Taylor, Jack A.

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 The Knowledge Bank at The Ohio State University Ohio State Engineer Title:  Dial Telephone Systems Creators:  Taylor, Jack A.  Issue Date:  1945-04  Publisher:  Ohio State University, College of Engineering  Citation:  Ohio State Engineer, vol. 28, no. 5 (April, 1945), 11, 26, 30.  URI:  http://hdl.handle.net/1811/36154    Dial Telephone SystemsBy JACK A. TAYLOR, EE. IVAn automatic telephone exchange, as somecynic once remarked, is merely a device for plac-ing the blame on the subscriber instead of theoperator. The first automatic telephone systemwas patented only three years after Bell's inven-tion of the telephone. The first practical systemwas developed by Strowger during 1889-91. Thissystem, known as the step-by-step is still in usein the installations of The Automatic ElectricCompany, and in the smaller installations of theBell System companies. By small cities is meantthose with about 100,000 or less telephones.At first, the step system required five wires to—Courtesy of Western Electric Company.Step-by-step selector switch.A p r i l , 1 9 4 5each phone which was rather expensive andclumsy. The system was gradually improveduntil today only two wires are required, thesame number as is needed by a manual exchange.Since this system is so widespread—all large Ohiocities except Cleveland and Cincinnati using it—and since it is the least complex, its operation willbe explained in detail.The fundamental unit of equipment in the stepsystem is the step-by-step switch, see fig. 1. Itconsists of two or three banks of contacts, awiper arm to connect with these contacts, severalmagnets to operate the wiper arm and a frameto hold the various parts. Each bank has 100contacts in it arranged in ten horizontal arcswith ten contacts to each arc. In the first set ofdial pulses each pulse operates the vertical mag-net and the ratchet lifts the arm up one step.During the interval before the next set of pulsesanother magnet operates and transfers the nextset of pulses to the horizontal magnet. Thismagnet then rotates the arm one step horizon-tally for each pulse. At the end of the call thereleasing magnet operates and springs bring thearm back to the rest position.The next step is to trace a call through theexchange and see what happens each step of theway. First is the subscriber's handset includingthe dial. This generates the pulses which controlthe selecting mechanism. The line from the sub-scriber is connected to a simple rotary switch atthe exchange which connects the caller to an idlefirst selector. As soon as the first selector isconnected it gives dial tone in the handset andthe number may be dialed. The first selectoruses the first set of pulses and connects the phoneto an idle second selector in the proper group.The second selector uses the second set of pulsesfrom the dial and picks an idle third selector inthe proper group and so on until the final se-lector is reached which uses the last two groupsof pulses and connect the subscriber to the properphone, or to be more exact, the number he dialed.The final selector then rings the called subscriberand when his handset is picked up the call iscomplete.The dial is the device which generates thepulses and transmits them to the exchange to(Please turn to page 26)P a g e 1 1N2!1 AND 2WIRE FEED SCREW MACHINEShave ALL the features fornn.c profitable productionBrown & Sharpe Mfg. Co.Providence 1, R. I., U.S.A.high productive capacityunusually rapid set-upsimple to operateBROWN & SHARPEHow this plant serves a town of 2500as the Community Refrigeration CenterMeat ChillingPage 26An ice plant of only 10 tons capacitya few years ago, the Greencastle (Pa.)Ice and Cold Storage now handles up to80 tons daily, sells ice refrigerators, sup-plies farmers with ice for cooling milk,chills 600 tons of cherries in ice waterbefore pitting, ices many refrigeratorcars.* It stores 100,000 bushels of apples,and freezes big hogsheads of peaches andberries, all from its own packing house.