High temperature switch: an important part of thermal monitoring

A high temperature switch can be found in many electrical products. Electric frying pans, heaters, dishwashers, clothes dryers and more use a high temperature switch because of the snap action design.

There is only around a 10 to 15 degree difference between a closing and opening temperature. For example, if the switch trips at 40 degrees Celsius, it will not trip again until the temperature reaches around 30 degrees Celsius. This temperature difference shows the important role that a high temperature switch plays in order to accomplish this.

The high temperature switch helps control items that are tripped, or switched on, when a device begins to overheat. A good example of this is the cooling temperature of a car that has been sitting overnight.

The function of a high temperature switch

Each high temperature switch is different - they each have their pros and cons and some applications are more appropriate for certain functions than others. Increasing technology has produced thermal devices that are much more accurate with a sensitive response time.

The rate of temperature change is not always a consistent process when it comes to the products in which they operate. The rate of heat flow can be quite erratic. When you are trying to make sure you choose the best high temperature switch for a specific application, you may need to employ a trial and error methodology.

Some of the ways used to specify a high temperature switch are:

• Consider the switch's set point. This refers to the contact points that open and close when preset temperature is reached.

• The degree of accuracy

• The switch reset temperature

• Understanding the switch action - the switch closes when the temperature rises (e.g. open on temp rise, close on temp rise, open on temp rise, close on temp fall, open on temp fall).

Engineering the design

The high temperature switch is an important part of an appliance's design. It protects the unit from damage or igniting a fire caused by overheating. Before an appliance is ready for the public, it must go through a series of tests designed to check the high temperature switch and other components for consumer safety. There are third party certification laboratories such as UL, ETL Semko and MET Laboratories. They test a design by administering a series tests exposing a unit to normal and abnormal conditions a required according to national standards. But a good designer will not rely on the results of these tests. Instead, a designer should use the tests to analyze and refine the high temperature switch and other components of the unit before sending it to the lab.

The complexity of thermal protection

When it comes to electrical appliances, the same exact designs will each exhibit differences in their heat output. The hotspots in each unit will be different, even if the design is identical. Designers must be aware of these complexities when it comes to installing the high temperature switch and other thermal components in the units they design.