US1146583A - Automatic telephone-exchange system. - Google Patents

Description

. F. R. McBERTY.

AUTOMATIC TELEPHONE: EXCHANGE SYSTEM APPLICATION FiLED SEPT. 1 3.1912.

w 1,146,583. Patented Jul 13, 1915.

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x F. R. McBERTY. AUTOMATIC TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED SEPT. 13, 1912.

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Patented July 13, 1915;

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KR. McBERTY. AUTOMATICIELEPH'ONE EXCHANGE SYSTEM.

' APPLICATION FILED SEPT; 13. 1912.

1,146,583. a Patented July 13, 1915.

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I F. R-'McBERTY. AUTOMATIC TELEPHONE sxcugmag SY ST EM] APPLICATION m SEPT. I3. 1912.

Patented July 13, 1915.

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APPLTJATION FILED SEPT13,191.2. 1,146,583, Patented July 133, 1915. f a SHEETS-SHEET 5.

F. R. McBERTY. AUTOMATH'J TELEPHONE EXCHANGE SYSTEM.

' APPLlCATiON HLED EPT.13, 1912. 1,146,583. Patented July 13, 1915.

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UNITED STATEL PATENT QFFTCE,

FRANK R. MQBERTY, 0F ANTWERP, BELGIUM, ASSIGNOR TO WESTERN ELECTRIC COMPANY, OF NEW YORK, N. Y., A CORPORATION OF ILLINOIS.

AUTOMATIC TELEPHONE-EXCHANGE SYSTEM.

Specification of Letters Patent,

Patented July is, 1915.

17 all whom/i1, may concern Be it known that I, FRANK R. McBERTv, a citizen of the United St es, and a resident of Antwerp, in the Province of Antwerp and Kingdom of Belgium, have invented new and useful Improvements in Automatic Telephone-Exchange Systems, of which the following is a specification.

This. invention relates in general to improvements in automatic switching apparatus for interconnecting the lines of a telephone exchange system, and is intended more particularly for a system in which the operation of the automatic switches for ext-ending connection from acalling line to a wanted line is brought about in response to the action of sending apparatus manipulated by the subscriber at the calling station, but certain of the features to be described will also be applicable, as will be apparent to those skilled in the art, to systems of other characters, as for example a semi-automatic system, in which some of the switching or controlling operations are performed by an operator at the central otli'ce.

In British Patent No. 26079 of 1910 there is described an automatic telephone switch ing system in which impulses transmitted from the calling station and representing the number of the wanted line are received at the central ofiice by registering devices which thereupon act as controllers to govern the selecting operations necessary to extend connection to the line represented by such registration. In the system of that patent the register equipment is adapted to be brought into association with a calling line by means of finder switches. switches may take an appreciable timeto establish connection with a calling line, especially where a large number of contacts must be passed over, and the subscriber must wait before sending his call until the register equipment has been connected to his line by the finders; otherwise impulses might be lost.

In order to permit the operation of the subscribers sender immediately upon the initiation of a call, as when the subscriber takes his telephone from its hook. the present invention provides for the direct association of a register-controllcr equipment with a calling line, without waiting for a line-finding or equivalent operation by Which Such finder the calling line is connected-to a first group dered inaccessible to other lines of the.

group, another register equipment being then available to be appropriated by any of such other lines which may call; Provision is made whereby, after the registration of the number of the wanted line, the register controller equipment is made free from the possibility of interference by the calling subscriber while its selector-controlling operations are taking place. This may be accomplished in a variety of Ways; in the system shown a cut-off relay is operated when the registration is complete, such relay positively disconnecting the calling line from its extensions leading to the registers and switches.

Another feature of the invention relates to the organization of the register-controller equipment by which different series of impulses are caused to act upon different registers or counters, as for registering the different digits of the number of the wanted line, the arrangement involving a fast-acting relayfor responding to each impulse,

a slow acting device such as a relay responsive only to the longer interval between the different series of impulses, and a quiclcacting shifting switch (preferably a sequence switch) brought into action bythe slow acting relay. In order to reduce the time required between the different series of impulses while maintaining a maximum difference in the characteristics of the fast and slow relays tosecure accuracy, the shift by which a register for a succeeding order of numerals is brought under control of the 'fast acting relay in substitution for the first register, is brought about by a fast-acting shifting switch (sequence switch) which responds to a single movement of the armature of the slow-acting relay, but makes no further changes in the register circuits upon the reverse movement which completes the oscillation of said armature. After regls- 'tration of a given order of numerals on one ister equipment, while at the same time making it selectable by a line finder which may be set in operation as a result of the same act, and which line finder upon connection to such line maintains a busy test upon the multiple test terminals, both calling and called, after the register equipment has been disconnected. In the particular system to be described, it is convenient to provide a line relay for each line, in normal connection between a battery and the line circuit, to respond upon the closure of the line circuit at the substation, said line relay When energized causing the actuation of a register relay which directly connects a register equipment to the line. It is desirable that this line relay should not remain in permanent connection with the line during the operations of registration and selection, and during conversation, and therefore a cut-off relay is provided for disconnecting said line relay after it has performed its function.

The present invention includes as one of its novel features the operation of said cutoff relay by alternative circuits, the first of which is closed when a register equipment is connected to the line, and'the second of which is completed when a line finder is in connection'with the line, the latter circuit being thus maintained after the register equipment hasfinished its work and has been disconnected.

A plurality of line-finders should be assigned to each. group of calling lines, and a feature of the present invention is the provision of means, whereby the seizure of a register equipment by a calling line causes an idle one otslich line finders to start in operation to find and make connection with such line. In the sfvstem as shown there is an automatic distributing switch for starting one line-finder after another as calls come in, and this distributing switch may conveniently be started by one of the contacts of the sequence switch associated with each register equipment, and this may be the same sequence switch which. also causes the various circuit shifts required in bringing the register and controller magnets'successively into operative relation to the devices with which they are to cooperate.

The stopping of a line-finder switch upon the terminals of a line may advantageously be governed by a test relay associated with thefinder, which relay is so related to the mechanism of the switch and its associated circuits that it is controlled alternately over successively established test circuits of lines terminating in the switch and a circuit es tablishcd by an interrupter or contact device forming a part of the switch. The test circuits referred to are multipled to corresponding test terminals on all th'e finder switches serving the lines of the group, and are normally closed. lvhen however, a line is calling, and until it has been connected to by a finder switch, the test circuit of such line is opened (as by the action of the same relay which connects a register equipment to the line). The test relay which controls the motive power of the line finder switch is connected to a test brush thereon and will alternately and continuously find circuit, when started, over the finder test terminals passed over, and the interrupter device, until the calling line is reached which will have .its test circuit open. whereupon, the test relay will cut otl' the motive power of the finder switch. The cireuit'tln'ough the interrupter device which forms a b 'anch from the circuit including the test relay and the test brush is useful not only to insure the energization of the test relay while the brushes are in transit from one set of terminals to the next. but also to secure the accurate stopping ot' the hue finder brushes centrally upon the terminals of the calling line.

