Electronic – What could be this particular thermometer used for


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
wire close to mercury

Best Answer

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

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