Micro850 and CCW: RA_IPID Loop Tuning

Spanishflea10

Member
Join Date
Jun 2015
Location
Santa Maria, CA
Posts
2
Long time listener, first time caller.

I have a Micro850 PLC controlling the temperature in seven fermentation vessels at a local brewery. Each vessel has an RTD which is connected to a SpectrumControls universal analog input module which accepts direct RTD inputs. The temperature is controlled using the add-in "RA_IPID" function block which outputs a Pulse Width Modulated digital output to actuate a solenoid valve on a chilled glycol jacket around the vessel. The PWM function is supposed to turn the digital output on and off based on a set time period to simulate the effect of an analog output. For example, if the time period is set to 30 seconds, a CV output of 100% will turn on the digital output for the entire 30 second period. if the CV output is 50%, the digital output will be on for half the set time period, 15 seconds.

So...my question/s. I CANNOT find any information about the actual PID math that is happening in the RA_IPID block so I don't know the range, units, starting values etc for the P, I, and D values. Anybody have experience with tuning a loop with the RA_IPID FB? The brewery has been working fine with values of:

Proportional Gain: 1
Time Integral: 0.5
Time Derivative: 0.5
Derivative Gain: 0.5

These values were complete guesses, but it works. I would love to get these loops tuned a little better, but it's hard to simulate the process, much less use the autotune function to tune a loop since the batch of fermenting beer provides the heat for the process and the batch of beer is expensive and shouldn't be 'experimented' with.

Anybody have any experience with a similar setup? I can email HMI and PLC programs if interested.

Bonus question: If anyone has any ideas for the best way to do a ramp/soak temperature profile with this hardware/software, I would love to discuss it.
 

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