This branch circuit, therefore, is arranged to be closed by the contact device or interrupter operated in the movement of the line finder brushes, said contact device acting to open the branch circuit only when the brushes are in accurate position upon the lerminals ot the line to be -tested. The line tinder test circuit may also be used, if desired, for another purpose, as for the operation of a message-counter or other ,toll device, which may be normalljv connected in such test circuit. but is preferably operated only by special current applied to said circuit under proper circumstances by apparatus associated with the selector switches.

In the particular system to be described, a distinct busy test circuit is provided in connection with each line, to guard against interference with a line when busy by a call l'romsomeolher line: such test circuit being represented by multiple test terminals upon all of the linal selectors which have access to suchline. Normally a potential is applied to all such test terminals from a battery, through the cut-oll relay that controls the connection of the line relay. of the final selector is responsive only to the The test relay full normal potential on the test terminal, and a line is made to test busy by reducing such potential. 'In the case Where connection is made to a line as a called line, the final selector establishes a path from the test terminal which reduces such test potential. Such a busy test guard is already known to those skilled in the art. ent invention provides means whereby such a test guard may be established immediately upon the appropriation of a register equipment when a line is calling As shown the same relay which connects the calling line to a register may also render the line selectable by a finder and non-selectable by a final selector, and as shown this is accomplished by having said relay whenrenergized open a branch which normally exists from the multiple calling test terminals of the line and close instead a branch to the multiple busy test terminals. This branch may be simply transferred from one test circuit' to the other, and when connected to the subscribers busy test wire will also serve to complete the circuit of the cut-off relay which disconnects the line relay. In order to maintain the potential reduced at the busy test terminals (and also maintain the cut-ofi relay energized) after the register seizing relay has been released and the register equipment disconnected, another branch from the busy test wire of the calling subscriber may be established by way of a special brush of, the line finder contacting with a multiple terminal of such test wire appearing on the terminal bank of the finder.

Another feature of the present invention relates to a practical organization of the system in such a way thatthe register-controllers may be set in accordance with a given system of notation or grouping of units, as the decimal system, and thereafter when acting as controllers, cause an equivalent selecting operation in accordance with some other system of notation or grouping. For example, it has been found advantageous to employ selectors each having direct access to two hundred lines, this being a particularly economical grouping, in view of average trafiic conditions. The register equipment which receives the impulses according to the decimal system, must therefore operate in a modified manner when controlling selection in groups of two hundred instead of groups of one hundred as in the decimal system, and in adapting itself also to the sub-grouping into which the two hundred units (lines) of the main group may be divided.

Some other features of my invention relate to the disposition andoperation of the various sequence switches (steering switches) used throughout the system shown. For example, the use of but a single sequence The presswitch coiiperating with both the line finder switch and the group switch individual to a connecting circuit; the sequence switch con trol of the registering and controlling equipment in its various stages of operation; and the sequence switch control of themessage charging or rabbeting circuits.

Another feature has more particularly to do with the relay system by which the breaking down of a connection established or being established may be accomplished. Forming a part of this feature of the invention are many improved operations and convenient arrangements among which may be mentioned the method of preventing the initiation of a new connection by either party to a connection until his receiver has been restored to its hook; the method of placing the control of a selector, residing in a linerelay, first under the control of a selecting circuit, then under the control of the calling party and finally under the joint control of the calling and called parties; and the disposition of the disconnection controlling (or supervisory) relays in association with a repeating coil at the final selector.

Other desirable and improved features forming a part of the invention will sulficlently appear from the description of the,

system shown. In this description, of course, the various novel features will be described in their application to a particular system, but it will be understood that they are capable of advantageous use in other systems where they may take forms differing widely from the forms herein shown, and,

while in the interests of clearness, specific descriptive language must be used, such language is not intended necessarily as defining the limits of the invention.

One form of the invention is illustrated in the accompanying drawings wherein Figures 1 to 4 show diagrammatically a system embodying the invention of which Fig. 1 shows a substation line herein to be considered as the calling subscribers line and also shows a suitable form of sending mechanism associated with the line at the substation, Fig. 2' shows a line finder switch serving the group of lines to which the line shown on Fig. 1 belongs, together with the connecting circuit and group switch to which 'in detail the register-controller devices included in Fig. 4 and indicate so far as is 'necessary for a complete understanding of grammatically illustrated in Figs. 1 to 4:,

Fig. 2 should be placed to the right of Fig.-

1, Fig. 3 to the right of under Fig. 1.

In the specific sending arrangement and apparatus shown, the subscribers sending mechanism at the substation is of the-type in which a contact device is operated intermittently to close a'circuit to ground from Fig. 2, and Fig. 4

. the line conductor to which it isconnected,

thereby causing corresponding intermittent shunting of the impulse receiving relays and 66 for the time being associated with the line at the central station. The contact device in its operation closes such'circuit to ground a number of times corresponding to each d'git of the designation of the desired line and is so constructed that the last slosure of the series of closures for each digit is of longer duration than the other closures of the series, such closure being of .sufiicient duration to accomplish the retraction of the slow acting shift relay 65 for purposes to be hereinafter described. The form of sender illustrated is one wherein the desired number is set up by manually operable levers, one for each digit, and upon the subsequent actuation of a power crank is brought into operation to transmit groups of impulses to tlie'central ollice in accordance with the digits of the number so set up. An instrument of this type is disclosed in the British Patent No. 15569 of 1911. The other substation apparatus is of the usual common battery arrangement and together with the sender is connected with the central office by means of the usual line conductors a, 7). There may also be associated with each line a message register such as is shown at 63.

It will be noted that the message register 63 is a number-indicator which counts or registers eachsuccessful connection; it may be of any well-known type. The term message register must be distinguished from the term register-controllei, the latter term desigiiating the ii'icchanisin shown in Fig. 4 which serves to receive the impulses representing the desired line and then to control the switches. The individual devices which receive the impulses are designated, herein as register-conti'ollers, there being a 1000s rogister-miiitroller, a 100 s register-controller, a 10s register-controller and a units register-controller. These form the essential parts of the registering and controlling equipments.

