Sierra Instruments, Inc.

- Model 780S-UHP - Ultra High Purity Immersible Thermal Gas Mass Flow Meter



The 780S is North America's #1 selling inline thermal mass flow meter (2009 Flow Research, Boston MA). Our ultra high purity 780S-UHP is the industry-choice for bulk gas distribution service in semiconductor fabs, in pharmaceutical production and other ultra-clean processes. Real-time monitoring of gas usage provides reliable information on consumption and usage patterns in the manufacturing area and may be used for both billing and diagnostic purposes.

The 780S-UHP is constructed with 316L electropolished tubing with 7-10 Ra (UHP) interior. The 780S-UHP is available in pipe sizes from 0.5 up to 12 inches (1.27 to 30.4 cm) and offered with buttweld connections and a VCR probe-connection fitting.

The 780S-UHP also features Sierra’s unique FlowTrak dual-plate flow conditioning element to eliminate velocity profile distortions as well as swirl and temperature stratification in the gas stream. This product reduces piping straight run requirements to as little as three upstream diameters.  As a result, you save money on installation costs when compared to an orifice-plate where at least 20 upstream piping diameters are required for optimal performance.

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

  • Optimized for bulk ultra high purity (UHP) gas custody transfer
  • Direct mass flow measurement
  • No moving parts, 100:1 turndown, low pressure drop
  • Reduce straight-run requirements with built-in flow conditioning
  • Validate in the field for easy in-situ calibration

  • Industry-choice for bulk gas distribution custody transfer service in semiconductor fabs
  • Ultra high purity interior finishes
  • Built and shipped to ultra high purity claen room standards
  • Sierra's state-of-the-art ISO 9000 closed loop calibration facility for best accuracy
  • Built-in flow conditioning elements drastically reduce upstream straight-run requirements
  • Buttweld connections and a VCR probe-connection fitting
  • Field Validation/Configuration to assure operating performance: Watch video...
  • Field rangeability
  • Flow totalizer and alarms
  • Very low pressure drop
  • No moving parts
  • Flow-range adjustment and validation and diagnostics
  • Dual-range capability
  • Large LCD display and pushbutton interface, remote enclosure mounting available
  • Free computer interface software.

  • Accuracy: +/- 1% of reading plus +/- 0.5% of full scale
  • Repeatability: +/- 0.2% of full scale
  • Pipe sizes from 0.5 to 12 inches (1.27 to 30.4 cm)
  • Flow range to 20,000 sfpm (100 smps)
  • 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
  • Turndown: 100:1
  • Temperature:
    • Operating: -40°F to 350°F (-40°C to 200°C)
    • Ambient: -40°F to 120°F (-40°C to 50°C)
  • High temperature (HT) option to 750°F (400°C)
  • Response time is one second to achieve 63% of final value
  • Power supply:
    • 18 to 30 VDC (regulated), 625 mA maximum
    • 100 to 240 VAC, 50/60 Hz, 15 watts maximum
  • Electropolished  7-10 Ra 316 stainless steel construction
  • Output signals: RS-232, 0 to 5 VDC, 0 to 10 VDC, 4 to 20 mA 
  • User definable pulse output for totalized flow
  • Digital communications: Foundation Fieldbus, HART, Modbus RTU, and Profibus DP
  • Hazardous-Area Location Enclosure (IP66) and NEMA 4X (IP65)
  • Approvals:
    • FM (USA) Class I, Div I, Groups B,C,D
    • CSA and CRN (Canada)
    • ATEX
    • CE
    • PED (EU)
    • GOST R (Russian Federation)
    • Chinese Pattern Approval (China)

  • Accuracy : +/- 1% of reading + 0.5 % of full scale
  • Repeatability : +/- 0.2% of 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 : .02% per psi for air, consult factory for other gases
  • Response Time : One second to 63% of final velocity value


Argon, helium, hydrogen, nitrogen, oxygen (consult factory for other gases)

Gas Pressure

Mechanical design pressure:
Compression fittings: 500 psig (34.5 barg)

Gas & Ambient Temperature

Gas . . . . . . . . . . . . . . -40° F to 250° F (-40° C to 120° C)
Ambient . . . . . . . . . . -40° F to 120° F (-40° C to 50° C)

Leak Integrity

5 X 10-9 cc/sec of helium maximum

Power Requirements

18 to 30 VDC (regulated), 625 mA maximum
100 to 240 VAC, 50/60 Hz, 15 watts maximum

Output Signal

Linear 0–5 VDC or 0-10 VDC proportional to mass flow rate, 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 rired)


Hard contact user-adjustable high and low
Dead band adjustable with Smart Interface software
Relay ratings: Maximum 400 VDC or VAC (peak), 140 mA


Alphanumeric 2 x 12 digit backlit LCD
Adjustable variables via on-board switches (password protected)
or with Smart Interface software
Adjustable variable; Full scale (50 to 100 %)
Time Response (1 to 7 seconds)
Correction factor setting (0.5 to 5)
Zero and span


Seven digits (9,999,999) in engineering units
Resettable by software, on-board switches or external magnet


Smart Interface Windows-based software
Minimum 8 MB of RAM, preferred 16 MB of RAM
RS 232 communication
Additional features: Alarm dead band adjustment
Zero cut-off adjustment
Linearization adjustment
Save / Load configurations
Flow meter validation

Wetted Materials

316L stainless steel
UHP: 7 to 10 Ra internal finish


Hazardous-Area location enclosure (IP66) or NEMA 4X (IP65)
Both are powder-coated cast aluminum

Electrical Connection

Two 3/4 inch NPT . . . Hazardous-Area location enclosure (IP66)
One 1/2 inch NPT . . . NEMA 4X Enclosure (IP65)


CE (All enclosures)
CSA (Explosion proof for Class I, Division 1, Groups B, C, D)
ATEX ( II 2 GD Ex d IIC T6 ... T2
IP 66 T70 °C ... T280 °C )
FM (Explosion proof for Class I, Division 1, Groups B, C, D; dust-ignition proof for Class II, III, Division 1, Groups E, F, G)
IP66, NEMA 4X T6 -40° C to 70° C ambient
PED optional

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