> 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-library/functionblocks/monitoring/airflowmeasuring.md).

# AirFlowMeasuring

## `AirFlowMeasuring` (FB)

FUNCTION\_BLOCK AirFlowMeasuring

### Short description

> Calculation of the current volumetric flow via an annular measuring nozzle\
> Typical application: calculation of the current volumetric flow of a fan

### Representation

<figure><img src="/files/10845191c8f20cb4e28ea320ecb2c1df1ee04ed1" alt=""><figcaption></figcaption></figure>

### Function description

#### General

This function block is used to calculate the current volumetric flow of a fan based on the pressure difference that is continuously measured by a measuring device (= annular measuring nozzle).

> **Detection of the current air density&#x20;*****rDensity***
>
> For calculations with reduced accuracy, specifying a constant is sufficient.\
> For calculations with increased accuracy, the air density must be calculated depending on the current temperature, the relative humidity, the air pressure and the saturation vapor pressure.\
> If the current value for air density falls below 0.1 kg/m³, it is limited to 0.1 kg/m³.

#### Selection of the calculation formula **eMode**

This setpoint / parameter is used to select the underlying calculation formula. The calculation formula and the **k\_Value** must always be requested from the fan manufacturer specifically for the plant.

| **eMode**                         | Formula                                                                                                      | Notes                                          |
| --------------------------------- | ------------------------------------------------------------------------------------------------------------ | ---------------------------------------------- |
| eAirFlowFormula.exclusiveAirtight | rOut = **k\_Value** multiplied by the square root of *rPressure*                                             | Manufacturer: e.g. EBM-Papst, Ziehl-Abegg      |
| eAirFlowFormula.inclusiveAirtight | rOut = **k\_Value** multiplied by the square root of ((2 multiplied by *rPressure*) divided by (*rDensity*)) | Manufacturer: e.g. Rosenberg, Gebhardt Nicotra |
| eAirFlowFormula.strangeForm       | Placeholder for extensions                                                                                   | *rOut* = 0.0 constant                          |

#### Calculation factor **k\_Value**

This setpoint / parameter is used to enter the calculation factor. The calculation formula and the **k\_Value** must always be requested from the fan manufacturer specifically for the plant.

### CODESYS

InOut:

| Scope       | Name        | Type            | Initial                           |
| ----------- | ----------- | --------------- | --------------------------------- |
| Input       | `rPressure` | `REAL`          |                                   |
| Input       | `rDensity`  | `REAL`          | 1.2                               |
| Output      | `rOut`      | `REAL`          |                                   |
| Input Const | `k_Value`   | `REAL`          | 200                               |
| Input Const | `eMode`     | eAirFlowFormula | eAirFlowFormula.exclusiveAirtight |


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