US1729851A - Telephone system - Google Patents

Description

Oct. 1, 1929. J. E. os'ruNE @ELEPHONE SYSTEM 9 Sheets-sheaf. '1

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TELEPHONE SYSTEM Filed Nov. 1, 1924 Q SheetS-Sheet 9 I III! III" Patented Oct. 1, 1929 UNITED STATES PATENT OFFICE JOHN E. OSTLINE, OF LIVERPOOL, ENGLAND, ASSIGNOR, BY MESN'E ASSIGNMENTS, TO

AUTOMATIC ELECTRIC INC., OF CHICAGO, I

LLINOIS, A CORPORATION OF DELAWARE TELEPHONE SYSTEM Application filed November 1, 1924, Serial No. 747,373, and in. Great Britain November 14, 1923.

The present invention concerns improvements in or relating to automatic or semiautomatic telephone systems and more particularly those systems in which call indicator working is employed, altl'iough a number of features of the invention are not limited to these conditions and may be applied in other circumstances than those immediately concerned with call indicator Operation.

One of the features of the invention is a special type of impulse repeater which is adapted to repeat the initial series of impulses received by it in one direction only and to repeat subsequent series of impulses in another direction only. This feature is of particular value in connection with call in dicator operation, in which it is often desirable that the necessary storage devices should be located at an automatic exchange and should be arranged to be common to as large a group of junction lines as possible and not individual to a particular junction line or to a group of junction lines leading to a particular exchange. Under these circumstances it becomes necessary that the register devices shall be taken into use prior to the transmission of the digit or digits serving for the selection of the particular exchange to which the call has to be routed and it is clearly unnecessary to store this digit or digits on the register devices. Hence the necessity arises for the one or more series of impulses which determine the desired exchange to be repeated to a switch or switches in the speaking route in order to effect the exchange selection and for subsequent series of impulses to be then repeated to the registering devices. An incidental advantage of this arrangei'nent is that it permits ample hunting time for the switch associated with the repeater serving to select an idle set of registering devices, since this time comprises the duration of a complete train of impulses and the pause at.

either end thereof.

lVhen a repeater is employed such as that described it will be apparent that the registering devices and the apparatus which may be associated therewith for sending out impulses over a trunk line in accordance with the setting of the registering devices will be used in common for trunk lines to various exchanges, which will be in general, of different lengths. Under these circumstances it becomes advantageous to provide compensating arrangements associated with the impulse sender for varying the resistance in the impulse transmitting circuit in accordance with the characteristics of the inter-exchange trunk line over which the impulses are to be sent. This modification of the resistance can conveniently be effected by devices similar to those used for registering the digits of the required number and adapted to be operated by a digit not forming part of the number to be transmitted over the trunk line.

Another feature of the invention concerns an improved type of register set which consists of a single step-by-step switch adapted to respond successively to each of the digits to be recorded and after each response to transfer the digit recorded to one of'a number of groups of storage relays. This switch can conveniently be a 25-point rotary line switch of known type, arranged to have two normal positions and to move always in the same direction, and each group of storage relays may comprise four relays which are energized in various combinations to make the necessary record.

According to a further feature of the invention a particular arrangement is provided in connection with an impulse sender for sending in this case cod-e impulses whereby the speed of the impulse generation may be accurately determined, and what is of more importance, as a result of the inevitable wear of the cont-acts the speed will tend to decrease rather than to increase. Under these circumstances, adjustment may originally be made for the impulse generation to take place at a speed as high as is consistent with the reliable operation of the devices responsive thereto; there is then no danger of unreliable operation of these devices in course of time, since the speed will tend to decrease rather than to increase. According to this arrangement the rate of generation of impulses is determined by a slow acting relay in conjunction with the controlling magnet of a step-bystep switch, the slow acting relay being adapted to control the operating circuit of said magnet and to be short circuited until said magnet is fully energized. For instance, the relay may be normally short circuited by an interrupter contact on the said magnet, the magnet in turn being energized over a back contact of the relay. A further advantageous arrangement contemplated according to the invention is to have a micrometer adjustment for this back contact so that the speed of impulses generated may be accurately determined.

Still another feature relates to a special load distributing arrangement whereby calls are distributed to each operator in turn irrespective of the number she has already awaiting attention. This sequence of operations is only disturbed if the number of calls awaiting attention at any particular position reaches a predetermined number or if the cords at that position are in use or if the operator has left the position.

A further feature relates to an arrangement whereby calls requiring special service not ordinarily provided by the regular call indicator operator can be routed to a special service operator by the momentary depression of a single special service key.

Yet another feature of the invention is concerned with an arrangement which comes into use momentarily when the transmission of the required number over the trunk line has been completed to test whether the calling subscriber is still on the line. In case he is not, the connection is then rel-eased and the number transmitted is not displayed to the manual operator.

These and other features not specifically mentioned at this point will be better understood from the description of a preferred embodiment of the invention which will now be given with reference to the accompanying drawings, though it will be understood that this is by way of example only and that various modifications in the circuit details might be made by those skilled in the art without exceeding the scope of the invention.

Figure I of the drawings shows a special repeater at the tandem exchange, a coder selecting switch, a selector which responds to the final exchange selecting digit, and a secondary line switch at the incoming end of the trunk line. This figure also shows a coder that is to say a device for registering the digits dialled together with a code sending switch for transferring these digits to the distant call indicator position in a particular code.

Figure 2 shows a trunk relay group and a special service trunk finder, and also the necessary switches for determining the sequence in which calls shall be dealt with by the de-coder and a special switch for dis tributing the load equally among the various operators.

Figure 3 shows the call indicator lamps and the decoder, the function of the latter being to respond to the code impulses sent over the trunk line and to control the lighting of tie appropriate call indicator lamps so as to display the number to the operator.

