Rockwell Automation MD65 User Manual Version 2.0 User Manual
Page 175
PID Set Up
I-7
PID Gains
The proportional, integral, and differential gains make up the PID
regulator.
•
PID Prop Gain (A134)
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 max frequency when the PID error is 100% of the
analog input range. A larger value for PID Prop Gain (A134)
makes the proportional component more responsive, and a
smaller value makes it less responsive. Setting PID Prop Gain
(A134) to 0.00 disables the proportional component of the PID
loop.
•
PID Integ Time (A135)
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 max frequency when the PID error is 100% for 2
seconds. A larger value for PID Integ Time (A135) makes the
integral component less responsive, and a smaller value
makes it more responsive. Setting PID Integ Time (A135) to 0
disables the integral component of the PID loop.
•
PID Diff Rate (A136)
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 (P035) when the process error is changing at
1% / second. A larger value for PID Diff Rate (A136) 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 (A136) to 0.00
(factory default) disables the differential component of the PID
loop.