PID Controller Action Option In PAC Control

[mrxivxiv]

Hi there! I’m currently configuring a PID controller using PAC Control Basic vR10.5a. Is there an option in PAC Control for a direct-acting or indirect-acting PID Controller?

I can’t seem to find an option in the “Add PID Loop” window.

PAC Control Help also mentions the details below:

"Equations Common to All Algorithms

Err = PV - SP
Span = (OutHi - OutLo) / (InHi - InLo)
Output = Output + FeedForward * TuneFF"

I need the error calculation to be SP - PV in my application.

How do I get around this without resorting to an error calculation outside of the PID controller?

Thank you.

[Beno]

Hi Michael. Welcome to the Opto 22 forums.

Short answer, use positive gain for indirect acting and negative gain for direct acting.

Its broken down on page 36 of the PID Tutorial.
Also the other formulas we use are on page 79, you hinted you wanted to see them.

[mrxivxiv]

Hi @Beno ,

Thank you for answering my question. Much appreciated! Just a follow-up question regarding the PID Output. How do you usually implement some sort of slew rate or ramp-up to avoid a sudden movement of the final control element? For example, if the current valve position is at 10% and I want to set it to 50%. I understand that there is a “Ramp Analog Output” command but I’m interested to know if there is another way to ramp up any variable.

[Beno]

The rate limit is here:

This is explained in both the PAC Control guide and on page 69 of the doc I linked above.