A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal.
The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays were used extensively in telephone exchanges and early computers to perform logical operations.
By watching this video you will know more about relays :
Relays are used for:
1) Amplifying a digital signal, switching a large amount of power with a small operating power.
2) A telegraph relay, repeating a weak signal received at the end of a long wire
3) Controlling a high-voltage circuit with a low-voltage signal, as in some types of modems or audio amplifiers
4) Controlling a high-current circuit with a low-current signal, as in the starter solenoid of an automobile
5) Detecting and isolating faults on transmission and distribution lines by opening and closing circuit breakers
6) Isolating the controlling circuit from the controlled circuit when the two are at different potentials,
Logic functions.
7) Time delay functions. Relays can be modified to delay opening or delay closing a set of contacts.
8) Vehicle battery isolation. A 12v relay is often used to isolate any second battery in cars, 4WDs, RVs and boats.
9) Switching to a standby power supply.
Relay has 5 pins. 2 input pins and 3 output pins. We connect input supply to these 2 pins. 3 output pins are POLE, NC and NO. NC means normally closed and NO means normally opened. The Output Supply or circuit which we want to control should be connected to NO and POLE.
When input supply is off electromagnet is off and hence armature is connected to NC pin. When we provide input supply then electromagnet is turned ON. Due to this armature is attracted towards the coil and connection between POLE and NO is established.
In simple words when supply is ON a closed connection is formed between NO and POLE.
By watching this video you will know more about relays :
Applications
Relays are used for:
1) Amplifying a digital signal, switching a large amount of power with a small operating power.
2) A telegraph relay, repeating a weak signal received at the end of a long wire
3) Controlling a high-voltage circuit with a low-voltage signal, as in some types of modems or audio amplifiers
4) Controlling a high-current circuit with a low-current signal, as in the starter solenoid of an automobile
5) Detecting and isolating faults on transmission and distribution lines by opening and closing circuit breakers
6) Isolating the controlling circuit from the controlled circuit when the two are at different potentials,
Logic functions.
7) Time delay functions. Relays can be modified to delay opening or delay closing a set of contacts.
8) Vehicle battery isolation. A 12v relay is often used to isolate any second battery in cars, 4WDs, RVs and boats.
9) Switching to a standby power supply.