Chapter 6 Introduction to Electropneumatic Introduction to Electro

Chapter 6 Introduction to Electro-pneumatic

Introduction to Electro Pneumatics Electro-Pneumatics Definition : § Electro-pneumatic term is defined from the words of electro which means electrical and pneumatic which means pressurized air. § The electro-pneumatics equipments and system is an integration of electrical and mechanical components with compressed air source. § Electro pneumatic is a pneumatic control system where air pressure and direction of valve are controlled by an electrical current.

Introduction to Electro Pneumatics Other Definition of Electro-Pneumatics is a method to transfer energy from one point to another using actuators which are driven by fluids under pressure (definition of pneumatic). Pneumatics restricts itself to gaseous fluids while hydraulics uses liquids to transfer the energy. Pressure of the pneumatic system can be controlled by § manually opening a valve, § automatically by detecting its pressure, § sending an electrical signal. The control of pneumatic components by electrical impulses (electrical signal) is known as electro-pneumatics.

Introduction to Electro Pneumatics Signal flow and component of an pneumatic control system

Introduction to Electro Pneumatics Signal flow and component of an Electro. Pneumatic control system

Introduction to Electro Pneumatics Pneumatic power section Solenoid actuated Directional control valves form the interface between the signal control section (electrical) and the pneumatic power section in an Electro-pneumatic system.

Introduction to Electro Pneumatics Electrical signal control section Solenoid valve

Introduction to Electro Pneumatics Advantages of using Electro-Pneumatics 1. Lesser wear-off parts. Lesser installation jobs. i. e. , Electrical control valve, Electrical switches 2. Replace tube in pneumatic system to electrical wire in electro-pneumatic 3. Less parts are used Reduce working space. 4. Sensor and Controller (such as PLC) can be included in the system E-260 Electrical signal input (switch panel) Push Button

Basic Electrical Device Seven basic electrical devices commonly used in the control of fluid power systems are 1. Manually actuated push button switches 2. Mechanical Position Sensor (Limit switches) 3. Pressure switches 4. Solenoids 5. Relays 6. Timers 7. Temperature switches Other devices used in electro pneumatics are 1. Proximity sensors 2. Reed switch 2. Electric counters

(A) Push Button Switch Push buttons are of two types i) Momentary push button (return to unactuated position when release) ii) Maintained contact or detent push button (has a latching mechanism to hold it in the selected position)

Push Button Switch

Example : Normally Open (N. O) and Normally Close (N. C) In pneumatic circuit : For example : 3/2 -way Push button (valve) Normally Open Normally Close In electrical circuit : For example : Push button switch Normally Open Normally Close

(B)Mechanical Position sensor (limit switch) (Pneumatic) 3/2 -way N. C valve with roller (Limit switch) (Electro-Pneumatic) Mechanical Position sensor (Limit switch)

Limit Switch Any switch that is actuated due to the position of a fluid power component (usually a piston rod or hydraulic motor shaft or the position of load) is termed as limit switch. There are two types classification of Limit switches depending upon method of actuations of contacts a) Lever actuated contacts b) Spring loaded contacts In lever type limit switches, the contacts are operated slowly. In spring type limit switches, the contacts are operated rapidly.

(C) Proximity sensor q Proximity sensor contain a transistor which conducts and switches (trigger ON) when something comes near to the sensors. q Some of the proximity sensor only work with steel material components － Inductive proximity sensor

Proximity sensor – Symbol and Sample Circuit Proximity Sensor Question : 1. Name the switch type used for START and STOP button. 2. What is the different between A 1 and A 2 in Electrical circuit?

(D) Processing element - Relay q Relay is an electrically actuated switch, contains a coil and a contactor switch or multiples contactors. q When power is applied to relay coil, the core magnetizes, drawing the contact assembly in. q This will change the state of all the contacts in the relay (i. e. , N. O contact becomes closed or N. C contact becomes open). q Relay uses small amount of power to control switching (advantage). The voltage applied to the coil doesn’t have to be the same as that in control circuit. q Relay is used to allow voltage control systems to switch large current/ high voltage

Sample circuit E-140 Contactor Coil When Toggle switch 1 S 3 is pressed, power is supplied to Relay (K 1) coil which result to the all contactors in relay change their state (open close or close open). Solenoid valve 1 Y 1 activate to ON

