What is “D” in PID? ... fundamentals of Derivative

Trends

Hello Ron,

I’m sorry that I didn’t get this on here sooner but here they are the trends that you were asking for. On the trends the yellow is the CV, the red is the SP, and the green is the PV. If you remember the PV is averaged. The white line on the trend is the PV instantaneous. The trend here is the system in auto. I did put it in manual and the PV did not look any different. Right now as you can see here the system reacts slowly to a change but it never seems to hit its actual set point. Let me know what you think. Thanks for the help.

Joel

Joel,

based on your description and the look of your (unfiltered pv) trend, looks to me like your system is seeing a disturbance with a period of about 40 seconds. Look at other process variables to determine what the source of this disturbance is - most likely it's another loop that's interacting with the subject one. Whatever's causing this look to your unfiltered pv will basically have the same period of oscillation.

If you don't find anything, go out to the process to investigate - could be a poorly tuned local loop, sticky valve, steam trap, or a host of other things.

Good luck with your investigation.

Jim

jvalle,

did Ron explain to you about porpotion?

Greetings adzlan,

no ... sorry, but I just never got around to it and it seemed like the interest in it sort of died out ... plus the company that I work for has been moving into larger offices on the other side of town ... this has kept me VERY busy for the past several weeks setting up my PLC lab at the new place ...

do you have any specific questions about the PID's proportional action? ... or are you just interested in general information? ... I'll eventually get around to doing this ... probably in the next four or five weeks ...

Hello Ron, Thanks for not forgetting about us. Also an upate for you on the loop I was trying to tune. I found out that there is a few physical problems in the process that give the radical changes that I have been seeing in the draft. I am trying to get these fixed and then Im going to try and tackle the pid once again. Thanks again for all of your help and I will keep you updated.

Joel

hello Ron,

you seem to be busy in the recent time.....but can you just give some general infomartion in porpotion...

i'm very glad with that....but it's okay if you are busy


adzlan