A major European gas manufacturer now specifies Sierra's Model 780S for natural gas flow measurement to their power generators. Previous generations of burner control systems had utilized three different technologies: a rotameter with integrated microprocessor to calculate density, a turbine meter with a fixed correction factor, and a thermal mass flow meter. The rotameter's poor rangeability (1:3) and fixed temperature and pressure calculations resulted in poor measurement accuracy. The turbine meter had similar problems, and was too costly. The thermal meter gave them a more accurate reading of mass flow, but it did not provide a method for field-configuration.
When the manufacturer first tested Sierra's Model 780S they compared it to their existing thermal meter and reported a reading error of approximately 10%. An investigation of the test conditions revealed that the competitive unit had been calibrated with air, and was scaled and linearized with a correlation based on a natural gas density of 90% methane. The manufacturer's actual gas was 96% methane, and the Sierra meter had been calibrated with this specified mixture. This demonstration convinced the manufacturer that proper calibration was the key to accurate measurement.
They have also found that the Model 780S field-configuration capability allows them to apply a correction factor to the device for a change in the natural gas mixture. This ability to "tune" combustion ratios significantly affects generator performance.
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