File:American telephone practice (1905) (14733257676).jpg

Identifier: americantelepho00mill (find matches)
Title: American telephone practice
Year: 1905 (1900s)
Authors: Miller, Kempster B. (from old catalog)
Subjects:
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Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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evident that when a metallic circuit line was connected witha grounded circuit line the talking circuit would be traced fromground at the subscribers station on the grounded circuit line,through the line circuit to the central office, thence to the tip sideof the metallic circuit line and back over the sleeve side of this lineto the sleeve side of the cord circuit and thence from the sleeve con-tacts of the jacks on the grounded circuit line to ground at the cen-tral office. The presence of the 600-ohm non-inductive resistancein the ground connection at the central office on the groundedTinewas to prevent the dead grounding of the test rings so as to keeptheir potential above that of the earth when a connection was madewith the line so that the line would give the proper busy test whileso connected. It is evident that if the test contacts of the groundedcircuit lines had been dead grounded the potential of the test ringswould have remained the same as that of the earth, regardless of
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4);»;l;l;hfiS- 232 AMERICAN TELEPHONE PRACTICE. whether the line was switched for use or not. Moreover, this con-dition would have short-circuited the test battery. The operation of the test is very simple. The test battery beingpermanently connected to the sleeve side of the cord circuit servesto raise the potential of all the test rings of the line as soon as, andas long as, any plug is inserted into a jack. When not connectedthe test rings are supposedly at the same potential as that of theearth. Therefore when an operator tests with the tip of a callingplug no current will pass through the circuit traced from the tip ofher calling plug through her telephone receiver to ground in casethe line is not busy, because there is no source of current in thecircuit. If, however, the line is busy, the difference of potentialbetween the test ring and the tip of the testing plug will be noticedby a click of the receiver. The circuit over which this testing cur-rent passes may be traced to gro

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