Write the PLC logic for the following problem.
- There are three motors (M1, M2 & M3), having a separate start and stop push button.
- M1 must be running before starting of M2 and M3 motor.
- M2 and M3 can start and stop without affecting M1 operation.
- Only two motors can run at the time. Starting of the third motor will shut down all the outputs immediately irrespective of its input.
PLC Program
Program Description:
Rung 0000:
Start/Stop PB latched with memory B3:0/0 for Motor 1.B3:0/3 is connected in series with latch memory to turn off all motors.
Rung 0001:
Start/Stop PB latched with memory B3:0/1 for Motor 2 .B3:0/0 is connected in series to turn on M2 only after M1.
Rung 0002:
Start/Stop PB latched with memory B3:0/2 for Motor 3 .B3:0/0 is connected in series to turn on M3 only after M1.
Rung 0003:
Turning on M1 when B3:0/0 turns ON
Rung 0004:
Turning on M2 when B3:0/1 turns ON
Rung 0005:
Turning on M3 when B3:0/2 turns ON
Rung 0006:
M2 and M3 outputs are connected in series to enable B3:0/3
Program Output:
When M1 turns ON,
When M1 & M2 turns ON
When the Third motor Turns ON,
Conclusion:
We can use this example to understand the programming logic in Allen Bradley PLC.