Toshiba G7 Series Applications Workbook page 13

Simplified PID flowchart
Setpoint
(frequency
(+)
command that
develops
desired
process
condition)
V = V - V
error setpoint feedback
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.
Proportional Gain times V
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
the below example, if V were to remain at the level shown, the output of the integral circuit would continue to increase linearly
error
with time (integral output is proportional to area of the rectangle = Proportional gain times V
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.
Proportional Gain times
DIFFERENTIAL GAIN
For additional assistance, please contact Toshiba Adjustable Speed Drive Marketing Dept. at (800) 872-2192
efesotomasyon.com -Toshiba inverter,drive,servo,plc
Proportional
Integral
error
(-)
Differential
Feedback (indicates actual process
condition)
Input to Proportional Circuit
V
error
Output of Proportional Circuit
error
Input to Integral Circuit
V
error
Output from Integral Circuit
Integral
Time
+
+
+
Time
Time
error
Time
Time
new frequency reference to
drive main circuit
vs. time graph. In
error
times time). The shorter the
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