6.4

Protective circuit of a solenoid coil

The electric circuit is opened or closed by a contact in the signal control section of the control system. When the contact is opened, the current through the solenoid coil suddenly decays. As a result of the rapid change in current intensity, in conjunction with the inductance of the coil, a very high voltage is induced briefly in the coil. Arcing may occur at the opening contact. Even after only a short operating time, this leads to destruction of the contact. A protective circuit is therefore necessary. Fig. 4.13 shows the protective circuit for a DC coil. While the contact is closed, current I1 flows through the solenoid and the diode is de-energized (fig. 6.4 a). When the contact is opened, the flow of current in the main circuit is interrupted (Fig. 6.5b). The circuit is now closed via the diode. In that way the current can continue flowing through the coil until the energy stored in the magnetic field is dissipated. As a result of the protective circuit, current IM is no longer subject to sudden decay, instead it is continuously reduced over a certain length of time the induced voltage peak is considerably lower, ensuring that the contact and solenoid coil are not damaged.


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i1

IM = I1

ID =0

IM

ID=IM

+24V 0V

i1= 0

+24V 0V

Fig. 6.4 (a), (b) : Protective circuit of a solenoid coil Auxiliary Functions

In addition to the protective circuit required for operation of the valve, further auxiliary functions can be integrated in the cable connection, for example: *

Indicator lamp (lights up when the solenoid is actuated)

*

Switching delay (to allow delayed actuation)


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VMPT-302 LC

Adapters and cable sockets

The protective circuit and auxiliary functions are integrated either into the cable socket or in the form of adapter inserts i.e. illuminating seal (Fig. 4.14). Appropriate adapters and cable sockets must be chosen to match the voltage at which the signal control section operates (for example 24V DC).


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Class of protection

Plugs, sockets and adapters are sealed in order to prevent either dust or moisture from entering the plug connection. If the adapter, solenoid coil and valve have different classes of protection, the lowest of the three classes of protection applies to the assembled valve, coil and cable conduit. Explosion protection

If it is intended to use electrically actuated directional control valves in an environment subject to explosion hazards, special solenoid coils approved for sch applications are required; these have molded cables.


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CHAPTER - 7 APPLICATION OF ELECTRO PNEUMATIC SYSTEM


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A lifting device transfers work pieces from the one roller conveyor or to another a different height. The task is to carry out the project engineering for the associated electro pneumatic control system. A positional sketch of the lifting device is shown in fig. 5.2. There are three pneumatic drives; *

Drive 1A lifts the workpieces.

*

Drive 2A pushes the workpieces onto the upper roller conveyor.

*

Drive 3A is used as a stopper, for releasing and interrupting this supply of workpieces.

Fig 5.2 : Positional sketch of the lifting device


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Note

The packages first have to be separated to be fed singly; this is done at an upstream facility. The optical proximity switch B6 is not taken into account for the purposes of further project engineering of the lifting device. 7.1

Drives for the lifting device

Cylinder 1A requires a stroke of 500mm and a force of at least 600N, cylinder 2A a stroke of 250mm and a force of at least 400 N. Cylinder 3A requires a stroke of 20 mm and a force of 40N. On cylinders 1A and 2A the advance and retract speeds of the piston rods need to be variable. The control system must allow soft braking of drives 1A and 2A. To prevent the possibility of secondary damage, in the event of an electrical power failure the piston rods for cylinders 1A and 2A are to be braked immediately and remain at a standstill. The piston rod of the stopper cylinder 3A is meant to extend in these circumstances. Movement cycle of the lifting device

The movement cycle of the lifting device is described in Table 5.2 (see positional sketch, Fig. 5.2). It comprises four steps.

Step

Movement piston rodcylinder A

Movement piston rodcylinder 2A

Movement piston rodcylindr 3A

End of step, step enabling condition

comments

1

None

None

Retract

B5 triggered (package present)

Open device

2

Advance

None

Advance

1B2 triggered

Lift package

3

None

Advance

None

2B2 triggered

Push out package

4

Retract

Retract

None

1B1, 2B1 triggered

Retract drives to initial position

Table 7.1 : Movement cycle of the lifting device


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Operator Control

The control system of the lifting device must enable the device to be run in a continuous cycle (continuous operation). A single cycle operating mode is also necessary in which the sequence is processed precisely once. The operator control equipment for the system must conform to the relevant standards (see section 7.4). The control panel for the lifting device is shown in Fig.5.3. The following operating functions are specified in more detail in relation to the lifting device: * * *

“EMERGENCY STOP”: When this is actuated, not only the electrical power supply, also the pneumatic power supply must be shut down. “Reset” : This returns the system to the initial position, i.e, the piston rods of cylinders 1A and 2A retract, the piston rod of cylinder 3A extends. “Continuous cycle OFF”: This stops the continuous cycle process. If there is already a workpiece in the device, it is transferred to t he upper roller conveyor. The piston rods of cylinders 1A and 2A retract. The device is subsequently in its initial position.

