could anyone help me how to solve this problem via rslogix? thank you

daba said:

It actually does not say that. It specifically says that the latched light is unlatched "after the third time the timer has timed to 20 s"

No other mention of when the light goes off, so I say it should stay on indefinitely if the input is turned off to stop the timer timing.

Click to expand...

Oh yeah, I read that wrong. Turning off the switch only stops the timer cycling and resetting. Hmm, maybe the timer should be retentive, so any timing is not lost if the switch goes off when .TT is 1.



Thanks!

drbitboy said:

Oh yeah, I read that wrong. Turning off the switch only stops the timer cycling and resetting. Hmm, maybe the timer should be retentive, so any timing is not lost if the switch goes off when .TT is 1.

Click to expand...

When coding an assignment, or a real job, you should never try to guess what the specification should say, or not say.

If there are any doubts, ambiguities, missing information, etc., then go back to the author of the "specification" and get the position clarified.

drbitboy said:

Oh yeah, I read that wrong. Turning off the switch only stops the timer cycling and resetting. Hmm, maybe the timer should be retentive, so any timing is not lost if the switch goes off when .TT is 1.



Thanks!

Click to expand...

I thought about a RTO as well, but the instructions are very basic.
"The timer will continue to cycle up to 20s and reset itself until the input switch is turned off."

Unfortunately, this is an exercise from a book, so the original author is not (easily) available.

Either way, I think it is apparent that the multi-timer solutions attempted by @ufomec and @oziken and me do not fit the specification.

So we are back to this: the driver of the program that meets the problem speicification will be:
An alternative approach could be this: But the behavior will be essentially the same.
There may be other contacts and/or logic on the rung feeding that TON, but that is the basic idea.

I suggest that @ufomec and @uziken (apparently only ~40km apart) code one of those examples and run it to see how it behaves, and then come back here to tell us what they think is happening and with any additional questions, although considering that the problem comes from a chapter about COUNTERS, perhaps that will be enough for them to finish on their own.

drbitboy said:

[/code]An alternative approach could be this:

Code:

----[TON  T4:0]---
    [Pre   20s]

  T4:0/DN    T4:0
---] [-------<RES>---

Click to expand...

You would need to do the counting between those rungs, or the RES would clear the .DN bit.

This "alternative" is generally considered better than the first method, because it doesn't waste a program scan to get the timer timing again.