FB(X:=XIN, W:=WIN, OUT=>COOLING);
The block is an implementation of a PI controller (with parameters: P-band, Integration constant, Offset, Min and Max values, and output value of an inactive controller).
|W||REAL||Setpoint (usually temperature)||0|
|X||REAL||Measured value (usually temperature).||0|
|CONTROLLERTYPE||CONTROLLERTYPE||Controller type (cooling/heating).||cooling|
|BP||BOOL||When set to TRUE, the I part is disabled (the controller acts as a P controller)||False|
|ENABLED||BOOL||Controller enable (FALSE = controller is deactivated).||True|
|OFF||REAL||Offset, added to the setpoint W.||0|
|MIN||REAL||Minimum output value OUT (usually 0).||0|
|MAX||REAL||Maximum output value OUT (usually 100).||100|
|DISVAL||REAL||Value of the OUT output when the controller is deactivated (ENABLED=FALSE).||0|
|OUT||REAL||Output signal (mostly valve or damper, 0 to 100%).|
|PFACTOR||REAL||P-part of the output signal|
|IFACTOR||REAL||I-part of the output signal|
There is a control deviation at the controller input, E=(W+OFF)-X. The controller output OUT is given by the relation OUT=-100/Xp*(E+1/Ti*∫e)+MIN, where XP is the proportional band. The integration part (I-part) is calculated as follows: When OUT=0 at t=0 and the inputs are W+OFF=0, X=-1, then the I-part rises to OUT=100 at t=Ti, see figure below. The I-part is limited to 0...100 before it is added to the P-part. The resulting value is finally limited by MIN and MAX, see figure at block B33. The I-part helps to achieve the exact control value.
The BP input sets the I-part to 0, if set to true.
The ENABLED parameter switches the controller off (ENABLED=FALSE, controller disabled, and OUT=DISVAL). If Xp<0 then Xp=0, see below. If MAX<MIN then OUT=MAX (or minimum from (MIN, MAX)).