Figure l shows a cord circuit and the rotary line switch associated therewith together with the meters, supervisory apparatus and operators equipment, and also a special service trunk finder and a special. service trunk.

Figure 5 is a diagrammatic representation of the general layout of the system from which main principles underlying it may be gathered, while Figure 6 is a table showing the code into which the Various numerical digits are converted for sending over the trunk line.

A description will first be given of the general lay-out shown in Fig. 5 where it will be assumed that connect-ion is to be extended from the calling subscriber A to the called subscriber A. Jhen the calling party A removes his receiver, his individual line switcn C will operate to select an idle trunk relay group TR with which is then associated an idle register .selector B. Upon receipt of the first digit this will be operated for instance to the eighth level and will then operate to select an idle director such as DI. llhe first selector E also responds to the first series of impulses and then operates to select a selector such as E". he director D1 will thenregister the remainder of the digits and send out suitable trains of impulses which will in general be different from those sent by the calling subscriber.

The first of these trains will operate a se lector such as the selector E, the wipers of which will be raised for instance to the eighth level and will then automatically be rotated in search of a free trunk to a repeater such as R. The repeater R is of special type so arranged that the first series of impulses re ceived by it are repeated to a succeeding selector such as D, while subsequent series of impulses are repeated over the coder selector OS to a coder which comprises all the apparatus enclosed in the dotted rectangle. Ac cordingly when the next digit is sent, the selector D will be operated, for instance, to the sixth level and will then select an ille trunk line to the secondary line switch SL at the required manual exchange.

During the transmission of this digit the coder selector CS will have selected an idle coder and subsequent digits transmitted will be directed to the digit recording s itch DES. and will thereupon operate in turn the compensating relay CR and the relays in the storage groups SS 8G 5G and 8G The purpose of the compensating relays GR is to adjust the resistance of the trunk line to standard value as will be more fully understood from the detailed description which follows. As soon as all the digits have been sent the secondar line switch SL is set in operation to s lect an idle trunk relayset D from among those rendered accessible by theload distributing switch LDS operating in conjunction with the position load distributing relay set LR. At the same time an idle marker S allotted by themarker distributor S is taken into use and this in conjunction with the set-up control switch S in due course effects the connection of the trunk relay group D to the de-coder D this will occur when the de-coder has dealt with calls which have come in prior to the one under consideration. lVhen the trunk relay group D is connected with the de-coder D the sending switch S in the coder is started up to send in code over i the trunk line the digits stored on the storage relay groups SG 8G 8G and SG lVhen this process is completed the coder is released and reverts to common use and the number transmitted over the trunk line in code having been de-code-d at the decoder is displayed by means of the storage relay groups D on the lamps L at the operators position.

The operator then inserts the plug attached to a cord in the most convenient position into the jack of the wanted subscriber, whereupon the trunk finder TF will bestarted up tofind the trunk relay set which has been used.

When this is found, the called subscriber will be rung and when he answers conversation may proceed in the usual manner. The decoder is released as soon as the operator inserts the plug and the set-up control switch S is then moved on into association with the next marker which has a call waiting to be dealt with. Upon the termination of the conversation the operator will be notified in the usual manner and will withdraw the plug, whereupon all the operated apparatus will be released.

In case the operator sees from the number which has been dialled that some special service is required which in the ordinary way it would not be her business to give, she will press the special service key at her position, whereupon instead of the trunk finder TF being started up, the special service position trunk finder STF is operated to find the particular trunk relay set in the manner pre viously described. VVhenit has been found the special service trunk finder SST is started up to select a trunk leading to a jack such as SS at a special service operators position over which the call may be dealt with by the special operator. The regular operator need only press the special service key momentarily and the de-coder is then released and the subsequent connections are made entirely automatically;

The operation of the system having been described in general'terms, a detailed description will now be given withreference to the circuit diagrams Figures 1, 2, 3 and 4 which should be placed together with the corresponding lines in alignment. Portions of the circuits are very similar to those disclosed in copending application No. 27,819 of 1923, but there are important differences as will be pointed out. 7

It will be assumed that the repeater in Fig. l is taken into use from the bank of an incoming selector such as E. As soon as the selector switches through, the following cir-' cuit is completed: battery, upper winding of relay 4, normally closed springs controlled by armature 45, upper trunkconductor 1, impulsing loop at the director, lower trunk conductor 2, normally closed springs controlled by armature 46, lower winding of relay 4 to earth. Relay 4 upon operating, at its armature 5 completes a circuit for release relay 7 and at its armature 6 prepares the impulsing circuit. Relay 7 operates when its circuit is completed, at armature 9 connects earth to release trunk conductor '3, at armature 10 completes acircuit for the right hand winding of the shunt field relay 15, at armature 54 prepares a circuit for the series relay 11 and at armature 8 completes a circuit for relay 31 which extends as follows: battery, upper winding of relay 31, back contact and armature 18, front contactand armature 8, armature 9 and its front contact, earth. Relay 31 thereupon operates and at armature 32 connects earth to the releasetrunk conductor 49, though this operation is without efi'ect at the moment. A circuit is also completed by relay 7 for starting up the coder selector switch as follows: battery, winding of line relay 33, back contact and armature 40, normally closed springs controlled by armature 23, back contact and armature 18, front contact and armature 8, armature 9 and its front contact, earth. By operating its armatures 3 4 and 35, relay 33 starts the coder selector hunting for an idle coder in known manner.

