The ATOMOX HeLIUM ANALYZER®, the ATOMOX HeLIOX ANALYZER® and the ATOMOX HAND HeLIUM ANALYZER® operate by comparing the thermal conductivity of the sample gas to the thermal conductivity of a reference gas housed in a sealed cell. This technique to determine helium was first reported in the scientific literature in 1908 and is still used today.

Thermal conductivity gas analysis is remarkably sensitive and is often used to measure hydrogen, carbon dioxide and other gases in addition to helium. These gases are normally measured in a background of air, but the sensors operate just as well in a background of nitrogen or when monitoring two inert gases.

The ATOMOX analyzers determine the helium composition by continuously comparing the sample gas to the reference gas. This comparison is performed in a two-cell explosion proof sensor housing. The reference gas is sealed into a closed cell and will not change. The sample gas flows through and across the other cell. A temperature-sensitive heated filament is mounted in each cell. These filaments are part of a Wheatstone Bridge circuit. When the sample gas composition changes, its thermal conductivity will also change. This means it will conduct a different amount of heat away from the filaments. Since the resistance of the filaments is a function of their temperature, their resistance changes when the sample gas composition changes. Any such change creates an imbalance in the Wheatstone Bridge, resulting in an electrical signal output proportional to the change. This technique allows the ATOMOX analyzers to provide an accurate measure of any change in sample gas composition.

The sensors used in the ATOMOX analyzers are assembled specifically for this  application. The expected life of the sensor is 10 years. The response time of the analyzer to changes or variations in gas mixtures can be affected by the length of the gas supply line, any mixing chambers in line or other physical obstructions. There generally is a quick (<15 sec.) response to any change in gas composition. The helium concentration is updated every 1 second while the unit is on.

The basic assumption for the analyzers to work is that the gases in the mixture are known (i.e. oxygen, nitrogen, helium). Minor amounts (< 1 % total) of trace gases will not significantly alter the output of the analyzer and can be ignored. The sensor is non-specific, it will not indicate if the test gas has CO, Argon or any other gas in the mix. It will only determine the relative difference in thermal conductivity of the test gas to the reference cell. It is assumed that the difference is the result of the addition of helium to the gas mixture.

The ATOMOX analyzers are not meant to replace good gas management practices or handling techniques. They are an additional tool to verify the content of helium in a scuba gas mixture.