CLD exam and auto reset Elapsed Time

[Lorache]

Hello,

I would like to know if someone could explain me why the auto reset function of the Express VI Elapsed Time does not work on the attached code for the Boiler CLD exam.

The auto reset option only works when I wire the "Set Start time"  from the cluster (current time in the previous state) into the "Set start time" of the Express VI Elapsed Time and I set up the Restart and Auto restart inputs to True.

This happens in both states "Pre-Purge B" and "Shutdown"

I have tried without subVIs and with subVIs but I do not understand why the auto rest does not work.

Thank you.

[crossrulz]

That is because you have the Reset input wired to a TRUE.  Therefore, your elapsed time should always be 0.  Do not wire that input.

[Lorache]

Sorry, that wasn't the last version of the code. The one I attach now is the one with Reset unwired and the auto reset = true and it does not work

[crossrulz]

It works just fine.  You just did not update the status indicator when the time does elapse.

[Lorache]

Thank you for you help.

However, only works fine the first time the sequence of steps is run. If I want to start the boiler and carry out the sequence again (without stopping the main running), after clicking "shutdown" button , the Boiler VI jumps over the "Pre purge B" state as the Express VI Elapsed Time has not been auto reset (I do not why). The same occurred the second time I click the shutdown button, the VI jump over the count to stop the boiler running.

[crossrulz · Accepted solution]

The AutoReset causes a reset from when the time had elapsed.  So it is using the time from the end of the previous run as the start time.

So what you should do is turn the AutoReset off and just reset the time when you first enter that state.  This would be one of the few good places to use the stacked shift register.

[billko]

I usually wire the "Time has elapsed" output to the "Reset" input via a shift register, initializing the shift register with TRUE.

[Lorache]

Crossrulz, Thank  you very much for you help!

I still don't understand why the Express VI Elapsed Time does not Auto reset when the time has elapsed to be ready for the second time the sequence is run. I guess I need more practise to understand it 100%. For now, I am happy with your solution of the stacked shift register.

Thank you!

[Blokk]

Here is an older post from me when I was just preparing for my CLD exam a few years ago. I simply did not like the Elapsed Time Express VI, so I designed some own variants. Try to put similar Timer subVIs together, this is a good way to practice for the exam! Also, when "it is in your head", it takes like 2 minutes to put together such timer VI which will act exactly as you want, and not as that Express VI was designed...

http://forums.ni.com/t5/Certification/timer-with-separated-input-settings/m-p/3045387