. Automatic telephony; a comprehensive treatise on automatic and semi-automatic systems . Fig. 144.—Thousand lines being expanded. on the second selectors that they formerly occupied on the first new numbers for these subscribers will be the old numbers with thefirst digit doubled. Thus, 245 will become 2245, etc. The remaininglevels of the newly installed second selectors are now available for open-ing new hundreds, so that the capacity is now 1900 lines instead of 1000lines. Connectors l& ?nd SelS. 1 1 CD. Fia. 145.—Fourth selectors for party lines in 5-digit system. The
. Automatic telephony; a comprehensive treatise on automatic and semi-automatic systems . Fig. 144.—Thousand lines being expanded. on the second selectors that they formerly occupied on the first new numbers for these subscribers will be the old numbers with thefirst digit doubled. Thus, 245 will become 2245, etc. The remaininglevels of the newly installed second selectors are now available for open-ing new hundreds, so that the capacity is now 1900 lines instead of 1000lines. Connectors l& ?nd SelS. 1 1 CD. Fia. 145.—Fourth selectors for party lines in 5-digit system. The next step in growth is to open a new thousand on some otherlevel of first selectors, exactly as was done on the second level this way, level after level may be expanded until it is a 10,000-linesystem. As the system grows, the number of first selectors must be increasedto take care of the increased traffic caused by the greater number oftelephones. 150 AUTOMATIC TELEPHONY Even if an exchange is not being expanded, not all of the subscribersneed have the same number of digits in their call numbers. Party linesare often rung selectively by separate groups of connectors, each equippedwith the kind and arrangement of ringing current to which a class of bellswill respond. The selection of these groups of connectors uses up the hundreds digitof the call number. In a 5-digit system, this selection occurs on thethird selectors. (Fig. 145.) This will use up one call number for eachtelephone, the same as individu
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttelephone, bookyear19
