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   Relays, Telephone

A relay is an electrical switch that opens and closes under control of another electrical circuit. In the original form, the switch is operated by an electromagnet to open or close one or many sets of contacts. It was invented by Joseph Henry in 1835. Because a relay is able to control an output circuit of higher power than the input circuit, it can be considered, in a broad sense, to be a form of electrical amplifier.

These contacts can be either Normally Open (NO), Normally Closed (NC), or change-over contacts.

  • Normally-open contacts connect the circuit when the relay is activated; the circuit is disconnected when the relay is inactive. It is also called Form A contact or "make" contact. Form A contact is ideal for applications that require to switch a high-current power source from a remote device.
  • Normally-closed contacts disconnect the circuit when the relay is activated; the circuit is connected when the relay is inactive. It is also called Form B contact or "break" contact. Form B contact is ideal for applications that require the circuit to remain closed until the relay is activated.
  • Change-over contacts control two circuits: one normally-open contact and one normally-closed contact with a common terminal. It is also called Form C contact.


Bronze Partners
Aleph International Corp.
Altech Corp.
American Relays, Inc.
American Zettler
Aromat Corp. (Matsushita Electric Works, America)
CII Products
CIT Relay and Switch
Clare Inc.
DARE Electronics, Inc.
EAC Electronics Co.
Fujitsu Components America, Inc.
Greenwich Electronics
Hamlin
Hasco Components International Company
Line Electric Products
Magnecraft
Master Electronic Controls (MEC)
MEDER electronic Inc.
Midtex Products
NEC Electronics Corporation
Omron Electronics LLC
Philips ECG
Picker Components
Pontiac Coil-Arkansas
Relay Service Company
RFE International, Inc.
SRC Devices
Stetron International, Inc.
Sumida America
Ventronics, Inc.
Wheelock, Inc.
Fix & Prog. Sinewave Oscillators - Frequency Devices

 

Books
ORIGINAL PRINTED PATENT APPLICATION NUMBER 65 FOR IMPROVEMENTS IN OR RELATING TO RELAYS FOR TELEPHONE OR OTHER WEAK CURRENT APPARATUS. (1910)
Curt (inventor) Stille

ORIGINAL PRINTED PATENT APPLICATION NUMBER 12,408 FOR IMPROVEMENTS IN AND RELATING TO RELAYS FOR TELEPHONE CIRCUITS. [1910]
Waldemar Otto Goswin (inventor). Droop

ORIGINAL PRINTED PATENT APPLICATION NUMBER 4,480 FOR A RELAY FOR TELEPHONE AND WEAK ALTERNATING CURRENTS. (1909)
Alexander (inventor). Nikiforoff

Cost 219: Survey of Text Telephones and Relay Services in Europe (Cost 219)
K.G. Olesen100.10:0/01

Great Customer Service on the Telephone (Worksmart Series)
Kristin Anderson

Excerpt - page 33: "... make the incoming voice louder. Ring signalers indicate a ringing telephone through flashing lights, vibrating wrist ... for individuals with sight impairment. RELAY SERVICES As of July 1993, all companies offering telephone service ..."
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Telephone Installation Handbook
Stephen Roberts

Excerpt - page 24: "... However, the fax machine or other device can disconnect the telephone outlet by operating relay contacts and thus take control of the line. This prevents ..."
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Understanding Telephone Electronics
Stephen J. Bigelow

Excerpt - page 35: "... Figure 1-20. Reed Relay Structure THE TELEPHONE SYSTEM I HORIZONTAL (ROW) STRAPS SEALED /~/~ GLASS ENVELOPE .p~,(w ..."
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Enterprise Networking: Fractional T1 to SONET, Frame Relay to BISDN
Daniel Minoli

Excerpt - page 82: "... 31 [1 99] S. Fleming, "Frame Relay' the Network-Based Solution," Telephone, 19 November 19911 [1.1011] D. ... to Supply Carriers with Frame Relay," Business Communication Review, September 1990, p. 81 [1 1041 J. ..."
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Electric Relays (Electrical and Computer Engineering)
Vladimir Gurevich

Excerpt - page 15: "... electric industry. In 1922 the plant was renamed the Petrograd Telephone plant "Krasnaya Zarya" and joined ... beginning of production of telephone relays in Russia. The first models of relays, produced by "Krasnaya ..."
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Introduction to Telephones and Telephone Systems (Artech House Telecommunications Library)
A. Michael Noll

Excerpt - page 38: "... This hook was called the switch-hook. The mechanism in today's telephone instrument that controls the flow ... is sensed by a line relay at the central office. ..."
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New miniature relay for telephone systems (Monograph) (Monograph)
C. F Spahn

Design characteristics of electromagnets for telephone relays, (Western Electric Co. Engineering Dept. Reprint) (Western Electric Co. Engineering Dept. Reprint)
Daniel D Miller

Cellular Telephones & Pagers: An Overview
Stephen Gibson

Excerpt - page 7: "... and a set of antennas, is connected by a dedicated telephone line or microwave radio relay link to the central switching and master control unit, the ..."
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Telephone Repair Illustrated
Stephen J. Bigelow

Excerpt - page 7: "... replaced by a discrete on/off switch that activates a sealed relay. The relay contains similar contacts to mechanical contacts, but it can be controlled digitally. Cordless and cellular telephones usually use a relay technique. The handset Traditionally, the handset ..."
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Logan Telephone leads community 'relay for life'.(Members makes a difference): An article from: The Exchange
Stacey Biggs

