This is a sensor that design type electro-mechanical temperature sensor or switch, that basically consists of two different metals such as nickel, copper, tungsten or aluminium etc, that are bonded together to form a Bi-metallic strip. The thermostat can be used itself as an electrical switch or as a mechanical way of operating an electrical switch in thermostatic controls and are used extensively to control hot water heating elements in boilers, furnaces, hot water storage tanks as well as in vehicle radiator cooling systems. This is a figure schematic for the sensor.
The thermostat consists of two thermally different metals
stuck together back to back. When it is cold the contacts are closed and
current passes through the thermostat. When it gets hot, one metal expands more
than the other and the bonded bi-metallic strip bends up (or down) opening the
contacts preventing the current from flowing. There are two main types of bi-metallic
strips based mainly upon their movement when subjected to temperature changes.
There are the “snap-action” types that produce an instantaneous “ON/OFF” or
“OFF/ON” type action on the electrical contacts at a set temperature point, and
the slower “creep-action” types that gradually change their position as the
temperature changes.
Snap-action
type thermostats are commonly used in our homes for controlling the temperature
set point of ovens, irons, immersion hot water tanks and they can also be found
on walls to control the domestic heating system. Creeper types generally
consist of a bi-metallic coil or spiral that slowly unwinds or coils-up as the
temperature changes. Generally, creeper type bi-metallic strips are more
sensitive to temperature changes than the standard snap ON/OFF types as the
strip is longer and thinner making them ideal for use in temperature gauges and
dials etc.
