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MELSEC-Q/QnA
4. FUNCTIONS OF PID CONTROL
4.2.4 Integral operation (I operation)
The control method for integral operation is described below.
(1) In the integral operation, the MV (manipulated value) changes continuously to
zero deviation when it occurs.
This operation can eliminate the offset that is unavoidable in proportional
operation.
(2) The time required for the MV in integral operation to reach the MV for proportional
operation after the generation of deviation is called the integral time. Integral time
is expressed as T
I
.
Condition
Integral Operation
When integral time T
I
is
shorter
Integrating effect increases and the time to
eliminate the offset becomes shorter.
However, hunting is more likely to occur.
When integral time T
I
is longer Integrating effect decreases and the time to
eliminate the offset becomes longer.
(3) The integral operation in step response with a constant E (deviation) is illustrated
in Fig. 4.3.
De
via
tio
n
MV
T
I
E
Time
MV in "P + I" operations
MV value in I operation
Kp . E
Time
MV value in
P operation
Fig. 4.3 Integral Operation with a Constant Deviation
(4) Integral operation is always used in combination with proportional operation (PI
operation) or with proportional and derivative operations (PID operation).
Integral operation cannot be used independently.
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