In response to the transmission of the nextdi it a corres ondin number of interru tions will be produced in the circuit of line relay 4 and it will de-energize accordingly. As soon as relay 4 firstpulled up, a circuit was completed over the trunk conductor 48 which circuit extends as follows: from battery by way of resistance 7 5, back contact and armature 28, front contact and armature 6, armature and its back contact, back contact and armature 24 t0 conductor 48, and through the lower winding of the line relay (not shown) of the selector D to ground. Consequently each time relay 4 deenergizes, this bridge is opened at armature 6 and the succeeding selector D, indicated by the dotted rectangle, is-

operated accordingly. Upon the first deen ergization of relay 4, a circuit is completed over armatures 10 and 13 for series relay 11 which energizes and being slow to release, remains energized throughout the series of im pulses. Relay 11 upon operating, at its armature 12 opens another point in the connection between release trunk conductor 3 and release trunk conductor 49 and at its armature 13 completes a circuit for the lower winding of relay 25. This relay is of the two-step type and in response to current flowing through its lower winding operates its lightly adjusted armature 27 whereupon earth is connected to both ends of its upper winding.

When the first series of impulses ceases, the selector D will hunt in known manner to find an idle trunk line to the required manual exchange, and having found one, will switch through. After having switched through, the selector D is held up by earth on release trunk conductor 49 by way of armature 32. The conductors 47 and 48 are now extended to the conductors 200 and 201 leading to the position selector having wipers 230, 210 and 231. The position selector is not operated at this time, however,notwithstanding the battery connection thru resistance to conductor 48, as conductor 47 over which the line relay 206 must be operated is free from operating potential at this time.

On the termination of the series of impulses and after a sufiicient time has lapsed to permit the selector D to complete the above mentioned trunk hunting operation and switch through, relay 11 deenergizes and earth is then removed from the middle point of the winding of relay 25 which accordingly oper ates fully, and at its armature 26 opens a point in its original energizing circuit, at armatures 28 and 30 opens the bridge across conductors 47 and 48 and at armature 29 and the front contact of armature 30 prepares a new impulsing circuit so that succeeding trains of impulses are sent to the coder, while at the front contact of armature 28 a circuit is prepared for relay 20.

In the meantime, the coder selector will have been hunting to find an idle coder, and when test wiper 53 engages a contact which is not earthed, switching relay 38 is not longer short circuited and energizes in series with rotary magnet 36 which is however not now operated. Thereupon wipers 50 and 51 are connected through to the outgoing trunk conductors at armatures 39 and 43, at armature 40 relay 33 is disconnected and at the front contact of this armature and the front contact of armature 41 earth fromarrnature 9 is connected to the test wiper 53, while at the front contact of armature 42 the impulsing circuit is prepared.

Upon the transmission of the next digit, the following circuit is completed on each deenergization of relay 4: battery, winding of magnet of the digit recording switch, winding of series relay 65, back contact and armature 74, lead 62, wiper 52, front contact and armature 42, front contact and armature 30, armature 6 and its back contact, armature 29 and its front contact, armature 10 and its front contact to earth. The digit recording switch is thus advanced by the operation of its driving magnet a number of steps corresponding to the value of the digit dialled. Relay 65 is energized in series with the magnet and at its armature 65 completes a circuit forrelay 67. This relay thereupon at its armature 68 prepares a circuit'for operating the storage relays and at armature 69 prepares a circuit for the relay 98.

At this point it may be desirable to eX- plain the purpose and operation of relays 92 and" 93. It Will be clear from what has already been said that access may be had from the repeater in Fig. 1 to any one of a number of exchanges as determined by the setting of the selector D. Furthermore the length of the trunk lines leading to the different exchanges may vary considerably and as the coder at the distant exchangecontains relays which are marginally operated by currents over the trunk line, it will be apparent that some difiiculty or at least inconvenience may be caused by the fact that these relays in the various decoders at the same exchange in order to operate reliably will have to be differently adjusted so as to respond correctly to codes transmitted from a number of other exchanges. In order to overcome this difliculty and to permit a standard adjustment of the relays in question, the compensating relays 92 and 93 have been introduced at the de-coder. The operation of these relays is controlled by sending an extra digit immediately preceding those which are to operate the storage relays in the coder and are subsequently to be displayed at the call indicator position. This is particularly easy to achieve if, as in the arrangement now being described, the digits dialled by a subscriber are received by a register translator or director from which impulses are sent out which will in general be difierent from those received by the director. The sending of an extra train of impulses in this case can be effected by making an additional cross connection to the impulse sender. The digit for effecting the compensation will preferably be either 1, 2, 3 or 4 and in response theretp either one or both or neither of the relays 92 and 93 will be operated. The contacts 94 and 96 controlled by them are arranged to short circuit the resistances 104 and 105 respectively, which are connected in the circuit over which the code impulses are sent.

Let it be assumed in the present instance, that the digit sent for compensating purposes is 3 and that the wanted subscribers number subsequently recorded in the coder is 4567. in response to the compensating digit 3 therefore the wipers 82, 83, 84 and 85 of the digit recording switch will be moved three steps, so that the wiper 82 comes into engagement with contact 106, while wiper 84 comes into engagement with contact 107. At the end of the series of impulses, relay decnergizes and a circuit is then momentarily completed from earth, armature 66 and its back contact, armature 68 and its front contact, wiper 82, contact. 106, lead 89, armature 99 and its back contact. winding of relay 93 to battery, and parallel thereto over wiper 83, contact 107, lead 90, armature 100 and its back contact, winding of relay 92 to battery. Relays 92 and 93 upon operating, at armatures 95 and 97 lock themselves up to the holding earth in the repeater by way of armature 73 and its back contact, and lead 63, and at armatures 94 and 96 remove the shunts around resistances 104 and 105, respectively, so that both these resistances are included in the code sending circuit over the trunk conductors: this case will clearly cor respond to a short trunk line to a nearby exchange. A circuit is also completed on the deenergization of relay 65 from earth at armature 66, armature 69 and its front contact, armature 103 and its back contact, up per winding of relay 98 to battery. Relay 98 is also of the two-step type similar to relay 25 and thereupon operates its light contact 102. Upon the deenergization of relay 67, earth is removedfrom the middle point of the winding of relay 98 and it then operates fully; at its armature 103 transfers its original energizing circuit to relay 108 and at armatures 99, 100 and 101 connects the leads from the various bank contacts of the digit recording switch througl'i to the relays of the first storage group. When armature 69 engages with its back contact a circuit is completed over the niultipled contacts in the bank of wiper 85 and said wiper and interrupter contact 81 for automatically restoring the digit recording switch to normal. This switch will from the nature of things never have to take more than 10 steps to respond to a particular digit and as it is convenient to use for this purpose an ordinary rotary line switch moving always in the same direction, which switch has 25 confacts, it will probably be desirable to multiple the contacts of the bank together in two halves so that the switch will have two normal positions. In this case therefore the switch will come to rest with wiper 85 rest ing on the dead contact 86.

