I bought a $3 regular thermometer at Walmart today and am marveling at
the precision that it required to make. How do they make thermometers
with such an inner diameter of the tube, and how do they fill it so
accurately? This is, also, quite old technology, so it must be rather
simple.
i
Good question...
I did find references to glass thermometers being regularly produced in
europe as early as 1666.
I don't know how they are made in mass production, but if I was
challenged to guess how it "could" be done I'd say:
The tubing is made by drawing out a larger diameter glass tube. There
may be a strip of opaque colored glass fused to the side first to
provide the backdrop. The bulb may well be "blown" by heating that end
until it closes over and then blowing in the other end in typical
glassblower fashion.
You could probably fill them through the open top end by submerging them
in the filling liquid, pulling a vacuum so all the air leaves the
thermometer, then bringing them back up to room pressure.
I'd expect you could establish the right amount of liquid in them by
heating them to a temperature you want to correspond to the full length
of the tube, so the excess spills out, then letting them cool so the
column retracts, and finally fusing the top end closed.
Sounds like something even I could learn to do if I absolutely
positively had to.
Or, you can make your own this way:
Some thermometer tubes are mated with one of a range of different length
scales to reduce the precision required in the tube. They are nearly always
longer than the scale and positioned to match the scale. Of course high
precision thermometers are individually calibrated.
Don Young
I don't know ow they are made but I do know that you should always but
thermometers in the summer time. That you way you get a lot more
mercury for your buck!
Errol
Of course. As far as how to fill it accurately, I would imagine the whole
filling system is at a temperature at the top of the scale - fill it to
the top, and as it cools it'll shrink down. But the volumes have
to be very precise. I'd also like to know how it's drawn, but the
filling I think is the easy part.
Try to imagine HOW they would be filled to the top.
In fact, the part of the tubing with the uniform hole is not all that
difficult to make with proper practice because of the way glass behaves when
it has a hole in it and is pulled.
The descriptions I have read for older methods involve pulling the
capillary tube, sealing one end, adding the reservoir end, open, pulling a
vacuum inside the whole thing, sealing the bottom. Not something I would
like to try with alcohol inside.
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