The P_PID control structure is displayed in the structure diagram. Setting function block parameters is initially performed by the PID parameters, i.e. the proportional action coefficient kp, the reset time tn and the rate time tv.
The D component can either be formed by the system deviation xd (input status bit 12 = 0) or the process variable x (input status bit 12 = 1). Should the D component be determined by the process variable x, then the D component will not be able to cause jumps when setpoint fluctuations (changes in input w) take place. Generally, the D component only affects disturbances and process variances.
A reversed behavior of the controller can be achieved by input status bit 16.
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input status bit 16 = 0: Causes the increase of the output value Y, for a positive xd.
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input status bit 16 = 1: Causes the decrease of the output value Y, for a positive xd.
Manipulated Variable Limiting
The defined limits YAO and YAU limit the output Y within the prescribed range.
Therefore YAU ≤ Y ≤ YAO.
The markers output word 1, status bit 3 (high limit marker) and output word 1, status bit 2 (low limit marker) signal that the defined limits have been reached or the output signal is being limited.
output word 1, status bit 3 = 1 if Y ≥ YAO
output word 1, status bit 2 = 1 if Y ≤ YAU
For limiting the manipulated variable Y, the upper limit YAO should be set greater than the lower limit YAU.
If manipulated variable limiting takes place, the anti-windup reset helps to ensure 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, that:
YAU+YP + Z ≤ YI ≤ YAO-YP-Z
