====== On/Off controller - heating ======

{{:en:mervis-ide:35-help:b31.png}}

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

B31_REVERSE_ON_OFF_CONTROL_SEQUENCE

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

<code st-iec>
PROGRAM B31_TEST
VAR 
   IN1, IN2:REAL;
  O1: BOOL;
   FB: LIB.CORE.V1_1.B31_REVERSE_ON_OFF_CONTROL_SEQUENCE;
END_VAR

   FB(X:=IN1, W:= IN2);
    O1:= FB.OUT;
END_PROGRAM
</code>

===== Library =====

LIB\CORE

===== Version =====

V1.1

===== Description =====

The block is an On/Off controller, parametrable according to CONTROLLERTYPE, bandwidth Xp, and offset OFF.

{{:en:mervis-ide:35-help:b31_1.png}}

===== Inputs =====

|Input         |Type                              |Description                         |Default value|
|ENABLED       |BOOL                              |Enable of operation.                |True         |
|X             |REAL                              |Controlled value (e.g. temperature).|0            |
|W             |REAL                              |Setpoint value (e.g. temperature).  |22           |
|CONTROLLERTYPE|[[en:mervis-ide:35-help:035-software_basic:060-libraries:015-proto|CONTROLLERTYPE]]|Controller type (Heating, Cooling). |cooling      |
|XP            |REAL                              |Hysteresis                          |1            |
|OFF           |REAL                              |Offset, added to the setpoint W.    |0            |

===== Outputs =====

|Output|Type|Description                           |
|OUT   |REAL|Output signal (usually heating valve).|

The output variable "OUT" has a flag since function block version 1.1 RETAIN to keep the last state when the PLC is restarted.

===== Function =====

The block is an implementation of a 2-state controller, or On/Off controller, where X is the controlled value, and W+OFF is the setpoint (the OFF parameter is an offset). It works as follows: Supposing temperature X is too low, then OUT=TRUE and heating (if CONTROLLERTYPE=HEATING) is activated. As soon as the measured temperature X rises above W+OFF, the block sets OUT=FALSE and heating goes off, which results in the temperature X falling. When temperature falls below X=W+OFF-XP, then OUT=TRUE, and heating is activated again. Temperature rises and the whole process repeats.

The offset OFF is used to compensate the W parameter. There are 3 ways to set the offset, see below. Off = 0: Heating controller. Off = Xp/2: Middle value is used as setpoint. Off = -Xp : Minimum level controller.

The ENABLED parameter may switch the controller off. When ENABLED=FALSE, then the controller is off and OUT=FALSE.

Note:\\
When X= W+OFF then OUT=FALSE. When X = W+OFF+XP then OUT is not defined (it depends if it is reached from left or right).

{{:en:mervis-ide:35-help:b31_2.png}}

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

{{:en:mervis-ide:35-help:b31_example.png}}