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PID Control Setting
PID control block diagram.
The following figure shows the PID control block diagram.
Figure 4.4.72 PID control block diagram
PID Tuning
Use the following procedures to start PID control,
(1) Enable PID control (set 10-03 to a value greater than "xxx0b").
(2) Increase the proportional gain (10-05) to the highest value possible without causing the system to
become unstable.
(3) Decrease the integral time (10-06) to the lowest value possible without causing the system to become
unstable.
(4) Increase the differential time (10-07) to the highest value possible without causing the system to
become unstable.
The PID control serves to maintain a given process within certain limits whether it is pressure, flow etc. To
do this the feedback signal is compared to the set value and the difference becomes the error signal for
the PID control.
The PID control then responds by trying to minimize this error. The error is multiplied times the value of the
proportional gain set by parameter 10-05. An increased gain value results in a larger error. However, in
any system as the gain is increased there is a point that the system will become unstable (oscillate).
To correct this instability, the response time of the system may be slowed down by increasing the Integral
time set by parameter 10-06. However slowing the system down too much may be unsatisfactory for the
process.
The end result is that these two parameters in conjunction with the acceleration time (01-14) and
deceleration (01-15) times require to be adjusted to achieve optimum performance for a particular
application.
PID output polarity can be selected with parameter 10-03 (setting = xx0xb: PID output forward, setting =
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