Ignoramus30333 wrote:
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. G

Or, you can make your own this way:

http://home.howstuffworks.com/therm1.htm

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"