About Us

After more than 20 years of manufacturing thermal gas mass flowmeters, Fox Thermal Instruments continues to lead the market in innovative, reliable, accurate, and full-featured flow meters. Our exceptional team of mechanical, electronic, and software engineers have helped to shape the thermal mass flow measurement industry.

Our goal is to serve a broad array of global customers by consistently providing high quality, cost effective solutions to our customers, with superior performance and outstanding on-time delivery.

Fox Facility

The 19,000 ft² Fox manufacturing facility houses administrative offices, a certified weld shop, an assembly work shop, and several state-of-the-art calibration labs. Our highly-trained staff ensures efficient, high-quality production and helps us maintain our technology and quality leadership position in the thermal mass flowmeter industry.

In an effort to improve delivery time, meet surge demands from our customers, and continue to manufacture on-shore, Fox continually upgrades our facility and systems.

Our Technology - How it Works

All thermal Gas Mass Flow Meters from Fox utilize the thermal sensing principle, a proven, accurate direct mass flow measurement technology. This technology performs at high levels of accuracy for a wide variety of gases.

Fox Thermal Flow Meters use a constant temperature differential (constant Δ T) technology to measure mass flow rate of air and gases. Fox Models FT2A and FT3 are equipped with the PowerPro™ Sensor while the Model FT1 has the DDC-Sensor™. Both thermal mass flow sensors consist of two Resistance Temperature Detectors (RTD’s). The sensor elements are constructed of a reference grade platinum wire wound around ceramic mandrels that are inserted into stainless steel tubes.

Benefits of Thermal Mass Flow Technology

There are many benefits of thermal gas mass flow meters over other flow measurement technologies:

  • Direct mass flow measurement of air and gases in standard volumetric units (ie SCFM or NM3/H) or mass units (ie LBS/M or KG/H)
  • No additional pressure or temperature compensation required
  • Repeatability and exceptionally broad measurement range: up to 1000:1 (100:1 typical)
  • Standard linear 4-20mA output proportional to mass flow rate
  • Low pressure drop
  • No moving parts
  • Cost effective
  • Insertion (all Fox models) and inline (FT2A/FT3 models only) configurations
  • Microprocessor bases, field rangeable electronics
  • Proprietary DDC-Sensor™ and PowerPro™ Sensor*
  • Measures flow rate and temperature

*Standard and high gas temperature range sensors are available.


The Fox DDC-Sensor™ is a new state of the art sensor technology used in the Fox Model FT1 Thermal Gas Flow Meter. The DDC-Sensor™, a Direct Digitally Controlled sensor, is unlike other thermal flow sensors available on the market. Instead of using traditional analog circuitry, the DDC-Sensor™ is interfaced directly to the FT1 microprocessor for more speed and programmability.

Fox’s DDC-Sensor™ provides a technology platform for calculating accurate gas correlations. The FT1 correlation algorithms allow the meter to be calibrated on a single gas in the factory while providing the user the ability to select other gases in the Gas-SelectX® gas menu. Fox’s Model FT1 with its DDC-Sensor™ and state-of-the-art correlation algorithms provide an accurate, multi-gas-capable thermal gas flow meter.

PowerPro Sensor™

Compared to a typical Differential Pressure type flowmeter, the PowerPro™ sensor offers better low flow or low end sensitivity and exceptional accuracy at high velocities.

The PowerPro™ Sensor operates at twice the power level than competitor sensors to achieve a higher sensitivity to flow; even at very low flow rates. A wider measurement range - 50 to 60,000 SFPM – and a fast response time (0.9 seconds) make the flowmeters that use the PowerPro™ Sensor able to measure accurately for a long list of industries and applications.

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