AD 250-1 stuck in a state

What could be the reason for stage jump not to work?

The servo 1 signal is set in its block, but the expected transition to S400 never happens - see attached screenshot.

Thank you!

Something else resetting S400, either between this point and the end or after a very short time so that you don't see it. That couple with something always setting S410. It's hard to tell without your current program.

Could you try and take a look please? The program grew even more complicated and hard to follow, though..

My guess is that C24 is getting set below rung 66 and then reset in rung 31 before it actually gets to rung 66 on the next scan. DirectSoft see's this and interprets the rung as true even though it is not actually true at that point in the program.

The thing to remember here is that communications happens at the start of the scan. This is where DirectSoft gets it's information from. Directsoft has no way of knowing what has happened subsequent to the start of scan as the ladder executes until the start of the next scan cycle. Pretty much every programming package works this way since there is no way to make up for communications latency and provide true real time status of memory.

The "tell" here that show's this is actually what is happening is that S400 is off. If C24 were actually true when it hit rung 66, S400 would be on.

Yes! Thank you!

aaa,

I counted 20 "SET" instructions in the short segment that you posted before giving up. This is a good example of how to write a program so that it is guaranteed to be hard to troubleshoot and difficult to change without leaving at least one SET occurance with too many RESETS or no RESET. Try writing this program with NO sets and resets and see how that works for you.

Lancie,

who said I gave up? I solved that problem and moved on to next one. The program is functional now, waiting for the motors to arrive to continue with high-speed stuff. But thank you for advice - it is my first attempt at PLC programming and I don't claim to know it all.

I learned that transitional contacts are bad (if they aren't used to monitor inputs), now SET and RST instructions are bad (i didn't understand why yet - could you elaborate?). Is there another, better way to enable an output in one stage and leave it on when moving to another?

Thanks everybody for smoothing up my learning curve!

aaa75 said:

Lancie, who said I gave up? I solved that problem and moved on to next one.
....
Is there another, better way to enable an output in one stage and leave it on when moving to another?

Click to expand...

Sorry, I meant that I gave up reading your program.

I suggest using a self-sealing contact for an Output. Using that method, all bits that turn it ON or OFF are right there on that network or rung. No need to search the entire program looking for Sets and Resets. If you need to stop or start this output in other Stages, then use Stage relays (with self-sealing contacts, not Set/Reset) in each stage, with stage contacts located in the original Output network.