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Module 1
We request you to please complete the Module 0 before taking this up.
Objective of this module
1. You should be able to design stand alone starter for motors.
2. You should be able to design hardwired control for multiple motors.
3. You should be able to design various timer based control systems.
4. You should be able to design control system without PLC.
[Control Circuit, Power Circuit]
The hardwired interlock circuits were used earlier when PLCs were not there, even today many applications are done with hardwired circuits as they are very economical and very simple. We will take up many Industry Oriented examples to learn these circuits, and hope that by the end of this module you would be able to successfully design any kind of interlock circuit.
We need following devices for design of control system, please go back to Module 0 if you have not fully understood the the concept behind following.
[MCBs, Push Buttons,Selector Switches, Indications, Relays, Push Buttons, Timers, Counters, Limit Switches, Proximity Switches, Power Supplies, Control Transformers.]
Example # 1. Design a control circuit which switches 'ON' a Relay by pressing a Push Button and Switches Off the Relay When some other Push Button is pressed.
[Difference between Relay and Contactor ?]
Before we proceed further, the main question is what is the supply available to us and what is the coil voltage of a relay ? So we must select the relay as per available power supply or must design the power supply if the relay operating coil is of different voltage.
Available Supply : 415 VAC between Phases and 240 VAC between Phase & Neutral.
So if the relay operating coil is of 415 VAC or 240 VAC, we do not need any special power supply design, we can use relay of the coil 415 VAC or 240 VAC. So let us say that we use a relay of 240 VAC.
Now we need two Push Buttons, one for making the relay 'ON' and another for making the relay 'OFF'....Push Buttons are passive components and require no power, they are manually pressed. As soon as we press 'ON' Push Button the 240 VAC supply should come across the relay coil, thats how relay will get actuated, so let us draw the basic circuit.
We know two wires between them 240 VAC is available (Phase-Neutral), we take the Phase wire and connect the same to one 'NO CONTACT' point of the Push Button, the other point of the 'NO CONTACT' is connected to the one terminal of "NC CONTACT' of the OFF push button, the other point of the OFF push button is connected to the one terminal (A1) of the coil of relay, the neutral wire of the supply is now connected to the other terminal (A2) of the relay coil.
Contd..........
