The following is the structure diagram of the PIDP1 block:
The PIDP1 control structure is displayed in the Structure diagram.
Setting parameters for the PIDP1 controller takes place first of all for the pure PID parameters, that is to say, the proportional action coefficient KP, the integral action coefficient KI and rate of differentiation KD.
The P, I and D components can be individually disabled while the corresponding input (KP, KI oder KD) is set to 0.
The D component is delayed by the time constant TD_LAG. 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. In principle, the D component only affects disturbances and process variances.
Control direction reversal
The opposite behavior of the controller can be attained by setting input REVERSE to 1. REVERSE = 0 results in an increased output value when there is a positive disturbance. REVERSE = 1 results in an decreased output value when there is a positive disturbance.
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 antiwindup 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
Several controller variants can be selected over the parameters KP, KI and KD:
|
Controller type
|
KP
|
KI
|
KD
|
|
P controller
|
> 0
|
= 0
|
= 0
|
|
PI controller
|
> 0
|
> 0
|
= 0
|
|
PD controller
|
> 0
|
= 0
|
> 0
|
|
PID controller
|
> 0
|
> 0
|
> 0
|
|
I controller
|
= 0
|
> 0
|
= 0
|
