Introduction to Bimetalic Temperature Sensors

The Bimetallic strip is a mechanical temperature sensor element. It converts temperature to a mechanical displacement. This displacement may be coupled to a switch for simple on-off function, to a needle of an indicator, or to a position detector for electronic output.

By far the most common application of the bimetallic strip is as a thermostat switch used for temperature and energy control.

Construction of the bimetalic strip

A bimetallic strip is simply constructed from two strips of different metals bonded together. Typically a welding process is used for bonding, but rivets, bolts, adhesive and other fasteners can also be used.

The operation of the bimetallic strip relies on the different expansions rates of the two metals to temperature change ( the different coefficients of thermal expansion of the metals).

Note: There is no reason to confine the principal of the bimetallic strip to metals - any two solids could in principal be used. The bimetallic strip may be coiled to make it more compact and sensitive, with temperature changes causing the coil to tighten or unwind.

Pressing a dimple into the bimetallic strip can produce a snap action with hysteresis - a characteristic that is good for temperature control.

As a matter of interest, the bimetallic strip can be scaled up or down. On a large scale, it can provide literally tones of force for mechanical control or other purposes. On a smaller scale, it can provide the force and movement for micro machine integrated circuits (MMIs).