Roger Hicks said:My 'master' is a mercury-in-glass Brannan that agrees with another, identical, Brannan to 0.1 C.
PeterB said:Roger,
The digital clock in my car agrees with my bedside radio clock too.
They are both 2 minutes slow.
regards
Peter
Roger Hicks said:What surprises me is that no-one has suggested the 'master/slave' model.
The master thermometer does not even need to be accurate, merely consistent, though accuracy is nice if you can get it. Mercury-in-glass lab thermometers (incliding the Kodak ones) are probably the most reliable; bimetallic dial drift most in my experience; and electronics may do almost anything without warning, no matter how reliable. Most don't, it's true, but they can.
All 'slaves' are calibrated to the 'master'. Let's say you have three thermometers, one 'master' and two 'slaves'. When the 'master' reads 20, one slave reads 19,5, the other, 20,5. For a standard 20, you therefore use the slaves accordingly.
Break a slave; replace it; recalibrate against the master. This one's 19.7. Fine. Still the same temperature...
My 'master' is a mercury-in-glass Brannan that agrees with another, identical, Brannan to 0.1 C. My 'slaves' vary widely for different purposes: spirit-in-glass, dial (for water baths), digital... Digital and dial are checked periodically; spirit-in-glass only when I acquire them.
Cheers,
Roger (www.rogerandfrances.com)
LOL Figures, been longer than that since I had to deal with them. But then I still remember the Atomic Energy Commission and Bureau of Biologicals. Thanks for the 'old' update.Phong said:> On this side of the pond, the ideal would be to obtain a thermometer
> certified by the NBS (National Bureau of Standards)
In case you didn't know, NBS has been NIST (National Institute of Standards and Technology - mentioned in some of the earlier posts) since the late 1980s.
- Phong
Claire Senft said:I must say the thought that a mercury thermometer enclosed in etched glass
being able to go out of calibration to be very surprising news that I find hard to fathom.
How could this happen?
glbeas said:You have to heat the theremometer enough that the mercury column rises all the way to the top and then some, forcing the bubbles together at the top. On cooling the column will retreat as on piece. Needless to say you need to be very careful not to overheat and break the thermometer in the process. Storing the thermometer in an upright position will help prevent this from recurring.
Roger Hicks said:Dear Claire,
Puzzles me too.
Cheers,
R.
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