pide

moorem235

Member
M
Join Date
Aug 2011
Location
Massachusetts
Posts
3
Having a problem with a Pid loop controlling temperature. I have manually tuned the loop but the temperature will not hit set point. I'm using a compact logix and the PIDE instruction. P = 25.0 I = .06 D = 0 set point is 1600 f max temperature is 2000 f the temperature usually stays about 100 f low. this application is for a landfill flare and I only have control of the cooling as the gas is rather consistent. I have a louver to control the heat. Other than not hitting set point the control is very acceptable.
 
You may want to check the BTU rating of your burner system and compare it to the BTUs needed. If that checks out, verify your fuel to air mix.
 
I’m not generating heat for use. I’m simply controlling the heat with a ambient air louver. Landfill flares burn methane gas to destroy the odor and greenhouse gases. I misspoke when the temperature gets close to set point it doesn’t seem to want to change the output enough to get to set point for hours.
 
Is the PID CV at maximum (or minimum) when your temperature is 100 degrees low or do you consistently run 100 degrees low regardless of the setpoint?

If you are at the limit of CV but can't reach the setpoint, then the prolem is the system rather than PID tuning. If you miss the setpoint by a consistent amount regardless of the setpoint, it sounds like there might be a deadband. Perhaps once the error gets inside the deadband, the PID function no longer makes corrections?

Was there originally a PID in the GE PLC before you converted to Compact Logix or did you add functionality when you converted? I don't recall a PID function from when I helped you restart the unit a couple of years ago.
 
yes it was a GE before. No dead band, the cv is about 54% so now what happens is the pid gets close to set point then reacts to slow increasing the P term doesn’t have much affect if I change the I term much it gets erratic.
 
Last edited:

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