What Is a Bimetallic Strip Thermometer?

bimetallic-strip-thermometer Credit: Ryerson Clark/E+/Getty Images

A bimetallic strip thermometer is a mechanical thermometer that is commonly used for its temperature control. This type of thermometer is robust, simple and has a wide temperature range. It contains two strips that are bonded together and made of dissimilar metals.

The strips have a fixed end and a free end. The principle behind the mechanism of a bimetallic thermometer is that the pair of strips bend at the free end when the temperature changes, and one of the strips expands more than the other. Bimetallic strips typically use a low thermal expansion alloy, such as Invar, and a high thermal expansion alloy, such as steel or stainless steel.

Bimetallic strip thermometers are constructed in two ways. The first method is a spiral strip, which involves coiling the bimetallic strip into a spiral that is attached to a dial that shows the temperature. The second method of constructing this thermometer is through a cantilever strip, which uses deflection to indicate temperature. The bimetallic strips are closely bonded together in a cantilever.

Bimetallic thermometers are often used to measure and control temperature in thermostats. The main advantage of using bimetallic strips is that a power source is not necessary. Moreover, they are sturdy, affordable and easy to use. However, they are not quite exact, and they do not function well at very low temperatures. Also, they cannot be used in applications where manual reading is not acceptable.