4 - 6
MELSEC-Q/QnA
4. FUNCTIONS OF PID CONTROL
4.2.5 Derivative operation (D operation)
The control method for derivative operation is described below.
(1) In derivative operation, an MV (manipulated value) proportional to the deviation
change rate is added to the system value to zero deviation when it occurs.
This operation prevents significant fluctuation at the control objective due to
external disturbances.
(2) The time required for the MV in the derivative operation to reach the MV for the
proportional operation after the generation of deviation is called the derivative
time. Derivative time is expressed as T
D
.
Condition
Derivative Operation
When derivative time T
D
is
shorter
Differentiating effect decreases.
When derivative time T
D
is
longer
Differentiating effect increases.
However, hunting of short cycle is more likely
to occur.
(3) The derivative operation when the deviation is a constant value stepped response
is shown in Fig. 4.4.
DV
Time
K
DV
T
D
Time
Manipulated value for proportional operation
Ma
ni
pu
la
te
d
va
lu
e
De
vi
a
tio
n
P
Fig. 4.4 Derivative operation when the deviation is a constant
(4) Derivative operation is always used in combination with proportional operation
(PD operation) or with proportional and integral operations (PID operation).
Derivative operation cannot be used independently.
Содержание Q Mode
Страница 1: ......
Страница 2: ......
Страница 14: ...A 12 MEMO ...
Страница 18: ...1 4 MELSEC Q QnA 1 GENERAL DESCRIPTION MEMO ...
Страница 48: ...4 14 MELSEC Q QnA 4 FUNCTIONS OF PID CONTROL MEMO ...
Страница 51: ...5 3 MELSEC Q QnA 5 PID CONTROL PROCEDURE MEMO ...
Страница 65: ...5 17 MELSEC Q QnA 5 PID CONTROL PROCEDURE MEMO ...
Страница 72: ...5 24 MELSEC Q QnA 5 PID CONTROL PROCEDURE MEMO ...
Страница 74: ...6 2 MELSEC Q QnA 6 PID CONTROL INSTRUCTIONS MEMO ...
Страница 120: ...9 28 MELSEC Q QnA 9 COMPLETE DERIVATIVE PID CONTROL INSTRUCTIONS AND PROGRAM EXAMPLES MEMO ...
Страница 125: ......
Страница 126: ......