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I found this thing, and have no idea what it is.

The tube is 30 mm long, about 5 mm in diameter. Both terminals are connected with two drops of glass. There seems to be a tiny wire or filament connecting both wires inside the tube.

The glass tube

Any suggestions?

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  • \$\begingroup\$ Long neon bulb? \$\endgroup\$ – Olin Lathrop Dec 15 '16 at 19:29
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    \$\begingroup\$ If you look carefully, You can see that the two electrodes are connected with a thin wire made from a different metal. I think it's some thermoelectric heat sensor, or something like that. \$\endgroup\$ – dnnagy Dec 15 '16 at 19:39
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    \$\begingroup\$ So do some measurements. Does it put out a few millivolts? Can you measure its resistance? Does resistance change when you measure it one way, compared with leads reversed? \$\endgroup\$ – glen_geek Dec 15 '16 at 19:41
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    \$\begingroup\$ Don't know but it seems to be good at maths. \$\endgroup\$ – Mario Dec 15 '16 at 19:42
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    \$\begingroup\$ Reed switch perhaps? \$\endgroup\$ – Bort Dec 15 '16 at 20:21
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I'm thinking more like RTD. With a thermocouple, the two leads would be two different materials. With an RTD, the very thin wire at the tip would be platinum, and its resistance would change in a calibrated way with temperature.

Can you put it under a microscope of some sort? I bet you'll find that there's a very tiny coil of the very fine wire embedded in the glass at the very tip.

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  • \$\begingroup\$ The bulk RTDs I've seen were larger than that. Even the thin-film types were larger. I'll stick with thermocouple for now. \$\endgroup\$ – Robert Endl Dec 15 '16 at 21:21
  • \$\begingroup\$ A thermistor is also possible. The resistance would be Much higher. \$\endgroup\$ – Robert Endl Dec 15 '16 at 21:24
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Looks like a "glass bead" style of thermistor. Very common, but usually much smaller. Does your DMM read it as resistor? Ohms changing when warmed with fingertip? Maybe it's a replacement part for a liquid probe.

Usually the glass bead thermistors look like a tiny glass sphere w/thermistor inside, or a thin solid glass rod with a little sphere at the tip. Not hollow.

Aha, here's one. Also another.

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Probably a thermocouple. Put a mV meter on the leads, put your finger on the tip and you should measure some 10s of mVs. Take your finger away and the mV should drift down to 0.

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Curious. Some pH electrodes look a bit like that. Some hint as to where it might have originated could help.

Maybe it's intended to break and open the circuit under some conditions such as shock (mounted with a weight, for example).

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  • \$\begingroup\$ I have absolutely no clue, where it is from, I found it in my grandfathers drawer:) \$\endgroup\$ – dnnagy Dec 15 '16 at 21:27
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    \$\begingroup\$ What did grandfather do? Safecracker? Rogue nuclear scientist? Minion to evil ringleader? \$\endgroup\$ – Spehro Pefhany Dec 15 '16 at 21:46
  • \$\begingroup\$ He was an EEG doctor. Tomorrow i will do some measurements, to find out what it is. \$\endgroup\$ – dnnagy Dec 15 '16 at 21:49
  • \$\begingroup\$ Okay, if you can look at the end to see if it is (or was) sharp that might be interesting. I'm thinking a probe of some kind. \$\endgroup\$ – Spehro Pefhany Dec 15 '16 at 21:59
  • \$\begingroup\$ pH electrodes don't look at all like that. \$\endgroup\$ – Robert Endl Dec 16 '16 at 0:18

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