Hello I have a question about a PID control circuit. I have an RTD that controls our modulating valve through a PID instruction. We had a quick power outage and once the power came back up and the PLC restarted. The modulating valve took back off in its original setpoint and operation without being put into auto or On. Also no-one had touched the HOA on the HMI after the outage . Is there any way to reset the control loop in the event of a power failure? Thanks
PID issues after power outage
- Thread starter mavrick
- Start date
Steve Bailey
Lifetime Supporting Member + Moderator
There is or ought to be, but to figure the details of how to do it you'll need to read the manual for the hardware you're using.
geniusintraining
Lifetime Supporting Member + Moderator
How quick? was it just a brown out, that may cause issues. We make a PID trainer and if the trainer is powered up before the PLC it has a mind of its own but if you power up the PLC first it works as intended.... that said there should be a 'first scan' setting/clearing in the program, mine does not but you should check yours to see if its there
geniusintraining
Lifetime Supporting Member + Moderator
If you can... try doing a controlled shut down and see if it comes back up normal also take a look at the program and see if the first few rungs are resetting anything
Is the 'modulating valve' part of the PLC or does a analog signal go from the PLC to the valve... it maybe a failsafe valve? but most of the time it should go to close (or full open)
Is the 'modulating valve' part of the PLC or does a analog signal go from the PLC to the valve... it maybe a failsafe valve? but most of the time it should go to close (or full open)
geniusintraining
Lifetime Supporting Member + Moderator
I would still try and see if the program has a reset in it and you just need to activate it... odds are the programer wrote a first scan to clear/reset everything and you can use that one, worth a look anyway.
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