Specifications

Chapter 1 - AsconACLib
33
1-3-25 HR_DRY_WET_BULB
FB Prototype HR_DRY_WET_BULB
Input parameters
Output parameters
Description This function block performs the Relative Humidity (HR) calculation by using the
dry and wet bulb method. The calculation consider the difference of temperature
between the TEMP_DRY and TEMP_WET valid input values which means they
have to be inside the range defined by LOW_LIM HIGH_LIM parameters,
otherwise they will be not computed. The calculation take care also about the
atmospheric pressure in order to perform the right compensation. The function
block returns also some other information used in the calculation like the saturation
pressure for both the temperature values and the steam partial pressure.
Default Values Table
Input Type Description Range
ENABLE BOOL Command to enable calculation
SEL_C_F BOOL
Temperature engineering unit
[°C or °F]
TEMP_DRY REAL
Dry bulb temperature input value
[°C or F]
LOW_LIM... HIGH_LIM
TEMP_WET REAL
Wet bulb temperature input value
[°C or F]
LOW_LIM... HIGH_LIM
P_ATM REAL Atmospheric pressure [kPa] 0.0... 1000.0
HIGH_LIM REAL
High limit for the AI channel value
[e.u.]
-3.4E-38... 3.4E
+38
LOW_LIM REAL
Low limit for the AI channel value
[e.u.]
-3.4E
-38
... 3.4E
+38
Output Type Description Range
ERROR BOOL Error status
ERR_CODE DWORD Error code [bit mask]
16#00 00 00 00…
16#FF FF FF FF)
HR_VALUE REAL
Relative Humidity calculated value [%] 0.0... 100.0
PSAT_DRY REAL
Water vapour dry bulb Saturation
Pressure calculated value [Pa]
-3.4E
-38
... 3.4E
+38
PSAT_WET REAL
Water vapour wet bulb Saturation
Pressure calculated value [Pa]
-3.4E
-38
... 3.4E
+38
ST_PART_P REAL
Steam Partial Pressure calculated
value [Pa]
-3.4E
-38
... 3.4E
+38
ENABLE
SEL_C_F
TEMP_DRY
TEMP_WET
P_ATM
HIGH_LIM
LOW_LIM
BOOL
BOOL
REAL
REAL
REAL
REAL
REAL
¡
¡
¡
¡
¡
¡
¡
BOOL
DWORD
REAL
REAL
REAL
REAL
ERROR
ERR_CODE
HR_VALUE
PSAT_DRY
PSAT_WET
ST_PART_P
¡
¡
¡
¡
¡
¡
Input Default Value
ENABLE FALSE
SEL_C_F FALSE = °C Degrees
TEMP_DRY 25.0