P controller - Cooling
Block name
B32_P_CONTROLLER
ST call
PROGRAM B32_TEST VAR XIN,WIN,COOLING:REAL; FB: LIB.CORE.V1_0.B32_P_CONTROLLER; END_VAR FB(X:=XIN, W:=WIN, OUT=>COOLING); END_PROGRAM
Library
LIB\CORE
Version
V1.0
Description
The block is an implementation of a P controller (with parameters: P-band, Offset, Min and Max values, and output value of an inactive controller).
Inputs
| Input | Type | Description | Default value |
| W | REAL | Setpoint (usually temperature). | 0 |
| X | REAL | Measured value (usually temperature). | 0 |
| CONTROLLERTYPE | CONTROLLERTYPE | Controller type (cooling/heating). | cooling |
| ENABLED | BOOL | Controller enable (FALSE = controller is deactivated). | True |
| XP | REAL | Proportional band | 30 |
| 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 |
Outputs
| Output | Type | Description |
| OUT | REAL | Output signal (mostly valve or damper, 0 to 100%). |
Function
There is a control deviation at the controller input, E=(W+OFF)-X. The controller output OUT is given by the relation OUT=-Xp/100×E+MIN, where XP is the proportional band. The resulting value is finally limited by MIN and MAX, see figure below. 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)).
Application example
Simple P controller using time scheduler TPG to block the controller outside of office hours.