To the average person, the word âcryogenicsâ likely evokes images with more of a basis in science fiction than fact: eccentric billionaires flash-frozen to preserve life indefinitely; a starship crew sleeping through the longest part of their journey; the neurotic owner of a â70s health-food store waking up in a 22nd Century police state.
In reality, though, cryogenic technologies are far more common and mundane than these motifs suggest. Strictly speaking, âcryogenicâ is applied to any technology or process involving temperatures below 150°C. Cryogenic technologies and processes are common in steel processing, natural gas transfer, power transmission, food preservation, and many other industries.
As the most common methods of cryogenic cooling involve the use of liquids â notably liquid helium, liquid hydrogen, or liquid nitrogen â level sensing, pressure sensing, and other liquid measurements are important to the proper function of many cryogenic systems.
Due to the extreme cold temperatures involved, great care needs to be taken when choosing or designing liquid level sensors for use with cryogenic systems. If this is a problem youâre familiar with, SMD Fluid Controls can help. Offering a wide selection of off-the-shelf sensing solutions in addition to OEM and custom design services, SMD can help with any level sensing application.
Challenges and Solutions for Cryogenic Level Sensing
The extreme cold temperatures involved in cryogenic technologies means that appropriate level sensors need to have two necessary qualities: a material that can withstand extremely cold temperatures, and an operating method that wonât be adversely affected. 
Non-contact sensors are ideal, as they tend not to have moving parts with which extreme cold temperatures might interfere. Properly-tempered stainless steel is a good material choice, as it is capable of withstanding extreme cold without cracking or warping.
Capacitive liquid level sensors are popular solutions for cryogenic applications, as they contain no moving parts are can easily be fabricated from stainless steel components. In such cases, the cryogenic liquid being measured is used as the dielectric material.
Another good choice for cryogenics is ultrasonic liquid level sensing. These sensors work by emitting an ultrasonic pulse at the liquid medium and determining the distance between the sensor and liquid surface based on the arrival of the return echo.
Optical level sensors, which use infrared light, are a viable option for point-level sensing in cryogenic applications, although if the continuous level measurement is needed the previous two designs would be preferable. Traditional float switches and plastic sensors should be avoided.