EMERGENCY STOP

Main switch

EMERGENCY STOP

Continous cycle on

Single cycle start

Automatic Continous cycle off

Manual


Reset

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Ambient conditions

The lifting device is used in a production shop in which the temperature fluctuates between 15 and 35 degrees centigrade. The pneumatic components of the power section and the electrical connections of the valves are to be dust-tight and splash-proof. The electrical components of the signal control section are installed in a control cabinet and must conform to the relevant safety regulations. Power supply

The following power supply networks are available: *

Compressed air network (P = 0.6 Mpa = 6 bar)

*

Electrical network (V = 230 VAC)

The electrical signal control section and the main circuit are to be operated with 24V DC. A power supply unit therefore needs to be provided to supply this voltage. 7.3

Overall conceptual design of the control system

The signal processing aspect of the lifting device is implemented as a relay control system. In view of the small number of drive units, the valves are mounted separately. As the linear guides of the lifting platform and of the pushing device are already part of the station, cylinders without integrated guides are used. Double-acting cylinders are used for drives 1A and 2A. Drive 3A takes the form of a single - acting stopper cylinder. Selection of cylinders

The cylinders are chosen on the basis of the requirements in terms of force and stroke, using catalogues obtained from pneumatics manufacturers. On account of the required drive force, cylinder 1A must have a piston diameter of at least 40mm, and cylinder 2A a piston diameter of at least 40mm, and cylinder 2A a piston diameter of at least 32mm. To ensure soft braking, cylinders with integrated adjustable end position cushioning are used for drives 1A and 2A. The following cylinders would be suitable, for example: *

Cylinder 1A : Festo DNGUL-40-500-PPV-A

*

Cylinder 2A : Festo DNGUL-32-250-PPV-A

A stopper cylinder is used for drive 3A; it is extended if the compressed air supply fails. This requirement is met by a Festo STA-32-20-P-A type cylinder, for example


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Selection of directional control valves for the control chain

In order to obtain the required behavior for drives 1A and 2A in the event of a power failure, the valves used are spring-centered 5/3-way valves with a closed mid-position. As the movements of the piston rods are relatively slow, valves of a comparatively small nominal size are adequate. Valves with 1/8-inch ports are used to match the smaller of the two cylinders directional control valves of the festo MEH-5/3G-1/8 type would be suitable, for example. A spring-return 3/2-way valve of the Festo MEH-3/2-1/8 type is used for actuation of stopper cylinder 3A. Pressure Sequence valve

The supply of compressed air for all three control chains must be shut off as soon as the electrical power supply fails or an EMERGENCY STOP is triggered. An additional, electrically actuated, spring-return 3/2-way valve is therefore necessary which enables the supply of compressed air only when the electrical power supply is functioning properly and no EMERGENCY STOP device has been actuated. In order to ensure that there is adequate flow, a Festo CPE14-M1H3GL-1/8 type valve is used. Speed regulation

The advance and retract speeds of drives 1A and 2A are regulated by means of exhaust air flow control. Function connectors reduce tubing work, because they are screwed directly into the cylinder bore. The type of connectors required are those with a one-way flow control function, for example festo GRLA-1/4 (cylinder 1A) or GFLA-1/8 (cylinder 2A). Selection of proximity switches

The proximity switches are selected to match the cylinders. It makes sense to use positiveswitching sensors. For example, inductive sensors of type SMTO-1-PS-K-LED-24 are suitable for cylinders 1A and 2A, and type SMT-8-PS-KL-LED-24 for cylinder 3A. For controlling the device (see movement sequence) two proximity switches are needed for each of cylinders 1A and 2A in order to detect the forward and retract ed end positions. In the case of cylinder 3A it is sufficient to have one sensor to detect the forward end position. Positive-switching optical sensors, for example festo type SOEGRT-M18-PS-K, are used to detect whether there is a workpiece ahead of the stopper cylinder or on the lifting platform. Allocation table for the lifting device

The subsequent steps of the project design process are made easier by listing the cylinders, solenoids, sensors, control elements and indicators (Table 5.3). Components belonging to an individual control chain are shown on the same line of the table.


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Drive/ function

VMPT-302 LC

Actuated solenoid

Control Element

Proximity switch

Advance

Retract

Cyl.1A

1M1

1M2

-

1B2

1B1

Control chain 1

Cyl.2A

2M1

2M2

-

2B2

2B1

Control chain 2

3M1

-

3B1

Cyl.3A Comp.air

Other

Advance

Retract

Comments

Other

Control chain 3 Pressure sequence valve

0M1 B5


Package on lifting platform S1

Main switch

S2

Emergency stop (Normally closed contact)

S3

Manual (MAN)

S4

Automatic (AUT)

S5

Reset

S6

Continous cycle ON

S7

Single cycle START

S8

Continous cycle OFF

[ 65 ]


VMPT-302 LC

Displacement - step diagram for the lifting device

The displacement-step diagram for the lifting device is shown in Fig. 5.4. it illustrates the steps in which the piston rods of the three cylinders advance and retract, and when the proximity switches respond.

S4 (AUT) S6 S7 1B1 ^ 2B1 ^ 3B1 B5 1

2

3

4

5=1

1 1B2 Cylinder 1A 1B1

0 2B2

1 Cylinder 2A

2B1

0 1 3B1 Cylinder 3A 0

Fig.5.4: Displacement-step diagram for the lifting device.


[ 66 ]

ELECTRO PNEUMATICS

VMPT-302 LC

CHAPTER - 8 SAFETY MEASURES FOR ELECTRO PNEUMATIC CONTROL SYSTEMS


[ 67 ]

ELECTRO PNEUMATICS

VMPT-302 LC

Numerous protective measures are necessary in order to ensure that electro pneumatic control systems can be safely operated. One source of danger is moving parts of machines and equipment. On a pneumatic press, for example, care must be taken to prevent the operator’s fingers or hands from being trapped. Fig 8.0 provides an overview of sources of danger and suitable protect ive measures. Fig.8.0 Moving parts of machines and equipment: sources and danger and protective measures

8.1

Source of danger

Electric current is another source of danger. The dangers and protective measures relating to

Dangers from moving parts of machines and equipment (Cylinder, axes, grippers, suction cups, clamping devices, presses, workpieces, etc.)

