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

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 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