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3098 Technical Manual Installation Procedure
2-3
The graph below gives an indication of the typical errors associated with using different reference chamber pressures for
natural gas with a reasonably constant specific gravity (in the range of 0.55-0.8). This is typical for natural gas metering
market, where the gas is available at a line pressure of 7 Bar abs.
As can be seen, below 7 Bar abs, the total error begins to increase; using a higher reference pressure will not improve
accuracy, but may encourage gas leakage. Therefore, for the conditions specified, 7 Bar is the recommended pressure.
Typical Total Error/°C vs Reference Chamber Pressure
For NATURAL GAS APPLICATIONS ONLY.
-0.035
-0.025
-0.015
-0.005
0.005
0.015
0.025
0.035
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10
Reference Chamber Pressure (Bar A)
Typ % of FS Specific Gravity /°C
-0.035
-0.025
-0.015
-0.005
0.005
0.015
0.025
0.035
Typ % of FS Specific Gravity /°C
This graph should only be used for natural gas applications, and.gives typical errors seen on the 3098 if it is not used at
the recommended reference chamber pressure.
If the span of specific gravity or change in supercompressibility, Z, is large, and the gas is not a methane/nitrogen mix,
then the best reference chamber pressure can still be determined. The calculation for doing this is explained in Chapter 4,
‘Accuracy Considerations’.
Once the desired reference pressure has been found, the 3098 can now be purge cycled and then calibrated.