Protection by enclosure/covering Cage Grid

Protection by control and signalling devices Warning lights EMERGENCY STOP Two-hand safety control

Protection by signal processing measures Protection against unsupervised startup Setup procedure

electric current are summarized in Fig 8.1.


[ 68 ]

ELECTRO PNEUMATICS

VMPT-302 LC

Fig 8.1 Electric current: Sources of danger and protective measures

Dangers from components through which electric current flows (Power supply units, sensors, signal processing, components solenoid coils of dielectrical control valves)

Protection against contact with high voltage Safety extra-low voltage Covering/housing Adequate distance Grounding

8.2

Protection during maintenance and repair work Main switch with interclocking

Protection of electrical equipment against environmental influences Protection against dust/foreign bodies Protection against water/moisture

Safety rules

In order to provide the best possible safeguards for operating personnel, various safety rules and standards must be observed when designing electro pneumatic control systems. The key standards dealing with protection against the dangers of electric current are listed below. *

Protection measures for Electrical Power Installations up to 1000V (DIN VDE 0100).

*

Specifications for Electrical Equipment and Safety of Machines (DIN/EN 60204).

*

Degrees of protection of Electrical Equipment (DIN-VDE 470-1).

When a person touches a live part, an electric circuit is completed. An electric current flows through the person’s body.


[ 69 ]


VMPT-302 LC

Effect of electric current on the human body

The effect of electric current on the human body increases with the intensity of the current and with the length of time in contact with the current. The effects are grouped according to the following threshold values. *

Below the threshold perception, electric current has no effect on the human body to human health.

*

Above the let-go threshold muscles become cramped and functioning of the heart is impaired.

*

Above the threshold of non-fibrillation, the effects are cardiac arrest or ventricular.

*

Up to the let-go threshold, electric current is perceived but there is no danger fibrillation, cessation of breathing and unconsciousness. There is an acute risk to life.

The threshold of perception, let-go threshold and non-fibrillation threshold are plotted in fig for alternating current with a frequency of 50 Hz. This corresponds to the frequency of the electrical supply network. For direct current, the threshold values for endangering human beings are slightly higher. Electrical resistance of the human body

The human body offer resistance to the flow of current. Electric current may enter the body through the hand, for example: it then flows through the body to reemerge at another point (such as the feet-see fig). Accordingly, the electrical resistance R M of the human body (Fig ) is formed by a series circuit comprising the entry resistance R 01 the internal resistance R 1 and the exit resistance R 02 (Fig ). It is calculated using the following formula:

R M



R01



R1



R02

The contact resistances R 01 and R 02 vary greatly depending on the contact surface and the moistness and t hickness of the skin. This affects the total resistance RM. It may range between the following extremes. *

Less than 1000 ohms (large contact surfaces, wet, sweaty skin)

*

Several million ohms (point contact, very dry, thick skin)


[ 70 ]

ELECTRO PNEUMATICS

VMPT-302 LC

I G ~

R 01

R 1

R 02

I

I R L

G ~

R M

R M

U ~

R E


[ 71 ]


VMPT-302 LC

Variables influencing the risk of accident

The current I through the human body is dependent on the source voltage V, the resistance RL of the electric line, the resistance RM of the person and the resistance RE of the ground (Fig). It is calculated as follows:

I

V 

R L



RM



RE

According to this formula, a high current, i.e. a high level of danger, is obtained in the following circumstances: *

When touching an electrical conductor carrying a high voltage V (Such as a conductor in the electrical supply network, 230V AC)

*

When touching a conductor at a low contact resistance R 0 and consequently low resistance R M (such as with large contact surfaces, sweaty skin, wet clothing)

10000 5000

Threshold of non-fibrillation

Threshold of perception

ms 2000 1000 500

t e m i T

1

2

3

Let-go threshold

200

4

100 50 20 10 0

0.1

0.2

0.5

1

2

5

10

20

50

100

200

500

mA

2000

Current I

Danger zones with AC voltage (frequency 50Hz/60 Hz)


[ 72 ]

ELECTRO PNEUMATICS

VMPT-302 LC

CHAPTER - 9 COMPONENTS DESCRIPTION OF ELECTRO PNEUMATIC TRAINER


[ 73 ]

ELECTRO PNEUMATICS

VMPT-302 LC

1. 3/2 – way valve with pushbutton actuator N.C. assy.:

* Design: directly actuated, one side, with return spring. * Pressure range: (-0.9 – 8 bar) * Nominal Flow rate 1 ..2: 60 l/min 2. Quick-exhaust valve assy.:

* * * * *

Quick-exhaust valve with built-in silencer. Design: Pop pet valve Pressure range: (0.5 – 10 bar) Nominal flow rate 1 …2: 960 l/min Nominal flow rate 2… 3: 1100 l/min.

3. 3/2-way roller lever Valve Act. N.C. assy.:

The roller lever valve is actuated when the roller lever is pressed, for example by the cam of a cylinder. After release of the roller lever, the valve is returned to its initial position by as return spring. * * * * *

Design: Pop pet valve, directly actuated, one side with return spring. Pressure range: (-0.9 to 8 bar) Nominal flow rate 1…2: 80 l/min. Nominal flow rate 1 .. 4: 500 l/min. Response time: Optimum.

