Brandon_ (Customer) asked a question.
Hey all.
I'm fairly new to the world of PID's. My only experience with them is using off the shelf process controllers.
My application is for beer fermenting, utilizing jacketed fermenters and a glycol chiller.
I've watched every video that I can find on PxK PID's, which has been good material to watch, but they all cover heating or pumping applications with analog outputs.
For background, my process and hardware; to cool fermentation vessels using a glycol chiller and solenoid valves. I'm reading the temps with Pt100 probes, which are converted to 4-20ma and read with P1-08ADL-1. There are two valves, one for the upper cooling jacket and one for the lower cone jacket. I'm currently cycling between the valves (especially during fermenter crashing) to prevent stratification and freezing of the beer closest to the jacket. Ideally there would be a duty cycle involved with the valves so they're not sitting there chattering away, which is an issue we have with the original process controllers and why I built our own system in the first place.
I have a working system currently with basic ladder logic, using a high setpoint and low setpoint to start and stop the cooling cycles, but I know it can be better.
Right now, I have the absolute basics of the instruction filled in. PV, SP, Input Range Max/Min. I'm getting confused / not understanding the output range / limits, process output (as it seems to be analog?) I don't have any good starting points for P, I, D or anything on the major advanced tabs. Normally I would just play with the programming until I figured it out but 1) this is a currently operating fermenter, so I'd like to have it somewhat "close" before I switch from my existing process to PID control and 2) it's a fairly slow process on how fast the beer heats during fermentation.
I'm really just looking for some pointers on setup and some base values before I transition over. I can offer free beer and a tour if you happen to find your way in to the Pittsburgh area :)
Phase 2, I think PID can benefit me, from my understanding of it, by keeping a closer temp to setpoint, based on my glycol temp.
During typical fermentation, we're at ~68F for ales and ~53F for lagers. When I crash a fermenter, I'm dropping it to 34F (to "crash" or settle out the yeast). For efficiency reasons, I keep the glycol temp around -6 tp -10F of whatever the coldest ferment is. IE, if we're fermented all vessels at 68F, the glycol temp is 60F. If I'm crashing at 34F, I'll drop the chiller to 25F. If I'm understanding the minor process of PID's, if I monitor my glycol temp as well, it will have a better chance of not over or under shooting my setpoint for the fermentation?
Any help would be much appreciated!!
-Brandon
Hi @Brandon_ (Customer)
Here is a post on the PID instruction.
https://accautomation.ca/productivity-1000-series-plc-pid-instruction/
This post uses simple math instructions to explain PID. It is a great learning exercise. It was done when the Click did not have a PID instruction.
https://accautomation.ca/click-plc-pid-using-factory-io/
Here are some references on PID control:
PID without a Ph.D. By Tim Wescott
Understanding PID in 4 minutes
PID Control – A brief introduction
PID Controllers Explained
Regards,
Garry
https://accautomation.ca/series/productivity-1000-plc/
Couple of things:
1) Read Help topic P167. This describes PID in Productivity. Toward the bottom of the article is an example for time proportioning outputs. This is the type of control that you're describing with valve actuation/duty cycle. The example shows how to set-up the timer pair.
2) For your application (jacketed cooling), you might benefit from cascade control. This is a more advanced topic and consists of using two PID's to control a process. This topic will definitely trip you up if you're not already familiar with PID.
3) " Ideally there would be a duty cycle involved with the valves so they're not sitting there chattering away, which is an issue we have with the original process controllers and why I built our own system in the first place."
Unfortunately, this could have been caused from the controller not being setup properly to start with. Most (even basic) process controllers have capability of at least single loop PID control with a time proportioned output with an adjustable time base. What type of process controller were you trying to use previously?