Dresser Model 10C25 Series K Installation, Operation, and Maintenance Manual
© 2018 Natural Gas Solutions North America, LLC
Page 58 of 74
14.1
Establishing Baseline Curves
Developing an original differential baseline curve is recommended when the meter is first installed.
Because any change in flow rate, line pressure, or specific gravity causes a change in the differential, at
least three (3) test points are required at gas flow rates from 25% to 100% of meter capacity. As shown in
Figure 76, the resulting points will be non-linear, so a minimum of three (3) points is necessary to
establish a curve. Plot the points on a graph, and then connect the points to form a curve. This method
provides an accurate baseline for comparison to later tests.
Figure 76: Differential curves change as pressure increases
To help with record keeping, a data chart like the one shown in Table 17 and provided in Appendix B
allows the technician to compare new test data to older data. A test under actual operating conditions
provides
the most reliable data for future checks of a meter’s operating condition. This is particularly
important when the line pressure is higher than 15 psig (200 kPa Absolute). Because meter differential
pressure increases with line pressure, multiple curves may be necessary for meters under varying line
pressure conditions.
Table 17: Sample Data Chart for Detailed Meter History of Differential Rate Tests
Differential
–
Rate Test Data
–
Sample Sheet
Meter Model:
Mfg. Serial No.:
Utility Serial No.:
Location:
Date Installed:
Register Reading:
Line
Pressure
Gas
Temp
Specific
Gravity
Volume
Measured
Run
Time
Rate (ft
3
)
Differential Pressure
Date
Tester
w.c.
% Change
Initial Tests
–
New Meter
