Quadratherm 640i and 780i – Sierra Thermal Mass Flowmeter

Industry’s Most Accurate Air / Gas Thermal Insertion Mass Flow Meters

The QuadraTherm® 640i is the most accurate insertion-probe thermal mass flow meter for air / gas mass flow rate measurement on the market today, achieving gas mass flow rate accuracy never before possible, +/- 0.75% of reading above 50% of full scale. The QuadraTherm 640i air / gas mass flow meter marks an accuracy breakthrough in thermal dispersion technology achieving extreme precision with “percent of reading” accuracy, which for the first time rivals accuracies of Coriolis technology for measuring mass air flow rate and other gases.

Each QuadraTherm thermal flow meter comes with onboard qMix(tm) gas mixing software which allows you to create custom gas mixtures in the field to compensate for gas compositional changes-no costly recalibration needed. Perfect for managing changes in flare gas composition in the field for upstream oil & gas flare gas measuring applications and other applications in which gas composition frequently changes.


  • Achieve high accuracy +/- 0.75% of reading
  • Eliminate drift with patented DrySense™ sensor
  • Validate in the field for easy in-situ calibration
  • Use qMix software to easily change gas composition in the field and retain accuracy Download Flare Gas Mass Measuring Tech Note
  • Backed by lifetime sensor warranty
  • Part of Sierra’s Big-3 iSeries family of flow meter technologies

Product Benefits

  • Patented breakthrough QuadraTherm “Quad” 4-Sensor thermal sensor technology
  • Patented zero drift DrySense™ velocity sensor
  • Lifetime warranty on sensor
  • “Percent of reading” accuracy, which for the first time rivals accuracies of Coriolis technology
  • Sierra’s state-of-the-art ISO 9000 closed-loop calibration facility matches each application for best accuracy
  • Greenhouse Gas (GHG) certified to meet EPA (40 CFR Part 98)
  • Ideal for high accuracy applications like custody transfer, wastewater treatment, hazardous areas, facilities management and general process control applications
  • Built-in flow conditioning elements drastically reduce upstream straight-run requirements
  • Features our proprietary Raptor OS operating system (formerly known as qTherm)
  • ValidCal™ Diagnostics: Field calibration validation and meter diagnostics to assure operating performance.
  • Multivariable outputs – gas mass flow rate, temperature and pressure
  • Total of four gases onboard; capability to change gas (Dial-A-Gas) in the field; Download Flare Gas Mass Measuring Tech Note
  • Capability to change pipe size (Dial-A-Pipe®) in the field
  • Unique multi-gas flow totalizer and alarms
  • High flows up to 60,000 sfpm (305 smps)
  • Range of process connections
  • Very low pressure drop
  • No moving parts
  • Free computer interface software
  • Free Raptor software to create custom gases or mixtures to compensate for compositional changes; upload mixtures to the unit in the field
  • Connected to the most up-to-date gases in our proprietary Raptor Gas Library, update the instrument via the web
  • An insertion version for pipes/ducts up to 72 inches (2 m) available – Model 640i
  • Large LCD display and pushbutton interface, remote enclosure mounting available
  • Multi-language display interface: English, German, Chinese, Spanish, Dutch

Quadratherm Overview and datasheet – PDF