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I'm looking for a way to measure temperatures in range of 40 to -200 °C (100 to −320 °F). The usual DS18B20 digital thermometer works only down to -55 °C (-67 °F).

A precision of 2 °C would be good enough.

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migrated from raspberrypi.stackexchange.com Jan 12 '16 at 20:29

This question came from our site for users and developers of hardware and software for Raspberry Pi.

  • \$\begingroup\$ Hello and welcome. I want to give this hint (as I used many of those sensors myself) lakeshore.com/Products/Cryogenic-Temperature-Sensors/Pages/… (I hope it does not come off as advertisement, I am not affiliated with Lakeshore). Thing is, those are dumb sensors, you'll have to build a control circuit yourself (e.g. a precision current source and precision voltmeter) - which could be part of good answers. \$\endgroup\$ – Ghanima Jan 12 '16 at 20:13
  • \$\begingroup\$ related but not a dupe: electronics.stackexchange.com/questions/87905/… \$\endgroup\$ – Ghanima Jan 12 '16 at 20:30
  • \$\begingroup\$ Please clarify if you are searching for a general technology or a specific product. \$\endgroup\$ – PlasmaHH Jan 12 '16 at 20:31
  • \$\begingroup\$ @ Ghanima : the link inside of the post you linked to the adafruit.com/products/269 will probably work form. Thnx! \$\endgroup\$ – Kris_R Jan 12 '16 at 21:41
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Answer is simple: thermocouple.

Thermocouple type K (chromel - alumel) works from -200°C and has very linear characteristics. It's very popular and cheap, many multimeters use it as a temperature sensor. Type T will be better for such low temperatures, but it is hard to buy and not as cheap as K.

Another solution is a platinum resistive sensor, like Pt100, but it is not as linear as thermocouple.

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    \$\begingroup\$ Where did you found that Pt100 has unpleasant characteristics below 0C ? ni.com/tutorial/7115/en \$\endgroup\$ – Marko Buršič Jan 12 '16 at 21:24
  • \$\begingroup\$ @MarkoBuršič My mistake, I've looked at wrong graph in some Pt100 datasheet. I've just edited my answer. \$\endgroup\$ – Jakub Rakus Jan 12 '16 at 21:35
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A commonly-used cheap sensor for LN2 is a standard silicon diode. Measure the forward drop at a constant current.

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