Tune the PID loop

Tune the PID loop to optimize the performance of the cooling group.

Caution: This procedure must be performed by APC authorized personnel only. The PID loop must be tuned after the equipment in the room is installed and running. The loop should be tuned periodically to account for changes in the room load.

1.Adjust the integral and derivative constants to zero and the proportional constant to 1.0.

2.Set the temperature setpoint value and start the cooling group.

3.When the temperature reaches a stable value, increase the proportional constant by 0.5. If the temperature does not respond to this change, adjust the setpoint.

4.Repeat step 3 until the temperature value starts to oscillate and the peak amplitude of the oscillations is constant.

5.Note the time, in minutes, between the peaks of the oscillations. This is the Ultimate Period, PU.

6.Note the value of the proportional constant. This is the Ultimate Gain, GU.

7.Compute the PID constants using the table below. Use the equations for that control method in the row to compute the values for each constant.

Control Method

Proportional

Integral

Derivative

 

 

 

 

P

0.5*GU

P + I

0.45*GU

0.54*GU/PU

P + I + D

0.6*GU

1.2*GU/PU

0.075*GU*PU

8. Set each constant according to these calculations.

You may need to further tune the PID loop in the following ways to account for changes in the room load:

Loop Behavior

PID Tuning Correction

 

 

Slow response to temperature changes

Increase the proportional multiplier or increase the

 

derivative multiplier.

 

 

Overcooling/undercooling after changes in the

Increase the derivative or the proportional multiplier.

room load or changes in setpoint

 

 

 

Environmental temperature never reaches the

Increase the integral multiplier.

setpoint

 

 

 

Overcooling/undercooling on constant room

Decrease the integral multiplier.

load

 

 

 

InRow RD 10 kW Air Cooled Operation and Maintenance

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APC ACRD101 manual Tune the PID loop, Control Method Proportional Integral Derivative, Loop Behavior PID Tuning Correction