Hi all,
I've been tasked with migrating a standalone control box with a Micrologix 1100 into an existing 5380 Compact Logix controller. It has a PID loop in it, and I've never set up a PID control from scratch in Logix 500, so I'd just like a sanity check.
The PID setup screen has the loop update time set to 0.30 (seconds) and the time mode set to STI. If I understand correctly, this uses the PLC's internal clock to automatically execute this PID instruction on a timed basis.
The help page for the PID setup screen tells me:
I've been tasked with migrating a standalone control box with a Micrologix 1100 into an existing 5380 Compact Logix controller. It has a PID loop in it, and I've never set up a PID control from scratch in Logix 500, so I'd just like a sanity check.
The PID setup screen has the loop update time set to 0.30 (seconds) and the time mode set to STI. If I understand correctly, this uses the PLC's internal clock to automatically execute this PID instruction on a timed basis.
The help page for the PID setup screen tells me:
I can't see anywhere that S:30 is set, and when I look at the data table it appears to be zero. That being the case, would I be correct in suggesting that this PID loop is incorrectly configured and is at the mercy of the PLC scan time for its consistency? And that, therefore, the existing tuning values will be useless because I'll now have to re-tune it with a loop update time that's actually fixed (and different)?When in the STI mode, this value [loop update time] must equal the STI time interval value S:30.