INDUSTRIAL AUTOMATION | Draw and explain standard start-stop-seal circuit in details.

 Standard Start-Stop-Seal circuit: 

 The Start-Stop-Seal circuit is as shown in figure. The power circuit consists of  3ph load (Motor) connected by a main contactor (M) to 3-phase supply. The control circuit consists of Start, Stop push-buttons and main contactor coil (M).  

 When Start push button is pressed, the contactor coil (M) gets energized and the motor is connected across supply. When Start push-button is released, supply to coil M is maintained through RUN (aux contact of M).  

 When STOP is pressed, M gets de-energized and motor gets disconnected from supply. 

OR

The inputs to this circuit are the “Start” and “Stop” conditions. You could imagine both are momentary buttons on an operator screen that are on while the operator is actually pushing the button. If the operator pushes the Start button, then the main contactor coil (M) will turn on, and it seals itself in until the operator pushes the Stop button. The reason that this pattern is “stop dominant” is that we want the Stop condition to take priority over the Start condition in the case where both signals are active. 

Imagine a case where the Start condition was stuck on for some reason. At least the operator could stop the motor, etc., by holding the Stop button on until they can turn the machine off with the main switch.