• Meats, poultry, vegetables, and creamare frozen and stored. Twelve hundredrefrigerated lockers are rented. Fresh-killed calves and sheep (4000 per month)are chilled before being shipped. • Theice cream bar sells lunches; a cold roomserves as a milk substation; beer wasformerly handled at wholesale. Quick-freezing of locally grown foods in greatquantity is the next step. • We believeevery progressive town can profit, in thepostwar world, from a COMMUNITYREFRIGERATION CENTER. You arewelcome to make use of the consulting-engineerinq service and equipment weoffer for this program.FRICK CO., Waynesboro, Pa.DIAL TELEPHONE SYSTEMS(Continued from page 11)operate the switches. The external part of thedial consists of a disk with ten holes in it num-bered from one to zero. Zero is given as tenpulses since naturally zero pulses would have noeffect at all on the various switches. There arealso letters marked on the dial but as far as theswitching equipment is concerned there are onlynumbers. The letters are only used since it issimpler to remember two letters and four digitsthan it is to remember six numbers. Inside ofthe case is a gear train with a 5 to 1 ratio anda contactor which gives two pulses for eachrevolution of the wheel attached to the end ofthe gear train. If 9 is dialed the last gear re-volves 4yo times and gives 9 pulses. The dialgives the pulses on the return to the rest positionand a governor is attached so the pulse speedis about ten per second. The whole system is ad-justed to this speed so forcing the dial to gofaster will probably result in the switch missinga step and getting a wrong number.If the standard switch was used for each sub-scriber it is easy to see that the total numberof switches would be prohibitive in a 10,000line exchange. Each person would need oneswitch for the first two digits, 100 switches forthe next two digits, and 100X100 or 10,000switches for the rest of the number. The wholeexchange would thus take 101,010,000 switches.So a modification has been developed which re-quires only 4000 switches for the exchange.The modified switch works as follows. Thefirst set of pulses send the switch up to theproper level and it then rotates automaticallyuntil it finds an idle selector in the next group.Thus instead of one-hundred second selectorsfor one first selector there need be one-hundredsecond selectors for one-hundred first selectors.To further reduce the cost and complexity everysubscriber's line is connected to a simple rotaryswitch instead of a step-by-step switch. Theserotary switches connect the calling party to anidle first selector.Now if a subscriber were calling 852284, i.e.UN. 2284, the line switch would pick out anidle first selector, and this first selector wouldgo up eight rows and pick out an idle selectorin the 800000 group. The second selector wouldthen go up five rows and pick an idle selector inthe 850000 group. The next selector would pickan idle selector in the 852000 group and the nextselector would pick the 852200 group. The finalselector would then go up eight and over fourand ring the number called.(Please turn to page 30)T h e O h i o S t a t e E n g i n e e r. . . BAR WORK a n dSECOND OPERATIONSFranklin's $64 Question Gave Electricity a JobHIGH DIELECTRIC STRENGTHLOW MOISTURE ABSORPTIONCORROSION RESISTANCECOMPRESSIVE STRENGTHTENSILE STRENGTHFLEXURAL STRENGTHIMPACT STRENGTHSTABLE OVER AWIDE TEMPERATURE RANGEMany More Properties—Combinedyou know, as you do, what your re-quirements are. If whatever you areworking on suggests a material ofexcellent electrical insulating char-acteristics, resistance to corrosion,mechanical strength, stability atusual temperatures, easy machine-ability, or a variety of other inter-related properties, our type oftechnical plastics may readily beindicated. Our latchstring is al-ways out to any inquiry.SYNTHANE CORPORATION, OAKS, PENNSYLVANIAPlan your present and future products withSunthane Technical PlasticsLIGHTNING streaked throughages, feared but unchallenged.Then to Benjamin Franklin itflashed the answer to a questionthat unlocked the future of elec-tricity.Technical plastics, Synthane, forexample have already answeredmany $1 to $64 questions for peoplewho make things. And may for you.The question, of course, shouldcome before the answer—for onlySHEETS-RODS-TUBES-FABRICATED PARTS [SYMTftANE] MOLDED-IAMINAIEO • MOLDED- MACERATEDA p r i l , 1945 Page 27Victory means new jobs for STEAMG-293In the wake of this