Emerson Micro Motion SGM Configuration And Use Manual page 28

Purging and calibration
March 2021
5.2.2 Two-point calibration vs. three-point calibration
Your choice of two-point calibration or three-point calibration depends on how many process gases you are
using.
Two-point Two gases are used for calibration. Standard and most common applications require
calibration only two calibration points to get the best accuracy. A two-point calibration produces
two calibration factors: K0 and K2. K1 is set to 0.
Three-point Three gases are used for calibration. Three-point calibrations are less common. For
calibration more information, see
Related information
Three-point calibration
5.2.3 Calibration gases
The calibration gases should match the main constituents of your process gas. The gases must cover the
lower and upper SG/MW range of the process gas and have similar compressibility characteristics.
Gas types and requirements
Analytical calibration gases are specified by purity grade or number of 9's. "High purity" or "4.5 nines
(99.995%)" grades are good choices for calibrating the SGM.
For example, if the SGM is measuring the specific gravity of natural gas, use pure nitrogen and pure methane
as calibration gases.
Table 5-1: Examples of calibration gases
Application
Natural gas
Hydrogen purity
Fuel to air ratio
Equipment requirements
• Cylinders must have a gauge regulator and hose.
• The hose needs to have a 0.25 in (6.4 mm) Swagelok
• The minimum gas bottle size for each of the calibration gases should be no less than 4.5 gallons (17 liters)
at a 20% higher of nominal pressure at the outlet of the regulator depending on the application.
Most gas suppliers can provide these items.
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Three-point calibration.
Two-point calibration gases
Methane and nitrogen
Hydrogen and nitrogen
Methane and propane
®
female connector.
Micro Motion Gas Specific Gravity Meters (SGM)
Configuration and Use Manual
MMI-20020954