How does a Helium analyzer work?

[battles2a5]

Random question. How exactly does a Helium analyzer work? I know O2 sensors work on a chemical reaction that produces a current which is then interpreted as an O2 partial pressure. But if Helium is a noble gas and doesn't react with any other elements, how can you measure He content accurately?

 

[ianr33]

I *think* it works by thermal conductivity

 

[Charlie99]

Atomox has a good description of how thermal conductivity is used to measure the helium content.

If you want more detailed info, look for info on "hot wire anemometers", since they use the same sort of principal -- except they measure the change in thermal conductivity caused by air flow rather than the change of conductivity from having a different gas mixture.

The field instruments based upon thermal conductivity can be fooled if you have gases other than the expected O2, N2, and He. There are more expensive lab instruments that work on other techniques, such as mass spectrometry that are more reliable.

 

[battles2a5]

Very cool. Thanks for the info.