40 BELL SYSTEM TECHNICAL JOVRSAL 



liHij) amiplciitl <i\cr a lest inink li\ ili.ilin^;. Lof.il si'lcclors do not 

 contain an>' c(|iii|>inont otluT tli.ui rontails aiul wiring in the trans- 

 mission circuits l)iit thc'Sf »an l»c tested in tlie same manner as con- 

 nectors if it is ilesired to ciieck the wiping contacts and wiring. Toll 

 selectors which invoUe e<|uipnient in the transmission circuit can 

 also 1)C teste<l in the s;ime manner as connectors. Trunks between 

 manual and machine switching offices can be most conveniently 

 tested from the manual office, the trunk loops being established 

 directly by dialing. 



To illustrate the general method of testing step-by-step machine 

 switching circuits, the lower diagram of Fig. 9 shows the schematic 

 circuit arrangement for testing trunks Iwtween two machine switching 

 offices. The transmission measuring set is located at office A in a 

 position so that it can be patched to the outgoing trunk repeater test 

 jacks and an arrangement for dialing and holding is connected to the 

 trunks through the measuring set. At office B the apparatus in one 

 trunk is disconnected and this trunk used as a test trunk by cross- 

 connecting it at the main distributing frame to a spare subscriber's 

 multiple terminal. All trunks in the group can then be tested by 

 dialing f)\er them, from office A, the numl)er of this spare terminal 

 at office B which automatically loops them back over the test trunk. 



Maintenance of Subscribers' Lines and Stations. The circuits 

 making up subscrilnrs" lines from switchboard to instruments con- 

 sist simply of pairs of conductors, almost always in cable, with the 

 necessary protective devices. These can be checked by certain 

 d-c. tests described in a recent |)aper." I-lquipment is also provided 

 in local test Ixiards for use in making talking transmission tests be- 

 tween the station and the test boards. Accurate machine methods 

 for determining the elficiency of transmitters and receivers have 

 been developed for testing new instruments and instruments returned 

 from service. 



General Scheme of Testing Exchange Area Circuits. The plan 

 being followed in the Bell System for systematically checking the 

 transmission conditions of exchange area circuits is to have all offices 

 tested periodically by men equipped with portable transmission 

 measuring sets who traxel from office to office. It has been found 

 by experience that after an office has once been tested and any trans- 

 mission troubles eliminated, it is only necessary thereafter to make 

 transmission tests at infre(|uent intervals, these subsequent tests 

 serving primarily as a check on .the local maintenance conditions. 



•W. II. Il.irilen, "Klitlric-.il 'IVsIs ,incl Tlu-ir Anplicalioiis in ihc Maintenance 

 III T< Irplione Transniivsirin," Hrll System Teclinical Journal, July, \9i4. 



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