APC ACRC301S User's Guide download pdf (Page 18)

Operation: Control the Environment

12 InfraStruXure InRow RC—Operation and Maintenance

How to tune the PIDs

A qualified service technician must tune the PID loop to optimize the performance of the cooling group.

1. Adjust the integral and derivative constants to zero, and the proportional constant to 0.7.

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, P

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

7. Compute the PID constants using the table below. Select the type of control from the rows of the

table, and use the equations in the columns to compute the values for each constant.

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:

Caution

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.

Control Method Proportional Integral Derivative

P0.5*G

––

P + I 0.45*G

0.54*G

–

P + I + D 0.6*G

1.2*G

0.075*G

Loop Behavior PID Tuning Correction

Slow response to temperature changes Increase the proportional multiplier or increase the

derivative multiplier.

Over-cooling/under-cooling after changes in

the room load or changes in setpoint

Increase the derivative or the proportional multipliers.

Environmental temperature never reaches

the setpoint

Increase the integral setting.

Over-cooling/under-cooling on constant

room load

Decrease the integral multiplier.

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APC ACRC301S User's Guide Page 18