Chapter 6 Introduction to ElectroPneumatic PREPARED BY MOHD

Chapter 6 Introduction to Electro-Pneumatic PREPARED BY: MOHD SHAHRIL SHARIFF

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.

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.

Signal Flow and Component of An Pneumatic Control System

Signal Flow and Component of An Pneumatic Control System (cont. )

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.

Electrical signal control section Solenoid valve

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)

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 3. Electric counters

(A) Push Button Switch Push buttons are consist 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)

(A) Push Button Switch. . (cont. ) • The contact of the push buttons, distinguished according to their functions, i) Normally open (NO) type ii) Normally closed (NC) type iii) Change over (CO) type. • NO type, the contacts are open in the normal position, inhibiting the energy flow through them • In the NC type, the contacts are closed in the normal position, permitting the energy flow through them • A changeover contact is a combination of NO and NC contacts.

(A) Push Button Switch. . (cont. )

(A) Push Button Switch. . (cont. ) 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)

(B)Mechanical Position Sensor (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.

(C)Pressure Switches Sensor §A pressure switch is a pneumatic-electric signal converter. §It is used to sense a change in pressure, and opens or closes an electrical switch when a predetermined pressure is reached.

(C)Pressure Switches Sensor (cont. ) §Bellow or diaphragm is used to sense the change of pressure. §Bellows or Diaphragm is used to expand or contract in response to increase or decrease of pressure. §When the pressure is applied at the inlet and when the pre-set pressure is reached, the diaphragm expands and pushes the spring loaded plunger to make/break contact. diaphragm type of pressure switch

(C) Proximity sensor q Proximity sensor contain a transistor which conducts and switches (trigger ON) when something comes near to the sensors. q There are 3 type of the proximity sensors namely inductive, optical and capacitive. q They normally have three electrical contacts. One contact for supply voltage , other for ground and third for output signal.

(C) Proximity sensor (Inductive) Used to detect any metals/good conductors.

(C) Proximity sensor (inductive)-(cont. ) Target Sensor Oscillation Amplitude Sensor output signal ON OFF

(C) Proximity sensor (inductive)-(cont. ) Advantages of proximity sensors are 1. They are self contained, rugged and extremely reliable 2. They have long service life 3. They have shorter switching time 4. They are compact and maintenance frees Disadvantages of proximity sensors are 1. Like reed switches , they cannot be used in environments subjected to magnetic fields (like resistance welding machine)

(C) Proximity sensor (inductive)-(cont. ) Applications of proximity sensors The proximity sensors can be used for various applications, These include: q. Sensing of end position of linear actuators like cylinders and semi rotary actuators q. They are used to detect metallic pieces on conveyor. That is presence or absence of work piece on conveyor q. They are used in press to detect the end position q. They are used to monitor drill breakage while drilling. q. They are also used as feed back devices in speed measuring devices

(C) Proximity sensor (Capacitive) Used to detect any high density objects.

(C) Proximity sensor (Capacitive)-(cont. ) Target

(C) Proximity sensor (Capacitive)-(cont. ) Advantages of proximity sensors are 1. They are widely used because of their ability to react with wide range of materials 2. They are suitable for detecting non metallic objects 3. They can be used to sense and monitor level in storage containers Disadvantages of proximity sensors are 1. They are sensitive especially in humid environment 2. Without the compensator ring, the sensor would be very sensitive to dirt, oil and other contaminants that might stick to the sensor.

(C) Proximity sensor (Optical) Used to detect any reflective objects.

(C) Proximity sensor (Optical)-(cont. ) Target Transmitter Receiver

(C) Proximity sensor (Optical)-(cont. ) Transmitter Receiver

(C) Proximity sensor (Optical)-(cont. )

(D) Reed Switch q Reed switch is one of the sensor which is operated by the magnetic field. q Usually fit directly onto cylinder with clips. q The piston of the cylinder has a magnet built into it and when the piston comes close to the reed switch, the contact is close (ON).

(E) Processing element - Relay q Relay is an electrically actuated switch, contains a coil and a contactor switch or multiples contactors of changeover contact type. q When power is applied to relay coil, the core magnetises, 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

(E) Processing element – Relay. . (cont. ) Return spring Coil Cover Armature 12 A 1 A 2 14 22 11 24 21 Symbol Contacts Coil connections Contact connections

(E) Processing element – Relay. . (cont. ) 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

(E) Processing element – Relay. . (cont. ) N. O and N. C wire / cable connection Normally Close (N. C) Example : Pin 21 22 Normally Open (N. O) Example : Pin 41 44

(E) Processing element – Relay. . (cont. ) Animation (Relay OFF)

(E) Processing element – Relay. . (cont. ) Animation (Relay ON)

(E) Processing element – Relay. . (cont. ) 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.

(F) 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.

(F) Solenoid DCV (cont. ) Working Principle §The double poppet armature is held by a spring against the inlet orifice sealing the supply at port 1 §Outlet port 2 is connected to exhaust port 3

(F) Solenoid DCV (cont. ) Working Principle §When the coil is energised the armature is pulled up closing the exhaust orifice and connecting the supply port 1 to the outlet port 2

(F) Solenoid DCV. . (cont. ) q There are 2 types operated of directional control valve using solenoid: 1. Directly operated valve 2. Pilot operated valve 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

3/2 DCV, Single Solenoid Operated, Spring Return (directly operated) §In the normal position, port 1 is blocked and port 2 is connected to port 3 via back slot 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.

(F) Solenoid DCV. . (cont. ) 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.

5/2 DCV, Double pneumatically Operated, Double Solenoid (piloted operated) 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 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, spring return 3/2 -DCV Single pilot operated, single solenoid, 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 International electrotechnical Commission 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.

Direct Control of Double Acting Cylinder Forward stroke: when push button PB 1 is pressed, coil Y 1 is energized and 5/2 way directional control valve changes over resulting to the forward position. Return stroke: when push button PB 1 is released , coil Y is deenergized resulting to the return position.

Control of Double Acting Cylinder OR Logic (Parallel Circuit) When PB 1 or PB 2 is pressed, coil Y 1 will be energized resulting the piston to the forward position

Control of Double Acting Cylinder ‘AND’ Logic When PB 1 and PB 2 is pressed, coil Y 1 will be energized resulting the piston to the forward position

Direct Control of Automatic Return of a Double Acting Cylinder

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

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 energized and 5/2 way directional control valve changes over resulting to the forward position. Return stroke: when push button PB 1 is released and PB 2 is pressed, coil Y 2 is energized and 5/2 way directional control valve changes over resulting to the return position.

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

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 something 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.

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 below