Hello, I am attempting to tune two PIDs for heating/cooling of a vessel jacket with steam and chilled water. This is the first time I attempt tuning a PID. So far, I have not been able to find the correct settings that will give the desired result since I need a Critically Damped response plus/minus 1 degree from setpoint. If my heating valve is wide open at 100% and close at setpoint I overshoot around 14 degrees C. In order for me to be within the 1 degree C overshooting, the heating valve can’t exceed 5% open for the final 15 degrees of heating. I am writing to see if an experienced programmer can shed some light that can guide me in the correct direction.
My setup is as follows:
Logix 5000 V31
CPU: 1769-L33ER
Analog Input Card: 1769-IF8, 4-20mA scaled for PID (0-16383)
Analog Output card: 1769-OF4, 4-20mA scaled for PID (0-16383)
RTD is a PT 100 range from 0-150
Steam/cooling valves are both Air to open valves 4-20mA
RTD channel input value goes to SCP set to: input min 0, input max 16383. Scaled min: 0 Scaled Max 1500. Stored at an Integer location.
Heating PID is set to: Dependent, SP-PV, update time 0.1, Derivative of PV, PV tracking, PV Unscaled min 0, PV unscaled max 16383, Engineering units min 0, Engineering Units Max 16383, CV min at 0% 0, CV max at 100% 16383.
Cooling PID has the same settings except for the action that is set to PV-SP.
Created a free running timer set to 100 milliseconds to execute both PID since they are located at the continuous task.
The heating PID output is moved to a SCP set to: input min 0, Input max 16383, scaled min 0, scaled max 16383 that is then moved to the output analog channel to control the valve. Heating and cooling SCP are both set in the same way.
I have tried to set the PID in several different scenarios like: with conditional logic, without conditional logic to no avail. I was contemplating the idea of opening the valve wide open until I reach a point and then switching for the PID to control the final stage of heating but so far have not been able to find a setting that would keep my PID within range. Another problem that I noticed is that for some reason the PID does not tend to close the valve much when reaching the setpoint, or even after reaching setpoint. Then after reaching the setpoint it continues to heat regardless of my settings. Manually I can control my valve output without any issues. Maybe I am missing something in my settings that I can’t seem to catch. I am about to lose my mind with this . Any help would be greatly appreciated.
My setup is as follows:
Logix 5000 V31
CPU: 1769-L33ER
Analog Input Card: 1769-IF8, 4-20mA scaled for PID (0-16383)
Analog Output card: 1769-OF4, 4-20mA scaled for PID (0-16383)
RTD is a PT 100 range from 0-150
Steam/cooling valves are both Air to open valves 4-20mA
RTD channel input value goes to SCP set to: input min 0, input max 16383. Scaled min: 0 Scaled Max 1500. Stored at an Integer location.
Heating PID is set to: Dependent, SP-PV, update time 0.1, Derivative of PV, PV tracking, PV Unscaled min 0, PV unscaled max 16383, Engineering units min 0, Engineering Units Max 16383, CV min at 0% 0, CV max at 100% 16383.
Cooling PID has the same settings except for the action that is set to PV-SP.
Created a free running timer set to 100 milliseconds to execute both PID since they are located at the continuous task.
The heating PID output is moved to a SCP set to: input min 0, Input max 16383, scaled min 0, scaled max 16383 that is then moved to the output analog channel to control the valve. Heating and cooling SCP are both set in the same way.
I have tried to set the PID in several different scenarios like: with conditional logic, without conditional logic to no avail. I was contemplating the idea of opening the valve wide open until I reach a point and then switching for the PID to control the final stage of heating but so far have not been able to find a setting that would keep my PID within range. Another problem that I noticed is that for some reason the PID does not tend to close the valve much when reaching the setpoint, or even after reaching setpoint. Then after reaching the setpoint it continues to heat regardless of my settings. Manually I can control my valve output without any issues. Maybe I am missing something in my settings that I can’t seem to catch. I am about to lose my mind with this . Any help would be greatly appreciated.