war will come new Jobs for steam — new opportunities along,with new problems for power engineers. Many signs point to new post-warindustries — different methods, techniques and processes; new conveniencesbeing dreamed up today for tomorrow's comforts. Then as now, steam willcontinue to be the leading power on land, on sea, and on the rails — helpingto build a better world—to set new standards of living—to provide livelihoods.With today's accelerated experience added to its long leadership in design-ing, building, and applying fuel burning and steam-generatingequipment, the vast Babcock & Wilcox organization will be betterfitted than ever to serve you, the power engineers of the future.BABCOCK & WILCOXTHE BABCOCK & WILCOX COMPANY85 LIBERTY STREET NEW YORK 6, N. Y.DIAL TELEPHONE SYSTEM(Continued from page 26)Besides doing all this the line tests each con-nection before it is made . and indicates anytrouble on a panel. It also tells what this troubleis and where it is located and finally it gives thebusy signal if any of the equipment is not idle.There are three other systems in use besidesthe step-by-step. They are the Northern Elec-tric's all-relay system and the Western Electric'spanel and crossbar systems.The all relay system is used only on small in-stallations, as the amount of equipment neededis proportional to the factorial of the numberof subscribers. However for installations of10,000 phones or less it is a strong competitorof step-by-step.Panel and crossbar are used only in largemetropolitan areas, e.g. Cleveland and Cincin-nati. The panel system was invented when step-by-step was becoming too unwieldy as the num-ber of telephones increased. The crossbar is amore recent invention and is being used in allnew installations instead of panel. The two arebuilt so they can be used in the same set of ex-changes, so panel is used now only to completeexisting exchanges.The distinctive feature of the panel and thecrossbar systems is in the manner of selectingidle lines. Interrupters are used to give a codefor each group. This code is applied continu-ously to the selector frame. When a certaindigit is called the code for that number is puton the selector arm. The selector arm thenmoves until it finds an idle circuit with the samecode on it. Since any number of contacts mayhave the same code on them, it is evident that thenumber of lines for each group may be variedto fit the traffic of that particular office. Forinstance the Walnut exchange would need a lotof connections for WA and UN but only a fewfor JE or FR as these exchanges are not calledso often. Thus the adaptability of the panel andcrossbar suits for large systems.The real development in the future for dialtelephones will probably be in the crossbar sys-tem, as the panel system is obsolescent, and itseems that only minor improvements remain tobe made in the step-by-step and the all-relaysystems."Why does the ocean roar?""You'd roar, too, if you had crabs on yourbottom!"Page 30 T h e O h i o S t a t e E n g i n e e rNITROGENA,., REDUCTION SALES COMPANYMAGNOLIA AIRCO GAS PRODUCTS CO.NATIONAL CARBIDE CORPORATIONPURE CARBONIC, INCORPORATEDTHE OHIO CHEMICAL & MFG. CO.WILSON WELDER & METALS CO., INC.Milk, too, is styled for modern war.. .streamlined by de-hydration to save weight... armored by nitrogen to avoiddeterioration. In fact, dehydrated foods of infinite varietyare protected by Nitrogen and Carbon Dioxide, two ofthe many gases produced by Air Reduction.In the food field these Air Reduction products are help-ing to build a new industry.In other fields Airco products and processes are revolu-tionizing war production — providing faster manufacturingmethods that will help build a better world after V day.* BUY UNITED STATES WAR B O N D S *AIR REDUCTION60 EAST 4 2 n d STREET N E W Y O R K 17, N . Y.OXYGEN, ACETYLENE AND OTHER ATMOSPHERIC GASES • GAS WELDING AND CUTTING APPARATUS • CALCIUM CARBIDEARC WELDING MACHINES AND SUPPLIES • CARBON DIOXIDE • "DRY ICE" • ANAESTHETIC AND THERAPEUTIC GASES AND APPARATUSA p r i l , 1945 P a g e 31Takes Betsy's Best to the Fighting Front

Dial Telephone Systems

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Dial Telephone Systems

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