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 during 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. \

Value range of the temperature in degrees Celsius rTemperature

The temperature in degrees Celsius may only take values between -20.0 and +50.0 degrees Celsius (inclusive). Values outside the range generate an error state (‘xError’ = TRUE) and an associated error message (‘xErrorCode’). No calculation of the wet-bulb temperature takes place.\

Value range of the relative humidity in percent rRelativeHumidity

The relative humidity in percent may only take values between +5.0 and +99.0 percent (inclusive). Values outside the range generate an error state (‘xError’ = TRUE) and an associated error message (‘xErrorCode’). No calculation of the wet-bulb temperature takes place.\

Output for indicating error states xError

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

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

2. Relative humidity outside the value range of the 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)	‘’