The circuits of the registering and controlling equipment are shown in Fig. 4, and the mechanisms are indicated in Figs. 5,

live teeth m the pitch of which is 6, 7, and 8. The operating magnets of the 1000s register-controllers are indicated by r1000 and 81000; those of the 100s register-controller by 1 100 and .9100; those of the 10s register-controller by T10, and 810 and those of the units register-con troller by 11 and 81. There is also provided a sequence switch, the clutch magnet of which is marked 205, (Fig. 4) serving among other things to bring the several register-controllers successively into service.

The structure of the 1000s register-controller is indicated in Fig. 5. It consists of a disk K supported on a shaft L, the disk having teeth. along its periphery adapted to be engaged and displaced by a pawl M mounted on an armature N of the magnet 11000, the armature being normally held retracted against a stop F by a spring 0. To restore the disk K the magnet 81000 is provided having a pawl Q mounted upon its armature R, the armature being norto this spring a spring 87 is provided having an insulated roller bearing upon the periphery of the disk K. The arrangement is such that with the roller on top of a tooth the lower contact is closed, and with the roller in anotch between contact is closed.

The disk K is provided with ten teeth 70, double that of the teeth 3), and five teeth 0, the pitch of which is equal to that of the teeth m.- The magnet r1000 is intermittently energized in response to the impulses representing the thousands digit of the desired line which. causes the disk K to be advanced in a clockwise direction, the number of steps corresponding to the number of impulses. When thedevice acts directly asa controller to determine a selecting operation, the magnet 81000 is intermittently energized by impulses transmitted from the selector and steps the disk K in a counter-clockwise direction. Due to the pitch of the teeth m, however, the number of impulses necessary to restore the disk K to its normal position is but one half of the number which caused its displacement.

In the system herein described the thousands register-controller does not act directly as a controller, the'system shown being for only two thousand lines. however, not indirectly by means of the spring 87 to assist in the control of selection in the manner to be hereinafter described. It is restored by a special impulse circuit through the magnet 81000 established after the completion of the selection controlling operation.

teeth the upper It does, h

1 troller.

. connections in the extension The .Lu-nbers of springs in the four registers described agree with the numbers of springs shown in Fig. 4. v

The 100s register-controller is shown in Fig. 6. It is also. provided with a disk K1 mounted on a shaft L1; similarly in this device magnets T100 and 5100 are arranged respectively to advance and restore the disk. It will i observed that this register-controller has two normal springs 85 and 86. The usual normal position for the disk is as shown with 86 closed. Under certain conditions, however, it is necessary that this register-controller should receive five extra impulses in order to accomplish the proper translation, in which case the disk operating under the control of the thousands registercontroller will not be stopped when the normal spring 86 is reached, but will stop when the second or sub-normal spring 85 is reached. When the hundreds impulses have been received from the substation a spring.

158 will close its lower or upper contact depending on whether the number of impulses sent in is odd or even.

In Fig. 7 is shown the 10s register-con- This is of the type described in' British patent specification No. 26,079/10. The disk K3 is mounted on a shaft L3. The magnet r10 steps the disk in a clock wise direction, and the magnet s10 restores it to normal, in which position contact 153 is closed. In this case as many impulses are required to restore the register-controller as operated no displace it.

In Fig. 8 is shown the units register-controller.- The disk K4 mounted on the shaft IA is driven in a clockwise direction by the magnet r and in a counter clockwise direction by the magnet s. In this register controller also there are provided two normal springs cooperating with the insulated stud U4. Which of these normal springs will operate eifectively to cause the stopping of the disk in its return movement will depend upon the set position of the hundreds register-controller in a manner to be described. It is sufficient for the present to say that While the same number of impulses will accomplish the restoration of the disk to its usual normal position, that is, with U4 in engagement with the spring 190, as were received from the sender, there are of which it is necessary that the units register-controller receive ten additional impulses before coming to a stop in which case the stoppage will be controlled by the second or subnormal spring 159.

The exact relation of the various springs and magnets in producing the proper translation 1S hereinafter made clear.

For the sake of simplicity of illustration and desgription but one disk is shown in Figs. 6 and 8 illustrating the hundreds and units register controller devices respectively. In practice, howe ver, th ee disks are preferably provided for the hundreds register (Fig. 6) which all revolve together on the shaft L1, and two disks for the units register which revolve together on the shaft L4. Referring to the hundreds registercontroller device, the first disk has ten teeth 791, the second disk has teeth m1 having double the pitch of pl but spaced entirely around the disk so that the register-controller may be returned to normal after a selecting operation, in which it has stopped in its second or subnormal position, by having the magnet energized from the interrupter 191 (Fig. 4) until the disk has been stepped around and the insulated stud U1 has closed the normal contact spring 86. The third disk has five teeth as shown at 01. Similarly the units register-controller shown in Fig. 8, is in practice constructed with two disks, the first having ten teeth [94 and the second having teeth m4 completely around its periphery and having the same pitch as 394. As in the case of the teeth m1 of the hundredsregister controller these teeth m4 are provided so that in case the disk s een brought to rest at the second or subnormal position with the stud U4 pressing on the spring 159, it may be returned to normal by having the $1 magnet energized from the interrupter 191 (Fig. 4:) until the disk has been stepped completely around and the stud has finally reached the spring 190 closing the contact.

There is associated with the register-controllers a sequence switch whose power magnet is numbered 205. A distributing switch whose power magnet is numbered 305 is also provided to start line finders hunting for calling lines. The line finder and group selector shown in Fig. 2 have a common sequence switch, the power magnet of which is indicated'by the number 105 and the final or line selector has also associated with it a sequence switch the is indicated at 505.. springs 73, 73?, 73", 73 belong to the line finder starter or distri uting switch 305', and the remaining sequence switch contacts of Fig. i belong to the registering and controlling equipment sequence switch. Sequence switches of the character indicated and referred to herein are fully disclosed inglg described in British Patent 20840 of In Figs. 2, 3 and 4 the switch the sequence switches are not shown in their actual arrangement, but are so located as to give a clear arrangement of the circuits. The position of the rotary elements of each "sequence switch and the distributing switch in which any of its contacts (except the conpower-magnet of which The distributing switch springs of l tacts coresponding to 111 of'the line finder sequence switch) are closed, are indicated by numbers placed adjacent to such contacts, each contact being open in all positions except those indicated by such reference nu merals. closed in the fourth and fifth positions of the line finder sequence switch of which it forms a part, as indicated by the numbers 4, 5 adjacent thereto, and the alternate contact is closed in the 9th position as indicated by the figure 9 adjacent to'such alternate contact; said contacts being open in all po sitions except those so indicated. In the case of the special contacts such as 111 the numbers are placed on the opposite side of 'the switch lever from its contact point and indicate positions in which the contact is opened, such contact being closed continuously while the rotary element of the sequence switch is in transit between posi- .tions indicated. It will therefore be under-' stood that the special. contact 111 of the sequence switch105 is closed continuously between positions 1 and 3, 3 and 5, '5 and 7, 7 andS, 8 and 9, 9 and 11, 11 and 12, and 12 and 1, but is open when the sequence switch is either resting in or passing through any one of these positions.