N. O and N. C wire / cable connection Normally Close (N. C) Example : Pin 21 22 Normally Open (N. O) Example : Pin 41 44

Animation (Relay OFF) Source : Uni. KL Electro-Pneumatic Lecture Note, 2008

Animation (Relay ON)

More about Relays q Relay has a few functions as a safety device: 1. The high voltage output (i. e. 240 V) can be switched ON through a contactor using relay with low voltage (i. e. 24 V) supplied to a coil. 2. The high current output can be switched ON through a contactor using relay with low current supplied to a coil. 3. Functioned as Safety control circuit for emergency power cut-off (EMERGENCY START and STOP button) to the whole circuit. q. Use in automation process Switching more than one outputs simultaneously using relay with a coil and multiple contactors. q. To control ON and OFF of various outputs sequences using several Relay.

(E) Solenoid DCV q Solenoid valve is an electro-mechanical device that built-in with a coil (solenoid) and a pneumatic Directional control valve. q Directional control valve (DCV) solenoid operated use electrical signals to control pneumatic valves. q They are used to start, to stop and/or to change the direction of air flow. q There are 2 types operated of directional control valve using solenoid: 1. Directly operated valve 2. Pilot operated valve

1. Directly operated valve Flow is releases to the consuming device via armature of the solenoid. In order to obtain a sufficient cross section of opening, a comparably large armature is required. This consequently requires a powerful return spring and the solenoid to generate a high force. It is therefore of a large design with high power consumption. 2. Pilot operated valve The valve piston is moved via an air duct from pressure port 1. This only requires a Low flow so that a comparatively small armature with minimal actuating force can be used. A minimum supply pressure is required in order to actuate the piston against the spring force. Solenoid can be configured in a small design and the power consumption and heat emission is thus reduced.

3/2 DCV single solenoid operated with spring return The cross sectional view of 3/2 way single solenoid valve in the normal and actuated positions are shown in Figure. In the normal position, port 1 is blocked and port 2 is connected to port 3 via back slot (details shown in the circle) When the rated voltage is applied to coil, armature is pulled towards the centre of the coil and in the process the armatures is lifted away from the valve seat. The compressed air now flows from port 1 to port 2, and ports 3 is blocked. When the voltage to the coil is removed, the valve returns to the normal position.

5/2 DCV single pilot operated single solenoid with spring return The cross section view of 5/2 way single solenoid in the normal and actuated positions are shown in Figure. In normal position, port 1 is connected to port 2, port 4 is connected to port 5, and port 3 is blocked. When the rated voltage is applied to coil 14, the valve is actuated through an internal pilot valve. In actuated position, port 1 is connected to port 4 , port 2 is connected to port 3, and port 5 is blocked. The valve returns to the normal position when the voltage to the armature coil is removed.

5/2 DCV double pilot operated double solenoid The cross section view of 5/2 way double solenoid in the normal and actuated positions are shown in the Figure when the rated voltage is applied to coil 14, the valve is actuated to a one switch in position with port 1 connected to port 4, port 2 connected to port 3, and port 5 blocked. When the rated voltage is applied to the coil 12, the valve is actuated to the other switching position with port 1 connected to port 2, port 4 connected to port 5 and port 3 blocked.

The symbols for the various solenoid/pilot actuated valves are given in below 3/2 DCV single solenoid with manual override with spring return 3/2 DCV single pilot operated single solenoid with manual override with spring return 5/2 DCV single solenoid with single manual override with spring return 5/2 DCV double solenoid with double manual override with spring return 5/2 DCV double pilot operated double solenoid with double manual override

Solenoid DCV 5/2 -DCV double pilot operated double solenoid 5/2 -DCV Single pilot operated single solenoid with spring return 3/2 -DCV Single pilot operated single solenoid with spring return

Sample circuit Pneumatic Power Component --- cylinder Final Control element --- Solenoid valve

Symbol in Electrical circuit Solenoid When Pushbutton switch (SW 1) is pressed, power is applied to Solenoid S 1 which then change the electrical signal to pneumatic signal and allow air flow to cylinder A (single acting with spring return) for rod to extend.

Sample Circuit connection Red cable is a connection from 24 V line. Blue cable is a connection to GND (0 V).

