A traditional relay is an electro-mechanical switch that opens and closes a set of contacts under the control of another electrical or electronic circuit that is known as the control circuit.
Relays are found everywhere in today’s modern life. They exist in most of our modern home appliances: microwave ovens, washing machines, TV’s, VCR’s and cassette recorders.
The relays switch on the turn table, lamp and buzzer in the microwave oven. Relays are also used in the washing machine to turn on electric motors and buzzers. Many relays are used in cars as well to turn on the horn, windows, motors and lights. These are commercial applications of the relay but the number and applications of relays in the industry are countless where they play a vital role.
The main function of a relay is to isolate high voltage/current circuits from control circuits or operator for different reasons: safety, protection and comfort of operator.
There are many applications of the relay. Here are only some:
- Domestic: home appliances, security systems
- Commercial: cars, elevators, lighting
- Industrial: automation, motor control, heating, lighting, hoisting, traction
The relay was invented by Joseph Henry in 1835 but it is still used widely nowadays. This invention led to a successful demonstration of the electrical telegraph in 1837 by Samuel Morse and Charles Wheatstone.
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