The following is the structure diagram of the PIDP block:
Setting parameters for the PID_P 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 disabled individually by setting the corresponding input (kp, ki or kd) to 0.
The D component is delayed by the time constant td_lag. The D component can either be based upon the system deviation ERR (d_on_pv = "0") or the controlled variable PV (d_on_pv = "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
Reversed behavior by the controller can be obtained by setting the reverse input. reverse = 0 has the effect that the output value increases with a positive disturbance. reverse = 1 has the effect that the output value decreases with a positive disturbance.
Manipulated variable limiting
The limits ymax and ymin limit the output within the prescribed range. Therefore ymin ≤ Y ≤ ymax.
The outputs qmax and qmin signal that the limit value has been reached, i.e. that the output signal is limited.
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qmax = 1 if Y ≥ ymax
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qmin = 1 if Y ≤ ymin
The upper limit ymax for limiting the manipulated variable must be greater than the lower limit ymin, otherwise the function block reports an error and does not function.
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 D component is not taken into consideration for anti-windup measures, so that peaks, caused by the D component, are not capped by 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
|
