Relay is an automatic electric switch. When supplied with an input, like electric, magnetic, light, thermal or any other signal, it'll switch the controlled circuit automatically to produce an abrupt change. When the input decreases to a certain degree, it'll return to default state and make the controlled circuit back to former state.


Relays could be classified by different methods or characteristics. As divided by their working principle or structure features, relays have the listed types.


Relay has a wide application. It has the following functions.

  • isolation between input circuit and output circuit
  • signal transformation
  • increasement for the input circuit
  • signal repetition
  • switch on different voltage or current
  • preserve of signal
  • circuit lockout
  • remote control