WetBulbTemperature

WetBulbTemperature (FB)

FUNCTION_BLOCK WetBulbTemperature

Short description

Calculation of the wet-bulb temperature in degrees Celsius Quantities: temperature, relative humidity Typical application: calculation of the wet-bulb temperature for adiabatic cooling

Representation

Interfaces

Inputs

Name	Data type	Value range	Initial value	Function
rTemperature	REAL	-20.0 to +50.0	0	Temperature in degrees Celsius
rRelativeHumidity	REAL	5.0 to 99.0	5	Relative humidity in percent

Outputs

Name	Data type	Value range	Initial value	Function
rWetBulbTemperature	REAL		0.0	Wet-bulb temperature in °C (error: +/- 1.0 percent in the specified temperature/humidity range)
xError	BOOL		FALSE	Output for indicating error states (TRUE = error)
sErrorCode	STRING		‘’	Output for indicating error messages

Function description

General

This function block is used to calculate the wet-bulb temperature in degrees Celsius. For this purpose, the current values of air temperature in degrees Celsius and relative humidity in percent must be provided.

Temperature range in degrees Celsius rTemperature

The temperature in degrees Celsius may only take values between -20.0 and +50.0 degrees Celsius (inclusive). Values outside this range generate an error state ('xError' = TRUE) and a corresponding error message ('xErrorCode'). No calculation of the wet-bulb temperature is performed.

Relative humidity range in percent rRelativeHumidity

The relative humidity in percent may only take values between +5.0 and +99.0 percent (inclusive). Values outside this range generate an error state ('xError' = TRUE) and a corresponding error message ('xErrorCode'). No calculation of the wet-bulb temperature is performed.

Output for indicating error states xError

This output is used to indicate error states (= TRUE):

1. Temperature outside the allowable range of temperature in degrees Celsius rTemperature

2. Relative humidity outside the allowable range of relative humidity in percent rRelHumidity

3. Wet-bulb temperature 'rWetBulbTemperature' > temperature 'rTemperature'

4. Wet-bulb temperature 'rWetBulbTemperature' < (temperature 'rTemperature' - 50.0)

In all other situations the output is not active (= FALSE).

Output for indicating error messages sErrorCode

This output is used to display context-dependent error messages in plain text.

CODESYS

InOut:

Scope	Name	Type	Initial
Input	rTemperature	REAL	0
Input	rRelativeHumidity	REAL	5.0
Output	rWetBulbTemperature	REAL	0
Output	xError	BOOL	FALSE
Output	sErrorCode	STRING(255)	‘’