# TwoPointFun

## `TwoPointFun` (FUN)

`FUNCTION` TwoPointFun: `REAL`

### Short description

> Linear conversion of a numerical input value by 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 value input                                   |
| *rX1*           | `REAL`    |             | 0             | Point 1 of the input range                           |
| *rY1*           | `REAL`    |             | 0             | Point 1 of the output characteristic                 |
| *rX2*           | `REAL`    |             | 100           | Point 2 of the input range                           |
| *rY2*           | `REAL`    |             | 100           | Point 2 of the output characteristic                 |
| *xMinMaxLimit*  | `BOOL`    |             |               | Enable / disable limiting at the analog value output |
| *iMinMaxOffset* | INTEGER   |             |               | Limit values 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 conversion process</p> |

### Function 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*). 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 the data type `REAL`. Due to an unsuitable selection of the parameters *rX1*, *rX2*, *rY1* and *rY2* and the value of the analog value input *rIn\_X* the limits of the data type may be exceeded.

#### 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 | Limiting of the analog value output active  |

#### Limit values *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      | Default 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 during the conversion process. The following errors are taken into account:

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

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

Legend: X = any

### Codesys

InOut:

| Scope  | Name            | Type   | Initial | Comment                                                                                      |
| ------ | --------------- | ------ | ------- | -------------------------------------------------------------------------------------------- |
| Return | `TwoPointFun`   | `REAL` |         |                                                                                              |
| Input  | `rIn_X`         | `REAL` |         | Analog value input                                                                           |
| Input  | `rX1`           | `REAL` | 0       | Point 1 of the input range                                                                   |
| Input  | `rX2`           | `REAL` | 100     | Point 2 of the input range                                                                   |
| Input  | `rY1`           | `REAL` | 0       | Point 1 of the output characteristic                                                         |
| Input  | `rY2`           | `REAL` | 100     | Point 2 of the output characteristic                                                         |
| Input  | `xMinMaxLimit`  | `BOOL` |         | Enable / disable limiting at the analog value output                                         |
| Input  | `iMinMaxOffset` | `INT`  |         | Limit values at the analog value output                                                      |
| Output | `xErr`          | `BOOL` |         | <p>FALSE: Conversion error-free<br><br><br>TRUE: Error during conversion process<br><br></p> |


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