Cryogenic skin temperature measurement

Hand-held laser thermometers are available. The device fires a ray of red light at the object and a sensor measures the reflected beam and infers temperature.

"Hand-held laser thermometers are available."

I have never seen one of these capable of reading below -50 C. If you know of one capable of measuring the range stated please could you let me know the make.

Nor have I. And I thought that the laser on all non contact thermometers was just for seeing what you are pointing at. I thought they all used IR detectors to get the temp.

I agree Nick,

Most non-contact temperature measuring devices are Infrared and have an integrated laser pointer so you can see what you are measuring (since we can't see IR). Even thermographic cameras use IR technology so the low end temp range tends to be around -50 or so.

Is there any reason you cannot use a thermocouple? K-type are extremely common (Ive used them for several experiments) and they have a range of about -325°F to well over 2000°F. You can cheaply read them with a handheld meter, or setup a data acquisition system and log real-time data.

If you would elaborate on your measurement, I can help you more. Do you require non-contact measurement? (then TC's are out!) Do you need real-time data? Price range? Accuracy and precision?

"Do you require non-contact measurement? (then TC's are out!) Do you need real-time data? Price range? Accuracy and precision?"

Thanks for your suggestions. I am at present using TC's, my problem is in fact ensuring good contact, as I believe that I am getting inaccurate but repeatable measurement due to this poor contact (or even an air gap between vessel surface and the TC). An accuracy of +- 3% would be more than good enough and real time data is required.

This is something I do on a daily basis.

As others have mentioned, IR thermometers rarely have range below -40 Celsius.

I use "T" type thermocouples (copper and constantan) and various data loggers with good results. The T type thermocouple wire is inexpensive and has a low temp range to just below liquid nitrogen temperatures (-195.8 C), however, if you need very high accuracy, you can use squids (superconducting quantum interference device) but expect to pay a fortune, cryogenic glue for such devices can cost hundreds of dollars for a few milliliters not to mention the cost of the equipment.

I purchase all of my thermocouple wire from Omega Engineering (on line) and have no problem with twisting the hot junction ends rather than weld.

I work for a company that sell liquid nitrogen storage vessels which we use independent measuring equipment of vessels in multiple ways.

If you goto www.planer.co.uk you can see our products.

Email me on nick@planer.co.uk if you have any further questions.

Nick

To get better contact, use a thermally conductive grease or epoxy. Which you choose will depend on the TC housing (if there is any) and if you want it to be removable or not. Just search on McMaster and find one suitable for that low temperature. A common steel epoxy from a hardware store for repairing car radiators, etc should work well enough (just make sure you rough the surface of the chamber so it sticks well). On the expensive side, Nusil Technologies makes good thermal grease that I use for satellite applications.

Once you have good contact, use a fiberglass blanket or some other insulator around the TC. This will keep the air from heating it and keep its temperature closer to that of the chamber wall.

If you can grind down a small depression so that the TC can be epoxied more or less in the wall, you will get the best results. This will allow conduction in line with the chamber wall, instead of just radially between the wall and TC. I doubt that is practical for your application, though.

I believe you can also get TC's that are embedded in flexible tape, kind of like strain gages, but I don't know any suppliers off hand. Those could be applied with a thin coat of epoxy and get very good contact.

Also check the calibration on the TC reader. Some need to be re-calibrated if they are used for relatively extreme low or hot temperatures.