====== PI controller - Cooling ======

{{:en:mervis-ide:35-help:b34.png}}

===== Block name =====

B34_PI_CONTROLLER

===== ST call =====

<code st-iec>
PROGRAM B34_TEST
VAR 
   XIN,WIN,COOLING:REAL;   
    FB: LIB.CORE.V1_0.B34_PI_CONTROLLER;
END_VAR
 FB(X:=XIN, W:=WIN, OUT=>COOLING);
END_PROGRAM
</code>

===== Library =====

LIB\CORE

===== Version =====

V1.0

===== Description =====

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).

===== Inputs =====

|Input         |Type                              |Description                                                                     |Default value|
|W             |REAL                              |Setpoint (usually temperature).                                                 |0            |
|X             |REAL                              |Measured value (usually temperature).                                           |0            |
|CONTROLLERTYPE|[[en:mervis-ide:35-help:035-software_basic:060-libraries:015-proto|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         |
|XP            |REAL                              |Proportional band                                                               |30           |
|OFF           |REAL                              |Offset, added to the setpoint W.                                                |0            |
|TI            |REAL                              |Integration constant                                                            |120          |
|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%).|
|PFACTOR|REAL|P-part of the output signal                       |
|IFACTOR|REAL|I-part of the output signal                       |

===== Function =====

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 [[en:mervis-ide:35-help:035-software_basic:060-libraries:020-basic-analogue-boxes:010-controllers:005-direct-acting-cooling:010-b32_p_controller|block B32]]. 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)).

{{:en:mervis-ide:35-help:b34_1.png}}

===== Application example =====

{{:en:mervis-ide:35-help:b34_example.png}}

A simple PI controller using analogue setpoint over a time program block TPG.