4. 5/2 –way Single Pilot Valve with Assembly:

The pneumatic single piloted valve is actuated by pneumatic signals, and following removal of the signal is returned to its initial position by a return spring. * * * * *

Design: Directly actuated, one side with return spring. Pressure range: (0 to 10 bar) Nominal flow rate 1…2: 500 l/min. Nominal flow rate 1.... 4: 500 l/min. Response time: Optimum

5. 5/2 Double Pilot Valve with Assembly:

The pneumatic double pilot valve is reversed by pneumatic signals form alternate sides. The circuit state is retained after removal of the signal until the next counteracting signal. * Design: Directly actuated, both sides


[ 74 ]

ELECTRO PNEUMATICS

* * * *

VMPT-302 LC

Pressure range: (0 – 10 bar) Nominal flow rate 1…2: 500 l/min. Nominal flow rate 1 .. 4: 500 l/min. Response time: Optimum.

6. Shuttle valve (OR) assy.:

The shuttle valve is switched through to the output by applying compressed air to one of the inputs (OR function). * Design: OR gate (shuttle valve) * Pressure range: (1 – 10 bar) * Nominal flow rate 1…2: 500 l/min. 7. Dual-pressure valve (AND):

The dual-pressure valve is switched through to the output by applying compressed air to both of the inputs (AND function). * Design: AND gate (dual-pressure valve) * Pressure range: (1 – 10 bar) * Nominal flow rate 1…2: 550 l/min. 8. Time-delay valve / adjust N.C. assy.:

The time delay can be set with an adjusting screw (infinitely variable). * * * *

Design – Return Spring. Pressure range - (2.5 – 8 bar) Nominal flow rate 1…2 - 92 l/min. Delay – 30s

9. One-way flow control valve assy.:

The one-way flow control valve is a combination of flow control valve and a non-return valve. The cross-section of the restrictor can be set by means of a knurled screw. * Design – Combined flow control valve. * Pressure range - (0.5 – 10 bar) * Nominal flow rate 0 – 220 LPM.


[ 75 ]

ELECTRO PNEUMATICS

VMPT-302 LC

10. Single-acting cylinder assy.:

* * * * *

Design – Piston cylinder Operating Pressure – 10 bar Stroke length – Maximum 50 mm Thrust at (6bar) – 169 N Spring return force minimal – 13.65N

11. Double-acting cylinder assy.:

* * * * *

Design – Piston cylinder Operating Pressure – 10 bar Stroke length – Maximum 100 mm Thrust at (6bar) – 188.5 N Return Thrust at (6 bar) – 158. 3 N

12. Manifold assy.:

Manifold with six (2x3) self-closing non-return valves. A common manifold (QS – 6x6 = multiple connector) for plastic tubing allows supply of compressed air to the control via six Individual ports (QS-4 for plastic tubing PUN 4 x 0.75). 13. Filter regulator with gauge assy. With Lubricator:

* * * * * * * * * * *

Filter control valve with pressure gauge, start-up valve, quick push-pull connectors and quick couplings, mounted on a swivel support. The filter with water separator removes dirt, pipe sinter, rust and condensed water. The pressure control valve regulates the supply air pressure to the set operating pressure and compensates pressure fluctuations. The filter bowl has a condensate drain valve. The start-up valve / shut off valve ventilates and vents the entire control. The 3/2 way valve is actuated by a rotary button. Design – Sintered filter Nominal flow rate – 750 l/min Input Pressure – Maximum (16 bar) Output pressure – Maximum (12 bar) Grade of filtration – 40 m Condensate quantity – 22 c.cm. Connector – G 1/8

14. Plastic tubing:

* PUN 6 x 1 * Exterior diameter – 6 mm


[ 76 ]

ELECTRO PNEUMATICS

VMPT-302 LC

* Interior diameter – 4 mm. * Blue – 15m 15. T – connectors(4):

These shall be for branching of the tubes for making circuitry. 16. 5/2 way Hand lever valve:

* ¼ Hand lever valve with * Flow – 1600 l/min * Work pressure – (0 – 8 bar) 17. Read Switch, Electronic with cylinder attachment:

The proximity switch consists of a sensor, the mounting kit, and the cable. This proximity switch gives a signal when it detects a magnetic field. The status is indicated by a LED. * * * *

Switching voltage – 10 –30 VDC Switching Current – Maximum 200mA Switching power – 6w Switch accuracy - ±0.1mm.

18. 3/2 way Single Solenoid Valve with LED, NC:

The status is indicated by an LED on the housing. The valve is equipped with a manual override. The electrical connections feature polarity reversal protection for the LED and the suppressor circuit. Pneumatic Technical data:

* Design – Spool valve, pilot controlled, with return spring. * Pressure range – 250 – 800 kPa (2.5 – 8 bar) * Response time at 600 kPa (6 basr) – On: 20 ms, Off: 30ms * Nominal flow rate 1 .. 2 – 500 l/min. * Electrical Technical Data: # Power Consumption – 1.5 W # Duty Cycle – 100% 19. 5/2 way Single Solenoid valve, with LED:

The status is indicated by an LED on the housing. The valve is equipped with a manual override. The electrical connections feature polarity reversal protection for the LED and the suppressor circuit.