Supply / Power component In Electro-Pneumatic system, the supply or power source component is divided into two, based on the system component. 1. Pneumatic － Compressor 2. Electrical －AC / DC power supply Symbol for 24 V DC IEC Standard JIC Standard

Direct control in electro-pneumatics Direct control is the control of an electro-pneumatic valve without using intermediate components such as a relay, a contactor or an industrial computer (PLC). The valve is connected directly to electric switch as shown in Fig. below Advantages of direct control • Simple and easy • Less wiring • Cheap. Disadvantages of direct control • Remote control is not possible • Switching more than one valve at a time is not possible • Latching is not possible • Design improvement is not flexible.

Indirect control in electro pneumatics Indirect control is the control of an electro-pneumatic valve using intermediate components such as relays, contactors or programmable logic controllers (PLC). Advantages of indirect control systems • Remote control is possible • Switching more than one valve at a time is possible • Latching is possible. • Flexible design improvement and development. • Incorporating logic operating conditions (OR, AND conditions) Disadvantages of direct control • Complicated • More wiring • More cost involved

Direct Control of Single Acting Cylinder Forward stroke: The circuit is closed when push button PB closes. A magnetic field is produced in the coil Y. The armature in the coil opens the passage for the compressed air. The compressed air flows from 1 to 2 of the 3/2 DCV to cylinder, which travels to the final forward position. Return stroke: When the push button PB is released, the circuit is interrupted. The magnetic field at coil Y collapses, the 3/2 way valve switches back to its original position as shown in Figure 1. 27. The compressed air in the cylinder then exhausts through port 3 of the DCV and the cylinder travel to the final rear position.

Indirect Control of single acting cylinder Forward stroke: The circuit is closed when push button PB closes. Closing of Push button PB energises a relay K 1. The coil Y is energised via normally open contact K 1 (indirect energising). A magnetic field is produced in armature of the coil Y opens the passage for the compressed air. The compressed air flows from 1 to 2 of the 3/2 DCV to cylinder, which travels to the final forward position. Return stroke: When the push button PB is released, the circuit is interrupted. Opening of Push button PB de-energises a relay K 1. The magnetic field at coil Y is collapses due to the opening of contact K 1 the 3/2 way valve switches back to its original position as shown in Figure. The compressed air in the cylinder then exhausts through port 3 of the DCV and the cylinder travel to the final rear position.

Direct Control of Double Acting Cylinder Forward stroke: The double acting cylinder is controlled by 5/2 way valve. When the pushbutton PB is pressed, coil Y is energised and the directional control valve is activated by compressed air via pilot control. The piston travels to the final forward position. Return stroke: When the push button PB is released, the circuit is interrupted. The magnetic field at coil Y collapses, the return spring of 5/2 becomes active and the 5/2 way valve switches back to its original position as shown in Figure 1. 29. The compressed air in the cylinder then exhausts through port 5 of the 5/2 DCV and the cylinder travel to the final rear position.

Indirect Control of double acting cylinder (using 5/2 way, single solenoid) Forward stroke: The circuit is closed when push button PB closes. Closing of Push button PB energises a relay K 1. The coil Y is energised via normally open contact K 1 (indirect energising). A magnetic field is produced in armature of the coil Y opens the passage for the compressed air through internal pilot. The compressed air flows from 1 to 4 of the 5/2 DCV to cylinder, which travels to the final forward position. Return stroke: When the push button PB is released, the circuit is interrupted. Opening of Push button PB de-energises a relay K 1. The magnetic field at coil Y is collapses due to the opening of contact K 1 the 5/2 way valve switches back to its original position as shown in Figure 1. 30. The compressed air in the cylinder then exhausts through port 5 of the DCV and the cylinder travel to the final rear position.