The digit 4 will now be sent out from the director, in accordance with which the wipers of the digit recording switch will be advanced four steps. When relay 65 deenergizes, a circuit will be completed from earth,

armature 66 and its back contact, armature 68 and its front contact, wiper 82, contact 109, lead 88, armature 101 and its front contact, armature 110 and its back contact for relay 111. Relay 111 at armature 112 completes a locking circuit for. itself to the earth on the repeater and at armature 113 prepares a circuit for sending the appropriate code 119, 110 and 120 transfers the connections of loads 88, 89, 90 and 91 to the second storage I relay group. I

The next digit on the assumption made above is 5; consequently upon the receipt of this digit the wipers 82, 83, 84 and 85 are stepped around into their fifth position. then relay 65 releases, a circuit is completed over wiper 84 for relay 121 which operates to prepare the code sending circuit at armature, 122 and at armature 123 locks itself up.

Relay 117 is similar to relays 108 and 98 and is partially energized when relay 65 releases and is fully energized when relay 67 releases and thereby transfers the operating circuits to the third storage group.

then the next digit 6 is sent, the digit recording switch takes six steps, whereupon on the deenergization of relay 65 circuits. are completed over wipers 82 and 84 for relays 125 and 126 which look up and prepare code sending circuits in the manner previously described. Relay 124 is operated fully when armature 69 leaves its front contact and transfers the operating leads to the fourth storage group and the connection over lead 116 to relay 127.

The transmission of the last digit 7 results in the operation of relays 128 and 129 which look up and prepare code sending circuits in the same manner as the other storage relays.

relay 127 operates its light contact 130 when earth is first connected to the middle point,

of its winding over lead 116 and when this earth is removed operates fully. At armatures 131,132, 133 and 134 the circuits for the fourth set of storage relays are opened so as to preventany accidental further operation, at armature 135 relay127 opens its own initial energizing circuit, at armature 136 it opens the initial energizing circuit of relay 7 5, at armature 137 prepares a holding earth connection to lead 63 'andat'armature 138 prepares a circuit over lead 139 for starting the sending of code impulses. Relay 7 5 was energized over armature 136 and its back contact at the same time as relay 127 was partially energized and at armature 78 opened the code impulse starting circuit, and at armature 76 removed earth from armature 137. Relay also by operating its armatures 77 and 79 connected itself over its upper winding in a locking circuit which extends as follows: battery, winding of line relay 206, of the incoming secondary line switch, back contact and armature 203, upper trunk conductor 200, through the selector D, conductor 47, armature 21 and its back contact, armature 39 and its front contact, Wiper 50, lead 60, armature 79 and its front contact, upper winding of relay 75, front contact and armature 66, lead 61, wiper 51, front contact and armature 43, back contact and armature 24, conductor 48, through the selector D, conductor 201, armature 204 and its back contact, earth.

Relay 206 is energized in this circuit and by operating its armatures 207 and 208 starts the incoming rotary line switch hunting for a free trunk .over which the connection may be completed. This hunting operation takes place in known manner and as soon as an idle trunk is found, relay 202 being no longer short circuited, energizes in series with magnet 209 and at its armatures 203 and 204 disconnects relay 206 and connects the trunk leads through, while at armature 205 it completes a locking circuit for itself. Relay 7 5 is not deenergized by the momentary opening of its circuit consequent on the operation of its armatures 203 and 204, and when this has taken place, the circuit for maintaining it energized extends as follows: from battery, upper winding of relay 212 back contact and armature 225, back contact and armature 224, back contact and armature 223, the trunk conductor 220, wiper 230, front contact and armature 203, conductor 200, thence over the previously traced circuit to conductor 201, armature 204 and its front contact, wiper 231, conductor 221, armature 226 and its back contact, armature 227 and its back contact, armature 228 and its back contact, armature 229 and its back contact, earth.

Before proceeding further with the description of the actual operation of setting up a call, it will be desirable to explain the circumstances under which a trunk such as that shown in Figure 2 is rendered accessible to an incoming secondary line switch. In order to ensure that calls shall be distributed equally among the operators so that no one operator receives more or less than her fair share, a set of position load distributing relays is provided for each position and these operate in conjunction with a load distributing switch which is common to a group of positions. The effect of these arrangements is that for each call that comes in a definite operators position is preselected so that the calls are distributed to each operator in turn until they have each received one, the subsequent distribution being continued in the same manner irrespective of whether the first call has been dealt with or not. Arrangements are also provided to prevent more than a certain number, in this case five, calls accumulating at any operators position and should this condition of aifairs arise, an alarm is given to a supervisor to indicate that the position is .overloaded. A position is also rendered inaccessible if the operator leaves it or if all her cords are in use as will be more fully explained hereafter.

