Description
Original instructions
Function description
The function block MFLOW calculates the mass flow of a gas in a throttle device resulting from the differential pressure and the temperature and pressure conditions of the gas.
The measure of the differential pressure can be replaced by the speed of the medium or with another measure with pressure and temperature compensation.
EN and ENO can be configured as additional parameters.
Formula
The full equation (i.e. with en_sqrt = 1, en_pres = 1 and en_temp =1) says as follows:
Meaning of the sizes
Variable
Meaning
SV
Gas pressure in absolute units
TA
Absolute gas temperature in Kelvin
Representation in FBD
Representation:
Representation in LD
Representation:
Representation in IL
Representation:
CAL MFLOW_Instance (IN:=DifferentialPressure, 
    PRES:=GasPressure, TEMP:=GasTemperature, 
    PARA:=Parameters, OUT=>ValueOfMassFlowRate, 
    STATUS=>StatusWord)
Representation in ST
Representation:
MFLOW_Instance (IN:=DifferentialPressure, 
    PRES:=GasPressure, TEMP:=GasTemperature, 
    PARA:=Parameters, OUT=>ValueOfMassFlowRate, 
    STATUS=>StatusWord) ;
Parameter description MFLOW
Input parameter description:
Parameter
Data type
Differential pressure (or other measure)
IN
Input
PRES
REAL
Absolute or relative gas pressure
TEMP
REAL
Gas temperature printed out in °C or °F
PARA
Parameter
Output parameter description:
Parameter
Data type
Differential pressure (or other measure)
OUT
REAL
Value of the mass flow, with temperature and pressure correction
STATUS
Status word
Parameter description Para_MFLOW
Data structure description
Element
Data type
Meaning
k
Calculating constants (see Calculation of the constant k
en_pres
"1": Activate the pressure correction
pr_pa
BOOL
"1": PRES is an absolute pressure
"0": PRES is a relative pressure
pu
REAL
Value, which in the used pressure unit 1  displays atmosphere
en_temp
BOOL
"1": Activate the temperature correction
tc_tf
BOOL
"1": TEMP will be expressed in degrees Fahrenheit
"0": TEMP will be expressed in degrees Celsius
en_sqrt
BOOL
"1": Calculation with Square Root