Terms used in meter setup and measurement (continued)Table 2-1:
Term Definition or usage
Wobbe index The ratio of the calorific value of a gas to its specific gravity. Measured in volu-
metric units (BTU/SCF, and MJ/SCM).
2.3 Core process variable: Specific gravity,
molecular weight, or relative density
The SGM can operate as a specific gravity meter, a molecular weight meter, or a relative
density meter. This represents the core process variable that gas process data is based on.
Your choice determines the set of process variables that the meter can report, the
methods used to measure and calculate them, and the data that you must supply during
setup and configuration.
The core process variable – specific gravity, molecular weight, or relative density – was
specified as part of the order. However, you can change it during calibration.
Related information
Core process variable and available gas process variables
Core process variable, gas process variables, and required data
2.3.1
Core process variable and available gas process variables
The gas process variables that the SGM can report are determined by the core process
variable that you select during calibration.
Core process variable and available process variablesTable 2-2:
Available process variables
Default measure-
ment unit
Core process variable
Specific gravity Molecular weight Relative density
Specific gravity Unitless ✓ ✓
Molecular weight g/mol ✓ ✓
Relative density Unitless ✓
Base density g/cm³ ✓ ✓ ✓
Line density g/cm³ ✓ ✓ ✓
Line compressibility Unitless ✓ ✓ ✓
Base compressibility Unitless ✓ ✓ ✓
Calorific value MJ/m³ ✓ ✓
Wobbe index MJ/m³ ✓ ✓
Energy flow MJ/hr ✓ ✓
Orientation and planning
8 Micro Motion
®
Gas Specific Gravity Meters (SGM)
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