
Solid State Relays

Relays are switches that open and close circuits. They control one electrical circuit by opening or closing contacts in another circuit. When a relay contact is normally open (NO), there is an open contact when the relay is not energized. When a relay contact is normally closed (NC), there is a closed contact when the relay is not energized. Applying electrical current to the contacts will change their state. Many relays use an electromagnet to mechanically operate a switch, but other operating principles such as solid-state relays are also used. Relays are used where it is necessary to control a circuit by a low-power signal or where several circuits must be controlled by one signal. Depending on the structural features and operating principle, relays are of different types such as monitoring, regulating, auxiliary and protective. Classification of the types of relays depend on the function for which they are used.
Solid state relays have no moving parts like electromechanical relays, but utilize electrical components and optical properties of solid state semi-conductors to perform IO switching functions and isolation. They are designed for applications that require high switching speed without arcing or contact noise. They are highly resistant to vibration and shock and are unaffected by the presence of dust, gases or other contaminants. Solid state relays are used in heating control applications for a compressor’s soft-start, fan, blower, heater and valve control. They are used in lighting applications for dimming and for their ability to operate silently and switch quickly. Because of their resistance to shock and vibration and non-arcing, motion control applications such as lifts, hoists conveyor systems and elevators are the perfect fit for solid state relays.
Products
Electromechanical relays (EMR) use physical moving parts to achieve the desired functionality. These moving parts include the contacts that switch between the normally open and normally closed stationary contacts in the relay. This movement is made possible by an electromagnet. When power is applied to this magnet, it will act on the movable contact causing the relay to switch. In an EMR, it is common to hear the switching sound that is represented as a “clicking” noise. This audible noise can be helpful when determining the functionality of the relay.
Solid-state relays (SSR) use a low power, electrical signal to generate an optical semiconductor signal that will transmit and energize an output signal. When this is activated, the input optical signal will act as the switch, allowing a higher voltage signal to pass through the relays output components. The internal circuitry of a SSR is far more complex than an EMR, but there are no physical moving parts.