Fig. 495. Telephone CircuitsView full size illustration.
The receivers used at the waystations are of high impedance and are normally connected, through the hook switch, directly across the line in series with a condenser. When the operator, at a waystation wishes to talk, however, he presses the key shown. This puts the receiver across the line in series with the retardation coil and in parallel with the secondary of the induction coil. It closes the transmitter battery circuit at the same time through the primary of the induction coil.
The retardation coil is for the purpose of preventing excessive side tone, and it also increases the impedance of the receiver circuit, which is a shunt on the induction coil. This latter coil, however,is of a special design which permits just enough current to flow through the receiver to allow the dispatcher to interrupt a waystation operator when he is talking.
The key used to close the transmitter battery is operated by hand and is of a non-locking type. In some cases, where the operators are very busy, a foot switch is used in place of this key. The use of such a key or switch in practical operation has been found perfectly satisfactory, and it takes the operators but a short time to become used to it.
The circuits of the dispatcher's office are similarly arranged, Fig. 495, being designed especially to facilitate their operation. In other words, as the dispatcher is doing most of the work on the circuit, his receiver is of a low-impedance type, which gives him slightly better transmission than the waystations obtain. The key in his transmitter circuit is of the locking type, so that he does not have to hold it in while talking. This is for the reason that the dispatcher does most of the talking on this circuit. Foot switches are also employed in some cases by the dispatchers.
Test Boards.It is becoming quite a general practice among the railroads to install more than one telephone circuit along their rights-of-way. In many cases in addition to the train wire, a message circuit is also equipped, and quite frequently a block wire also operated by telephone, parallels these two. It is desirable on these circuits to be able to make simple tests and also to be able to patch one circuit with another in cases of emergency.
Fig. 496. Test BoardView full size illustration.
Test boards have been designed for facilitating this work. These consist of simple plug and jack boxes, the general appearance of which is shown in Fig. 496. The circuit arrangement of one of these is shown in Fig. 497. Each wire comes into an individual jack as will be noted on one side of the board, and passes through the inside contact of this jack, out through a similar jack on the opposite side. The selector and telephone set at an office are taken off these inside contacts through a key, as shown. The outside contacts of this key are wired across two pairs of cords. Now, assume the train wirecomes in on jacks1and3, and the message wire on jacks9and11. In case of an accident to the train wire between two stations, it is desirable to patch this connection with a message wire in order to keep the all-important train wire working. The dispatcher instructs the operator at the last station which he can obtain, to insert plugs1and2in jacks1and10, and plugs3and4in jacks3and12, at the same time throwing the left-hand key. Then, obtaining an operator beyond the break by any available means, he instructs him likewise to insert plugs1and2in jacks9and2, and plugs3and4in jacks11and4, similarly throwing the left-hand key. By tracing this out, it will be observed that the train wire is patched over the disabled section by means of the message circuit, and that the selector and the telephone equipment are cut over on to the patched connections; in other words, bridged across the patching cords.
Fig. 497. Circuits of Test BoardView full size illustration.
It will also be seen that with this board it is possible to open any circuit merely by plugging into a jack. Two wires can be short-circuited or a loop made by plugging two cords of correspondingcolors into the two jacks. A ground jack is provided for grounding any wire. In this way, a very flexible arrangement of circuits is obtained, and it is possible to make any of the simple tests which are all that are usually required on this type of circuit.
Blocking Sets.As was just mentioned, quite frequently in addition to train wires and message circuits, block wires are also operated by telephone. In some cases separate telephone instruments are used for the blocking service, but in others the same man handles all three circuits over the same telephone. The block wire is generally a converted telegraph wire between stations, usually of iron and usually grounded. It seldom ranges in length over six miles.
Fig. 498. Blocking SetView full size illustration.
Where the block wires are operated as individual units with their own instruments, it is unnecessary to have any auxiliary apparatus to be used in connection with them. Where, however, they are operated as part of a system and the same telephone is used on these that is used on the train wire and message wire, additional apparatus, called a blocking set, is required. This blocking set, shown in Figs. 498 and 499, was developed especially for this service by the Western Electric Company. As will be noted, a repeating coil at the top and a key on the front of the set are wired in connection with a pair of train wire cords. This repeating coil is for use in connecting a grounded circuit to a metallic circuit, as, for instance, connecting a block wire to the train wire, and is, ofcourse, for the purpose of eliminating noise. Below the key are three combined jacks and signals. One block wire comes into each of these and a private line may be brought into the middle one. When the next block rings up, a visual signal is displayed which operates a bell in the office by means of a local circuit. The operator answers by plugging the telephone cord extending from the bottom of the set into the proper jack. This automatically restores the signal and stops the bell.
