Extremely Low Temp Thermometer

[talshiar99]

I am looking for a thermometer that will measure down to -200C. Anyone know what type I should be looking for?

 

[f95toli]

Depends on what type of accuracy you need and how much you are willing to pay. Down to about 100 K a platinum resistor should work very well.
However, I would recomend a silicon diode since they are a bit easier to work with, try to find a model that follows a standard curve (for example the LS#10 curve).

If you have $100 to spend I would go for a LS-10 from Lakeshore, they are easy to work with and even the uncalibrated version follows the standard-curve very closely.

You could also try a simple carbon resistor, the problem is that unless you find the right brand (Allen-Bradley is the best but they don't manufacture carbon resitors any more) the reproducibility is quite bad.

As a final option you could try using a standard surface mounted Schottky diod (you would of course have to calibrate it yourself). they tend to be quite good down to about 20K, but again, reproducibilty can be a problem.

 

[chocbrucemousse]

An infrared thermometer mdight do the trick, prolly about $50 you could get one that went that low.

 

[talshiar99]

Infrared wont work below like 40, already tried. We would have loved non-contact...that and they are fun to play with however they cant go low enough.

So just hook it up to a DMM that has a temp measurement or does lakeshore selll specific equipment?

 

[f95toli]

Lakeshore sells temperature controllers but they are quite expensive (and they are nnto very good, I like Neocera's controllers better. A general tempera´ture controller will cost $1500-$2500 but if you don't need a heater control etc you might find something cheaper, there are smaller units try http://www.scientificinstruments.com/ (they also sell sensors).

You can also use a good DMM, you need to measure resistance in 4-point mode. . The accuracy of your your measurment will be determined by how well you can measure the resistance. You can then take the resistance yoiu get and get the temperature from a calibration curve, if you have a real controller you of course don't have to do this because they have the curves buil-ut and will indicate the temperature directly.