About Us

After more than 20 years of manufacturing thermal gas mass flowmeters, Fox Thermal 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. Explore the Fox Facility, Technology, and the extensive awards and certifications of Fox Products by navigating the menu to the right.

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 Models FT1, FT4A & FT4X have 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 and Fox Thermal leads the industry for accuracy, quality, and innovative design. Benefits of Thermal Mass Flow Technology:

  • Direct mass flow measurement of air and gases in standard volumetric units (e.g., SCFM or NM3/H) or mass units (e.g., 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, Inline & remote* styles
  • Measures flow rate and temperature

The Fox Thermal Difference:

  • Microprocessor-based, field-rangeable electronics
  • DDC-Sensor™ proprietary flow sensor design*
  • Gas-SelectX® field selectable gases / gas mixes without affecting accuracy*
  • CAL-V™ and Zero CAL-CHECK® Calibration Validation*
  • Free FT View™ Software to configure meter, print calibration validation certificates, run simulations, and more!*
  • Data Logger with 7-year history*

*features vary by model number


The Fox 2nd generation DDC-Sensor™ is a new state-of-the-art sensor technology used exclusively in the Fox Models FT1, FT4A & FT4X Thermal Gas Flow Meters. 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 meter's microprocessor for more speed and programmability.

Fox’s unique DDC-Sensor™ provides a technology platform for calculating accurate gas correlations. The 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(s).

Competitors' sensors utilize fragile, cantilevered (only welded at one end) elements, whereas the sensor elements of the DDC-Sensor™ are welded to the sensor window at both ends for extra stability and strength. This enhanced design eliminates the sensor element vibration - found most often at high flow rates - which can potentially lead to metal fatigue and failure.

The sensor elements are in direct contact with the process flow. In applications where slag, ice or other foreign particles are traveling down the pipe, cantilevered elements are subject to damage requiring factory repair. The Fox 2nd generation non-cantilevered sensor design is much more rugged and robust.

Fox Models FT1, FT4A & FT4X, with their 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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