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Part 3: Biogas Flow Meter Measurement-The Solution


Sep 16, 2013

In recent weeks, I’ve shared some exciting advancements in the biogas industry in regards to renewable energy management. From harnessing biogas energy from landfills to the digester gas produced at wastewater treatment plants, one thing is paramount: Adjusting for changing gas composition is critical to obtaining accurate flow meter measurement for optimal biogas energy collection.  Many flow meter companies want to play in this growing market, but few can solve the inherent problem: How can the flow meter automatically adjust for changing gas compositions without recalibration? In this final biogas post, I’ll share how Sierra’s innovative flow meter design has revolutionized the biogas industry, making the need for constant recalibration a thing of the past—thanks to a design that maximizes four sensors instead of two.

The Solution: Flow Meter Technology for Changing Compositions


Sierra’s four-sensor QuadraTherm technology has moved thermal insertion flow meter technology into a realm of unprecedented accuracy. Readings of +/-0.75% of reading are now possible as opposed to the 2.0% readings of older thermal technologies.

QuadraTherm Thermal Flow Meter

Along with this new 4-sensor technology, traditional analog measurement circuits, like the Wheatstone bridge, have been superseded by more powerful, hyper-fast microprocessors that run comprehensive flow-measurement algorithms to compute mass flow. This proprietary algorithm set serves as the “brain” of the mass flow meter, using inputs from the 4 sensors, to solve the first law of thermodynamics for the sensor in the biogas flow stream, allowing precise calculation of heat convected away by biogas mass flow; providing accurate mass flow measurements in a fraction of a second. This algorithm allows management of gas composition because now recalibration is not required every time the gas changes.

Powerful Flow Meter Combination


By combining four-sensor technology with this algorithm set, the meter has the capability to change gas and compositions without losing accuracy. This new technology creates many benefits:


  • The meter can hold up to four user customizable gas mixtures onboard and store biogas composition in a proprietary gas library, easily accessed through user software.

  • Engineers and operators have access to this gas library, which contains all the gas properties needed to make algorithmic gas mass flow rate calculations.


Once sampling has determined the biogas composition, operators can use a simple software tool to create and name a proprietary biogas mixture. This allows operators and engineers to use just one meter, with one calibration for varying gas compositions, offering a major cost savings compared to continuous sampling devices.

Four-sensor thermal technology: Highly adaptable

The 4-sensor quadratherm mass flow meter pictured in  meets the criteria for successful biogas measurement by managing changes in:


  • Gas composition

  • Gas mass flow rate

  • Gas temperature

  • Gas pressure

  • Outside temperature

  • Pipe conditions (size and roughness)

  • Flow profile


These changing conditions can all be managed with accurate readings without sending the flow meter back to the factory for recalibration, reducing downtime and saving money. Traditional two-sensor thermal flow meters need to be sent back to the factory for recalibration each time the gas composition changes or the application specification changes. This means that during the lifetime of the product, thousands of dollars will be saved in calibration costs, shut downs and loss of gas monetization through loss of accuracy.

The result is Sierra’s QuadraTherm Series of mass flow meters, perfect for successful biogas measurement in any environment. Tell us in the comments below. And be sure to read our free white paper download on Precise Biogas Measurement.

How have you solved the problem of precise biogas measurement with changing gas composition?

Scott Rouse, Product Line Director
Written By:
Scott Rouse, Product Line Director
Sierra Instruments

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