Given that biogas composition may change from time to time, and thermal mass flow meters are calibrated to a specific mixture of methane and carbon dioxide, Sage provides correction factors for the user to apply if there are variations from the original calibration.

Biogas Correction Factors

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Sage Metering can calibrate our meters for any digester gas, landfill gas, or biogas mix. However, it may be useful to have correction factors for a typical calibration, if the gas composition changes. The following correction factors assume that the initial calibration was set up for 60% methane (CH4) and 40% carbon dioxide (CO2):

    • 65% CH4 and 35% CO2 – Multiply the reading by 0.982 to correct for a new composition
    • 70% CH4 and 30% CO2 – Multiply the reading by 0.965 to adjust for a new composition
      Angling the thermal mass flow sensor in the pipe
      Tilt the enclosure 45 degrees (forward or backward) for applications where condensation may develop on inside the walls of the pipe.
    • 55% CH4 and 45% CO2 -Multiply the reading by 1.0185 to correct for a new composition

If there are less significant changes than the above examples, the corrections are linear in between stated cases.

Water vapor correction is also linear between the following examples:

    • 100% saturated with H2O vapor (non-condensing) – multiply the readings by 1.042
    • 50% saturated with water – multiply the reading by 1.021

Also, mount the sensor 45-degrees to avoid droplets hitting the sensor and causing spikes (see the illustration).

How to Overcome 9 Thermal Mass Flow Meter Limitations

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