Thermocouple housing materials?

[deltawars]

I'm building a cryogenic cooler and I need to accurately measure temperatures around ?196 °C but there are many different thermocouple housing materials like ceramic, stainless steel and glass but what is the difference between them?

[qwaarjet]

The housings are mainly for environmental protection and ease of mounting. glass is chemically inert, ceramics  are good for high temperatures, stainless is good all around. Generally unless you have a chemical reason not to use stainless is the way to go. I mainly use stainless or weld the thermocouple to the object of interest. Though most the the cryogenic systems I have used use silicon diodes instead of thermocouples for temperature measurement.

[LukeW]

Thermocouples are not the most common or most accurate choice of sensor in cryogenic applications. They are mainly just used in very high temperature systems.

Lakeshore (who are well known for professional temperature sensors in scientific and technical cryo applications) has some good info on their website.

http://www.lakeshore.com/Products/Cryogenic-Temperature-Sensors/Pages/default.aspx

[plesa]

I suppose that Pt100 is good candidate.. On instruments which I used in the past was only Pt100 ( basic cryoexperiments and level sensing of LN).
Check the class of the RTD ( at LN temperature can be used B with error about 1.3 K or Y (1/5B) with error about 0.8K).
As insulation was used PTFE, RTD were exposed to LN, only mechanical protection needed.

[deltawars]

Thanks for the information guys I find it very helpful, but I can't thank LukeW enough for the link, temperature sensors able to measure -273 Celsius and I cant believe the price I thought they would cost a lot more.