Suppose in the present instance that the position at which the trunk shown is located has two calls awaiting attention and that the wipers 242 and 243 of the load distributing switch have just arrived again on the contacts 244 and 245 associated with this position. In these circumstances relay 234 will be energized in the following circuit: earth, armature 241 and its back contact, wiper 242, contact 243, winding of relay 234 to battery. The operation of relay 234 which then takes place closes contact 237 whereby a locking circuit is prepared for relay 233 and contact 238 whereby an energizing circuit is prepared for relay 233 and earth is removed from the position busy common lead 232 so as to render the idle trunks in this position selectable. vVhen the switching relay 202 of the incoming rotary line switch switches through a circuit is momentarily completed as follows: earth, front contact and armature 207, front contact and armature 205, wiper 210, release trunk conductor 222, normally closed springs controlled by armature 218, common lead 232, armature 235 and its front contact, winding of relay 233 to battery. Relay 233 accordingly operates, at armature 235 completes the previously prepared locking circuit for itself and at armature 236 completes a circuit extending from earth, front contact and armature 235, contact 245, wiper 243, relay 239 to battery. Relay 239 upon operating, at armature 241 opens the circuit of relay 234 and at the front contact of this armature completes a circuit for the driving magnet 240 so that the distributing switch takes one step. Relays 233 and 234 are thus deenergized and earth is replaced on the common lead 232. It is then impossible for any further calls to come to the position in question until a call has been received by each of the other positions unless they are inaccessible for any of the reasons mentioned above. In such a case, earth would be connected to the lead corresponding to lead 246 and relay 239 would be again energized over the back contact of the armature corresponding to armature 236. The distributing switch therefore takes a further step and no call is received at that particular position.

To return now to the consideration of the operations taking place in the trunk relay set, relay 212 energizes in series with relay when the line switch switches through. Thereupon at its armature 213 it completes a circuit for relay 217, at armature 214 prepares a locking circuit for itself, at armature 215 prepares a circuit for relay 247. and removes earth from contact 302 in'the bank of wiper 300 and at armature 216 connects earth over the common lead 316 to the wiper 317 of the marker distributor.

It should be explained that in order to ensure that calls arriving at a position are dealt with in the proper order, a number of markers are provided, in the case considered five, this representing the maximum number of uncompleted calls that it .is desirable should exist simultaneously at any one position. These markers have two banks which are connected. to the various trunk relay sets in the position. The order in which the markers are taken into use is controlled by a marker distributor, of which only one is provided per position and it is further necessary to have a set up control switch, the function of which is to connect up the decoder in turn to various trunks which have been taken into use so that the number may be sent in the special code from the recording devices at the tandem exchange, so as to operate the proper lamp and indicate to the operator the wanted numher. The necessity for the set up control switch as well as the marker distributor is on account of the difference in the rate at which calls arrive at the position and the rate at which the operator deals with them. Thus if four calls come to a position almost simultaneously the marker distributor will operate to assign four markers in quick succession; the set-upcontrol switch, however, will lag somewhat and will move on to permit the display of the fourth call after the other three have been displayed and dealt with.

Let it be assumed that when the call arrives the marker distributor is in the position shown, the marker shown is in any'other position and the set up control switch wipers are resting on the contacts next before those with which they are shown in engagement. Accordingly when relay 212 operates a circuit will be completed as follows: earth, armature 252 and its back contact, front contact and armature 216, common lead 316, wiper 317 of the marker distributor, contact 318 associated with the marker shown on which it is resting, armature 311 and its back contact, winding of relay 312 to battery. Relay 312 is thereupon energized and by operating its armatures 313 and 314 starts the selected marker hunting for the contact 302 in the bank wiper 300, from which earth has been removed by the operation of armature 215. hen this contact is found, relay 305 is no longer short circuited and energizes, thereby at contact 311 opening the circuit of relay 312 and at contact 310 completing a locking circuit for itself. Furthermore at armature 309 a circuit is completed for the driving magnet 324 of the marker distributor which thereupon operates so as to allot another marker and at armature 308 a circuit is completed for relay 327 in the setup control switch. Relay 305 also at armature 306 removes one earth connection from lead 337 of the chain busyingcircuit and at the front contact of this armature lights the marker pilot lamp 469 at the operators position so as to indicate which marker is in use, at the same time by operating relay 470 lighting lamp 47 2 to show that a call is awaiting attention.

following circuit is completed: earth, front i contact and armature 313, front contact and armature 31.0, wiper 300, armature 302, armature 215 and its front contact, lower winding of relay 247 to battery. Relay 247 thereupon operates, at its armature 245 prepares a circuit for relay 259, at armature 249 prepares a locking circuit for relay 260, at armature 250 prepares a locking circuit for itself through its own upper winding, at armature 251 completes a locking circuit through its own lower winding which circuit also serves to maintain relay 305 energized, at armature 252' removes earth from the marker start common lead 316 and at armature 253 prepares a locking circuit for relay 254.

The operation of the set-up control switch must now be considered. ready mentioned, it is assumed that wiper 325 is standing on the contact immediately before contact 326 and that the de-coder is connected to the trunk corresponding to this contact. Under these circumstances, relay 327 will be energized by earth over the armature similar to 308 of the marker in use for the other connection and relay 330 will also be energized. This state of affairs Wlll continue until the call has been completely decoded, whereupon in a circuit which will be traced subsequently, the

earth connected to the contact upon which wiper 325 is standing 1S removed momentarily and is then replaced over the bank contact of the armature corresponding to 307 in the other marker. When this occurs, relay 230 deenergizes, but owing to the operation of armature 308, relay 327 will remain energized and a circuit will consequently be again completed over armatures 328 and 331 for relay 334. This relay, by operating its armatures 335, and 336, starts the set-up control As has been al-.

