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1 OVERVIEW
1.4 PID Control
This section explains "proportional operation", "integral operation" and "derivative operation"
performed for PID control using the process control instructions.
1.4.1 Proportional operation (P operation)
This section explains the control method using proportional operation.
(1) Proportional operation is the action that compares the deviation (difference between the set
value and the process value) to find the manipulated value.
(2) The change in relationship between deviation (DV) and manipulated value (MV) using
proportional operation is shown using the following numeric expression.
Kp is called the proportional gain or proportional constant.
(3) The proportional operation when the deviation is a constant stepped response is shown in Fig.
1.3.
(4) The manipulated value fluctuates between
As Kp becomes larger the manipulated value corresponding to the deviation also becomes
larger making the compensation operation stronger.
(5) Offset occurs in proportional operation.
1 - 6
MV
Kp • DV
Fig. 1.3 Proportional operation when deviation is constant
DV
Time
K DV
P
Time
10 and 110%.
MELSEC-Q
1 - 6
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