RS 5000 PID Control Loop

Hello,
I'm having issues with a PID control loop. I am working with 5000 software and Contrologix controller.

The control loop has been in process for a couple years and the valve works correctly in manual. This control loop has a bump less transfer implemented as well when going from manual to auto.

My issue is when i go from manual on the valve such as (41%) to auto the output will go to 0% in the PID instruction. I have checked through the PID controller tag and everything seems to operate correctly.

With that said in the ladder logic there are MOV instructions that can move a 0 into the maxoutput or output in the event of a certain input going true or during a shutdown process. I have tried to verify all these inputs are false and they appear to be not causing conflict.

Any thoughts on what may cause this? Its a random issue that I have not seen before. The valve works fine in manual so i don't think its a field device. Thank you for the help

If you could post the logic, it would help a lot. It sounds like one of the MOV instructions is happening anyway, sometimes it's a matter of the order the logic is solved.

Even though the output goes to 0% at transfer, does the PID function correctly eventually?

what is the error (SP-PV) or (PV-SP) when switching to manual?


is this PID part of a cascade?

i cant post the logic due to the work policies , i know that complicates things. As for does it eventually reach the set point , it looks like it may but at the movement is so slow i dont have time to allow the valve to catch up do to the process getting so far behind.
It seems to take a couple minutes to make up 1% of valve movement

the error is SP-PV no cascading

Do you have the "PV Tracking" selected in the Configuration Tab?
What is the setpoint before and after the manual selection?

drbitboy said:

what is the error (SP-PV) or (PV-SP) when switching to manual?

Click to expand...

Sorry that was not clear: I meant what is the value of the error when switching to manual?

Yes i have the PV tracking checked in the PID instruction
Before the manual selection the set point will vary a few degrees from what is in the set point to what actual temperature is but when selecting between manual to auto the set point will be set to what the RTD (process variable) reads when auto is selected.

When you say manual, is that field manual or software manual?

Software manual is supposed to be bumpless from man to auto by default. But, field manual requires the output to be connected to the TieBack.

so when going from manual to auto i'm not sure what the error is because the PID gives a value of zero
As for going from manual to auto the error is typically 0 as well because the process variable gets placed into the set point with the PV tracking

When referring to manual i am referring to both , when the manual HMI button is pushed the SWM output is then true and then the valve percentage is dropped into the PID SO.

Is it possible the P, I, (D used?) values are too low to give meaningful control? That might explain the error value being so low when transferring from manual to auto. Could you post the details of the PID?

mavrick said:

so when going from manual to auto i'm not sure what the error is because the PID gives a value of zero
As for going from manual to auto the error is typically 0 as well because the process variable gets placed into the set point with the PV tracking

Click to expand...

Sorry, I was not clear again.


Before the switch from manual to auto, it sounds like the SP is the same as the PV because of PV tracking.


What are the SP and PV immediately after switching to auto?


I suspect the PV does not change much at the switch.

The SP and PV are both 215.7 at the time when switching from manual to auto

keep in mind all the values are the same as far as i know and have been working fine for 3 years until today