Emerson Micro Motion SGM - Equations Used to Calculate Specific Gravity, Molecular Weight, and Relative Density

Table 2-3: Gas measurement when the primary process variable is molecular weight (continued)
Process variable to be reported
Process data provided
by the SGM
Required process data
from external devices
Required user-
specified values
Energy Flow
Mass units
Line density
Calorific value
Mass flow rate (direct
input or calculated)
Volume units Calorific value
Volume flow rate
(direct input or
calculated)
(1) Used when you want process variables to represent the gas in the measurement chamber.
(2) Used when you want process variables to represent the gas at the location of the temperature probe.
Table 2-4: Gas measurement when the primary process variable is relative density
Process variable to be reported
Process data provided
by the SGM
Required process data
from external devices
Required user-
specified values
Relative density Relative density
Base density Relative density Base density of air
Line density
Temperature data from
meter (RTD)
(1)
Base density
Line compressibility
Base compressibility
External temperature
(2)
Line pressure
Base temperature
Base pressure
Line compressibility
Temperature data from
meter (RTD)
(1)
Relative density
External temperature
(2)
Line pressure
% CO2
% H2
% N2
Base compressibility Relative density
% CO2
% H2
% N2
Base temperature
Base pressure
(1) Used when you want process variables to represent the gas in the measurement chamber.
(2) Used when you want process variables to represent the gas at the location of the temperature probe.
2.4 Equations used to calculate specific gravity,
molecular weight, and relative density
2.4.1 Primary process variable = specific gravity
The following equations are used when the primary process variable is specific gravity.
Specific gravity
SG = K0 + K1 × τ + K2 × τ
2
SG
Specific gravity of process gas
Orientation and planning Configuration and Use Manual
March 2021 MMI-20020954
18 Micro Motion Gas Specific Gravity Meters (SGM)