[ 77 ]

ELECTRO PNEUMATICS

VMPT-302 LC

Pneumatic Technical data:

* Design – Spool valve, pilot controlled, with return spring. * Pressure range – 250 – 800 kPa (2.5 – 8 bar) * Response time at 600 kPa (6 basr) – On: 20 ms, Off: 30ms * Nominal flow rate 1 .. 2 and 1 .. 4 – 500 l/min. * Electrical Technical Data: # Power Consumption – 1.5 W # Duty Cycle – 100% 20. 5/2 way Double Solenoid valve, with LED:

The statuses are indicated by an LED on the housing. The valve is equipped with two manual override. The electrical connections feature po larity reversal protection for the LED and the suppressor circuit. Pneumatic Technical data:

* Design – Spool valve, with pilot control. * Pressure range – 150 – 800 kPa (1.5 – 8 bar) * Response time at 600 kPa (6 bar) – 10 ms * Nominal flow rate 1 .. 2 and 1 .. 4 – 500 l/min. * Electrical Technical Data: # Power Consumption – 1.5 W # Duty Cycle – 100% 21. Hand Sliding Valve: * 3/2 way valve * 1/8” – G thread * Flow – 0- 400 l/min Working Pressure – (0-8 bars)


[ 78 ]

ELECTRO PNEUMATICS

VMPT-302 LC

CHAPTER - 10 EXPERIMENTAL SECTION


[ 79 ]

ELECTRO PNEUMATICS

VMPT-302 LC

BASIC PNEUMATIC SECTION


[ 80 ]

ELECTRO PNEUMATICS

VMPT-302 LC

EXPERIMENT - 1 CIRCUIT DIAGRAM

Single acting cylinder

2 1

1 AND Gate

2

1 3/2 Push but ton valve

2

3

1 3/2 Push but ton

3

Component Description FRL Nu mber 1 Compressor


1

Desc ri pt io n Compressed air supply Ai r ser vi ce un it , sim pli fi ed rep res entat io n

1


1

Two pressure valve

2

3/2 Push button valve

[ 81 ]

ELECTRO PNEUMATICS

VMPT-302 LC

EXPERIMENT - 1 CONTROL THE SINGLE ACTING CYLINDER USING TWO WAY PRESSURE VALVE Aim

To construct a pneumatic circuit to control the single acting cylinder control by Two-way pressure valve. Apparatus Required

Compressor air FRL Two-way pressure valve Single acting cylinder Procedure

1.

Draw the circuit diagram.

2.

Connect the compressor air supply to FRL unit.

3.

Any two of the outputs of FRL unit directly connected to 3/2 push button valve inlet first and second.

4.

Both 3/2 push button valves outputs to give AND Gate input.

5.

Check the all circuit.

6.

Open the hand slide valve. The air passes in both 3/2 pushbutton valves input port.

7.

When both push button is press the cylinder should be activated.

Truth table

Input 1

Input 2

Output

ON OFF OFF ON

ON OFF ON OFF

ON OFF OFF OFF

Result

The pneumatic circuit of two way pressure valve was simulated.


[ 82 ]

ELECTRO PNEUMATICS

VMPT-302 LC



2 1

1 OR Gate

2

1 3/2 Push button valve

2

3

1 3/2 Push button

3

Component Description FRL Number

Compressor


Description

1

Compressed air supply

1

Air service u nit, simplified representation

1


2


1

Shuttle valve

[ 83 ]

ELECTRO PNEUMATICS

VMPT-302 LC

EXPERIMENT - 2 FOR USING OR GATE CONTROL TO SINGLE ACTING CYLINDER Aim

To construct a pneumatic circuit to control the single acting cylinder. Apparatus Required

Compressor air Tube 3/2 push button valve Shuttle valve Single acting cylinder Procedure

1.


2.


3.

Any two of the output of FRL unit to first 3/2 push button valve inlet and second 3/2 push button valve inlet.

4.

Both 3/2 push button valves outputs to give shut the valve inlet ports.

5.

Check the all circuits.

6.

Open the hand slide valve. The air passes in both 3/2 push button valve inlets.

7.

Press any one push button valve. The cylinder will be activated.

Truth table

Input 1

Input 2

Output

OFF ON OFF ON

OFF OFF ON ON

OFF ON ON ON

Result

Thus the single acting cylinder controlled by OR Gate.


[ 84 ]

ELECTRO PNEUMATICS

VMPT-302 LC


Double acting cylinter

4

5

2

1 3 5/2 Single pilot valve

2

1

3 3/2 Push butt on valve

Component Description Number FRL Compressor


Description

1


1

Air servi ce un it, si mpl if ied r epresent atio n

1


2

Double acting cylinder

1

5/2 Single Pilot valve

[ 85 ]

ELECTRO PNEUMATICS

VMPT-302 LC

EXPERIMENT - 3 FOR USING 5/2 SINGLE PILOT VALVE, CONTROL TO DOUBLE ACTING CYLINDER Aim

To construct a pneumatic circuit to control the single acting cylinder. Apparatus Required

Compressor air FRL 3/2 Push button valve 5/2 single pilot valve Air tube Procedure

1.


2.


3.

Connect any one of the outputs o FRL unit to 5/2 single pilot valve inlet port 1.

4.

Again one of the outputs of FRL unit to connect to any to 3/2 push button valve inlet.

5.

3/2 push button valve output connect to 5/2 double pilot valve (port 12).

6.

Both outputs of 5/2 double valve directly connected to double acting cylinder.

