Hello,

i have q question for this PID in Tia portal.

The HOLD what exactly do in the PID because e have tried  but  i have seen 2 thinks.

with HOLD enable :

1. if the  PV change example for temperature is going up down the units to the output are change

example 15848 to 15858 (max min 10 Numbers)

2. if the PV stay the same and change the SP ( Set Point ) i see the same units to the output change.

not to much but change example from 15848 to 15858.

but if i disable the HOLD the PID Start Working normal.

why is making this change with the HOLD enable?

Thanks,

Hello TeoTheNtal;

In FB 41 CONT_C the only occurrence of the word "HOLD" is the INT_HOLD parameter, which controls the application of the Integral gain. See the following diagram and tell us if that is the parameter you are inquiring about:

PID Cont_C FB 41 diagram

https://support.industry.siemens.com/cs/ww/en/view/589983

CONT_C is designed so that you can use it as a simple P controller, a PI controller, a PD controller (not very stable, not easy to tune) and a full PID controller. You do that by enabling or disabling the integral or derivative calculations that the function is doing, before launching the controller. The INT_HOLD parameter stops the integral action in the controller, which tends to smooth pout the variance of the error over time. If your loop was tuned as a PID or even a PI controller, then stopping the integral action would make the control purely reliant on the error (PV_SP) in the system, multiplied by the proportional gain factor of the loop parameters.In other words, it would tend to make the loop response less stable, more unstable as the error grows.

In certain processes, we have blocked the integral portion of the loop to stop the integral action of a PI or PID controller, in order to "give a boost" to the final action element, when its response is sluggish. But generally this should be a short-term solution, in the long term.

The screenshot below is taken from the System and Standard functions manual , section 28.1 (for the S7-300 and S7-400 CPUs). You can check with the Step 7 online help if anything has been changed for its operation under Step 7 Professional.

https://support.industry.siemens.com/cs/ww/en/view/109751826

Hope this helps,

Daniel Chartier