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Subject: Re: Calibrated Thermometers



"Greg "_"" wrote:
: In article ,
: "Richard Knoppow" wrote:

: > That is hand work so the cost of
: > a certified calibration is high. Even relativelly low cost
: > digital thermometers appear to be accurate enough for color
: > work, i.e., 1/2 degree F. in the relevant temperature range.

: Not sure if its NIST certified, but the calibrated 10th degree C
: thermometer is being offered at about 35.00 USD.

At that price I doubt it would be traceble to NIST standards and certainly
hasn't been certified by NIST.

Once upon a time (longer then my memory of a lot of fine details) I worked in
calibration lab. One of the things we did was calibrate thermometers. While
I have calibrated thermometers accurate to 1/10C I managed to avoid doing much
of it. :-) One thing I do know is that electronic "thermometers" actually accurate
to 1/10 of a degree in F or C are very expensive and delicate. While a mercury
thermometer is non-linear they are very repeatable. In fact the scales of "better"
mercury thermometers have the scale painted on by hand!! It is subjected to a number
of temperatures and a person marks the scale at the indicated reading. As you
may expect the more measured points the higher the price!!

When a thermometer is "calibrated" it is brought to varying temperatures and the reading
is compared to the actual temperature. When it is returned you recieve a sheet of paper
with the indicated and actual temperature of the measurement points. As Richard has pointed
out a mercury has a proper insertion depth. If that depth isn't marked the column of
mercury should be submerged.

What I have at home is a mercury thermometer that gets NIST traceable calibrated once a year
at 68, 75, 100 and 125 degrees F. I then use it to check the thermometers that I use for
daily use.

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