switch hunting. In the case under consideration it will only have to take one step and it will then encounter the contact 326 from which earth has been removed by the operation of armature 307. Relay 330 thereupon energizing, at armature 331 opens the circuit of relay 334 and at armature 332 completes the following circuit, earth, front contact and armature 335, front contact and armature 352, front contact and armature 329, wiper 325, contact 326, armature 307 and its front contact, wiper 301, contact 303, winding of relay 254, armature 214 and its front contact, lower winding of relay 212 to battery. The circuit thus completed serves to maintain the relay 212 energized when its upper winding is disconnected on the operation of relay 254. Relay 254 at its armatures 224 and 227 connects the trunk leads 220 and 221 through by way of the leads 27 6 and 277 to the code re ceiving relays 501, 502 and 503, at armature 255 prepares a testing circuit for a purpose which will be explained subsequently, at armature 256 completes a locking circuit for itself which also serves to maintain relay 330 energized after relay 334 releases, at armature 267 completes a circuit for relay 500 and at armature 258 prepares a circuit through the lower winding of relay 260.

In consequence of the operation of relay 254 the feeding current is disconnected from the winding of relay at the coder and in consequence thereof it deenergizes after a short interval. A. circuit for starting the sending of the code impulses is then completed as follows earth, armature 76 and its back contact, armature 137 and its front contact, back contact and armature 73, armature 138 and its front contact, armature 7 8 and its back contact, lead 139, first contact in the bank of wiper 142 and said wiper, lead 146, armature 71 and its back contact, lead 147, winding of magnet 143 to battery.

It will be as well to describe at this point the inter-operation of magnet 143, its interrupter contact 144 and the relay 70. Relay 7 0 is arranged to be normally short circuited by the interrupter contact 144 over leads 145 and 146 but when the contact 144 is opened on the operation of the magnet it is enabled to energize and thus opens its own contact 71, whereby the circuit of the magnet 143 is opened and it releases. The contact 71 is provided with a micrometer adjustment, the operation of which serves to determine accurately the rate of generation of impulses. This adjustment is normally set to effect the generation of impulses at a rate which is as high as possible consistent with the reliable operation of the devices controlled thereby and in case any wear should occur, the efi'ect will be to make the generation of impulses take place at a. somewhat slower rather than a quicker rate; consequently there is no danger of faulty operation due to impulses being sent .too quickly when any such wear has taken place after the lapse of time. If and when the reduction in speed becomes appreciable it is a comparatively simple matter to re-set the contact 71 of the relay 70 by means of the micrometer adjustment so that the impulses will again be generated at the maximum permissible rate.

Returning now to the operation in this par ticular case, the code sending switch thus commences to rotate its wipers when the above circuit is completed. On the first step wiper 142 finds earth over its second contact, all the contacts in the bank of wiper 142 being multiply connected to earth with the exception of two, one corresponding to the normal position of the switch which is connected to lead 139 and the twenty third contact 148 which is connected to lead 149 and controls the release of the coder in a manner which will be described fully hereafter. The effect of these multipled contacts is that as soon as the switch is stepped off normal, it continues to step round under the joint control of interrupter contact 144 and the contact 71 of relay 7 0 until it again reaches normal position. Wipers 140 and 141 of the code sending switch are connected respectively to the lead 60 and 61 and thence over the trunk line to the relays 501, 502 and 503 in the decoder. The banks of these wipers are so connected up that for each digit which it is desired to send incode the switch takes four steps.

The impulses sent over the trunk line are of three kinds which may be termed positive, light negative and heavy negative, and of the relays which respond to them, relay 501 is polarized in such a manner as to respond to what is termed a positive impulse, relay 503 is polarized in the opposite direction so as to respond to a negative impulse while relay 502 is marginally adjusted and will only respond when a stronger current is sent over the line, this corresponding to what has been termed a heavy negative impulse since no heavy positive impulses are employed. It is also ar ranged for reasons which will appear subsequently that a negative impulse, either of the'light or heavy variety is always sent out on the second and fourth of the four steps of the sender switch, while a positive impulse may be transmitted only on the first and third steps. The combinations of these impulses which are used to characterize the various digits are shown in the table in Fig. 6 which also indicates which relays (assumed numbered from right to left) of a storage group must be operated in order that these particular impulses shall be generated.

In the present case it will be remembered that the number received by the coder was 34567, of which the first digit 3 was only employed for determining which compensating resistance, if any, should be included in the circuit: consequently it is clearly unnecessary and undesirable that this should be transmitted to the decoder. The relays 92 and 93 therefore, operated by the compensating digit have no contacts having direct connection with the banks of wipers 140 and 141.

Since in accordance with the digit 4, only relay 111 of the first storage group is operated, when the code sending switch arrives at the position for sending the first impulse for the first digit, that is to say, after taking two steps from its normal position, no circuit will be completed; consequently no effect is produced at this time.

On the next step, however, an impulse, is sent over the following circuit: battery, resistance 105, resistance 104, high resistance 151, back contact and armature 154, contact 150, wiper 140, lead 60, wiper 50, front contact and armature 39, back contact and armature 21, conductor 47, conductor 200, armature 203 and its front contact, wiper 230, conductor 220, armature 223 and its back contact, armature 224 and its front contact, lead 276, relay 501, relay 502, relay 503, lead 277, front contact and armature 227, back contact and armature 226, conductor 221, wiper 231, front contact and armature 204, lead 201, lead 49, armature 24 and its back contact, armature 42 and its front contact, wiper 51, lead 61, wiper 141, contact 153 to earth. Current in this direction constitutes what is understood as a negative impulse and as the high resistance 151 has been included in the circuit rather than the low resistance 152 it will be a light negative impulse and consequently only relay 503 will be operated. A circuit is there upon completed as follows: earth, armature 506 and its front contact, armature 505 and its front contact, armature 516 and its back contact, lower winding of relay 509 to battery. Relays 508 and 509 are each of the two-step type having a light contact which alone is operated when the relay is energized through one winding only: consequently armature 513 is now operated. On the termination of this impulse, when the code sending switch steps on to the next contact and relay 503 is deenergized, relay 509 pulls up completely, at armature 512 prepares a locking circuit for relay 508, at armatures 514 and 515 alters the connections to the first set-up relay group, and at armature 516 opens its own initial energizing circuit and prepares circuits for the lower windings of relays 508 and 517.

