Setting function block parameters is initially performed by the pure PID parameters, i.e. the proportional action coefficient GAIN, the reset time TI and the rate time TD.
The D component is delayed by the time TD_LAG. The ratio between TD/TD_LAG is called differential gain VD. The D component can either be formed by the system deviation ERR (D_ON_X = 0) or the controlled variable PV (D_ON_X = 1). Should the D component be determined by the controlled variable PV, then the D component will not be able to cause jumps when reference variable fluctuations (changes in input SP) take place. Generally, the D component only affects disturbances and process variances.
Control direction reversal
A reversed behavior of the controller can be achieved by reversing the sign of GAIN. A positive value on GAIN causes the increase of the output value, for a positive error variable. A negative value on GAIN causes the increase of the output value, for a positive error variable.
Manipulated variable limiting
The limits YMAX and YMIN limit the output within the prescribed range. Therefore YMIN ≤ Y ≤ YMAX.
The markers QMAX and QMIN signal that the limits have been reached or the output signal is being limited.
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QMAX = 1 if Y ≥ YMAX
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QMIN = 1 if Y ≤ YMIN
For limiting the manipulated variable, the upper limit YMAX should be greater than the lower limit YMIN.
If manipulated variable limiting takes place, the anti-windup reset should make sure that the integral component cannot exceed all limits. The anti-windup measure is only implemented if the I component of the controller is not disabled. Anti-windup limits are identical to those for the manipulated variable. The anti-windup measure disregards the D component, to avoid the capping of the D component peaks through the anti-windup measure.
The anti-windup reset measure corrects the I component in the form, which means:
Selecting the control types
There are various controller types, which can be selected via the EN_P, EN_I and EN_D parameters.
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Controller type
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EN_P
|
EN_I
|
EN_D
|
|
P controller
|
1
|
0
|
0
|
|
PI controller
|
1
|
1
|
0
|
|
PD controller
|
1
|
0
|
1
|
|
PID controller
|
1
|
1
|
1
|
|
I controller
|
0
|
1
|
0
|
The I component can also be disabled with TI = 0.
