calibrate freezer thermometer

[alp664]

What's the best way to calibrate a liquid-in-glass thermometer for the -80 degree freezer? We have a NIST thermometer, but not sure how to do the calibration. Do we just place them side by side in the freezer, or do we need to make a solution?

[Lcsmrz]

Temperatures can vary significantly in refrigerators and freezers. For all of my calibrations, I rubber band them together and immerse them to the line on the stem in some appropriate solution for a sufficient time to approximate temperature equilibrium.

Lately, I've been busy (read: lazy) and have been sending mine to a ISO calibration lab once a year.

[eric1980]

I will band the thermometers together and immerse them into a single urine bottle containing neat glycerol. Then I will throw the whole setup into the freezer for about an hour. Read the temperature as fast as possible.

I use glycerol because (I hope) that they will maintain the thermometer reading while I read it.

[Likewine99]

I have borrowed our BioMed's calibrated, digital temperature thing, the one they use to calibrate temps throughout the hospital.

It gets away from the liquid in glass, has been certified by an outside source and has a better temp range than the NIST thermometer we have in Chem.

I use the neat glycerol solution too.

[eric1980]

I could borrow the calibrated digital thermometer with a wired probe from my BioMedEngineering. I could have the probe in the freezer while seeing the reading without having to open the freezer. It would be convenience +1 for me. ; )

But I was instructed not to calibrate glass-in-alcohol/mercury thermometers against a calibrated digital thermometer. I couldn't get a reason why.

To me, regardless of the type of thermometers, the readings must be correct.

Do guys calibrate your thermometers regardless of types?

[eruenitz]

Glycerol will not stay liquid at -80 deg C See http://www.dow.com/glycerine/resources/table8.htm

Methanol will stay liquid up to -97 deg C a better choice for the liquid in which to immerse probes. I would use a thermocouple calibrated against a NIST thermometer to calibrate a freezer or refrigerator and have done so.