Another ladder logic question

[DonNH 3]

Another simple problem I believe . . .

I'm turning on a motor, keeping it on for a specified time, then shutting it off.

The thing is, I have to use a function block to turn on the motor (ARCL connection with mobile robot).

So, I'm setting variables MotorOn to activate the timer once the initial function block is complete , and Timer_done to activate the function block to turn off the motor.

This works fine, unless I try to stop the motor before the timer has expired, by turning off the Start_motor switch. In that case, Timer_done never becomes True, so the motor continues indefinitely.

Seems like there should be a fairly simple way to activate the Motor_Off function block when the Start_motor switch is turned off.

 

 

[b.k.n. 3]

I would use a normally closed contact of the Start_motor put ahead of the Motor_Off function...?

[DonNH 3]

I thought I had already tried this (added as an OR branch), but I just did it and it works.

Looks wrong when monitoring as the rung activates as soon as the connection is made between the PLC and AMR, but that's correct.

[Crossbow 295]

You can use TP instead of TON so you always get the same length output no matter how long Start_motor stays on (or doesn't).