7.

When is press 3/2 push button valve the cylinder will be activated.

Result

The direct control of a double acting cylinder was simulated.


[ 86 ]

ELECTRO PNEUMATICS

VMPT-302 LC



4

5

2

3 5/2 Double pilot valve

2

1

2

1

3

3 3/2 Push button valve


Component Description Number FRL Compressor

1


1

5/2 Double Pilot valve

1


Description

Air serv ice u ni t, sim pli fied r epres entati on

2

3/2-Push button valve

1


[ 87 ]

ELECTRO PNEUMATICS

VMPT-302 LC

EXPERIMENT - 4 DOUBLE ACTING CYLINDER CONTROL BY USING 5/2 DOUBLE PILOT VALVE Aim

To construct a pneumatic circuit to control the double acting cylinder using 5/2 double pilot valve. Apparatus required

Compressor Air tube 3/2 push button valve 5/2 double pilot valve FRL unit Procedure

1.


2.


3.

Two outputs of FRL unit directly connected to 3/2 push button valves inlets. The both outputs connected to double pilot (Port 12, Port 14).

4.

3/2 double pilot outputs (2, 4) are connect to double acting cylinder.

5.

Check for all circuit.

6.

Observe the working of cylinder.

Result

Thus the double acting cylinder controlled by 5/2 double pilot valve.


[ 88 ]

ELECTRO PNEUMATICS

VMPT-302 LC


3

2

3/2 Roller lever valve

1 W 1

W1

W 2

W2


1

3/2 Roller lever valve 2

3

One way flow control valve

4

5

2

3

5/2 Double pilot valve 1

Component Description FRL Compressor


Number Description 1

Compressor

1

5/2 Double pilot valve

2

Fl ow cont ro l val ve

2


1


[ 89 ]

ELECTRO PNEUMATICS

VMPT-302 LC

EXPERIMENT - 5 CONTINUOS RECIPROCATING OF DOUBLE ACTING CYLINDER CONTROL THE 5/2 DOUBLE PILOT VALVE Aim

To construct a circuit to control the forward return stroke of a double acting cylinder by pilot pressure. Apparatus required

Air compressor. Air tube. Double acting cylinder. 3/2 roller lever valve. 5/2 double pilot valve and flow control valve. Procedure

1.


2.

Connect compressor air supply to FRL unit.

3.

Connect any one of the outputs of FRL unit to 5/2 direction control unit port 1.

4.

Connect port 4 of DCV to blank end of the double acting cylinder.

5.

Connect the output of FRL unit to the input of two 3/2 roller lever valves to give pilot pressure for 5/2 double pilot valve.

6.

The output of the two roller valves are connected to the either side of the 5/2 double pilot valve properly.

7.

When the FRL valves is opened the higher pressure air enters the blank end of the cylinder through DCT and the piston moves forward.

8.

At the end of the forward stroke the piston rod pressure the roller valve. The output of roller valve is sent to double acting cylinder to change the position.

9.

Now the high pressure air from FRL unit is sent to rod end of the double acting cylinder through the second position of the DCV the piston retracts.

10.

At the end of the return stroke the roller valve is pressed. The output of the roller valve is sent to DC change the piston. This is repeated until the FRL valve is closed.

Result

The continuos reciprocating of double acting cylinder was simulated.


[ 90 ]

ELECTRO PNEUMATICS

VMPT-302 LC

EXPERIMENT - 6 CIRCUIT DIAGRAM 3

2

W1


1

W2 W 2


1

W 3

W3



1

2 3

3/2 Roller lever valve 2

3

One way flow control valve

4

5

2

3

5/2 Double pilot valve 1

FRL Compressor

Component Description Number Description 1 1


Co mp res sed air s up pl y Air service unit , simplified representation

1

Do ub le ac ti ng c yl in der

1


1

5/2 Double pilot valve

3

3/2 way roller lever valve

2

Distance rule

[ 91 ]

ELECTRO PNEUMATICS

VMPT-302 LC

EXPERIMENT - 6 STUDY THE CIRCUIT USING (A+B-A-B) Aim

To design a circuit for the sequence A+B-A-B. Apparatus Required

Compressor FRL 5/2 Double pilot valve Single acting cylinder Double acting cylinder 3/2 Roller lever valve. Air tube Procedure

1.


2.

Connect the compressor air to FRL unit

3.

Are both outputs of FRL unit connected to all components.

4.

Test your all circuits.

5.

You will open the hand slide valve.

6.

Observe the working of cylinders.

Result

The circuit diagram for the sequence is drawn and executed.


[ 92 ]

ELECTRO PNEUMATICS

VMPT-302 LC

ELECTRO PNEUMATIC SECTION


[ 93 ]

ELECTRO PNEUMATICS

VMPT-302 LC

Mechanical Circuit

Electrical Circuit

24V

3

Single acting cylinder Push button switch

14 2 S1 1

Solenoid co il

3

S1 3/2 Single sol enoid valve

FRL

0V

Compressor

Material Description Number

Description

1


1

Air service unit, simplified representation

1

3/2-way valve, pneumatically operated

1


1

Electrical connection 24V

1


1

Pushbutton (make)

1

Valve solenoid


[ 94 ]

ELECTRO PNEUMATICS

VMPT-302 LC

EXPERIMENT - 1

Controlling the single acting cylinder using electrically. AIM

To construct a pneumatic circuit to control the single acting cylinder electrically using push button switch. APPARATUS REQUIRED

Compressor, FRL, solenoid coil, electrical trainer, single acting cylinder and batch card. PROCEDURE

1.


