A bi-metallic strip is a thin strip of two metals bonded together back-to-back (usually rectangular in shape) that has one metal coating one side and another metal coating the other side. As the temperature changes, the expansion of the two metals being different causes the metal strip to bend toward the side of the metal with less expansive reaction to the heat. A bi-metallic thermometer uses this expansion to indicate temperature on a gage or scale (a mechanical action).
A strip made by firmly attaching two different metals side by side, which when heated bends, and on cooling returns o original shape is called bimetallic strip for example iron brass strip. This bending is due to the difference in values of co-efficient of linear expansion of two metals that is one metal expands more than the other over the same rise of temperature. Bimetallic strip is used in making circuit breakers in electrical heating circuit devices.
Bimetallic thermometer is a device which works on the principle of thermal expansion in which bimetallic strip is used to determine the temperature of the body. A bimetal strip can be used to make a simple thermometer, which is easy to read.
In such type of thermometer, is used in shape of a coil. One end of a coil is fixed and a pointer is attached to the free end. When the temperature rises, the bimetallic strip coils itself into an even tighter spiral due to different expansion rates of the two metals, which form the bimetal strip, and the pointer moved across the temperature scale. The bending of bimetallic spiral type strip changes with temperature and the pointer indicates the reading on the scale
Power source not required Robust, easy to use and cheap but not very accurate. Can be used to 500 °C Limited to applications where manual reading is acceptable, e.g. A household thermometer Not suitable for very low temperatures because the expansion of metals tend to be too similar, so the device becomes a rather insensitive thermometer
A bi-metallic strip is used to convert a temperature change into mechanical displacement. Mechanical clock mechanisms are sensitive to temperature changes which lead to errors in time keeping. A bimetallic strip is used to compensate for this in some mechanisms.In the regulation of heating and cooling, thermostats that operate over a wide range of temperatures the bi-metal strip is mechanically fixed and attached to an electrical power source while the other (moving) end carries an electrical contact.A direct indicating dial thermometeruses a bi-metallic strip wrapped into a coil. One end of the coil is fixed to the housing of the device and the other drives an indicating needle. A bi-metallic strip is also used in a recording thermometer.