Telephone Switching Systems
Richard A. Thompson

Excerpt - page 35: "... a contact that closes or makes when the switch or relay is operated. The relay's electromagnetic coil is represented by a ..."
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Relays: Literature As an Epoch of the Postal System (Writing Science)
Bernhard Siegert and Kevin Repp

Excerpt - page 256: "... for further delivery.37 But even that, the text's last remaining relay, was eliminated in point 5: Invent a combination of telephone and Parlograph. This really can't be too difficult. The day ..."
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Old Time Telephones : Restoration & Repair
Ralph O. Meyer

Excerpt - page 37: "... Commercial induction coils 37 Line Line 4-4 Circuit of Edison's telephone that is based on his patent, applied for in 1877. was accomplished with relays. The concept of matching impedances, however, does not appear in ..."
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Voice over Frame Relay
William A. Flanagan

Excerpt - page 1: "... long, variable transmission delay across X.25 networks). Voice over frame relay (VoFR) is a compromise. Compared to the best quality available from the Public Switched Telephone Network (PSTN), V6FR is usually lower quality, but not much ..."
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Telephone Sales Management and Motivation Made Easy
Valerie Sloane and Theresa Arvizo Jackson

Excerpt - page 0: "... worked with such a warm and friendly group of people." Relay this comment to a job applicant or toot your horn about employee longevity. And sell the advantages of telephone sales over both retail store sales which keep you on ..."
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Broadband Networking ABCs for Managers: ATM, BISDN, Cell/Frame Relay to SONET
Robert P. Davidson

Excerpt - Front Matter: "... T1 networks. New broadband technologies such as frame and cell relay, SONET and SDH (the synchronous digital hierarchy , SONET'S European equivalent), as well as ATM, have entered the telephone company/post, telephone, and telegraph authority (Telco/ PTT) networks. ATM, for ..."
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Telehealth Nursing Practice Core Course, Second Edition
Maureen Espensen and Penny Meeker

Excerpt - page 83: "... all staff members should know how to access the state relay telephone service for the hearing impaired and communicate with a hearing ..."
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Which Telephone Service Provider? The Official Guide to Choosing the Best Local Phone Service Provider for Business
James Harry Green

Manufacturing the Future: A History of Western Electric
Stephen B. Adams and Orville R. Butler

Excerpt - page 122: "... including Wanda Beilfuss, Mary Volango, and Theresa Zajac - assembled telephone relays in a room separate from the rest of the department; ..."
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Wireless Horizon
Dan Steinbock

Excerpt - page 147: "... The 3C Era: Japan's Service Innovation 147 nationwide telephone and TV relay networks, while the Ministry's laboratories initiated an extensive R&D program, ..."
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The Basement Bugger's Bible : The Professional's Guide to
Shifty Bugman

Excerpt - page 134: "... is taken off hook, current flows, energizing coils and closing relay switch, connecting a parallel tap to line; tap can be line- powered or self- powered. Relay specifically designed for telephone interface devices; photo shows an M-949. C) Line-powered series interface ..."
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Military Innovation in the Interwar Period
Williamson R. Murray and Allan R. Millett

Excerpt - page 266: "... ati had receivers Without the bottlenecks and delavscaused by telegraph relays or telephone switching stations. They relied on encryption rather than radio silence ..."
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Modern Digital and Analog Communication Systems (The Oxford Series in Electrical and Computer Engineering)
B. P. Lathi

Excerpt - page 405: "... satellite based cellular network (iridium telecommunication system). The network would relay telephone calls via 66 small satellites launched into low earth orbit ..."
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Pillar of Fire : America in the King Years 1963-65 (America in the King Years (Paperback))
Taylor Branch

Excerpt - page 436: "... advance word from the President on the twin crises, frenzied relays of telephone and radio locators fetched two men ashore from vacation fishing ..."
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Complete Idiot's Guide to Conversational Sign Language Illustrated: (Ilustrated) (The Complete Idiot's Guide)
Carole Lazorisak and Dawn Donohue

Excerpt - Back Matter: "... Hearing loss that occurs naturally due to the aging process. relay telephone services/relay network A service that involves a third-party operator who ..."
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Mobile Cellular Telecommunications: Analog and Digital Systems
William C. Y. Lee

Excerpt - page 643: "... can be provided at either the cell site or the telephone company relay site. 7. The fixed cellular system will expect a longer ..."
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A History of Modern Psychology
C. James Goodwin

Excerpt - page 396: "... line, in the most famous of the Hawthorne studies, the Relay Assembly Test Room (RATR) study. ... to assemble electrical relays for telephones. Five workers did the actual assembly, and the sixth kept ..."
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Fundamentals of Physics
David Halliday, Robert Resnick, and Jearl Walker

Excerpt - page 890: "... radio and television signals. Microwaves from radar systems and from telephone relay systems may reach us. There are electromagnetic waves from lightbulbs, ..."
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Fundamentals of Physics
David Halliday, Robert Resnick, and Jearl Walker

Excerpt - page 890: "... radio and television signals. Microwaves from radar systems and from telephone relay systems may reach us. There are electromagnetic waves from lightbulbs, ..."
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Microcontroller Projects Using the Basic Stamp 2nd Edition
Al Williams

Excerpt - page 215: "... coupling the speaker to the phone's microphone. Figure 4.4 A telephone interface. Relay Red Telephone Green An Example 1:1 600 10 ohms .1.."
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Heating, Cooling, Lighting: Design Methods for Architects
Norbert Lechner

Excerpt - page 173: "... brought the price down to make PV useful for powering telephone relay stations, buoys, railroad signals, and other electrical installations remote from ..."
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Electronic Filters, Amplifiers & Oscillators - Frequency Devices
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