Bulb thermometers are good for measuring temperature accurately, but they are harder to use when the goal is to control the temperature. The bimetallic strip thermometer, because it is made of metal, is good at controlling things.
The principle behind a bimetallic strip thermometer relies on the fact that different metals expand at different rates as they warm up. By bonding two different metals together, you can make a simple electric controller that can withstand fairly high temperatures. This sort of controller is often found in ovens.
In this diagram, the green metal would be chosen to expand faster than the blue metal if the device were being used in an oven. This causes the strip to bend upward, making contact so that current can flow. By adjusting the size of the gap between the strip and the contact, you control the temperature.
By: Vanessa Low