lVhen the code sending switch advances to its next position, a circuit is completed in consequence of the operation of relay 111 as follows: battery, resistance 105, resistance 104, high resistance 151, front contact and armature 113, fourth contact in the bank of wiper 141 and said wiper, lead 61, wiper 51, front contact and armature 43, back contact and armature 24, conductor 48, conductor 201., armature 204 and its front contact, wipcisely or 231, conductor 221, armature 226 and its 21 and its back contact, armature 39 and its.

front contact, wiper 50, lead 60, wiper 140, fourth cont-act in its bank, earth. It will be noticed that the direction of current flow in this circuit is opposite to that in the circuit previously traced and that this current accordingly constitutes a positive impulse. The effect of this positive impulse is to operate only relay 501 which completes a circuit as follows: earth, armature 506 and its front contact, armature 507 and its front contact, armature 514 and its front contact, armature 523 and its back contact, relay 524 to battery. Relay 524 thereupon operates, at its armature 525 looks itself up by way of lead 526 to the earth on armature 506 and at its armature 527 prepares a circuit of the upper winding of relay 528.

The code sending switch will now take another step whereupon a light negative impulse will be transmitted over a circuit presimilar to that previously traced for such an impulse; the effects at the decoder are however slightly different in this case,

owing to the operation of relay 509. As soon as relay 503 picks up, a circuit is completed for the lower winding of relays 508 and 517 which thereupon operate their light contacts 511 and 518, respectively, thereby short circuiting their upper windings. On the ter- -1ni11ation of'the impulse when armature 505 leaves its front contact, both these relays energize fully over their two windings in series. Relay 508 at its armature 510 opens the locking circuit of relay 509, which thereupon deenergizes and at armature 512 opens the locking circuit of relay 508 so that both these relays are thus deenergized. Relay 517 operates its contacts 519, 520, 521, 522 and 523 whereupon its own energizing circuit is transferred to a similar relay of the set cor responding to the second digit and the operating circuits are transferred to the second set-up relay group. The setup and storage relays corresponding to the second and third digits are not shown since they are similar in all respects to those for the first digit; their position is indicated by the dotted rectangles.

The next digit to be transmitted in code is 5 and reference to the table in Fig. 6 will show that this is done by sending a light negative impulse followed by a heavy negative impulse. The effect of the initial light negative impulse is similar to that described previously, namely, that relay 509 is energized and locked up but that none of the set-up relays is energized,

Upon the receipt of the following heavy negative impulse, relay 502 is operated as well as relay 503 whereby a circuit is completed over armature 504 and its front contact, armature 515 and its front contact, armature 521 and its front contact for the fourth relay in the second set-up group which thereupon locks up to lead 526 and prepares a circuit for the corresponding relay in the storage group. This impulse also has the effect of energizing relay 508 and the changeover relay corresponding to 517 after which both relays 508 and 509 deenergize, and the circuit is left in readiness for the receipt of the next digit.

The digit 6 now to be transmitted involves the sending of a positive impulse in'the first position of the code sending switch for this digit, that is to say, with the wipers resting on the eleventh contacts. A circuit substantially identical with that over which this impulse is sent has been traced in connection with the sending of the digit 4 and it need not be repeated. The effect of the de-coder is to energize the first relay in the third set-up group which thereupon locks up and pro pares the circuit for the corresponding storage relay as before. The'light negative impulse which is then sent merely serves to operate the relay 509. In the next position of the sending switch no impulse is sent at all and in the following position a heavy negative impulse which as previously described operates the fourth relay of the set-up group and restores relays 508 and 509 to normal.

The final digit 7 is sent by means of two negative impulses, the first of which effects the operation of the second relay 530 in the fourth set-up group. This relay locks itself up at its upper armature and at its lower armature prepares spending storage relay. Relay 509 is also energized and locked up by this impulse in well knownmanner. The succeeding heavy negative impulse effects the completion of a circuit for the fourth set-up relay 533 which operates in a similar manner to the others. Relays 508 and 509 restore to normal in the usual manner and upon the termination of the impulse relay 531 is energized. This operates armatures 529, 532, 534 and 535 whereby the fourth digit relay set is disconnected so as to prevent any subsequent accidental operation; at armature 536 opens the circuit of relay 542 which has previously been energized though in this case without useful function, at armature 537 prepares a circuit for energizing the storage relays and at armature 538 prepares a circuit for relay 543.

For the sake of convenience of description it will be assumed that when the decoder is taken into use for the call under consideration the operator has already dealt with the previous call and consequently there is no number displayed on the call indicator lamps.

a circuit for its corre- This assumption is not altogether consistent with the previous assumption employed for explaining the operation of the set-up control switch but this is immaterial as regards the proper working of the apparatus and simplifies the description of the subsequent operations. l/Vith this assumption therefore, a short while after the energization of relay 531, after relay 542 has deenergized owing to its circuit being opened at armature 536, the following circuit is completed: earth, armature 544 and its back contact, armature 547 and its back contact, armature 537 and its front contact, armature 549 and its back contact, lead 552 to battery through the up per windings of the storage relays whose circuits have been previously prepared by the operation of their corresponding set-up relays. The storage relays thereupon operate and lock up to lead 553 to which earth is connected over armature 506 and its front contact, normally closed springs controlled by armature 546 and armature 548 and its back contact.

