Solid State Relay is referred to as SSR. It is a new type of non-contact switching device composed entirely of solid electronic components. It uses high-power triodes, power field effect transistors, one-way thyristors, two-way thyristors and modules among other electronic components. It has unique switching characteristics and can connect and disconnect electrical circuits without contacts or sparks. It is also called a contactless switch. SSR is generally a four-terminal active device, including two control terminals and two output terminals. Input and output terminals are reliably isolated. When a control signal is applied to the input terminal, the output terminal switches on or off.