This function block represents a PID controller containing the following elements:
- proportional term
- integral term
- differential term
- integral wind-up avoidance logic
- setup of controller output; with auto/manual selection
The controller implements the following continuous transfer function:
Internally, a velocity algorithm is used. The internally generated differential term is added at the last stage; This allows a smooth auto/manual transition and a transient-free parameter setting.
By connecting the D-Term to the X input, the controller will only react to changes in the controlled variable, but not to changes in the setpoint value.
Operating modes in "Manual" mode:
a) The controller works with a manual differential signal input.
b) The manual signal input Yh is interpreted as an absolute value and is channeled directly to the controller output Y as well as to the internal integral sum.
Overall controller implementation:
I-term (trapezoid rule):
When the controller output is being limited, the I-term is switched off until the limit condition is over, this condition is recognized as a sign-reversal in the error signal.
|Controlled variable (sensor input)
|Proportional gain input
|Reset time in [s]
|Derivative time in [s]
|Manual set input/manual differential input
|Manual mode parameter
|Upper limit input
|Lower limit input
|I-term is off
|D-term is off
|Y+ adds the manual input Yh to Yi (manual mode a)
|Y- subtracts the manual input Yh from Yi (manual mode a)
|Mode select input: Yh is channeled directly to Y (manual mode b)
|Limit Yu reached
|Limit Yo reached
The symbol indicates, whether the controller runs in manual or in automatic mode.