Level measurement on Carbon Dioxide tanks at AIR LIQUIDE

Application Report | Chemical

  • High reliability with reduced installation and maintenance costs
  • Accurate level measurement on moving product surfaces
  • TDR technology: optimized cost/performance ratio


AIR LIQUIDE - world leader in industrial/medical gases and related services – operated with weighing systems to estimate the level of their Carbon Dioxide tanks.

Measurement requirements

During the filling, CO2 is at -20 C and 20 bar to avoid it freezing inside the pipes. The tank diameters vary from 1.3 up to 3 meter without specific internals. CO2 has a low dielectric constant of εr 1.6. Weighing systems used so far, are costly and greatly increase the weight of the installation. Ice build-up, due to the cryogenic liquid (CO2) results into uncertain measuring values. Capacitance probes, pressure transmitters and float systems were tested as alternative solutions to these systems; all of them with limited success.

KROHNE Solution


  • Universal 2-wire TDR (Guided Radar) Level Meter
  • Coaxial probe
  • Connection type: G 3/4“ A ISO 228

KROHNE already sold more than 200 of these devices to AIR LIQUIDE and other CO2 suppliers (e.g. MESSER, LINDE).

Customer benefits

The OPTIFLEX 1300 C with coaxial probe amplifies the reflection from the product surface and provides the perfect solution for this low dielectric product (εr 1.6). In addition, the outer sheath of this probe type is drilled with multiple holes, interspaced every 2 cm to maximize the product transfer inside. So, even if it came to stratification due to different product densities, the instrument would always measure the correct surface. Commissioning is reduced to a Quick setup operation; a few seconds later, the instrument is ready. Pressurizing the tank with gas up to 20 bar does not affect the zero measurement and during the filling, level starts immediately after opening the valve. The customers are impressed by the measurement stability and linearity; the product surface is boiling and the trend shows a perfect trace. By replacing the weighing systems with the OPTIFLEX 1300 C, the weight of the installation was cut in half. The competitive price of our device answered the need for a better cost/performance ratio.

Products used


Guided radar (TDR) level transmitter for heavy-duty level and interface applications

  • Continuous measurement of level, distance, volume, mass or liquid-liquid interface
  • Measuring range: 0.2…35 m / 0.7…115 ft (liquids), 0.2…35 m / 0.7…115 ft (solids)
  • -50…+300°C / -58…+572°F; -1…300 barg / -14.5…4350 psig