Relay

related topics
{system, computer, user}
{math, energy, light}
{@card@, make, design}
{car, race, vehicle}
{rate, high, increase}
{style, bgcolor, rowspan}
{school, student, university}

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.

A type of relay that can handle the high power required to directly drive an electric motor is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called "protective relays".

Contents

Basic design and operation

Full article ▸

related documents
LORAN
Rectifier
Loading coil
Amstrad CPC
Commodore 1541
10 Gigabit Ethernet
Session Initiation Protocol
Pulse-code modulation
Quality of service
DV
Direct Connect (file sharing)
RS-232
Computer multitasking
Handoff
X Window System
X10 (industry standard)
Reduced instruction set computer
Mandriva Linux
Genera (operating system)
Virtual memory
BIOS
Universal asynchronous receiver/transmitter
Set-top box
IEEE 802.11
Webcam
Workstation
Digital Enhanced Cordless Telecommunications
Throughput
Three-phase electric power
File Transfer Protocol