Motor delays

[ktmracing308]

How would you write logic for starting 6 motors with 30 second delay between each motor?

 

[Ken Roach]

Welcome to the PLCTalk forum !

This sounds, of course, like a homework question. And it's tradition here to put the most effort into students who show their work or explain their thinking.

I would use a self-resetting Timer instruction whose Done output added 1 to a counter every time it completed a cycle.

The value of the counter would then be compared to a constant (1,2,3,4,5,6) on a rung that controls the motor starter.

Additional aspects you might want to think of:

1. What starts the sequence: a pushbutton, or an HMI, or an event in the PLC ?

2. Can the sequence be stopped before it completes ?

3. Should you confirm that each motor has started, and not proceed with the sequence if one stalls or fails to start ?

4. Should the operator be able to stop the sequence in the middle ? Should all the motors stop if the sequence is stopped, or should just the ones that have already started keep running ?

5. If the sequence is stopped, what happens when you start the sequence again ?

Something that sounds very simple in theory can get much more complex when you consider all the possible failure, interruption, and restart modes.

Again, welcome to the PLCTalk community !

 

[ktmracing308]

Thank you for the quick reply. Yes you are correct, homework question! But just a push button to start the sequence. And a push button to stop once all motors are running. Interuptions or anything like that doesn't matter.

 

[Ken Roach]

Well, then show your work so far, even if it's just how to make a pushbutton start a repeating timer.

If you are programming for a particular PLC make and model, let us know so that we can use the appropriate memory addressing syntax and instruction set.