PIDE Instruction Problem in RS Logix 5000

vel_sathish

Member
Join Date
Feb 2007
Location
Tamilnadu
Posts
15
Hi,
In one of our project, we are using PIDE Instruction block (FBD) for all closed loop controls operated through MMI. In that, when the Controlled variable (CV) is in Minimum or Maximum condition many times the PIDE block is automatically got strucked. At that time my CV is in the same value even the PV & SP got changed in Auto Mode. So I once again forced to change the mode from Auto to Manual again to Auto mode, then only the CV is changing according to the PID values. I have faced the same issue for some other projects also. The RS Logix 5000 software Ver is 15.02. let me know ur valuable feedback for the above.

Regrds,
S.Sathish
 
During normal operations the PIDE may look like it is stuck at the high limit or the low limit. In this case the CVHAlarm or CVLAlarm will be set. If there is a large change in the PV or SP, the proportional gain or the derivative gain can send the internal accumulator beyond the limits.

The value is then clamped before it is sent to the CV or CVEU. The CVHAlarm or CVLAlarm will be set in this circumstance. This is normal operation of the PIDE. However, this can be avoided if desired by programming.

One possible way to avoid this is to use the CVLAlarm to set the "CVSetPrevious" input to true and set the "CVPrevious" input value to 0 or the low clamp, this will reset the PIDE internal accume to exactly to the low value. The same method could be used on the high side as well.

Another method would be to retune the PIDE so that the proportional [or derivative] have relatively smaller gains so that they do not cause this effect as much Another possibility if only seeing this effect when going from manual to auto, would be to start the process as some nominal value, wait until the PV stabilizes, then switch to auto mode. This will prevent the PIDE from seeing a large PV change.

There are other ways of handling this as well depending on the situation
 

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