Fig. 499. Blocking SetView full size illustration.
Below these signals appear four jacks. One is wired across the train wire; one across the message wire; and the other two are bridged across the two pairs of patching cords on each side of the set. The operator answers a call on any circuit by plugging his telephone cord into the proper jack.
If a waystation is not kept open in the evening, or the operator leaves it for any reason and locks up, he can connect two blocks together by means of the block-wire cords. These are arranged simply for connecting two grounded circuits together and serve to join two adjacent blocks, thereby eliminating one station. A jack is wired across these cords, so that the waystation operator can listen in on the connection if he so desires.
In some cases not only are the telephone circuits brought into the test board, but also two telegraph wires are looped through this board before going to the peg switchboard. This is becoming quite a frequent practice and, in times of great emergency, enables patches to be made to the telegraph wires as well as to the telephone wires.
Dispatching on Electric Railways.As interurban electric railways are becoming more extended, and as their traffic is becoming heavier, they approximate more closely to steam methods of operation. It is not unusual for an electric railway to dispatch its cars exactly as in the case of a steam road. There is a tendency, however, inthis class of work, toward slightly different methods, and these will be briefly outlined.
On those electric railways where the traffic is not especially heavy, an ordinary magneto telephone line is frequently employed with standard magneto instruments. In some cases the telephone sets are placed in waiting rooms or booths along the line of the road. In other cases it is not feasible to locate the telephone indoors and then iron weather-proof sets, such as are shown in Figs. 484 and 485, are mounted directly on the poles along the line of railway. With a line of this character there is usually some central point from which orders are issued and the trainmen call this number when arriving at sidings or wherever they may need to do so.
Another method of installing a telephone system upon electric railways is as follows: Instead of instruments being mounted in booths or on poles along the line, portable telephone sets are carried on the cars and jacks are located at regular intervals along the right-of-way on the poles. The crew of the car wishing to get in touch with the central office or the dispatcher, plugs into one of these jacks and uses the portable telephone set. At indoor stations, in offices or buildings belonging to the railroad, the regular magneto sets may be employed, as in the first case outlined.
On electric railway systems where the traffic is heavy, the train or car movements may be handled by a dispatcher just as on the steam railroad. There is usually one difference, however. On a steam road, the operators who give the train crews their orders and manipulate the semaphore signals are located at regular intervals in the different waystations. No such operators are usually found on electric railways, except, perhaps, at very important points, and, therefore, it is necessary for the dispatcher to be able to signal cars at any point and to get into communication with the crews of these cars. He does this by means of semaphores operated by telephone selectors over the telephone line. The telephone circuit may be equipped with any number of selectors desired, and the dispatcher can operate any particular one without operating any other one on the circuit. Each selector, when operated, closes a pair of contacts. This completes a local circuit which throws the semaphore arm to the "danger" position, at the same time giving the dispatcher a distinctive buzz in his ear, which informs him that the arm has actuallymoved to this position. He can get this signal only by the operation of the arm.
Each semaphore is located adjacent to a telephone booth in which is also placed the restoring lever, by means of which the semaphore is set in the "clear" position by the crew of the car which has been signaled. The wall-type telephone set is usually employed for this class of service, but if desired, desk stands or any of the various transmitter arms may be used.
It is necessary for the crew of the car which first approaches a semaphore set at "danger," to get out, communicate with the dispatcher, and restore the signal to the "clear" position. The dispatcher can not restore the signal. The signal is set only in order that the train crew may get into telephonic communication with the dispatcher, and in order to do this, it is necessary for them to go into the booth in any case.
[A]We wish particularly to acknowledge the courtesy of the Western Electric Company in their generous assistance in the preparation of this chapter.
[A]We wish particularly to acknowledge the courtesy of the Western Electric Company in their generous assistance in the preparation of this chapter.
ToC
REVIEW QUESTIONSON THE SUBJECT OF TELEPHONYPages11—68
REVIEW QUESTIONSON THE SUBJECT OF TELEPHONYPages69—134
REVIEW QUESTIONSON THE SUBJECT OF TELEPHONYPages135—226
REVIEW QUESTIONSON THE SUBJECT OF TELEPHONYPages227—270
REVIEW QUESTIONSON THE SUBJECT OF TELEPHONYPages271—320
REVIEW QUESTIONSON THE SUBJECT OF TELEPHONYPages321—358
ToC
The page numbers of this volume will be found at the bottom of the pages; the numbers at the top refer only to the section.
