Bimetallic Thermometers & Thermostats – Bimets

bimetalBimetallic thermometers, or simply Bimetal or Bimet thermometers are contact temperature sensors found in several forms if you know where to look, e.g. inside simple home heating system thermostats.

Bimets are based simply on the difference in thermal expansion coefficient of two metals (that’s the Bi-Met part).

They’re the coil of metal that has some electrical contacts affixed to it. They are more familiar to many people in industry and commerce as miniature pocket dial thermometers that many people use to check the temperature of fat in a deep fryer or a vat on a process line.

Perhaps the best part is that the pocket thermometers are sealed and do not require batteries! The major uses are where a quick check of the temperature of an object is desired, or, in the case of the thermostats, a simple, reliable, low cost sensor that provides the input and sometimes a good part of the control action in a home heating system.

(Nowadays electronic thermostats are more commonly seen and since they need a battery to power the clock inside them, they usually have a different type of temperature sensor, one that also runs with a battery.)

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