P controller - Cooling
- Block name
- ST call
- Library
- Version
- Description
- Inputs
- Outputs
- Function
- Application example

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.

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