Solid State Devices
How They Work:
There are many different types of controls that fall into the classification of solid state devices. Basically, these devices are activated by increases in temperature and or current, but have no moving parts. One important aspect to consider is that since there are no moving parts to make or break an electrical circuit, then in some cases, the device is never really achieves a true open circuit status. In many instances, the device becomes "non-conductive" under the effects of changes in temperature and will only remain in an "open" state as long as the device remains under load.
The most common types of solid state devices fall into two categories. These are (1) Polymer devices or (2) Ceramic devices. There are also devices called thermistors types of solid state devices are cheaper than other thermal controls, however they do not have the ability to carry current.