Problem with PID loops on redundant controller system


Hi, there is a problem with PID loops on redundant controller system.
PID loops on IO unit will reinitialized thereself when system switch from one controller to the other, for example,
a PID loop’s initial value:
SetPoint 80
mode manual
Gain -20
I 0.05
then I change these values through PID button On PAC Display Runtime as follow:
SetPoint 50
mode auto
Gain -30
I 0.03
I find these values work good, so I leave it there, I want to test whether the redundancy system work well, I make the qualified backup contrller become active through the PAC Redundancy Manager, then I find all the PID loop parameters go back to initial status,
SetPoint goes back from 50 to 80
mode goes back from auto to manual
Gain goes back from -30 to -20
I goes back from 0.03 to 0.05
according to #1700 document, we know that PID loops run on the IO side, which means all PID loop’s parameter should save on the IO unit’s memory, so, why does this problem happen ?

I don’s use any PID commands in the strategy.

Thanks for all reply


Sounds like when switching controllers that the redundant controller reinitializes the I/O unit therefore rewriting the saved or default pid parameters to the brain.
Try unchecking the enable communications checkbox in the I/O unit configuration dialog and putting the command set I/O unit configured flag in your power up chart followed by enable communication to all I/O units. This tells the controller when it boots up that the I/O unit has it’s configuration and not to initialize it.
Be sure that when you change your pid settings you save the configuration to flash.

Alternatively, when you do change pid settings, open the pid inspection window in PAC control and click on save settings. The only thing I’m not sure about with this is that the saved pid settings will propagate to the redundant controller (all things being well and good in the universe, it should)

I hope this helps


Thanks for your replay, Nick
I do as you said, add commands in powerup chart, but it doesn’t work.
when I change a PID parameter, then switch the controller, the I/O unit always has power, then why does PID reinitialize itself ?
I think redundancy system should keep these changes automatically


[INDENT]Hi leeveney,
You might want to contact PSG (our Product Support Group) for some FREE! help sorting this out.