9.2 Details of Function Codes
9-67
Chap. 9 FUNCTION CODES
Differentiation time (J05)
Sets the differentiation time for the PID processor.
- Data setting range: 0.00 to 600.00 (sec.)
D (Derivative) control
The PID operation having the
proportional relationship of deviation
between derivative of the commanded
(frequency) and control amounts is
called the D control. The D control
outputs derivative of the control amount.
For rapidly change, this control makes
the system react quickly.
The effectiveness of ID control is expressed by a parameter of differentiation time. Setting a
long differentiation time will quickly converge on a system control error (deviation) caused by
P control. Setting it too long makes the system tend to oscillate more. Setting it too short will
suppress the convergent effect to the deviation caused by the system operation.
Descriptions combined use of P, I and D control are shown below.
(1) PI control
PI control, which is a combination of P and I control, is generally used to minimize the
deviation caused by P control. PI control acts to minimize at all times the deviation caused by a
variance of the commanded amount or external disturbance to the system as stationary events.
However, the longer integration time set, the slower the system response.
Use P control alone for loads with integral component ratio that takes very large part of control
amount.
(2) PD control
When PD control is applied to a system, the moment that a deviation occurs, the system
instantaneously generates a control amount much greater than that of D control (frequency) to
suppress the deviation. If the deviation converges, the P control amount may decrease.
A load including the integral component in the equipment to be controlled may oscillate from
the action of the integral component if the P control alone is applied. In this case, use PD control
to reduce the oscillation caused by P control for keeping the system stable. That is, PD control
should be applied to any system that does not contain any braking actions in its process.
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