2.

Electro controller gives - voltage to pneumatic panel.

3.

Input of push button is getting from solenoid valve output.

4.

Connect the air supply to FRL unit.

5.

Check all the connections carefully

6.

Test the circuit.

7.

Observe the working of the cylinder using the 3/2 single solenoid valve.

Result

Thus the movement of single acting cylinder was carried out using the 3/2 single solenoid valve.


[ 95 ]

ELECTRO PNEUMATICS

VMPT-302 LC

Mechanical Circuit

Electrical Circuit

24V

24V SPDT


4

2 W1

W1

W2

solenoid coil

3

5 1

W2

5/2 Double solenoid valve

FRL

0V

0V

Compressor


SPDT -

Description

2

Pushbutton (make)

2


2


2

Valve solenoid

1


1


1

5/2 way valve

1


Single Pole Double Through


[ 96 ]

ELECTRO PNEUMATICS

VMPT-302 LC

EXPERIMENT - 2

Actuation of double acting cylinder using 5/2 double solenoid valve through SPDT switch. AIM

To develop a electro pneumatic circuit to actuate a double acting cylinder. APPARATUS REQUIRED

Compressor, FRL, Electrical controller, 5/2 Do uble solenoid valve, SPDT switch and Data Card. PROCEDURE

1.

Provide power supply to the pneumatic trainer from control trainer by interfacing 24V + and -

2.

Using the SPDT switch energize the corresponding solenoid valve to get the desired movement in the cylinder.

3.

Design and draw the pneumatic circuit.

4.

Supply the Air to FRL unit.

5.

Assemble all the components.

6.

Check all the connections carefully.

7.

Test the circuit.

8.

Observe the working of the cylinder using the 5/2 double solenoid valve.

Result

Thus the movement of the double acting cylinder was carried out using the 5/2 DCV.


[ 97 ]

ELECTRO PNEUMATICS

VMPT-302 LC Electrical circu it

Mechanical circui t

+24V

1 3


Push button switch 4

4

2

W1 5 5/2 Single pilot valve

W1

3

Solenoid coil

1

FRL

0V Compressor

Material Description Designation

Description

1

Pushbutton (make)

1


1


1

Valve solenoid

1


1


1

5/2 way valve

1



[ 98 ]

ELECTRO PNEUMATICS

VMPT-302 LC

EXPERIMENT - 3

Electrically control Double acting cylinder using pushbutton switch. AIM

To construct a pneumatic circuit to control the single acting cylinder electrically using push button switch. APPARATUS REQUIRED

Compressor, FRL, 5/2 Double solenoid valve, electrical trainer, single acting cylinder and Batch card. PROCEDURE

1.

Draw the circuit diagram and connect the air supply to FRL unit.

2.

Connect the electrical circuit from 24V DC source to ON/OFF switch.

3.

Solenoid are connected to the pushbutton switch.

4.

When the solenoid is given a signal by a push button switch. DCV is activated to double acting cylinder.

5.

When off button is pressed the signal solenoid are cut and the solenoids are de-energized and the DCV comes to the original position.

RESULT

Thus the double acting cylinder is controlled electrically operated switch.


[ 99 ]

ELECTRO PNEUMATICS

VMPT-302 LC

Pneumatic circuit diagram

Electrical circuit diagram

24V

3 3


3 Push button switch 14

S1 2

Make switch 4

2 S1 On delay timer A1

3

1

T1

A2

3/2 Single solenoi d valve

FRL

5

S1 Solenoid coil

0V

Compressor 3


Description

1

Distance rule

1


1


1

Air service unit, FRL

1

3/2-Single solenoid coil

1


1

Pushbutton (make)

1

Relay with switch-on-delay

1


1

Make switch


[ 100 ]

ELECTRO PNEUMATICS

VMPT-302 LC

EXPERIMENT - 4

Actuation of single acting cylinder using Time delay valve used to on delay timer. AIM

To develop an electro pneumatic circuit for actuation of single acting cylinder using timer. APPARATUS REQUIRED

Compressor Air, FRL, Time delay valve, electrical controller, single acting cylinder, 3/2 single solenoid valve and Batch card. PROCEDURE

1.

Provide power supply to electrical controller by interfacing the +ve to +ve and -ve to -ve.

2.

Provide power supply to pneumatic trainer from electrical controller by interfacing 24 +ve to +ve and -ve to -ve.

3.

Using the SPDT switch energize the corresponding solenoid to get the desired movement of the cylinder.

4.

Actual the time delay circuit.

5.

From dime delay give connection to single along cylinders to actual cylinder according to time set.

6.

Design and draw the pneumatic circuit.

7.

Connect the air supply.

8.

Test the circuit.

9.

Observe the working of the cylinder.

Result

Thus the movement of single acting cylinder was carried out using time delay.


