Chapter 15 The PID function of K200S MASTER-K
15-10
The figure 15.12 shows the variation of PV according to the several different reference
values ( b ). As shown in the figure 15.12, the small reference value produces small
deviation value, and it makes the control system response be slow.
In general, control system is required to be adaptable to various external or internal
changes. Especially, it should shows a stable transit response with the sudden change of
the SV to be robust to load disturbance and/or measurement noise.
Fig. 15.12 The PI control with several reference values
15.2.7 Integral windup
All devices to be controlled, actuator, has limitation of operation. For example, the motor
has speed limit, the valve can not flow over the maximum value. When the control system
has wide PV range, the PV can be over the maximum output value of actuator. At this
time, the actuator keeps the maximum output regardless the change of PV while the PV
is over the maximum output value of actuator. It can shorten the lifetime of actuator.
When the I control action is used, the deviation term is integrated continuously. It makes
the output of I control action very large, especially when the response characteristic of
system is slow.
This situation that the output of actuator is saturated, is called as ‘windup’. It takes a long
time that the actuator returns to normal operating state after the windup was occurred.
Time
PV
b=0.7
b=0.1
SV
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