Triggering another timer after the first one.

Originally posted by cartierusm:

I mean I don't get exactly what's going on,...

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What part don't you understand? It would probably be helpful with your future interactions with control systems to clear up any questions you have with the logic you posted.

Keith

kamenges, I get the general idea of why the circuit works, but not the specifics.

I don't understand why you need to assign a bit, c1, instead of just having the falling edge of Y103 trigger the timer. Also not sure why the timer and c1 is on the same rung as Y103 and triggering C1. As I said this is all very new to me. So I don't understand how c1 is triggering c1. The rest I get c1 triggering a timer and so forth. It's just that first rung I don't get.

Thanks.

http://accautomation.ca/click-plc-timers-and-counters/

The above link may help you out with the timers in the Click PLC.
Regards,

Thanks I'll check it out.

Originally posted by cartierusm:

I don't understand why you need to assign a bit, c1, instead of just having the falling edge of Y103 trigger the timer.

Click to expand...

That sentence can be interpreted two ways. Are you asking why an on delay timer needs to have a continuous input to function or are you asking why would some idiot develop a timer that needs a continuous input to operate?

Most plc instructions are level sensitive as opposed to edge sensitive. On delay timers are no different. If the enable of an on delay timer is removed the timer will reset. The enable to an on delay timer must be on at least as long as the time duration of the timer in order for the timer output to become true. That's just the way the timer works.

As for why is it the way it is, that has alot to do with history and audience. PLCs were developed way back when to replace relay control systems. Since end users were used to relay systems the plc developers made the functions in the plc act like the physical devices they were replacing. Any physical timer I have ever seen that calls itself an on delay timer requires a continuous input in order to run to completion. there are pulse timers and toggle timers that operate differently but a true on delay timer requires a continuous input, just like the software on delay timer you are working with.

Keith