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The combined uses of P, I, and D actions are described below.
(1) PI control
PI control, which is a combination of P and I actions, is generally used to minimize the remaining deviation caused by P
action. PI control always acts to minimize the deviation even if a commanded value changes or external disturbance
steadily occurs. However, the longer the integral time, the slower the system response to quick-changed control.
P action can be used alone for loads with very large part of integral components.
(2) PD control
In PD control, the moment that a deviation occurs, the control rapidly generates greater MV (manipulated value) than
that generated by D action alone, to suppress the deviation increase. When the deviation becomes small, the behavior of
P action becomes small.
A load including the integral component in the controlled system may oscillate due to the action of the integral
component if P action alone is applied. In such a case, use PD control to reduce the oscillation caused by P action, for
keeping the system stable. That is, PD control is applied to a system that does not contain any damping actions in its
process.
(3) PID control
PID control is implemented by combining P action with the deviation suppression of I action and the oscillation
suppression of D action. PID control features minimal control deviation, high precision and high stability.
In particular, PID control is effective to a system that has a long response time to the occurrence of deviation.
Follow the procedure below to set data to PID control function codes.
It is highly recommended that you adjust the PID control value while monitoring the system response waveform with an
oscilloscope or equivalent. Repeat the following procedure to determine the optimal solution for each system.
- Increase the data of J03 (PID control P (Gain)) within the range where the feedback signal does not oscillate.
- Decrease the data of J04 (PID control I (Integral time)) within the range where the feedback signal does not oscillate.
- Increase the data of J05 (PID control D (Differential time)) within the range where the feedback signal does not
oscillate.
Refining the system response waveforms is shown below.
1) Suppressing overshoot
Increase the data of J04 (Integral time) and decrease that of J05 (Differential time.)
2) Quick stabilizing (moderate overshoot allowable)
Decrease the data of J03 (Gain) and increase that of J05 (Differential time).
3) Suppressing oscillation whose period is longer than the integral time specified by J04
Increase the data of J04 (Integral time).
4) Suppressing oscillation whose period is approximately the same as the time specified by J05 (Differential time)
Decrease the data of J05 (Differential time).
Decrease the data of J03 (Gain), if the oscillation cannot be suppressed even though the differential time is set at 0
sec.
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