I came across this rather strange looking thermometer. It seems to have two scales and some kind of wires inside it.

There are two terminals at the top. Is it a thermostat? But it seems to be too long for one. Should be at least an arm length.

It seems to be very old to as I was unable to find anything on google about it with its name or data on it.

front view lower terminal Upper scale and electrical terminal Update: Terminals wire close to mercury

  • \$\begingroup\$ I think you need to improve your photography skills a bit and do some image cropping. Where are the wires? Where are the terminals? What is the screw-like thing in the top half? What moves when you turn the screw? Is there an adjustable contact that the mercury wets when it expands enough? Where is the bottom contact in that case? \$\endgroup\$ – Transistor Nov 24 '17 at 20:05
  • \$\begingroup\$ I'll add a picture for the terminal. My initial picture was of higher quality, but the size is too large to be uploaded. \$\endgroup\$ – The_Vintage_Collector Nov 24 '17 at 20:08

Yes, it is a thermometer that is used in water-based thermostats. There is a tiny wire attached to a magnet inside on a threaded rod, and the top knob has a magnet, so when rotating the top you can move the wire position relative to mercury level. This makes an on-off switch that is used by electronics to control bathtub heater.

ADDITION: This device is called "mercury contact thermometer", or "glass contact thermometer", and they are still in use, example here. From the link, contact rating is 20 mA 36 V. Here is another one, enter image description here

  • \$\begingroup\$ Thanks. I didn't know it was a knob to move a wire. Until now I had just tried to remove it only. Just tried now and the small black metal piece close to 30C as in picture 2 is moving. Also do you happen to know the voltage and current ratings for them if you have come across any? \$\endgroup\$ – The_Vintage_Collector Nov 24 '17 at 20:25
  • \$\begingroup\$ @The_Vintage_Collector, I did use this kind of devices maybe 40 years ago. It was a closet-circuit thermal regulation in a water circulation system used for scientific experiments. There is a magnetic coupler that turns the threaded rod inside the glass, and the nut on this rod moves attached wire. Not sure about the current of this switch, but it should be small, milliamps likely. \$\endgroup\$ – Ale..chenski Nov 24 '17 at 20:36
  • \$\begingroup\$ Thank you for the name and the link to specs. I had tried different combinations of names with mercury on Google but nothing came up. The link above says 32V 26mA. So, probably it might be used to activate some sort of relay or something I assume. I wasn't sure of the voltage before because too much means the voltage could cause an arc and the mercury might solidify at that point and ruin the device. \$\endgroup\$ – The_Vintage_Collector Nov 24 '17 at 21:34
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    \$\begingroup\$ @The_Vintage_Collector, yes, this is an outdated piece of equipment. Knowing exactly what I am looking for, it took me almost an hour to find it on Google. And yes, the contact is usually feed a transistor amplifier, which, in turn, controls a much more powerfull heater, in a kW range. \$\endgroup\$ – Ale..chenski Nov 24 '17 at 21:40
  • \$\begingroup\$ Wow..these old equipments are pretty interesting. Nowadays most things are electronic and pretty easy & precise, but people don't really care how it works. These old stuffs like this one is easy to understand. I mean most people who used them knew how it would have worked unlike with electronic ones today. \$\endgroup\$ – The_Vintage_Collector Nov 24 '17 at 21:59

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