The group selector switch 400 (Fig. 2) and the line or final selector switch 500 (Fig. 3) are of the same general design and are of the multiple brush type. A switch of this general character is disclosed in the British Patent No. 26841 of 1909.

The line finder shown to the left of Fig. 2 is of the same general construction as the group switch except that the brushes are not latched but are normally in position to trail over the fixed terminals and the switch has no normal position. To establish connection with a calling line, the brush frame 100 is rotated by the power shaft to which it is coupled by a magnetic clutch, and the brushes are trailed over the row of terminals. There are four brushes on the line finder to traverse the sets of four fixed terminals allotted to each line. The construction of the magnetic clutch may be like that of the selector switches.

Description of 0pcmt270n.Assume. that the subscriber whose substation is shown on Fig. 1 desires connection with the subscriber whose substation is shown on Fig. 3, and whose number is 1149. The calling subscriber therefore sets his sender mechanism to indicate 1149, and having removed histelephone receiver from its hook, operates the power lover of the sender. Upon removing the receiver, a circuit is established,

through line relay 53, which is energized and closes a circuit through the lower winding of first register relay 54C, energizing such relay to close a holding circuit through its upper winding which circuit includes the For example, contact 81 top is lower winding of relay 52, and resistance 60. Belay 52 does not attract its armature because of the presence of resistance 60 in the circuit. Relay 54 closes the line conductors a, b to the conductors 61 and 62 leading to the registering and controlling equipment to which such relay is individual, such equipment being the one shown in Fig. 4. Relay 5 1 also closes a circuit through message register 63, and cut-off relay 51, causing the cut-01f relay to be energized, thereby removing the control of the line relay from the calling subscriber, and also so reducing the potential on the test conductor of the line leading to the final selectors, due to the parallel path to ground through the message register, that such line will test busy therein. The message register is of such construction that it will not be actuated by current through. the cut-off relay 51.

If the registering and controlling equipment shown in Fig. 4 had been busy the circuit for energizing the relay 54 would not have been established as the sequence switch spring 57 top would have been open. In

this case, however, the spring 57 bottom would have been closed and the second register relay 55 would have been energized instead, over a circuit including the top front contact of the line relay 53 and the conductor 56 The energization of the second register relay 55 results in precisely similar efiectsas the energization of the relay 54 except that its locking circuit includes the topwinding of the cut-off relay 52 and that the second registering and controlling 'mechanism instead of the first is connected to the calling line.

When the subscriber sets the levers 0, cl, 6, f, of the sender mechanism to the number of the desired subscriber and pulls the crank, which winds up the spring, and releases it, the levers of the sender are returned to the normal position. Each of the levers has attached thereto a segment having tooth-like projections, which in passing below a spring 9 connect earth to the conductor b of the subscribers line. After all the teeth of a segment have passed below the contact spring and all-but one of the set of impulses which determines the thousands digit have been sent to the exchange, a connection to earth of longer duration will be produced by the wheel h when a projection of this wheel reaches the spring Now the second segment 61 in passing below -the spring 9 causes a set'of impulses corresponding to the number of the hundreds digit to flow through the conductor 5, the last of which produced by the wheel h, is of longer duration and so on, until all the sets of impulses have been sent to the exchange when the sender mechanism will have returned to its normal position.

When the calling subscribers line is connected to the conductors 61 and 62 leading to the first registering and controlling equipment a circuit -is closed through his substation for the relays 65 and 66 in parallel, and the relay 68. The energization of such relays by this circuit take place immediately upon the seizure of the equipment. The earth closures to the conductor 6 by the segment 0 of the sender mechanism short circuit the relays 65 and 66 but are not of sufficient duration to cause the retraction of the armature of the slow acting marginal relay 65. Only the quick-acting relay 66 responds to all closures. Thus relay 65 functions as a timing device which regulates the movement of the sequence switch 205 during the registration period. The relay 68 remains energized as long as the receiver is off the switch-hook and will if released close a circuit to start the sequence switch 205 for the restoration of the equipment to normal, as will be hereinafter described. The first energization of relay 65 closes a circuit over spring 69 bottom, for the register sequence switch power magnet 205. The sequence switch moves from position 1 to position 2. In passing from position 1 to position 2 an impulse is sent to .the distributing switch power magnet 305 over spring 70 bottom thereby causing the distributing switch toadvance one step, and cause an idle line finder to seek the calling line.

The distributing switch, indicated by power magnet 305 and the contact springs associated with it, is controllable by-any one of the plurality of registering and controlling equipments accessible to the group of lines, as is indicated by the multiple conductors leading from the circuit closed at the register sequence switch spring 70 bottom. This switch operates to pre-select an idle line finder of the group which it controls and immediately upon the seizure of one of the registering and controlling equipments by the controlled line starts such pre-selected line finder hunting such line,- then pre-selecting another idle line finder preparatory to the establishment of the calling condition in some other line of the group. This distributing switch is constructed in the same manner and acts similarly to a sequence switch but has no normal position. Assuming that it stands in its first position upon the initiation of the call being described, the impulse transmitted to its power magnet 305 by the closure of the register sequence switch spring 70 bottom will cause it to move out ofits first position into its second position. ,Such movement will caiise the contact spring 73 top to close a circuit over the finder sequence switch'spring 74 bottom to drive such sequence switch out of its first position and into its third position. It will be observed that as soon as the operation of the line finder sequence switch, and thereby the line finder itself has thus started, the finder sequence switch spring 74 opened the circuit to the finder sequence switch at its bottom contact and closed at its top contact a connection to ground. This same operation takes place in the apparatus of each of the finder switches when taken for use, and it will therefore be seen that if, when the distributing switch comes into the second position, the second line finder, z. 6., the one individual to the conductor leading from the distributing contact spring "('3 is in use a circuit will be established to the power magnet of the distributing switch and it will move to its third position. In this manner the distributing switch will continue to move from position to position until it has found a line finder which is idle and will there remain until upon the initiation of another call. it is necessary that it should start another line finder. The distributing switch has started into operation the line finder apparatus shown in Fig. 2 to produce the hunting and seizure of the, calling line, and meanwhile, the registration of the call is progressing.

