*
For additional assistance, please contact Toshiba Adjustable Speed Drive Marketing Dept. at (800) 872-
2192
52
PROPORTIONAL GAIN
Note that PIDs for quickly-changing process variables have higher proportional gains than do their
counterparts for slowly-changing process variables. The higher the proportional gain, the smaller the rise
time. With increased proportional gain usually comes increased overshoot and increased chance of
oscillation.
INTEGRAL GAIN
Also known as reset
,
integral gain
is not really a gain at all, but a time. The integral time (units seconds
per repeat) defines how long it takes the integral circuit output to go from zero to the level set by the
output of the proportional circuit. The integral action is therefore influenced by the proportional action.
The output of the integral circuit represents the area under the V
error
vs. time graph. In the below example,
if V
error
were to remain at the level shown, the output of the integral circuit would continue to increase
linearly with time (integral output is proportional to area of the rectangle = Proportional gain times V
error
times time).
The shorter the integral time, the stronger the effect of the integral action
. If you have a
system that never quite gets to the setpoint (there is steady-state error), decrease the integral time.
Output from Integral Circuit
Input to Proportional Circuit
Time
Time
V
error
Output of Proportional Circuit
Proportional Gain times V
error
Input to Integral Circuit
V
error
Time
Integral
Time
Time
Proportional Gain times
