Monitoring temperature (approximately) of a -80°C Freezer ?

I am completely new to Arduino but have the idea that I could manage - with some help from others - to do some (coarse) temperature monitoring with one, or even several, -80°C freezers in a bio-laboratory.

Actually the purpose of the system is not really a precise temp. monitoring, but more of an alarming system which would alert when the temp. in one of the freezers is crossing a certain threshold (e.g. -60°C). The precision should be better than +/-5°C in the relevant temperature range [-80°C, -50°C].

The professional systems I am aware of make use of PT1000 temperature sensors, but when I googled for “Arduino PT1000” I found a number of dis-encouraging comments of that combination - at least for my (lower) level of knowledge (extra circuits and highest precision reference voltage needed).

It would help to know if my (presumably) low level requirements could be accomplished with a more simplistic Arduino setup with some additional resistors, caps and cables. Any chance?

PS: Later I could add an Ethernet shield (and some code) for accessing the status remotely.

Resistors, caps, and cables are unlikely to solve your problem. You will need some type of temperature sensor. For example, the US Sensor PT103J2 works down to -80C and can be put into a voltage divider circuit to probably get you the accuracy you need.

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Check - - they have a lot of temp sensor info

If I had a biolab I would monitor the freezers quite closely with multiple sensors in different places. (at least 2) 1) to see trends in the temperature which can predict upcoming trouble, and 2) the sensor can become encapsulated in a block of ice while other parts are not cold enough.

Add 1) If I see a rise during the day climbing up and up it can indicate an alarm during the night (I dont like alarms especially not in the night :)

Add 2) happened to my previous food freezer...

$15 thermocouple amplifier (with cold junction compensation) giving a 10mV per deg output, and $5 of thermocouple wire. Robust and simple. If you damage the sensor wire, you just cut it and solder a new junction.

You may need to make a calibration look-up table due to non-linear behavior in the temperature range you are interested in.