As the sequence switch 205 of the registering-controllers moves into position 2, the thousands register magnet r1000 is connected to the front contact of the quick-acting relay 66 over spring 71, and as this relay 66 responds to the successive impulses produced by the subscribers sender, the magnet 71000 is correspondingly actuated, and the register disk is thus advanced one step for each such impulse. When the relatively long earth closure takes place at the end of the thousands impulses, the armature of relay 65 is released, and closes its back contact, establishing a circuit over spring 69 top to power magnet 205. The sequence switch moves into the third position. In this position the hundreds register magnet r100 is connected to the front contact of relay 66 over spring 71 bottom, and when relay 65 is again energized, circuit is closed to power magnet 205 over spring 69 bottom and sequence switch 205 moves to position 4. n In both positions, 3 and 4, the magnet r100 is connected to the selecting circuit and re ceives the hundreds impulses in the same way that the magnet r1000 received the thousands impulses. When the hundreds impulses have been thus registered, relay 65 is again released and closes its back contact thereby sending the sequence switch 205 into position 5. In a similar manner the tens and units impulses are received and registered by the tens and units magnets 7'10 and 71, which will be connected in turn to the front contact of the relay 66, over the, springs 71 and 71 in the 5th and 6th positions and 7th and 8th positions respectively. When all of the pulsations corresponding to mains energized.

,the various digits of the number of the desired line have thus been registered, the final long earth closure depriving relay of current, closes the circuit to power magnet 205 through spring 69 top, driving the sequence switch 205 from position 8 to position 10.

As the sequence switch moves through position 9, at spring 72 bottom a circuit is closed direct to the conductor 58 (Fig. 1), thereby short-eircuiting the resistance 60. permitting sufiicient current to flow to energize the second cut-ofi' relay 52, which by attracting its armatures disconnects the subscribers station from the line during the subsequent selecting operations which are to be controlled'by the register-controllers, as will hereafter be described.

It. will be observed that a line which is idle has its test terminal 104 grounded through its message register 63; also a line which forms a part of an established connection has the same test terminal grounded in the same manner; when, however, a line is calling this ground connection is removed by one of the register relays 54 or 55, so that the line may be seizedby a line finder. In

view of the fact that the register relay by which this ground connection is opened 1s maintained operated until the selection-controlling operation is completed it is necessary that a ground connection be applied to ,the test terminal 104 as soon as the line is seized to render it nonselectable by other line finders. This is done by the finder sequence switch spring 76 top which conmeets the conductor leading to the brush 1 04 to ground through a resistance substantially equal to the resistance of the message register 68.

11] The finder sequence switch 105 (Fig. 2) when it passed from position 1 to position 3, closed circuit for the finder test relay 75, over spring 76 bottom, and when the brush 104 of the line finder is on a terminal104 of anon-calling line, to earth. Relay 7 5 when energized closes a circuit ovorspring 77 for 1 power magnet 106 of the line'finder to battery, said power magnet 106 causing the brush carriage 100 of the finder to rotate.

long as the brush 104 passes over terminals 104 of non-calling lines, relay relVhen the brush 104 passes from one terminal to another; 6. 0., when the brushes are not centered upon the terminals of the lines, the finder interrupter 109 will maintain, a circuit for relay 75 independent of the circuit through the test brush 104, to hold said relay 75 energized, said independent circuit being broken by the interrupter when the brushes rest in proper position upon the line terminals. When the brush 104 reaches the terminal 10f. of the calling line, the test relay no longer finds circuit to earth, (this path being open'by reason of the excitation either of relay 54 or 1,14e, 5ss

relay 55) and said test relay 75 will become deenergized. The circuit for the power magnet 106 is therefore broken at the front contact of relay 75, and the circuit of the holding magnet 110 is closed through the alternate back contact of said relay and spring 78, The brushes 101104 are now in connection with the terminals 101104of the calling line. Relay 75 also closes a circuit through spring 79 top, for the sequence switch power magnet 105. The finder sequence switch now moves from position 3 intq position 5, in which movement spring BTtop is closed in positions 4 and 5, connecting relay 80 to the brush 101.

When the register sequence switch (Fig. 4) is in one of the positions 1-8 in which the subscribers impulses are being received by the registers, relay 80 is energized, its

circuit beingover spring 81 top, brush 101,

upper back contact of relay 52, the subscribers station, lower back contact of relay 52, trontcontact of relay 54, conductor 62, wind ings of relays 65 and 66 in multiple, and spring 64 bottom. The finder sequence switch 105 remains in position 5 as long as the register sequence switch 205 is in one oi' the positions 1 8 and the relay 80 is energized.

At the same time that the ground was applied to the test terminal 104 by the finder sequence switch spring 76 top as above described to render the line non-selectable in any other finder switch, a substitute circuit was provided for the cut-oil relay 51, by the finder sequence switch spring 96. This circuit which includes the brush 103 and terminal 103, maintains the cut-off relay 51 energized so long as it is necessary that the line to which the cut-oil relay is individual should be non-selectable as a called line 11.0. until the breaking down of the connection and the restoration of the apparatus to normal. By means of this alternative circuit and the line finder is stopped.

over the spring 96 the cut-off relay 51 is no longer dependent on the circuit heretofore established by the iegister relay 54 or 55 and the line relay is maintained disconnected from the line.

As soon as all impulses have been received and the sequence switch 205 (Fig. 4) moves from position 8 into position. 10, the circuit of relay 80 (Fig. 2) is opened at spring 64 bottom (Fig. 4), and it becomes deenergized, at its back contact closing a circuit through spring 02 top for sequence switch power magnet 105 causing said se quence switch 105 to move from position 5 into position 7. At positions 6 and 7 of this sequence switch the selecting or fundamental circuit is closed: earth, spring 83. bottom, brush 101, terminal 101, upper front contact of relay 54, conductor 61, spring 64 top (Fig. 4), windings of relays 65 and 66 in .102, spring 84 top, winding of relay 80 to battery. Relays 66 and 80 are energized before the line finder sequence switch reaches .its position 7, in which position a circuit for the power magnet of the brush-chooser l?) of the group switch 400 is closed over spring 88 bottom and armature of relay 80. The brush-chooser therefore begins to rotate.

