Fuentek's Tech Transfer Blog

Cryogenic and Non-Cryogenic Optical Liquid Level Instrument for Stratified Conditions

A simplified, cost-saving measurement device using optical transmission properties

Innovators at NASA’s Marshall Space Flight Center have developed a unique prototype for measuring the liquid level in a tank, employing the properties of optical transmission. The technology is simpler and less expensive than other optical sensing techniques, and it provides far greater accuracy and faster results in cryogenic conditions than typical cryogenic liquid metering methods. The innovation is ideal for both cryogenic and non-cryogenic ground tank metering applications, as well as zero-gravity systems that include stratification or settling techniques.


  • Versatile: Operates at high and low temperatures and pressures, functions in corrosive environments, and provides highly accurate metering for both cryogenic and non-cryogenic liquids
  • Precise: Allows accurate liquid level measurements to 0.1% of the optical fiber length
  • Fast: Offers a very rapid response time (up to gigahertz data rate), enabling measurement of rapidly changing fluid levels or sloshing liquids
  • Safe: Requires no electrical signals in the tank, thereby avoiding an explosion hazard
  • Flexible: Accommodates snaking through access ports or shaping to fit tank contours
  • Economical: Can be incorporated directly into a plastic tank, reducing costs and eliminating the need for holes in the tank in some applications



  • Rocket propulsion testing
  • Engine fuel tanks
  • Cryogenic tanks


  • Liquid hydrogen fuel tanks
  • Petroleum, gasoline, and liquid natural gas tanks

Foods and Pharmaceuticals

  • High-temperature, contamination-free storage and transportation


  • Jet engine fuel tanks

Why it is better
Other optical sensors developed to measure liquid levels in a tank require complicated tank modifications and detection instruments, contributing to greater cost and complexity. Other typical cryogenic tank metering systems employ an array configuration of thermocoupled or other temperature or resistive devices. These systems register the thermal change between the liquid and gas fluid phases, which significantly limits their accuracy in cryogenic conditions. In contrast to these systems, NASA’s device is simple and straightforward to implement, with a very inexpensive design. The technology allows operation at high temperatures and pressures and in corrosive environments, and it can precisely measure liquid levels to 0.1% of the sensor length with gigahertz data acquisition rates.