Indirect Control of double acting cylinder (using 5/2 way, double solenoid) Forward stroke: when push button PB 1 is pressed, coil Y 1 is energised and 5/2 way directional control valve changes over. The piston travels out and remains in the final forward position until a signal is applied to coil Y 2. The 5/2 directional control valve will remain in the last position because it is double solenoid valve and has no return spring. Return stroke: When the push button PB 1 is released and PB 2 is pressed. Opening of Push button PB 1 de-energises a relay K 1. The magnetic field at coil Y 1 is collapses due to the opening of contact K 1. Closing of PB 2 energises Y 2 and the piston returns to its original position as a result of changeover of the 5/2 way valve. The 5/2 way directional control valve will not switch over if there is an active opposing signal. For example, if Y 1 is switched on and a signal is given to Y 2, there will be no reaction as there would be an opposing signal

Control of Double Acting Cylinder OR Logic (Parallel Circuit) The piston of a double acting cylinder is to travel out when either one of two pushbutton switch is pressed. It is to return when both are released. When push button PB 1 or PB 2 are pressed. Coil Y 1 is energised. The directional control valve switches over and the piston travels to the final forward position. When both the push button switches are released, the signal is removed from Y 1 and the cylinder travels back to its original position.

Control of Double Acting Cylinder AND Logic The piston of a double acting cylinder is to travel out when either one of two pushbutton switch is pressed. It is to return when both are released. When push button PB 1 or PB 2 are pressed. Coil Y 1 is energised. The directional control valve switches over and the piston travels to the final forward position. When both the push button switches are released, the signal is removed from Y 1 and the cylinder travels back to its original position.

Latching circuits Definition of latching: It is a process where the relay contacts remain on without keeping the relay coil energized. In other words, it is required somethings to keep the circuit powered for a certain function even though a pushbutton switch is released to the open position

Latching Circuit with Dominant OFF When Start button (PB 1) and Stop button (PB 2) are pressed simultaneously, if the circuit goes to OFF position/relay coil is not energised , then such a circuit is called Dominant OFF latching circuit. Refer to Figure , a) When we press START push button PB 1 is pressed and released , following operations occurs: 1. Relay coil K 1 in branch 1 ( vertical) is energised. All Contact K 1 closes 2. Notice that there is a NO contact of K 1 in branch 2 , which is connected parallel to PB 1. This NO contact of K 1 latches the start push button. Therefore even if the PB 1 is released, NO contact of K 1 in branch 2 keeps coil K 1 energised. 3. There is another NO contact in branch 3, which is connected to Y 1. When push button PB 1 is pressed this also remain closed, as a result cylinder moves forward and remains there until stop button PB 2 is pressed. b) When we press STOP push button PB 2 is pressed momentarily and released , following operations occurs: 1. Relay coil K 1 in branch 1 ( vertical) is de-energised. All Contact K 1 opens 2. NO contact of K 1 in branch 2 , which is connected parallel to PB 1 is now open. This NO contact of K 1 no more latches the start push button. 3. NO contact in branch 3 is also open now, which is de-energises. As a result cylinder moves back to its home position and remains there until start button PB 1 is pressed again.

Latching Circuit with Dominant OFF

Latching Circuit with Dominant ON When Start button (PB 1) and Stop button (PB 2) are pressed simultaneously, if the circuit goes to ON position/relay coil is energised , then such a circuit is called Dominant ON latching circuit. Refer to Figure, a) When we press START push button PB 1 is pressed and released , following operations occurs: 1. Relay coil K 1 in branch 1 ( vertical) is energised. All Contact K 1 closes 2. Notice that there is a NO contact of K 1 in branch 2 , which is connected parallel to PB 1 and in series with PB 2. This NO contact of K 1 latches the start push button. Therefore even if the PB 1 is released, NO contact of K 1 in branch 2 keeps coil K 1 energised. 3. There is another NO contact in branch 3, which is connected to Y 1. When push button PB 1 is pressed this also remain closed, as a result cylinder moves forward and remains there until stop button PB 2 is pressed. b) When we press STOP push button PB 2 is pressed momentarily and released , following operations occurs: 1. Relay coil K 1 in branch 1 ( vertical) is de-energised. All Contact K 1 opens 2. NO contact of K 1 in branch 2 , which is connected parallel to PB 1 is now open. This NO contact of K 1 no more latches the start push button. 3. NO contact in branch 3 is also open now, which is de-energises. As a result cylinder moves back to its home position and remains in home position until start button PB 1 is pressed again.

Latching Circuit with Dominant ON

Direct Control of Automatic Return of a Double Acting Cylinder

Indirect Control of Automatic Return of a Double Acting Cylinder ( double solenoid)

Oscillating motion of a double acting cylinder (Forward )

Oscillating motion of a double acting cylinder (Return )