On 2/4/2018 10:51 AM, (PeteCresswell) wrote:
I've been trying to buy four refrigerator/freezer thermometers and it's
frustrating how inaccurate/inconsistent they are.

For Instance:

- 4 thermometers of same make/model, hanging on the same rack.

- Alcohol bulb/glass tube - you'd think basic physics...

- Each reads a different temp from 68 to 74 degrees.

Only thing I can think of is that the card behind the glass thingie is
misaligned, but looking at these things, there does not seem to be enough
physical room for those kinds of errors.
....


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Omega has a line of low-cost glass lab thermometers but don't specify
accuracy on them, either; they have others of lab quality that are $10+
or so each instead of $5-6.

They used to have an ambient-air monitor that was pretty good that we
used to use to monitor air temp around the boilers but it doesn't seem
to be available any longer and the one other I looked at from another
vendor was also listed as discontinued. That's all the time I had...

The problem with inexpensive bulb thermometers is that the capillary
dimension has to be exceedingly precise in order to control both the
linearity and scaling and doing that drives the price up -- actually,
like matching v-belts; to get precise ones they would just select from
the run those that matched given calibration but as somebody else noted,
the ordinary Walmart/drugstore/etc., ones will not have gone through
much if any screening at all; what you get is a measure of the
manufacturing process variability by doing the comparisons you've done.

But, the time/effort required to do screening adds up so even moderately
accurate ones get to be fairly pricey pretty quickly.

If a bulb thermometer serves the purpose, probably one of the
secondary-school lab suppliers or the like will be the best bet.

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