The most convenient and reliable hazardous area clamp on flow meter for the Hydrocarbon Processing Industry!

The H831 is the only Clamp-on Ultrasonic flow meter certified for installation in Zone 1 ( FM Class 1, Div. 1 to come) hazardous areas with the ability to report standard volume flows and API determination in the Hydrocarbon Processing Industry.

The FLUXUS H831 is FLEXIM’s new hazardous area rated flow and analytical measuring system for the hydrocarbon processing industry (HPI). This sophisticated and highly accurate non-intrusive flow meter combines very precise ultrasonic flow and sound speed measurement, advanced calculation features and diagnostics with a robust, durable and industry minded “fir for purpose” explosion/ flameproof housing. The H831’s nonintrusive flow meter built-in HPI computer calculates API gravity, operational density, density at base conditions and kinematic viscosity. Volumetric flow rates reported by the meter are automatically compensated for live temperature and pressure inputs according to industry standards ASTM1250, GPA TP25 and D4311 thus allowing for precise and dynamic standard volume flow measurement of liquid hydrocarbons even in the most demanding environments.

In addition to advanced and sophisticated measurement capabilities, the FLUXUS H831 flow meter is equipped with a hydrocarbon-specific database for a wide range of applications and process conditions ranging from light hydrocarbons to crude oils/refined products to heavy hydrocarbons at refineries, tank farms, oil terminals and transport liquid pipelines. Since Oil and Gas processes and operations vary from location to location, application-specific parameterization is also easily possible via a user-friendly editable table residing in the transmitter and allowing customization of liquid names and physical properties (density, API).

Typical applications for the FLUXUS H831 are mass balance, leak detection and interface detection, product identification in tank farms and oil terminals, quality check measurements and verification or temporary replacement of stationary measuring devices.


  • Explosion proof/ Flameproof flow measurement of liquid hydrocarbons FM Class I, Div. 1 and ATEX / IECEx Zone 1 areas
  • Fit for Purpose: Process Inputs (pressure and temperature) enabled for Hydrocarbon Processing Applications and standard flow reporting according to industry standards ASTM1250, GPA TP25 and D4311
  • Highly Cost Effective: No pipe work, No process shut-down, Virtually maintenance-free
  • Matched, paired and wet calibrated flow transducers (traceable certification to national standards)
  • Excellent zero-point stability and drift-free
  • Wide turndown ratio
  • Independent of pipe size, material, operating pressure, medium and temperature (from as low as -170 °C up to +630 °C)
  • Free of wear and tear and abrasion
  • Not prone to clogging or corrosion
  • No pressure loss or risk of potential leaks and fugitive emissions
  • AMV Logo


Industry Applications

Technical Facts

Measurement uncertainty of the measuring system (volumetric flow rate)
±0,3 % of reading ±0.005 m/s
Measurement uncertainty at the measuring point (volumetric flow rate)
±1,0 % of reading ±0.005 m/s
0.15 % of reading ±0.005 m/s
HPI Measurement Uncertainty
Normalized Volume:
+/-1% (crude oil, refined products, liquefied gases, heavy oils)

Operating density, normalized density Repeatability:
+/-1% (with field calibration of speed of sound)
Flow velocity range
0.01...25 m/s
Ex zone transmitter
FM Class I - Div1
Power supply
100-230VAC, 24DC
Available transducers
Shear Wave & Lamb Wave

for Ex zones:
FM Class I - Div1

for pipe sizes range:
10mm ... 6500mm

for temperature range:
-40°C ... +240°C / WI: -200°C ... +630°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