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Flow-X─ Function Reference
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Flow-X General functions - fxSGERG_C
fxSGERG_C
Description
This function performs the SGERG calculation in USC units.
The Standard (or Simplified) GERG TM5 1991 Virial Equation (SGERG or SGERG-88) has defines a
method to calculate the Compressibility Factor (Z) for Natural Gases. The SGERG calculation is
equivalent to the AGA8 Gross Characterisation Method, however .the results are slightly different
Instead of the full compositional analysis (as used by the AGA 8 Detailed Characterization method), the
Gross Characterisation Method (SGERG) uses a restricted set of input variables for its equation,
comprising Relative Density, Superior Calorific Value, Carbon Dioxide and Nitrogen together with
pressure and temperature.
Compliance

GERG Technical Monograph 5, Standard GERG Virial Equation, 1991
Boundaries
The standard specifies a maximum uncertainty of the compressibility factor of 0.1% provided the inputs
lie in the following range.
Pressure 0 .. 1740 psi(a)
Temperature 17 .. 143 °F
Gross heating value 509 .. 1288 Btu/ft3
Relative density 0.55 .. 0.90 -
Carbon dioxide 0.00 .. 0.30 mol/mol
Nitrogen 0.00 .. 0.50 mol/mol
Hydrogen 0.00 .. 0.10 mol/mol
Function inputs and outputs
Function inputs Remark EU Range Default
Name Optional tag name, tag description and
tag group
Pressure Observed pressure psia 0..30000
Temperature Observed temperature °F -250
..500 0
Relative density At the reference conditions according to
input 'Reference conditions' - 0..2 0
Gross heating value At the combustion and reference
conditions according to input 'Reference
conditions' Btu/ft3 0..2500 0
Nitrogen mol/mol 0..1 0
Carbon dioxide mol/mol 0..1 0
Hydrogen mol/mol 0..1 0
Method Calculation method:
1: All inputs are known
2: Unknown Nitrogen mole fraction
3: Unknown Carbon Dioxide mole fraction
4: Unknown Gross Heating Value
5: Unknown Relative Density - 0
Reference conditions Reference conditions that correspond
with the values of inputs 'Relative density'
and 'Gross heating value'.
Combustion temp. / metering temp. / 1