Motor Stop Interlock for Changing the Direction PLC Program

Write a PLC program where you can’t change the motor direction unless the stop push button is pressed first.

For instance, If the clockwise (CW) push button (PB) is pressed the motor runs in CW and if the counter-clockwise (CCW) push button is pressed the motor does not change its direction unless the stop push button is pressed first.

Note: the best practice to learn the PLC programming is to start writing the PLC program, take your time before you review the answer.

Inputs and Outputs:

I0.0: CW Push Button (Normally Open contact)

I0.1: CCW Push Button (Normally Open Contact)

I0.2: Stop Push Button (Normally Closed contact)

Q0.0: Motor CW

Q0.1: Motor CCW

Motor Stop Interlock for Changing the Direction

PLC Program description

Network 1:

• When the CW PB is pressed and the Motor CCW is not running the set bit in the flip flop is energized.
• When the stop PB is pressed the reset bit in the flip flop is energized.
• If the CW PB is pressed while the Motor CCW is running the set bit would never be energized

Network 2:

• When the CCW PB is pressed and the Motor CW is not running the set bit in the flip flop is energized.
• When the stop PB is pressed the reset bit in the flip flop is energized.
• If the CCW PB is pressed while the Motor CW is running the set bit would never be energized. 

Conclusion

There is an interlock between the two motor directions that it is not allowed to toggle between the two directions unless the motor is stopped.

Author: Karim Ali Anwar

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