File:The practical telephone handbook and guide to the telephonic exchange (1906) (14569741367).jpg

Identifier: practicaltelepho00pool (find matches)
Title: The practical telephone handbook and guide to the telephonic exchange
Year: 1906 (1900s)
Authors: Poole, Joseph
Subjects: Telephone
Publisher: New York, Macmillan Co.
Contributing Library: Northeastern University, Snell Library
Digitizing Sponsor: Boston Library Consortium Member Libraries

View Book Page: Book Viewer
About This Book: Catalog Entry
View All Images: All Images From Book
Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image:
r relays areadapted to respond only to a certain strength of current,which can be varied for the different stations. (4) Polarised bells or relays, responding only to currentsin a certain direction. (5) Multiplex circuit system, in which various combina-tions of the two wires of a loop and an earth connection areformed and connected to the ringing apparatus of the variousstations. (6) Inductance and Condenser system, in which the PARTY-LINE WORKING 273 several bells or relay circuits are so modified by the additionof inductance coils and condensers that some of the bellsonly respond to a weak and high frequency current, and othersonly to a stronger and lower frequency current. (7) The Wheatstone Bridge method, in which a rheostator adjustable resistance at the exchange enables the operatorto so adjust the resistances of the line circuit that all the bellsexcept that of the station required may be cut out or short-circuited. So far systems Nos. 2, 4, 5, and 6, or combinations of these,
Text Appearing After Image:
Fig. 278 have proved the most promising in practice, and a short de-scription will now be given of two or three arrangementswhich have proved specially promising. The Hibbard System.—This, which is extensively used inAmerica, is based on Nos. 4 and 5 methods. Biassedpolarised bells are used. This form of bell is an ordinaryringer, whose armature is fitted with a light spring, so thatin its normal condition it is drawn down on to one pole, asshown in Fig. 278. With unidirectional current such bellswill only respond to either positive or negative direction ofcurrent according to which side of the armature the spring isattached. Two stations fitted with oppositely biassed bells are con- 274 PRACTICAL TELEPHONE HANDBOOK nected to each leg of the loop and to earth, as shown in Fig. 279,thus making a 4-party line. The calling is done from thecentral by a series of four ringing keys, on pressing any oneof which the appropriate unidirectional vibratory currentfrom a commutated alternating g

Note About Images