| By :
Sarah Simmons
A bi-metallic temperature switch is a switch that responds to temperature changes. This type of device is also known as a thermal switch, or sometimes as a thermal reset. Typically, a bi-metallic temperature switch will open at a preset high temperature often with an audible "plink"-type sound, and then re-close when the temperature drops. This sort of action can protect a device from heat or power overload caused by varying scenarios. The bi-metallic temperature switch is so called because it is formed of two strips of different metals which expand and contract at different rates as it is heated. Typical metal pairings used in temperature switches include steel and copper, or steel and brass. The strips are held together their entire length by either rivets, or welding, or brazing. Glass bulbs often encapsulate the bi-metallic strip so as to protect it from short circuits or dust. Many thermal switches are programmable to be activated at different temperature thresholds, so it is important to be mindful of the environmental parameters that allow thermal switches to operate without condensation forming, which may cause a potential short. Thermal switch bi-metallic strips are capable of breaking the flow of electricity in a circuit, thus shutting off either a portion of a device, or a device in entirety, protecting both the device, the environment around the device, and any operators of the device. Temperature Switch Applications Bi-metallic temperature switches are found in various types of thermostats, power supplies, and portable heaters, among many other products. The thermal switch protects these devices by cutting power when the device or ambient temperature gets too hot. These switches are also great for maintaining a certain temperature. Thermal switches also find application in light fixtures. Recessed lighting is one application where excessive heat is an issue. This can lead to a "cycling" effect, where lights turn on and off every few minutes as the thermal switches reset. Christmas lights use the characteristics of temperature switches to achieve flashing, sparkling, or twinkling effects. Thermal switches also play a key part in the starting of older fluorescent lights. Another useful application of bi-metallic strips can be found in liquid temperature sensors and switches. If bi-metallic strips are properly jacketed in a non-corrosive housing, they are able to function in almost any liquid or gas environment. Oftentimes, temperature switches can also function as temperature sensors. To protect against thermal overload, a semiconductor switch often utilizes an integrated temperature sensor. This switch can also be set up to present either a real or a mechanical user with an interface that communicates a changed temperature reading. Temperature sensors are critical for monitoring potentially device-harming or environment-damaging situations. Every Temperature Switch Is a Thermal Cutoff By nature, every temperature switch is a thermal cutoff. A thermal cutoff is an electrical safety device that interrupts an electrical circuit by breaking the flow of electricity when heated to a specific temperature. Temperature switches should not be confused with temperature fuses, which are a type of thermal fuse that is a single-use device.
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