A
Automanual system218automatic distribution of calls223automatic switching equipment222building up a connection224characteristics of218operation219operator's equipment220setting up a connection224speed in handling calls224subscriber's apparatus219Automatic desk stand158Automatic Electric Company's telephone system149automatic sub-offices201connector185function of185location of186operation of186first selector operation179function of line switch152line switch153,163bridge cut-off173circuit operations167guarding functions173line and trunk contacts164locking segment172master switch171relation of, to connectors174structure of166summary of operation174trunk ratio165trunk selection165multi-office system196party lines202release after conversation196rotary connector202second selector operation182selecting switches153,175release mechanism178side switch175subdivision of subscribers' lines152subscribers' station apparatus158operation160bell and transmitter springs160ground springs160impulse springs161release springs163ringing springs163salient points163trunking154connector action157first selector action156line switch action154second selector action156two-wire automatic systems203two-wire and three-wire systems157underlying feature of trunking system153Automatic telephone systems135arguments against135attitude of public141complexity136expense140flexibility140subscriber's station equipment142automatic vs. manual143comparative costs142definition135methods of operation143fundamental idea147grouping of subscribers145local and inter-office trunks148Lorimer system144magnet vs. power-driven switches144Automatic telephone systemsmethods of operationmultiple vs. trunking145outline of action146Strowger system143testing148trunking between groups145Automatic wall set158
B
Blocking sets355Busy test48busy-test faults50potential of test thimbles49principle49
C
Circuits321applications322composite326phantom321transmission over324transpositions323railway composite327ringing327simplex324Common-battery multiple switchboard69assembly106Dean multiple board93cord circuit94line circuit93listening key94ringing keys94test94Kellogg two-wire multiple board84battery feed88busy test90complete cord and line circuit88cord circuit86line circuit85summary of operation91supervisory signals87wiring of line circuit92multiple switchboard apparatus97jacks99lamp jacks100relays101Stromberg-Carlson multiple board96cord circuit96supervisory signals97test97Western Electric No. 1 relay board69capacity range80cord circuit71functions of distributing frames77line circuit69modified relay windings79operation72operator's circuit detail75order-wire circuits78pilot signals79relay mounting80testing—called line busy75testing—called line idle74wiring of line circuit76Western Electric No. 10 board80circuits81economy84operation83test83Common-battery switchboard11advantages of operation11common battery vs. magneto12cord circuit20battery supply20complete circuit21supervisory signals21cycle of operations23jacks30lamps24mounting25line signals14direct-line lamp14direct-line lamp with ballast15line lamp with relay17pilot signals17mechanical signals27Kellogg28Monarch28Western Electric27relays28switchboard assembly31Composite circuits326Connector185Cord circuit20Cord circuitbattery supply20complete circuit21supervisory signals21Cord-rack connectors66Cummings-Wray selector342
D
Dean multiple board93Dispatchers' keys339Dispatching on electric railways356
G
Gill selector341
H
Housing central-office equipment249arrangement of apparatus in small manual offices252combined main and intermediate frames253floor plans for252types of line circuits255automatic offices267typical automatic office270central-office building249fire hazard249provision for cable runways251provision for employes251size of building250strength of building250large manual office256
I
Intercommunicating systems282common-battery systems283Kellogg plug type284Kellogg push-button type285Monarch system287Western Electric system285definition282limitations282for private-branch exchanges290simple magneto system282
J
Jacks30
K
Kellogg mechanical signal28Kellogg trunk circuits125Kellogg two-wire multiple board84Keyboard wiring67
L
Lamp mounting25Lamps24Line signals14direct-line lamp14direct-line lamp with ballast15line lamp with relay17pilot signals17Line switch163Long-distance switching293definitions293center-checking297operators' orders294by call circuits294by telegraph294particular party calls295switching through local board293ticket passing296trunking295high-voltage toll trunks295through ringing295two-number calls294use of repeating coil293waystations297Lorimer automatic system144,205central-office apparatus208connective division210sectional apparatus209switches213interconnector214interconnector selector214primary connector213rotary switch213secondary connector214signal transmitter controller214operation215subscriber's station equipment206
M
Magneto multiple switchboard53branch-terminal multiple board58arrangement of apparatus61magnet windings61operation60field of utility53modern magneto multiple board63assembly66cord circuit64test62Magneto multiple switchboardseries-multiple board54defects57operation56Measured service310local service316meter method316prepayment method318ticket method316rates310toll service311long haul311short haul311timing toll connections312units of charging311Mechanical signals27Kellogg28Monarch28Western Electric27Mercury-arc rectifier circuits237Monarch visual signal28Multi-office exchanges, necessity for109Multiple switchboard43busy test48cord circuits46diagram showing principle of47double connections46field of each operator51field of utility43influence of traffic52line signals45multiple feature43