The non-intrusive ultrasonic gas flow meter for operation in hazardous areas with intrinsically safe process inputs

The FLUXUS G831 gas flow meter is a high performing ultrasonic clamp on meter specifically designed for measurement of dynamic flows in the process industry. This sophisticated, versatile, and accurate gas flow meter has everything you need - faster processing capabilities, advanced diagnostics, bidirectional communication protocols, digital outputs and process inputs. In keeping with all other FLEXIM products, the G831 offers ease of installation, retrofittable design, accuracy, and outstanding performance. 

The FLUXUS G831 gas flow meter is a high performing ultrasonic clamp on meter specifically designed for measurement of dynamic flows in hazardous areas (ATEX, IECEx Zone 1 and FM Class I, Div. 1 approved) and perfectly suited for demanding industrial and process applications in and out of the oil field and the chemical industry.

With its explosion proof housing, compact design, and the corrosion resistant ATEX, IECEx Zone 1 – FM Class 1. Div. 1 rated transducers mounted in “fit for purpose” rugged mounting fixtures, the system’s mechanical stability and permanent contact with the pipe surface is assured.

The FLUXUS G831 gas flow meter allows for inherently bi-directional gas flow measurement of operational (gross) volumetric flowrate. The addition of intrinsically safe process inputs for pressure and temperature at the meter location means the FLUXUS G831 flow meters can now provide standard volumetric flow and mass flow.

The FLUXUS G831’s two measurement channels make the device perfectly suited for difficult measurement points, and it is completely unaffected by gas density, viscosity and composition as well as temperature and pressure. 

Synchronized Channel Averaging (SCA)

In cases where response time expectations and requirements are higher. Using the new Synchronized Channel Averaging method (SCA), the G831 ultrasonic flow meter sends signals both in the direction of the flow and against the flow every 1 millisecond. These signals are averaged simultaneously resulting in better flow profile representation, a more stable output and minimizing cross flow effects in highly dynamic flows with demanding inflow conditions.

The non-intrusive design of the G831 flow meter means the transducers are mounted on the outside of the pipe wall. This way the system does not suffer from wear and tear or clogging and creates no risk for leaks or pressure drops inside the pipe.

Due to its matched and paired transducers as well as internal temperature compensation (compliant to ANSI/ASME), the measurement system is drift free and zero stable ensuring accurate readings. The gas flow meter can be applied on inner pipe diameters ranging from 6 mm up to 2100 mm (with no limitations on pipe wall thickness or material) and media temperatures from -40°C up to 100°C.


  • ATEX / IECEx Zone 1FM Class I, Div. 1 approvals
  • Bi-directional flow measurement of liquids and gases
  • Cost effective: No pipe work, no process shut-down, maintenance-free
  • Zero-point stable and drift free - Carefully matched and temperature compensated transducers (fully ANSI / ASME compliant)
  • Retrofittable - No pipe modification required, no process shut-downs
  • Maintenance Free - Free of wear & tear and abrasion, not prone to clogging or corrosion, no fugitive emissions
  • High tolerance to entrained solids and gas wetness
  • Independent of pipe size, material, operating pressure, and gas composition
  • Flexible configurable outputs
  • AMV Logo


Industry Applications

Technical Facts

Measurement uncertainty at the measuring point (volumetric flow rate)
±1…2 % of reading ±0.005 m/s
Measurement uncertainty of the measuring system (volumetric flow rate)
±0,3 % of reading ±0.005 m/s
0.15 % of reading ±0.005 m/s
Flow velocity range
0.01...25 m/s
Ex zone transmitter
FM Class I/Div. 1, FM Class 1/Div. 2, ATEX/IECEx Zone 1
Power supply
100-230VAC, 24DC
Available transducers
Shear Wave
for Ex zones
FM Class I/Div. 1, FM Class 1/Div. 2, ATEX/IECEx Zone 1
for pipe sizes range
10mm ... 6500mm
for temperature range
-40°C ... +240°C / WI: -200°C ... +600°C
4-20mA active/passive
4-20mA HART active/passive
4-20mA passive (Ex ia)
Temperature (Ex-ia)
4..20mA (Ex-ia activ)
Digital communication
Foundation Fieldbus-Ex-ia
Profibus PA-Ex-ia
4..20mA HART (Ex-ia passiv)
Advanced Meter Verification (AMV)
Additional Information
For more detailed Information please download the Technical Specifications