[ 101 ]

ELECTRO PNEUMATICS

VMPT-302 LC

Mechanical Circuit

Electrical Circuit 24V 1

2

3

3


3 Push button switch

T1

4

Make Make switc h 4

2 Off delay timer A1 T1

S1

5

3

1

A2 S1

3/2 Single solenoid v alve

Solenoid coil 3

0V FRL

Compressor


Description

1


1


1


1

3/2-way valve with pushbutton

1


1

Pushbutton (make)

1


1

Make switch

1

Valve solenoid

1

Relay with switch-off delay


[ 102 ]

ELECTRO PNEUMATICS

VMPT-302 LC

EXPERIMENT - 5

Actuation of single acting cylinder using OFF delay Timer. AIM

To develop an electro pneumatic circuit for actuation of a single acting cylinder using OFF delay Timer. APPARATUS REQUIRED

Compressor Compresso r Air, FRL, 3/2single acting cylinder, cylinder, electrical e lectrical contro co ntroller, ller, single acting acting cylinder, cylinder, Timer, T imer, Batch chord. PROCEDURE

1.

Provid Providee power power suppl supply y to pne pneum umati aticc traine trainerr from from electri electrical cal control controlle lerr by by inter inter faci facing ng 24+ and 24-.

2.

Prov rovide 24V powe ower supply to tim timer.

3.

Any Any one one of of the the outpu outputt of FRL FRL uni unitt direc directt conne connect ct to 3/2 3/2 sing singlle solen solenoi oid d val valve ve..

4.

Sing Singlle sol solenoi enoid d val valv ve out out put put is conne connect ct to si single gle acti acting ng cyl cylinder. der.

5.

Give + +2 24V and -24V in Timer.

6.

Outp Outpu ut of Tim Timer con connecte ected d to to sol solen enoi oid d coi coill.

7.

Check t he all circuit.

8.

Observe rve the the work orking of cylinder.

9.

Observe the the working circuit.

Result

Thus the movement of single acting cylinder was carried out using time delay.


[ 103 ]

ELECTRO PNEUMATICS

VMPT-302 LC

Mechanical Circuit Q1

Q2


Flow control valve

Material Description 4

Number Number

2

W1

W2

5 5/2 Double Double sol enoid valve

3 1

FRL

Description

1

Compressor

1

FRL

1

5/2 Double Solenoid Valve

1

Flow control valve

1 1

Double acting cylinder Proximity sensor

1

Solenoid coils

Compressor

Electrical Circuit +24V

1

2

Q1

3

4

Q2

Proximity Sensor W1

W2 Solenoid Coil

Solenoid Coil

0V


[ 104 ]

ELECTRO PNEUMATICS

VMPT-302 LC

EXPERIMENT - 6

Continuos actuation of double acting cylinder using magnetic proximity sensor. AIM

To construct a pneumatic circuit to control the double acting cylinder electrically using magnetic proximity sensor. APPARATUS REQUIRED

Compressor Air, FRL, 5/2 double solenoid valve electrical controller, sensor, double acting cylinder and flow control valve. PROCEDURE

1.

Draw the circuit diagram

2.

Connect the circuit diagram in all components.

3.

Connect air supply to FRL unit.

4.

Connect the electrical circuit from electrical controller to panel [24+ and 24-)

5.

Connect from proximity sensor output to 5/2 double solenoid valve input.

6.

Check all circuit in panel.

7.

Test the circuit.

8.

Observe the working in double acting cylinder activated.

Result

Thus the movement of double acting cylinder was carried out using the magnetic proximity sensor.


[ 105 ]

ELECTRO PNEUMATICS

VMPT-302 LC

Mechanical Circuit

P1

P2

P3

P4



Flow control valve

4

2

4

S1

S3 5


2

S2

S4 5

3 1

3 1


FRL

Compressor

Electrical Circuit Material +24V

2

1

5

3 4

Number

6 7

3

3

3

3

4

4

4

4

1 1 2

S1

S2

Solenoid coil

S3

S4

1 2 1 1 4 4 1

Description Compressed air supply Air service unit, simplified representation Double acting cylinder 5/2 Way valve One-way flow control valve 5/2-way valve, with selection switch Electrical connection 0V Pushbutton (make) Valve solenoid Electrical connection 24V

0V

Description


[ 106 ]

ELECTRO PNEUMATICS

VMPT-302 LC

EXPERIMENT - 7

Simulation of Electrically sequencing circuit using a double acting cylinder and miniature cylinder. AIM

To simulate the electrically sequencing circuit using Push button switch. APPARATUS REQUIRED

Compressor Air, FRL, 5/2 Double solenoid valve, electrical controller, double acting cylinder, Miniature cylinder then batch card. PROCEDURE

1.

Draw the circuit diagram

2.

Connect the mechanical circuit in panel.

3.

To give the wiring connection as for as above the diagram.

4.

Check for all circuit.

5.

Test the circuit.

6.

Observe the working of the cylinders.

RESULT

Thus the sequence of double acting cylinders was carried out using push button switch.


[ 107 ]

ELECTRO PNEUMATICS

VMPT-302 LC

Mechanical Circuit P1

P2

P3


P4


Flow control valve

4

2

4

S1

S3 5


2

S2

S4 5

3 1

5/2 Double solenoi d valve

3 1

FRL

Compressor

Electrical Circuit +24V 1

2

3 4

5

6

Push button switch

P3

4

P2

Proximity Sensor

S1

S2

8

7

P1 Proximity Sensor

4

P4

S4

S3

Solenoid Coil

0V

Number 1

Comp ressed air supply

1

Air service unit, simplified representation Double acting cylinder

2 1 2 1 1 1 4 4 2


Description

5/2 Way valve On e- wa y flow co ntro l val ve 5/2-way valve, with selection switch Electrical connection 0V Electrical connection 24V Magn eti c p ro xi mity sw it ch Valve solenoid Distance rule

[ 108 ]

Lab Manual of Pneumatics control

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