[NAFEX] Cold Temps and Thermometer Calibration

hwparker at verizon.net hwparker at verizon.net
Thu Nov 6 21:27:51 EST 2008


Glass ASTM thermometers are available to minus 112F ; not electronic.

On Nov 6, 2008, at 5:56 PM, Richard MURPHY wrote:

> 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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Hank Parker

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