Sierra Instruments, Inc.

- Model 640i - 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 on board 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 fequently changes. Learn more.

Boiler MACT Certified

The QuadraTherm thermal mass flow meter is also ideal for compliance for Boiler MACT regulations for inlet fuel measurements for area source boilers (40 CFR 63, subpart JJJJJJ) and for major source boilers (40 CFR 63, subpart DDDDD). Learn

The QuadraTherm air mass flow meter features a patented four-sensor design--three precision platinum temperature sensors and one patented DrySense mass velocity sensor. This allows for precision air and gas flow measurement. Available in either an insertion version or inline version, this mass flow meter includes Sierra's proprietary Raptor OS operating system.

QuadraTherm's four-sensor technology provides the critical inputs for Raptor's living, learning algorithm set and gas database that accurately manages changes in gas and pipe selection, gas temperature, gas pressure and outside temperature. Also easily change gas composition in the field while retaining accuracy with qMix software.

Mass Air Flow Meter Operating Principle: Thermal dispersion technology provides direct mass air flow measurement featuring no pressure or temperature compensation needed; no moving parts; low pressure drop; and high turndown.

  • 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
  • Backed by lifetime sensor warranty
  • Boiler MACT certified for area source boilers (40 CFR 63, subpart JJJJJJ) and for major source boilers (40 CFR 63, subpart DDDDD)
  • Part of Sierra's Big-3 iSeries family of flow meter technologies

  • Patented breakthrough '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 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)
  • Optimized (CH4) as well as N20, SF6, HFCs, PFCs and CO2, per the EPA mandate
  • Ideal for high-accuracy applications like custody transfer, wastewater treatment, hazardous areas, facilities management and general process control applications
  • 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
  • Free qMix™ software to create custom gases or mixtures to compensate for compositional changes; upload mixtures to the unit in the field 
  • Capability to change pipe size (Dial-A-Pipe) in the field
  • Unique multi-gas flow totalizer and alarmsHigh flows up to 60,000 scfm (305 smps)
  • Small-diameter, 3/4-inch (19.1 mm) sensor probe
  • Pipe/duct sizes up to 72' (2M)
  • Low and high pressure hot tap
  • An inline flow conditioned version is also available - Model 780i
  • Very low pressure drop
  • No moving parts
  • Free computer interface software
  • Connected to the most up-to-date gases in our proprietary Raptor Gas Library, update the instrument via the web
  • Large LCD display and pushbutton interface, remote enclosure mounting available
  • Multi-language display interface: English, German, Chinese, Spanish, Dutch
  • Certified for Boiler MACT measurement meeting EPA regulations for area source boilers (40 CFR 63, subpart JJJJJJ) and for major source boilers (40 CFR 63, subpart DDDDD)

  • Accuracy: +/- 0.75% of reading above 50% of full scale*
  • Repeatability: +/- 0.15% of full scale 
  • Flow range 0 to 60,000 sfpm (0 to 305 smps) 
  • Turndown 100:1
  • Measure all inert gases and all non-condensing clean gases
  • Flammable gases: methane, propane, hydrogen, digester gas, natural gas
  • Corrosive gases compatible with 316L stainless steel
  • Gas/ambient temperature: -40°F to 392°F (-40°C to 200°C)
  • 1-inch (25.4 mm) diameter protective sensor shield option for improved sensor protection. Learn more.

*Verified by an independent NIST & NVLAP accredited lab

  • Response time is three seconds to achieve 63% (one time constant) of final value
  • Power supply: 100 to 240 VAC (0.4 Amps RMS at 230 VAC); 24 VDC +/- 10%, 1 Amp
  • 316 stainless steel construction
  • Output signals: RS-232, 4 to 20 mA flow, 4 to 20 mA temperature, 4 to 20 mA pressure (optional)
  • Alarm output (contact SPST/opto relays)
  • User definable pulse output for totalized flow
  • Digital communications: Foundation Fieldbus,HART, Modbus RTU, and Profibus DP
  • Hazardous-Area Location Enclosure (IP66)
  • Approvals:
    • cFMus–Explosion proof for Class I, Div I, Groups B,C,D
    • ATEX
    • IECEx
    • GOST R
    • Chinese Pattern
    • CE–European Conformity