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1.3.4 Integral action (I-action)
An integral action is an action which continuously changes the manipulated value (MV) to eliminate the deviation (E)
when there is any.
The offset caused by a proportional action can be eliminated.
In an integral action, the time from a deviation occurrence until when the manipulated value (MV) of the integral action
becomes equals to that of the proportional action is called integral time, and is indicated as TI.
The following table describes the difference of actions depending on the value of T
I, integral time.
The following figure shows an integral action of step responses where the deviation (E) is a fixed value.
An integral action is used as a PI action in combination with a proportional action, or PID action in combination with a
proportional and derivative actions.
An integral action cannot be used by itself.
Condition Integral action
TI is a small value
The integral effect gets large, and time to eliminate the offset gets short.
Though, the temperature process value (PV) tends to fluctuate around the set value.
T
I is a large value The integral effect gets small, and time to eliminate the offset gets long.
E
Manipulated value of the Proportional action
Manipulated value of the Integral action
Manipulated value of the Proportional action + Integral action
Time
Time
T
I
Deviation
(E)
Manipulated
value (MV)
K
P E