Currently I'm working on a university project based on Star/Delta Starter on PLC. I wrote program using LD, that switches on the circuit with a motor rotating forward (of course with star/delta starter - here I've used TON timer), then with another start button called "Start back" after pressing "STOP" I can turn the motor on backwards. Everything is working fine. Now I'm trying to figure out how I can set the delay after pressing STOP button (let's say 8 seconds) to block user with pressing START button with another direction.

For example, motor has been started forward, then we press stop and we cannot press "START BACK" until 8 seconds will elapse (to secure the motor).

I was trying to use TOF timer 2 times (one timer for Forward and one for Backwards) but it doesn't solve the problem. Is there any logic way to solve this problem?

Thanks in advance,



1 Answer 1


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  • ErrBim is an error if there is no signal from motor protection switch (Bimetal NC), when set it has to be cleared by an acknowledge signal (Proc.ErrClearPulse)
  • StartBtn is a start button NO, that is evaluated with positive change, when it switches from 0->1
  • StopBtn is a stop button NC
  • ESTOP is the emergency stop signal NC, if not present it stops all
  • S_ON is a intermediate flag
  • K_ON is the output for the main contactor
  • InterlockT is a timer that prevents a quick re-start, Off Delay
  • StarT is a timer for star/delta changeover, On Delay
  • K_Star is an output for star contactor
  • K_Delta is an output fro delta contactor


It could be also in one single network, depends on your engineering software. If you need fwd/bkw is almost the same, except you do split into two sections, then you OR the InterlockT with fwd OR bkw contactor output.

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