The earth connection to lead 552 also extends over armature 258 and its front contact through the lower winding of relay 260 to battery so that this relay is operated. At armature 261 it closes another point in the circuit of relay 259, at armature 263 prepares a circuit for relay 266, at armature 264 removes earth from test contacts 27 3 and 274, at armature 265 opens the locking circuits of relays 212 and 251 and at armature 229 removes earth from the lower trunlr conductor and substitutes battery for a purpose which will be described subsequently. Relay 260 also at its armature 262 completes the following locking circuit for itself; earth, back contact and armature 268, upper winding of relay 260, front contact and armature 262, back contact and armature 270, front contact and armature 249, lead 272, lower winding of relay 539 to battery. Upon the release of relays 212 and 254, the trunk relay set is disconnected from the common leads to the decoder, and earth is removed from the contacts engaged by wiper 300 of the marker and wiper 325 of the set-up control switch. In consequence, relay 305 is deenergized and the marker is rendered available for use in setting up another connection and the set-up control switch steps on as previously explained and controls the association of the de-coder with another trunk relay group.

Relay 539 operates when its circuit is completed, at armature 545 completes a circuit for relay 540, at the same time opening the initial energizing circuit of the storage relays, at armature 545 completes the display circuit whereby the required number is displayed to the operator by the lighting of the appropriate call indicator lamps and at armature 546 connects a further earth to lead 553 to replace that which is removed by the deenergization of relay 500 when its circuit is opened at armature 257. Since relay 539 energizes before relay 500 'deenergizes this latter operation is effected without discontinuity and the storage relays remain operated. The deenergization of relay 500, however, removes earth from lead 526 whereby the operated setup relays are deenergized and also the change over relays such as 517 and 531. The operation of relay 540 which takes place at this time opens another point in the connection to lead 552 and prepares a circuit for relay 541.

The condition of affairs so that only relays 217, 247 and 260 in the trunk relay group are energized and the marker and set-up control switch have been released as well as the de-coder proper. Only relays 539 and 540 remain energized and the storage relays which are effecting the display of the number to the operator. These conditions persist until the operator deals with the call.

Consider now therefore thestate of affairs at the coder upon the completion of the sending of the code impulses. The code sending switch continues to operate in the manner described until it has made'a complete revolution, i. e., until wiper 142 arrives once more on the contact connected to lead 139 which is .not now earthed. When it reaches its twenty-third contact, however, wiper 142 finds earth through the low resistance relay 72 instead of direct and relay 72 is thereby energized. At its armature 73 it removes the locking earth from all the operated storage relays in the coder and also the change over relays 98, 117, 124, and 127 and these accordingly deenergize. Moreover at its armature 74 it completes the following circuit: from earth front contact and armature 74, lead 62, wiper 52, front contact and armature 42, front contact and armature 31, armature 6 and its front contact, armature 28 and its front contact, winding of relay 20 to battery. Relay 20 upon operating, at armatures 21 and 24 switches the speaking leads through at armat-ure 22 opens the circuit of the busy relay 17 and at armature 23 completes a locking circuit for itself at the same time releasing the coder selector and the coder which then reverts to common use. The switching through of the speaking leads has no particular effect at the moment.

Returning now to the further progress of the call, the operator, upon noting the number displayed on the call indicator lamps, will take up a plug associated with a convenient idle cord circuit and will test the jack of the wanted subscriber by touching the tip of the plug against the ring of the jack. If the called line is busy a circuit will be completed as follows: battery through the winding of the sleeve relay such as 411 associated with another operators cord, ring of jack, tip of plug, normally closed contacts controlled by armature 412, lead 413, winding 414 of the induction coil to earth; this circuit will consequently induce a click in the operators head set over the plug 415.

It will be assumed, however, in the present case that the wanted number is idle when called and consequently the operator will insort the plug fully into the subscribers jack,

whereupon a circuit 1s completed from battery, winding of relay 411, ring of plug, sleeve of jack, subscribers cut-off relay toearth. The sleeve and cut-off relays operate in series and the latter clears the subscribers line of'its normal battery and earth connections in the usual manner. Relay 411 upon operating, at armature 412 disconnects the operators head set and completes the upper speaking lead, at armature 418 lights the supervisory lamp 419 and at armature417 completes a circuit for the rotary, line switch associated with the cord as follows: earth, armature 417 and its front contact, normally closed springs controlled by armature 420, armature 421 and its back contact, winding of relay 404 to battery. Relay 404 thereupon energizes and starts the line switch hunting in the usual manner for the contact 274 associated with the trunk over which the call is to be completed from which earth was removed by the operation of relay 250. When the marked trunk is found, relay 405 is operated whereby the speaking leads 7 from the calling subscriber are switched through, relay 404 is disconnected and earth is connected over wiper 403 to the test contact associated with the trunk line in use. A circuit is thereupon completed for relay 266 which operates and at armatures 223 and 228 cuts off the battery connections from the trunk line, at armature 267 places a further earth connection on release trunk 222 and at armature 269 completes a locking circuit for itself.

Furthermore at armature 269, relay 266 breaks the circuit of relays 260 and 539 so that both these relays deenergize, the former at armature 265 opening the circuit of relay 247 which also deenergizes. Upon the deenergization of relay 539 a circuit is completed for relay 541 which at its armature 548 opens the locking circuit of the storage relays so that they deenergized. Furthermore, at armature 545 the circuit for the lamps is broken so that the number displayed is extinguished. All

the apparatus associated with the decoder is thus released.

It may happen, however, if the operator is working at high speed that another call will have come to the decoder while she was completing the first. In this case all the appropriate set-up relays will have been operated and further operations will be awaiting the earthing of lead 552. This occurs when relay 540 deenergizes whereupon the storage relays are again operated in accordance with the new

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