Hi all, splitting out from this thread because it's a somewhat different question to the original.
I have to migrate some code from a Micrologix 1100 to a 5380 Compact Logix. It includes a PID loop. I was hoping not to have to re-tune the loop, because many engineers have spent a lot of time working out the optimal values for this loop, and I'd rather not reinvent the wheel. I figured initially that as long as I configure the loop the same and put the same tuning values in, I should get more or less the same response regardless of platform.
However, the programmers of the ML1100 did not set up the loop update of the PID correctly. They set it to 30ms, but then executed it every scan in the main routine. So the PID loop thinks the update time is 30ms, but the actual update time is whatever the scan time of the PLC happens to be.
I'll be onsite tomorrow and will check the scan time of the PLC. If I find that it is, e.g. 10ms, is there a rule-of-thumb or guesstimate that I could apply to my gain parameters to compensate for the fact that the PID thinks it's updating at one-third the rate it actually is?
I have to migrate some code from a Micrologix 1100 to a 5380 Compact Logix. It includes a PID loop. I was hoping not to have to re-tune the loop, because many engineers have spent a lot of time working out the optimal values for this loop, and I'd rather not reinvent the wheel. I figured initially that as long as I configure the loop the same and put the same tuning values in, I should get more or less the same response regardless of platform.
However, the programmers of the ML1100 did not set up the loop update of the PID correctly. They set it to 30ms, but then executed it every scan in the main routine. So the PID loop thinks the update time is 30ms, but the actual update time is whatever the scan time of the PLC happens to be.
I'll be onsite tomorrow and will check the scan time of the PLC. If I find that it is, e.g. 10ms, is there a rule-of-thumb or guesstimate that I could apply to my gain parameters to compensate for the fact that the PID thinks it's updating at one-third the rate it actually is?