Sierra Instruments, Inc.

- Model 628S - Intake Air Mass Flow Metering



Our AirTrak 628S Thermal Mass Flow Meter was originally designed to work specifically with our BG3 Particulate Partial Flow Sampling System as an extremely fast, accurate, and repeatable engine air intake mass flow meter. In addition, the instrument has proven to be an excellent solution in all engine testing applications.

The meter has an extremely fast 200 millisecond response-time sensor making it ideal for the toughest transient test cycles where flow excursion can approach 10:1 within less than two seconds. Dual-Plate laminar flow profile conditioning elements inside the flow body maintain top performance in heavily constrained piping environments common in engine test cells, where long-straight pipe runs simply do not exist. In addition, the versatile microprocessor-based instrument integrates the functions of easy flow-range adjustment, meter validation and diagnostics in the field, sensor allignment guage for perfect installation, and a rugged probe-mounted NEMA 4X (IP65) housing.

Operating Principal: Thermal dispersion technology for direct mass flow measurement featuring no pressure or temperature compensation needed, no moving parts, low pressure drop, high turndown.

For raw exhaust mass flow measurement, our ExhaustTrak line of rugged, accurate and fast response-time mass flow meters are ideal for direct measurement of engine exhaust.

Note: To learn about ALL of our gas mass flow measurement and control instrumentation, visit our Flow Division.

  • 200 millisecond response time to changes in flow rates
  • High accuracy 1.0% of full scale over a broad range
  • Outstanding 100:1 turndown
  • Minimal flow blockage and low pressure drop
  • High accuracy at low idle conditions
  • Field adjustment of critical flow meter settings
  • Digital electronics, field calibration validation

  • High performance research-grade
  • Field validation of calibration
  • Plug and play with BG3 partial flow sampler
  • 100:1 turndown gives high accuracy at low idle conditions
  • Low pressure drop
  • Field validation of calibration
  • No moving parts
  • Dual-plate laminar flow conditioning element for constrained piping environments
  • Smart electronics permit field adjustment of critical flow meter settings
  • 2 x 12 backlit LCD display
  • CE approved


  • Accuracy of Point Velocity: +/- 1% of reading above 10% full scale
  • Repeatability:
    +/- 0.5% of full scale below 10% full scale
    • +/- 0.2% of reading above 10% full scale
  • Temperature Coefficient:
    • +/- 0.02% of reading per °F within ± 50°F of customer specified conditions
    • +/- 0.03% of reading per °F within ± 50°F to 100°F of customer specified conditions
    • +/- 0.04% of reading per °C within ± 25°C of customer specified conditions
    • +/- 0.06% of reading per °C within ± 25°C to 50°C of customer specified conditions
  • Pressure Coefficient: 0.02% per psi for air
  • Response Time: 200 milliseconds to 63% of final velocity value

Size and flow Range (100:1 turndown):

Note: Air maximum flow rates for tube sizes over 8' will be provided upon request.

  • Gases: Air and clean dry gases
  • Gas Pressure: 120 psig (8 barg) maximum design pressure
  • Gas Temperature: 14° to 176°F (-10° to 80°C)
  • Ambient Temperature: 32° to 120°F (0° to 50°C)
  • Power Requirements: 18 to 30 VDC (regulated), 625 mA maximum
  • Output Signal
    • Linear 0–5 VDC, 1000 ohms minimum load resistance or
    • Linear 4–20 mA proportional to mass flow rate, 700 ohms maximum resistance power supply dependent User-selectable. Active non-galvanically separated or passive galvanically separated (loop power required)
  • Alarms:
    • Hard contact user-adjustable high and low dead band adjustable with Smart Interface™software
    • Relay ratings. Maximum 42 VAC or 42 VDC, 140 mA
  • Displays:
    • Alphanumeric 2 x 12 digit backlit LCD
    • Adjustable variables via on-board switches (password protected) or with Smart Interface™software
    • Adjustable variables. Full scale (50 to 100 %)
    • Time Response (1 to 7 seconds)
    • Correction factor setting (0.5 to 5)
    • Zero and span
  • Totalizer
    • Eight digits (9,999,999) in engineering units
    • Resettable by software, on-board switches or external magnet
  • Software
    • Smart Interface™Windows™-based software Minimum 8 MB of RAM, preferred 16 MB of RAM RS 232 communication
    • Additional features:
      • Alarm dead band adjustment
      • Low flow cut-off adjustment
      • Linearization adjustment
      • Save / Load configurations
      • Flow meter validation
  • Wetted Material
    • Probe: 316SS
    • Flow Body: 316SS tubing
    • Sensor: 304SS, glass coating epoxy
  • Enclosure: NEMA 4X (IP65) powder-coated cast aluminium
  • Electrical Connections: One 1/2-inch female NPT

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