TECO-Westinghouse PA7300 Series, Installation And Operation Manual

Page: 135 / 154

c. How to adjust
The PID control function is a control system that matches a feedback value to the set point.
Combining P (Proportional, Bn-14), I (Integral, Bn-15), and D (Derivative, Bn-16) makes control
possible even for a mechanical system with dead time. The PID control function, using different
detected sensors, can be used for speed, pressure, flow, or temperature etc. applications.
(1) PID control operations.
In order to distinguish the separate PID control operations. The figure below shown the
changes in the control input when the deviation between the target set point and the feed
back is held constant.
Fig. 14 PID Control Operations
• P Control: A control input proportional to the deviation is asserted. The deviation cannot
be zeroed by P control alone.
• I Control: A control input which is an integral of the deviation is asserted. This is effective
for matching the feedback to the target value. Sudden changes, however,
cannot be followed.
• D Control: A control input which is an integral of the deviation is asserted. Quick response
to sudded changes is possible.
• PID Control: Optimum control is achieved by combining the best features of P, I,
and D control.
App-5
PA 7300 APPENDIX
Deviation
Control input
Time
Time
PID control
I control
P control
D control