The first step in the process of translation will now be considered. The subscribers sender is constructed to transmit the impulses representing the number ofthe wanted line on the usual decimal basis, each digit being represented by a corresponding number of impulses and one additional impulse, that is to say, the digit 0 must be represented by one impulse, the digit 1 therefore requires two impulses, and so on. We have assumed the wanted line to he'No. 1149'; the subscribers sender will, therefore, transmit two, two five and ten impulses successively which will' be registered by the displacement of the d isks K, K1, K2, K3, respectively a corresponding'number of steps in a clockwise direction.

The system described uses two hundred point line switches, the terminals being arranged in ten levels of twenty sets of terminals each. The group switches similarly are two hundred point machines, there being ten levels and each level having twenty trunks leading to a grou ofv final or line selectors. The first level of the group switch, therefore, has trunks leading to final-switches on which are multipled lines 0499, the second level trunks leading to final switches on ,which are multipled lines 200399 and so on,

the final level having contacts representing a group of trunks ending in final switches serving lines 18001999. The number of the desired line, which was assumed to be 1149, will therefore be reached over an idle trunk in the 6th level.

By studying the grouping it is apparent that the final switches having access to the lines in an even thousand are reached over the first five levels of the group switch, while final switches having access to lines in an odd thousand are reached over levels six to ten of the same group switch. Therefore the hundreds register controller in its controlling operation must come to the position in which it will cause the cessation of selection in the group switch either in a number of steps e iual to half the number of impulsessent in from the substation or equal to half the number of impulses so sent in plus five additional steps. Of course it will be apparent that when the number of hun-' dreds impulses received from the sub-station is odd, that is when they represent an even hundreds digit, the number of steps taken by the hundreds register controller in its counter-cloclnvise or controlling movement will be one-half of the next higher even number, plus the five additional steps, if necessary. The five additional steps, it will be obvious, are necessary when and only when the thousands digit of the number of the desired line is odd. In the case assumed, therefore. the thousands digit being odd, the hundreds register controller must not cause the cessation of the selecting operation until it, and the group selector brush-chooser, have taken six steps, that is one (half of the two hundreds impulses received) plus the five additional steps rendered necessary by the factthat the desired line is to be selected in the upper half of the group switch. The control of this operation of the hundreds register controller resides in the thousands register controller. The function of the thousands register controller, therefore, in 35 the system shown, is to determine which contact, 86 or 85, on the hundreds register controller shall be effective when closed to cause the cessation of selection in the group switch and the stopping of the hundreds register controller. This is done by means ofthe' teeth 0 and the contact spring 87 of .the thousands register controller; If the thousands digit is zero (or in the case of a large system also if it is 2, 4, etc.) selection in the group switch will be in the lower half thereof and the five additional steps in the hundreds register controller will be unnecessary. Therefore the contact spring87 of the thousands register controller is so arranged with 100 relation to the teeth 0 thereon when it has taken the one step in response to the impulse from the sender, thatthe roller on the spring 87 will remain on the long tooth upon which it normally rests. The spring 87Will there- 105 fore maintain the ground connection for the conductor leading to the contact 86 of the hundreds register controller, see Fig. 4,

which is the normal contact and therefore when the hundreds register controller has reached its normal position, the contact 86 being closed, the circuit will be established to cause the change-over""or shifting operation by the register sequence switch to remove the hundreds regi-ster controller from the cooperative relation to the fundamental circuit and substitute therefore the tens. register-controller. In the case assumed, however, the desired line is in the second thousand; that is, its thousands digit is one. Therefore the thousands register-controller has taken two steps and the roller of the spring 87 now rests in one of the notches between the teeth 0 and such spring is in position to close the ground to the contact 85 of 185 the hundreds register-controller. :Since no ground is connected to the contact 86, there fore, before the change-over and stopping of the hundreds register-controller can take place, such register-controller, must be I stepped around to its sub-normal position in which the stud U1 closes the contact 85;

' that is to say in the case assumed, the hundreds register-controller will. take six steps in its counter-clockwise or controlling movement. If the thousands-digit hadbeen 2 or l,- etc., the number of thousands impulses would have been odd and since the thousands register-controller would have taken an odd number of steps the roller of the spring 87 would be resting upon one of the teeth' 0 and the operation would have been as described when the tl'iousands' digit was zero.

It has been stated that in the system shown, the function of the thousands regi ter-controller is to determine which of the normal positions, that is, the normal or sub normal positions of thehundreds registercontroller, shall be effective for causing the cessation of the selecting operation in the group switch. It will be obvious in a sys tem of 2000 to 20,000 lines that such thousands register-controller will also have the function of determining selection in an additional series of group selectors and that an additional or fifth register-controller will be necessary in each equipment to determinein which group of two thousand lines of the twenty thousand lines the selection in this additional group selector should take place;

The translation between the thousands reg"- ister-controller and this additional registercontroller would take place along precisely the same lines as between the register-controllers shown herein audit will be obvious to one skilled in the art that the system. may

be expanded in this manner, not only to serve 20,000 lines but also to serve 200,000 lines or evenmore, all that is necessary being the ad dition of the corresponding register-controllers and group selectors. Translation also takes place in the final selector under the combined control of the hundreds registercontroller and the units register-controller So far as the hundreds register-controller is concerned, it is produced by the contact device 158 and the-teeth 01, such deuice controlling whether or not, the self-locking relay 156 will be energized and locked to control the ground connection to the contact devices 159 and 190 of the units register-controller. lfthe hundreds digit is odd (1, 3, '5, etc.) a circuit will be prepared which, in the 8th and 9th positions of the register sequence switch, will energize and cause the locking up of the relay 156, to place the ground controlled by its right hand arma ture on the contact 159. On the other hand if the hundreds digit is even (0, 2, l, etc.) when the sequence'switch is passing through the 8th and 9th positions no circuit will be established for the locking relay 150 and the ground will remain connected to the contact 8 190. In this way it is determined whether trolling operation be steppedv a number of steps equal to the number of impulses which it receives from thesender, or such number of steps plus ten additional steps' The operation of the units FGQlSlZBIfiOIItIOllBI will be more fully described in relation to the establishment of a connection.

