> For the complete documentation index, see [llms.txt](https://support.powerio.com/hub/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://support.powerio.com/hub/codesys-hvac/en/hvac-knx-library/funktionen/twopointfun.md).

# TwoPointFun

## `TwoPointFun` (FUN)

FUNCTION TwoPointFun : INT

### Short description

> Linear conversion of a numerical input value by means of a characteristic curve defined by two points.\
> \
> Typical application: Scaling of process raw values\\

### Interfaces

#### Inputs

| Name            | Data type | Value range | Initial value | Function                                              |
| --------------- | --------- | ----------- | ------------- | ----------------------------------------------------- |
| *rIn\_X*        | REAL      |             |               | Analog input                                          |
| *rX1*           | REAL      |             | 0             | Point 1 of the input range                            |
| *rY1*           | REAL      |             | 0             | Point 1 of the output characteristic curve            |
| *rX2*           | REAL      |             | 100           | Point 2 of the input range                            |
| *rY2*           | REAL      |             | 100           | Point 2 of the output characteristic curve            |
| *xMinMaxLimit*  | BOOL      |             |               | Enable / disable the limit at the analog value output |
| *iMinMaxOffset* | INTEGER   |             |               | Values of the limits at the analog value output       |

#### Outputs

| Name          | Data type | Value range | Initial value | Function                                                                                                                       |
| ------------- | --------- | ----------- | ------------- | ------------------------------------------------------------------------------------------------------------------------------ |
| *TwoPointFun* | REAL      |             |               | Linear conversion of a numerical input value                                                                                   |
| *xErr*        | BOOL      |             |               | <p>\* <strong>FALSE:</strong><br>Conversion error-free<br>\* <strong>TRUE:</strong><br>Error during the conversion process</p> |

### Functional description

#### Analog value output

The analog value output is calculated from the analog value input *rIn\_X* depending on the linear characteristic defined by the two points P1(*rX1*/*rY1*) and P2(*rX2*/*rY2*) calculated according to the defined linear characteristic curve.\
In the event of a conversion error ( *xErr* = TRUE ) the analog value output remains unchanged.\\

> **Formula**
>
> rOut\_Y = (((rX1-rIn\_X)\*(rY2-rY1))/(rX1-rX2))+rY1\\
>
> **Restrictions**
>
> The analog value output is of data type REAL. Due to an unsuitable selection of the parameters *rX1*, *rX2*, *rY1* and *rY2* as well as the value of the analog value input *rIn\_X* it can lead to an overflow of the data type limits.\\

#### Enable / disable the limits *xMinMaxLimit*

The limits of the analog value output can generally be enabled and disabled with this input.\\

| *xMinMaxLimit* | Limits            | Notes                                        |
| -------------- | ----------------- | -------------------------------------------- |
| FALSE          | none              | Analog value output without absolute limits  |
| TRUE           | Y\_min and Y\_max | Limitation of the analog value output active |

#### Values of the limits *iMinMaxOffset*

The limits of the analog value output are only active if the input *xMinMaxLimit* is active ( = TRUE ).\
The limit values Y\_min and Y\_max are then calculated as follows:\\

> **Formulas**
>
> > Y\_min = rY1 - ((ABS(rY2-rY1))\*iMinMaxOffset)/100\
> > Y\_max = rY2 + ((ABS(rY2-rY1))\*iMinMaxOffset)/100\\

| *rY1* | *rY2* | *rY2* - *rY1* | *iMinMaxOffset* | *Y\_min* | *Y\_max* | Notes           |
| ----- | ----- | ------------- | --------------- | -------- | -------- | --------------- |
| 0     | 100   | 100           | 0               | 0        | 100      | Standard limits |
| 0     | 100   | 100           | 10              | -10      | 110      | Positive offset |
| 0     | 100   | 100           | -10             | 10       | 90       | Negative offset |

#### Digital output *xErr*

The digital output *xErr* signals an error in the conversion process. The following errors are considered:\
\\

* *rX1* AND *rX2* = 0
* *rX1* = *rX2*
* *rY1* AND *rY2* = 0
* *rY1* = *rY2*

| Error during the conversion process | *xErr* | Notes                               |
| ----------------------------------- | ------ | ----------------------------------- |
| FALSE                               | FALSE  | Conversion error-free               |
| TRUE                                | TRUE   | Error during the conversion process |

Legend: X = any\\

### Codesys

InOut:

| Scope  | Name            | Type   | Initial | Comment                                                                                          |
| ------ | --------------- | ------ | ------- | ------------------------------------------------------------------------------------------------ |
| Return | `TwoPointFun`   | `INT`  |         |                                                                                                  |
| Input  | `iIn_X`         | `INT`  |         | Analog input                                                                                     |
| Input  | `iX1`           | `INT`  | 0       | Point 1 of the input range                                                                       |
| Input  | `iX2`           | `INT`  | 100     | Point 2 of the input range                                                                       |
| Input  | `iY1`           | `INT`  | 0       | Point 1 of the output characteristic curve                                                       |
| Input  | `iY2`           | `INT`  | 100     | Point 2 of the output characteristic curve                                                       |
| Input  | `xMinMaxLimit`  | `BOOL` |         | Enable / disable the limit at the analog value output                                            |
| Input  | `iMinMaxOffset` | `INT`  |         | Values of the limits at the analog value output                                                  |
| Output | `xErr`          | `BOOL` |         | <p>FALSE: conversion error-free<br><br><br>TRUE: error during the conversion process<br><br></p> |


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