Does there exists a sort of shrink tubing with good thermal conductivity?

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Why go through the hassle when tiny glass bead thermistors are
available that you can epoxy into the hole?

http://www.ge-mcs.com/download/temperature/920_308a.pdf

Or dip the thermocouple in molten glass.

tm

On a sunny day (Sun, 16 Jan 2011 17:16:16 -0600) it happened John Fields wrote in :

exchanger.

Becaue there is already one in there?????? (see above text). I want a THERMOCOUPLE, as I have a thermocouple interface.

0 C).

ning.

hanger.

Omega Engineering

sells stainless sheathed thermocouples. With a reasonable probe and lead length, they're not too expensive. I think the last we bought were under $25. If you want the fastest transition time, go with a grounded probe, otherwise go with ungrounded (un/grounded means the gunction is in contact w/the sheath).

On a sunny day (Sun, 16 Jan 2011 18:25:16 -0500) it happened "tm" wrote in :

Yes that would work. Just have to go and melt some glass. Anywhere between 570 and 1470 C IIRC. Its a 'cool' idea, may just try it

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Problem with temperature coefficient of expansion between the metal
and the glass, I think, so the glass will crack off as it cools.

But, dipping the thermocouple into some beryllia loaded epoxy and then
centering it in a teflon tube until the epoxy cures might work.

On a sunny day (Sun, 16 Jan 2011 15:42:51 -0800 (PST)) it happened " snipped-for-privacy@gmail.com" wrote in :

Yes, I know about omega.com, but I am making my own thermocouples from transformer wire and resistor wire, works perfectly, I twist the ends together and then solder those. Costs nothing (wire comes from an old wire wound resistor, and the transformer wire from an old transformer).

that one has some other multi-stranded copper, was a first try, latest ones are much thinner. Seems to be within one degree C.

The glass coating can be very thin and flexible. Maybe even a glass frit and fire it with a torch.

tm

Place a layer of Kapton film between the couple and what you're monitoring. Then wrap it with heat shrink tubing or tape.

--
David
dgminala at mediacombb dot net

..

es are much thinner.

Well, that is just too cool! I've made a lot of motors and coils from wire salvaged from deflection coils out of old TVs, but can't remember making my own scratch-built thermocouples! Now I see the tie-in from where you were making your own instruments and getting calibration curves (I only read the group occasionally...). A long time ago, I worked at Texas Instruments, and we made our own TCs from TC wire, but welded the junctions together using a special hydrogen/oxygen torch. All the twisted pairs would fail when used in acid baths. I bet the metal sheathing idea would still work, assuming the wires were insulated except for the tip. Metal-filled epoxy might be another way to go. Can you get JB Weld or similar?

What T-coefficient did you find for your DIY thermocouple? With a quick and dirty test I found about 38µV/°C for a TC using resistance wire (Monacor 62.4?/m 0.1mm) & roadrunner prototyping wire (lacquered copper wire 0.2mm).

Regards, Gio

On a sunny day (Sun, 16 Jan 2011 19:56:10 -0600) it happened "Dave M" wrote in :

Yes, that could work. I will experiment a little later with the variuos methods suggested.

On a sunny day (Mon, 17 Jan 2011 12:26:39 +0100) it happened "GRe" wrote in :

It is a type T, I just compard it by puting it on my temperature controlled soldering iron, it has a digital display, and it was tracking to +190 C within 1 degree C. It is porbably better, but the biggest problem was keeping a good thermal contact. I did not go any higher as I do not need that high, and the electronics is designed to go lower, not higher:

On a sunny day (Sun, 16 Jan 2011 23:44:00 -0800 (PST)) it happened " snipped-for-privacy@gmail.com" wrote in :

I could probably weld the ends, but this works just fine. Yes all this stuff is part of a larger plan... I am not using any acid or that, just very cold stuff, and up to maybe 70 C.

exchanger.

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Well, then, since the dimensions are so tiny, I don't think that
thermal conductivity is going to be a problem, particularly.

Try tiny polyimide (Kapton) tubing, like you can get here:

http://www.smallparts.com/translucent-amber-miniature-polyimide-tubing/dp/B003TLNL5I/ref=sr_1_2?sr=1-2&qid=1295279407

exchanger.

There used to be heat-shrink teflon tubing available

0 C).

ning.

hanger.

Thermo couples leak a lot of heat via the leads. So you cna get some funny readings if the leads are in air that is a much different temperature from your piece of metal. (Wrap the leads onto the metal piece if you have room.)

I found Sil pads have a much better thermal conductivity than thin Kapton tape. (For wahtever that is worth.)

George H.

On a sunny day (Mon, 17 Jan 2011 09:57:28 -0600) it happened John Fields wrote in :

C).

opening.

exchanger.

I found tha tthe slightes amount of air, or play between thermocuple and object, will severely degrade the thermal contact.

Yes thin walled would probably work, and then with heat sink paste. I will try out some things later.

exchanger.

"Heat leak" depends a lot on configuration. One good trick is to have the thermocouple glued as deep as possible in a low diameter bored hole :

| ____ Fill with glue /---------------' / < x============================== thermocouple wires \---------------. |

Doing so, the 'radial' thermal resistance of glue will be lower than the longitudinal thermal resistance of the thermocouple wires and the solder temperature will be what you want. IOW make sure the leaked heat doesn't come from the solder environment.

Just use small bifilar thermo wires, not the heavy shielded one, small heat shrink tubing, use an as small as practical hole diameter filled with glue and you'll be OK.

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Thanks,
Fred.