As the line finder sequence switch 1.05 went into position 7 the relay was energized, and the brush choosing power magnet 409 started to 'rotate its spindle. For each step taken by the brush chooser a ground circuit is closed to the battery side of the fundamental circuit by the interrupter 407. Although relay 80 (Fig. 2) remains ener- "gized this intermittent ground at the interrupter short circuits the stepping relayv 66 at the register, 4) hence relay 66 releases its armature and again attracts it .once for each step taken by the brush choosing mechanism; and at each excitation of said relay 66 a local circuit is closed for the stepping magnet 8100 of'the register, whereby the latter is stepped back or in a counterclockwise direction in unison with the advance of the l')1"LlSl1-h00$6l". It has been assumed that the number of the desired line is 1H9 and therefore the trunk lines leading to final selectors in which such line is accessible appear in the sixth level of the group switch. Therefore the hundreds register-controller and the group selector brush-chooser) will take six steps before the registencontroller causes the cessation of the selection by the opening of the fundamental circuit. This necessary operation will take place because the contact spring 87 ofthe thousands register-controller which has taken two steps, has in its set position, open the ground circuit normally connected to the contact 86 and closed the ground. circuit to contact 85.'

causing such relay to be deiinergized imme diately the brush-chooser interrupter opens the shunt to ground as the brush-chooser 'coines into position to trip the sixth set of brushes. Relay 80 deiinergized breaks at its front contact the circuit of the brushchooser power magnet 40a and the rotation of the brush-chooser ceases Relay 80 also closes at its back contact a circuit to the sequence switch power magnet 105 over sequence switch spring 92 top, which moves the sequence switch from position 7 to position 8. This is the trunk hunting position. In position 8 of the sequence switch a driving circuit for the brush carriage of the group selector is closed over back contact of relay 90, and spring 91, to power magnet .406, whereupon the brush carriage rotates and the selected set of brushes having been released hunts for an idle trunk in the selected group. The brush 403*, which is connected to earth oy'er spring 95 bottom, left (high resistance) winding of relay 93, and relay 90, trails over the test terminals 403, and when it comes in contact with .2 terminal which is supplied with battery through resistance 92 (Fig. 3) and spring 92, and which is not shunted by earth from another group switch circuit, the test relay 93 (Fig. 2) will be energized, and in closing its front contact will place a low resistance shunt through its locking Winding around its relatively high resistance left hand winding, to cause this particular final switch to test busy to hunting brushes of other group switches. As soon as the brushes of the group switch are accurately centered upon the terminals of a non-busy trunk line the shunt about the relay is opened at the interrupter 410 and the relay 90 is energized, breaking the circuit of the power magnet 106 at its back contact, and closing a circuit through the brush holding magnet 408 over its front contact and spring 9+1. Furthermore, it closes a circuitv to sequence' switch power magnet 105 over spring 92 bottom, thereby moving the sequence switch into position 9, in which position the line finder terminals 101 and 102 of the calling subscriber are connected through to the final se-.

lector 500 at springs 81 and 8-1 bottom. The terminal 10a to which the message register is connected is furthermore extended through to the final selector at the spring 95 top, and the ground applied to this terniinal to render it non-calling is transferred from'the upper contact of spring 76 to the upper contact of spring 05 through the test relays. The circuit of the cut-off relay 51 remains closed orer spring 90 top (Fig. 2). The fundamental circuit is now closed for selecting the tens digit of the wanted line, earth for this fundamental circuit being connected through spring 97 bottom (Fig. 3), and battery through the line relay 98 (Fig. and spring 99 bottom. This fundamental circuit, since the register sequence switch is in position 12, the line finder sequence switch in position 9 and the final sele tor Sequence switch in position 1, will include and energize the stepping relay 66,

Fig. 4, and the line relay 98, Fig. The energization of the line relay 98 closes,

through spring 150 bottom, a circuit to drive the final selector sequence switch into its second position in which the fundamental circuit will remain unchanged and .the line relay energized but in which a circuit Will be established to cause the power magnet to rotate the brush-chooser spindle, such circuit being through the front contact of the relay 98 and spring 151 bottom.

At each step taken by the brush choosing mechanism apath to'ground from the battery side of the fundamental circuit is closed through the interrupter 507 of the brushchooser and spring 152 top. The line relay 98 (Fig. will remain energized until the fundamental circuit is again broken at the spring 64 (Fig. 4). Relay 66 (Fig. 4) however at each step of the brush-chooser is deenergized to restore the tens register-controller disk, which in restoring closes after the required number of steps a circuit over spring 153 and spring 151 top to the sequence switch power magnet 205 and the register sequence switch moves into position 14. As the sequence switch moves from position 12 into position 14, the fundamental circuit is opened'at spring 0 top, and relay 98 at the line switch (Fig. 3) will be deenergized when the brush-chooser comes into position to release the proper set of brushes. A circuit is closed from the back contact of relay 98 to sequence switch power magnet 505 over sequence switch spring 155 top, and this sequence switch now moves into position 5.

As explainedabove, the line or final selectors 500 are 200'point machines,arranged in 10 levels of 20 lines each, the first 10 terminals of each level corresponding to the even hundreds of the particular 200-line group, while the second 10 terminals of each level correspond to the odd hundreds of the particular 200-line group.

In the number under consideration, viz., 1149, the hundreds digit is odd, consequently the terminals of this line will he in the second half of the selected level of the final selector. Therefore in bringing the selected set of brushes upon the terminals of the desired line, it will be necessary to select the 20th terminal of the row, instead of the 10th. The register sequence switch in passing through positions 8 and 9 closes the circuit of the translating relay 156 (Fig. 4) at spring 157 top to contact 158 on the hundreds register. Since in the present instance the hundreds register has been set by an even number of impulses, that is ;an odd hundred, relay 156 is energized and locks itself in a local circuit through spring 70 top. .Theenergization of relay 156 selects the second or sub-normal contact 159 of the units register 11 to control the termination of the unitsselecting operation,

and this contact is arrange-d ten steps behind the ncrmal, so that the units register before closing this contact muststep back as many steps as it was advanced by the impulses received from the subscriber, and ten steps in addition.

lVith the register sequence switch 205 (Fig. 1) at position 15, and the final selector sequence switch 505 (Fig. 3) at position 5, the control of the final or units selection in the final selector will. take place. The fundamental circuit being closed at springs 99 and 97 bottom and the relays 98 and 66 being energited, a circuit for the brush carriage power magnet 506 of the final selector is closed by relay 98 bver .spring 160 top and the brushes 501, 502 503 are rotated. Upon passing the brush choosing spindle the selected set of brushes is released and for each set of terminals reached the interrupter 510 at the top of the switch closes a ground circuit to the battery side of the fundamental circuit over spring 161 top and spring 152 top, and the stepping relay 66 is thus intermittently. operated to close and open the local circuit containing the stepping magnet $1 of the units reg,- ister-controller. It will be recalled that ten additional impulses are involved in this particular selection so that the register does not stop when the spring 190 is closed, but goes on until the spring 159 is closed, which will be after twenty impulses have passed through relay 66, when a circuit is closed for the power magnet of the register sequence switch 205 over spring 154: bottom, and right hand front contact of the relay 150. The register sequence switch 205. will move from its fourteenth position.

