Core Process Variable: Specific Gravity, Molecular Weight, Or Relative Density; Two-Point Calibration Vs. Three-Point Calibration; Calibration Gases - Emerson Micro Motion SGM Series Configuration And Use Manual

Purging and calibration
5.2.1 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
5.2.2

Two-point calibration vs. three-point calibration

Your choice of two-point calibration or three-point calibration depends on your process
gas.
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A two-point calibration produces two calibration factors: K0 and K2. K1 is set to 0.
A three-point calibration produces three calibration factors: K0, K1, and K2.
5.2.3

Calibration gases

For a two-point calibration, you need two calibration gases. For a three-point calibration,
you need three calibration gases. The calibration gases should match the main
constituents of your process gas.
You can use the calibration gases in their pure forms or at defined specific gravities. If you
cannot match the process gas exactly, select calibration gases that match its
characteristics, especially its compressibility characteristics.
Tip
For the highest measurement accuracy, use calibration gases in their pure form. This avoids issues
with stratification and other inconsistencies in the calibration gas.
During the calibration, you will be required to enter data for each calibration gas:
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Core process variable and available gas process variables
Core process variable, gas process variables, and required data
Two-point calibrations are typically used for process gases with two main
constituents.
Three-point calibrations are typically used for process gases with three main
constituents.
If the SGM is operating as a specific gravity meter, you must enter the specific
gravity of the gas.
If the SGM is operating as a relative density meter, you must enter the relative
density of the calibration gas.
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Micro Motion Gas Specific Gravity Meters (SGM)