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Tuning Combustion Ratios in the Field

FlatTrak 780S Thermal Inline Mass Flow Meter

For a major European gas manufacturer, the burner control systems in their power generators had long relied on three different technologies for natural gas mass flow measurement. These included a rotameter with integrated microprocessor to calculate Burner Control 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 they first tested Sierra's FlatTrak™ 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 780S 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 field-configuration capability of the 780S 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 improves generator performance.

Here’s what makes Sierra’s FlatTrak 780S an ideal choice:
  • Measures mass flow directly with one meter
  • 100:1 turndown for accurate monitoring of peak and low flow situations
  • In-line flow conditioning eliminates piping straight-run requirements
  • Removable probe for easy cleaning
  • Generates minimal pressure drop across the instrument