User Manual Owner's manual

Rockwell Automation Publication 280E-UM001B-EN-P – July 2012 331
PID Setup Appendix D
PID Gains
The proportional, integral, and differential gains make up the PID regulator.
• Parameter 234 (PID Prop Gain)
The proportional gain (unitless) affects how the regulator reacts to the
magnitude of the error. The proportional component of the PID regulator
outputs a speed command proportional to the PID error. For example, a
proportional gain of 1 would output 100% of maximum frequency when
the PID error is 100% of the analog input range. A larger value for (PID
Prop Gain) makes the proportional component more responsive, and a
smaller value makes it less responsive. Setting (PID Prop Gain) to 0.00
disables the proportional component of the PID loop.
• Parameter 235 (PID Integ Time)
The integral gain (units of seconds) affects how the regulator reacts to
error over time and is used to get rid of steady state error. For example, with
an integral gain of 2 seconds, the output of the integral gain component
would integrate up to 100% of maximum frequency when the PID error is
100% for 2 seconds. A larger value for (PID Integ Time) makes the integral
component less responsive, and a smaller value makes it more responsive.
Setting (PID Integ Time) to 0 disables the integral component of the PID
loop.
• Parameter 236 (PID Diff Rate)
The Differential gain (units of 1/seconds) affects the rate of change of the
PID output. The differential gain is multiplied by the difference between
the previous error and current error. Thus, with a large error the D has a
large effect and with a small error the D has less of an effect. This
parameter is scaled so that when it is set to 1.00, the process response is
0.1% of (Maximum Freq) when the process error is changing at 1%/
second. A larger value for (PID Diff Rate) makes the differential term have
more of an effect and a small value makes it have less of an effect. In many
applications, the D gain is not needed. Setting (PID Diff Rate) to 0.00
(factory default) disables the differential component of the PID loop.
Guidelines for Adjusting the PID Gains
1. Adjust the proportional gain. During this step it may be desirable to
disable the integral gain and differential gain by setting them to 0. After a
step change in the PID Feedback:
• If the response is too slow increase Parameter 234 (PID Prop Gain).