Sierra FastFlo™ 620S Insertion Thermal Mass Air Flow Sensor

The FastFlo™ 620S is an insertion thermal mass air flow sensor designed to give you a highly reliable, responsive and affordable mass flow measurement for light industrial applications where a NEMA 4X (IP65) enclosure is acceptable. This mass airflow sensor:

  • Includes a compact, versatile, microprocessor-based transmitter
  • Integrates flow-range adjustments, and meter validation and diagnostics
  • Gives you the ability to "field-validate" your meter’s calibration

Sierra Instruments’ FastFlo™ 620S Immersible Thermal Mass Flow Meter provides an economical solution for gas flow measurement applications. The meter’s sensor offers long-term reliability and 200 millisecond response to changes in flow rate.

The versatile microprocessor-based transmitter integrates the functions of flow-range adjustment, meter validation and diagnostics in a probe-mounted NEMA 4X (IP65) housing. Mass flow rate and totalized flow, as well as other configuration variables, can be displayed on the meter’s optional 2 x 12 backlit LCD panel.

The meter also provides an optical/galvanic isolated 4-20 mA output and two alarm outputs. The programmable transmitter is easily configured via RS-232 and Sierra’s Smart Interface™ Windows™ based software or three push buttons in the device. Modbus RTU is also supported. The 620S is suitable for pipes or ducts from 1-inch to 48-inches (DN50 to DN1200).


  • Fast response flow meter ideal for gas mass flow measurement applications
  • 200 millisecond response to changes in flow rate
  • Smart electronics permit field adjustment of critical flow meter settings
  •  Field validation of flow meter calibration
  • Outstanding rangeability
  • Optional 2 x 12 backlit LCD display
  • Minimal flow blockage and low pressure drop
  • CE approved
  • Optional Modbus RTU


  • Measure air and all clean inert gases
  • Accuracy: +/- 1% of full scale
  • Repeatability of +/- 0.2% of full scale
  • Pipe sizes from 3.7" (9.3cm) up to 24" (61cm)
  • Small-diameter, 3/8-inch (9.5mm) sensor probe
  • 100:1 turndown
  • Temperature:
    • Gas: -40°F to 176°F (-40°C to 80°C)
    • Ambient: -40°F to 120°F (-40°C to 50°C)
  • Response time is 200 milliseconds to achieve 63% of final value
  • Power supply 15 to 18 VDC (regulated), 625 mA draw maximum
  • Output signals: Linear 0–5 VDC and 4-20 mA
  • User definable pulse output for totalized flow
  • Digital communications solutions include:  Modbus RTU
  • Enclosure NEMA 4X (IP65); remote electronics mounting available
  • CE approved

Download Datasheet: Sierra Fast-Response Insertion Thermal Mass Air Flow Sensor


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