How do they make thermometers?
 

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"

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

"Jeff Wisnia" wrote in message
...
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"

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


On 14 Jan 2005 03:08:35 GMT, 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

On Tue, 18 Jan 2005 01:29:18 GMT, Errol Groff wrote:

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!

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.

--
Mike Firth
Hot Glass Bits Furnace Working Website
http://users.ticnet.com/mikefirth/hotbit46.htm Latest notes

"Dave Hinz" wrote in message
...
On Tue, 18 Jan 2005 01:29:18 GMT, Errol Groff
wrote:

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!

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.

"Mike Firth" wrote in message
...
.... Not something I would
like to try with alcohol inside.


You, or the glass tube?