Omron CJ1G-CPUxx, Instructions Manual

Page: 705 / 1144

684
Data Control Instructions Section 3-18
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.
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
compensates for that drawback. In response to a sudden disturbance it deliv-
ers a large manipulated variable and rapidly restores the original status. A
correction is executed with the manipulated variable made proportional to the
incline (derivative coefficient) caused by the deviation.
The strength of the derivative action is indicated by the derivative time, which
is the time required for the manipulated variable of the derivative action to
reach the same level as the manipulated variable of the proportional action
with respect to the step deviation, as shown in the following illustration. The
longer the derivative time, the stronger the correction by the derivative action
will be.
PID Action
PID action combines proportional action (P), integral action (I), and derivative
action (D). It produces superior control results even for control objects with
dead time. It employs proportional action to provide smooth control without
Pi Action and Integral Time
PI action
P action
Ti: Integral time
Deviation
Manipulated
variable
Step response
I action
Integral Action
Deviation
Manipulated
variable
Step response
0
0
Derivative Action
PD Action and Derivative Time
PD action
P action
Td: Derivative time
D action
0
0
Ramp response
Deviation
Manipulated
variable
Step response
0
0
Deviation
Manipulated
variable