Omron SYSMAC CVM1 Series Operation Manual page 339

PID and Related Instructions
Integral Action (I)
Combining integral action with proportional action reduces the offset according
to the time that has passed. The strength of the integral action is indicated by the
integral time, which is the time required for the manipulated variable of the inte-
gral action to reach the same level as the manipulated variable of the proportion-
al action with respect to the step deviation, as shown in the following illustration.
The shorter the integral time, the stronger the correction by the integral action
will be. If the integral time is too short, the correction will be too strong and will
cause hunting to occur.
Deviation
0
Manipulated
0
variable
Deviation
0
Manipulated
0
variable
Derivative Action (D)
Proportional action and integral action both make corrections with respect to the
control results, so there is inevitably a response delay. Derivative action com-
pensates for that drawback. In response to a sudden disturbance it delivers a
large manipulated variable and rapidly restores the original status. A correction
is executed with the manipulated variable made proportional to the incline (de-
rivative coefficient) caused by the deviation.
Integral Action
Step response
Pi Action and Integral Time
Step response
Ti: Integral time
Section 5-24
PI action
P action
321