[NAFEX] Cold Temps and Thermometer Calibration

Richard MURPHY murphman108 at msn.com
Thu Nov 6 17:56:34 EST 2008


Hello Fellow Fruit OCD Victims;

If someone intends to buy a thermometer to measure down to -50 F, be careful.

Most calibration labs are going to use Boiling Water for 100 C, and an Ice Bath for 0 C, correcting for atmospheric pressure wherever they happen to be. Then your accuracy below Zero is anyone's guess. Don't assume this slope to be linear very far below zero. It ain't the case. A colder temp calibration can be performed using liquid nitrogen and some special equipment, but this is probably beyond the reach of most of us.

At least look for one that CAN be calibrated (adjusted or internally compensated) and maybe some day you will be lucky enough to know somebody that works in a place that has calibrated thermometers, and will tweak it for you. Finally, it is damn hard to guarantee an Absolute temperature reading to (an expensive tool) better than 0.5 C. Too many sources of measurement error. The farther below zero you go, the accuracy can be far, far worse than that.So when we talk of 25 versus 26 F, it's a complete wash. If you have Black wires to your temp sensor, it can translate sunshine into heat!

Murph
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