Description

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.

and 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	REAL	Input
PRES	REAL	Absolute or relative gas pressure
TEMP	REAL	Gas temperature printed out in °C or °F
PARA	Para_MFLOW	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	WORD	Status word

Parameter description Para_MFLOW

Data structure description

Element	Data type	Meaning
k	REAL	Calculating constants (see Calculation of the constant k
en_pres	BOOL	"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

Base	Lower limit	Upper limit
Hexadecimal	16#0	16#FFFF
Octal	8#0	8#177777
Binary	2#0	2#1111111111111111

Data	Representation in one of the bases
0000000011010011	16#D3
1010101010101010	8#125252
0000000011010011	2#11010011

REAL

The REAL type is encoded in a 32 bit format.

The possible value ranges are shown in the figure below:

When a result is:

between -1,175494e-38 and 1,175494e-38, it is considered to be a DEN;
less than -3.402824e+38, the symbol -INF (for - infinity) is displayed;
greater than +3.402824e+38, the symbol INF (for + infinity) is displayed;
undefined (square root of a negative number), the symbolNAN is displayed.

NOTE: The IEC 559 standard defines two classes of NAN: the silent NAN (QNAN) and the signaling NAN (SNAN). A QNAN is a NAN with a most significant fraction bit while an SNAN is a NAN without a most significant fraction bit (bit number 22). QNANs can be propagated via most arithmetic operations without throwing an exception. As for SNANs, they generally indicate n invalid operation when they are used as operands in arithmetic operations (see %SW17 and %S18).

NOTE: When a DEN (non-standardized number) is used as an operand, the result is not significant.