user16353: I'm looking for a way to measure temperatures in range of 40 to -200 °C (100 to −320 °F). The usual solution DS18B20 works only down to -55 °C (-67 °F).
Any ideas?
p.s. 
Precision of 2 °C would be good enough.

user10907: I did a search on "cryogenic temperature sensors" and found these from Lake Shore Cyrotronics – the price is shocking. It appears that you can use silicon diodes as cryogenic temperature sensors, so you might be able to use less expensive parts if you don't need a ton of accuracy.

user4143: You probably want a K-type thermocouple (the most common type).
They have a range of around -200°C to +1350°C (depending on probe).
Alternatively a Resistive Temperature Device (RTD) can be used, since these have a typical range of around -240°C to 650°C with higher accuracy.
This might be of help to you: http://digital.ni.com/public.nsf/allkb/C50FA55B3B2F85D9862572D00083350E

16353: <p>I'm looking for a way to measure temperatures in range of 40 to -200 °C (100 to −320 °F). The usual solution DS18B20 works only down to -55 °C (-67 °F).</p>

<p>Any ideas?</p>

<p><em>p.s.</em> 
Precision of 2 °C would be good enough.</p>
 10907: <p>I did a search on "cryogenic temperature sensors" and found these from <a href="http://www.lakeshore.com/products/Cryogenic-Temperature-Sensors/Pages/default.aspx" rel="nofollow">Lake Shore Cyrotronics</a> – the price is shocking. It appears that you can use <a href="http://www.lakeshore.com/products/cryogenic-temperature-sensors/silicon-diodes/dt-670/Pages/Overview.aspx" rel="nofollow">silicon diodes</a> as cryogenic temperature sensors, so you might be able to use less expensive parts if you don't need a ton of accuracy.</p>
 4143: <p>You probably want a K-type thermocouple (the most common type).</p>

<p>They have a range of around -200°C to +1350°C (depending on probe).</p>

<p>Alternatively a Resistive Temperature Device (RTD) can be used, since these have a typical range of around -240°C to 650°C with higher accuracy.</p>

<p>This might be of help to you: <a href="http://digital.ni.com/public.nsf/allkb/C50FA55B3B2F85D9862572D00083350E" rel="nofollow">http://digital.ni.com/public.nsf/allkb/C50FA55B3B2F85D9862572D00083350E</a></p>
