File:Electrical instruments and telephones of the U.S. Signal corps (1911) (14753417041).jpg

Identifier: electricalinstru00unitrich (find matches)
Title: Electrical instruments and telephones of the U.S. Signal corps
Year: 1911 (1910s)
Authors: United States. Army. Signal Corps
Subjects: Military telegraph -- United States Military telephone -- United States
Publisher: Washington, Govt. print. off.
Contributing Library: University of California Libraries
Digitizing Sponsor: MSN

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:
ition of the first cut and.having allowed a reasonable percentage error, on the second cut it ishighly prol)able the faulty section will be cut off. It has been foundthat generally the error of determination will fall within 1 per cent. A word may be said regarding the telephone receiver as a detectorof feeble currents. It is much more sensitive than the average piv-oted galvanometer and will stand infinitely more abuse. However,in noisy places the galvanometer may be substituted for the telephonein this test to advantage. If the fault has a high resistance, so that the four or five cells ofbattery permissible in the manner of connecting shown in diagramcan not send sufficient current through, then some form of rathersensitive galvanometer becomes necessary Avith the increased batteryand change of connections required. In place of the battery in figure1()0, connect the galvanometer. In place of the telephone receiver,connect a battery of from 20 to 100 cells in series. Then proceed as
Text Appearing After Image:
with the telephone receiver, noting that for each break or irregularityof contact of the searcher wire there may be a kick of the galvanom-eter, due to capacity or inductance of the current, and that balanceis obtained only when the galvanometer shows no deflection when thesearcher wire is at rest. (Fig. 1()1.) A fault in a single conductor cable, or one involving all the con-ductors of a multiple cable, may be located if two additional wiresof sound insulation between the points connected by the faulty cableare available. As the lengths and resistances of these wires are immaterial, tem-porary or roundabout wires may be utilized. The method of procedure is as follows: Stretch a single piece ofresistance wire A B (figures 162 and 163) whose length is some evennumber of parts, say 1,000 sixteenths of an inch. The two sound out-side wires / and A and the defective one L arc connected at the dis-tant end. The galvanometer, battery, and searcher are connected, as ELECTRICAL INSTRUMENTS U.

Note About Images