The register sequence switch moving out of position 1 interrupts at spring 72 the 52 and 5d (Fig. 1)

circuit through relays whereupon individual to the calling line, these relays are connecting the register-controller equipment and relay 52 again connecting the subscribers line to the terminals 101 and 102 of the line finder 100. Furthermore, the register sequence switch 205 moving out 0 position 1% opens at spring G-lc top, and relay 98 (Fig. 3) is deiinergized, as soon as the brushes are centered on the selected terminal, and opens the circuit through power magnet 506 at its front contact, at the same time closing the circuit through holding magnet 508 at its back contact and spring 162 top, The deenergization of the line relay 98 at this time also closes 505, which moves and is carried from position 5 to its 11th position by spring 511. The 8th position. is used only in hunting trunks leading to a private branch exchange.

As the sequence switch 505 is moving into position 6, the register-controller circuits are clearing out, hence when the relay 52 deenergized, relay 5% disthe fundamental circuit.

the circuit for sequence switch turn closes a circuit and when spring 97 for relay 98 over spring 166 bottom. At positions 6, 7 and 8 of the final selector sequence switch line is being tested, the test circuit being fromthe middle point of the battery over the left hand winding of relay 167, spring to the testv 168 top, relay 169, brush 503, terminal of the called subscribers line, and through the cut-off relay 51 of this subscriber to full battery.

If the potential on the test terminal of the 505, the called selected line is the full testing potential; that is if there is no other connection to.

ground from the conductor connected thereto, the relay 167 will be energized. The

lowering of potential on this test terminal from the fact that the may result either line desired is already calling, in which case the connection to the test conductor 1s one similar to any one of those described herein-- before, whereby the cut-off relay 51 of the calling line was energized, or it may be because some other-final select-or has seized such line as a called line and by means of the test circuit such as the one under discus son has served to operate the cutoff relay 51 of such line, corresponding to the relay 51 shown on Fig. 1.

Assuming that the line desired is idle, the

relay 167 is energized and closes a circuit for the relay 17 0, which circuit includes the spring 181 bottom. Relay 17 0 is immediately energized and closes at its right hand armature a circuit, through the right hand winding of the relay 167. direct to the brush 503 in substitution for the original test circuit through the left sis hand .winding of such relay as already traced. It should be noted that the relay 169 is polarized and its response depends upon the direction of current flow in the test circuit. The object of having this relay polarized however, since it relates solely to private branch exchange trunk hunting and party line ringing, which features in themselves form no part of the invention herein, will not be discussed. It 1 is sutficient to state-that in all cases where the line selected and tested is an ordinary subscribers line, the direction of the current in the test circuit will be such as to causetherelay 169 to attract its armature; consequently, when the sequence switch comes into position 8, it will find already prepared a circuit through the front contact of the right hand armature of the relay'169, and

the spring 1.55 bottom. This circuit Will drive the sequence switch out of its 8th position and it will, under the control of its spring 511, move into its 11th position. .It

will be observed, however, that this circuit controlled by the polarized relay 169 for driving the sequence switchis necessary if the called line on being tested is found idle as in that case the energization of the test relay 167 in position 6 or position 7 and as a result thereof the locked energization of the relay 170 establishes a circuit for the final sequence switch in its 8th position through the front left hand outer contact of relay 170 and spring 155 bottom. In any case therefore if the line tested is either an ordinary subscribers line or is an idle line of any character the sequence switch will not stop in its 8th position.

It will be observed that when the relay 17 0 was energized in the 6th and 7th positions of the sequence-switch it closed for itself a locking circuit including its inner left front contact and the spring 17 7. This circuit is maintained until the sequence switch passes out of its 9th position. In the 9th position, however, the sequence switch closes another locking circuit for the relay 170, through spring 178 bottom and front contact of the line relay 98,. This circuit will be opened as the sequence switch passes out of its 11th position. At this time another circuit has'been established for relay 17 0 including the front contact of relay 167 and the spring 181 bottom; this circuit is closed in the 11th and 12th positions of the sequence switch. In the 12th position of the sequence switch the original locking circuit for the relay 170 is reestablished through the spring 177 bottom. It will thus be observed that in the normal operation of the system when the selected line has been found idle and the calling subscriber has not replaced his receiver upon its hook, the relay.

170, having been energized in the 6th or 7th position of the final sequence switch, will be maintained energized until the restoration of the final selector apparatus has begun.

When the final sequence switch arrives in I its 11th position, it is immediately driven to the 12th position by a circuit over the spring 155 bottom andthe outer left front contact of the relay 170. In the 12th position the ringing current is applied to the desired line over left hand armature of the relay 169, ringing cut-off relay 171, spring 172 bottom andbrush 502, and ground over spring 173 bottom and brush 501 Depending upon the polarity of the current source connected to the cut-off relay of the desired line, the relay 169 will determine whether positive or negative ringing current will be applied -to the called line. The passage of the ringing current through the relay 171 will not energize such relay so long as the talking circuit is open at the subscribers sub-station. W hen, however, the called subscriber answers by removing his receiver from its hook, the talking circuit is closed and sufli- 175. This change in control is for the purv pose of controlling the breaking down of the connection from either the calling or called station.

Dis-connecting and message registering or coin collecting. 'The breaking down of the connection may result from either the calling or called subscriber restoring his receiver to the switch-hook. In either case, however, the subscriber whose receiver has not been restored will be held locked to the connection so that hisline circuit will not assume a condition as ifcalllng, and seize a registering and controlling equipment.

It will be assumed that the called subscriber 17 1 restores his receiver to the switch-hook first. Relay 175 will then be deenergized,thereby opening the circuit of relay 98. Relay 98 on being deenergized, closes a circuit for sequence switch 505 over spring 155 top, which thereupon moves from position 13 into position 15. In positions 14 and 15 a circuit is again closed over front contact of relay 165 and spring 166 bottom and relay 98 again becomes energized.

When the sequence switch reaches its fifteenth position it is continued in motion by a circuit over spring 178 top, inner left armature of relay 170, front contact of relay 167, and spring 181 bottom. It thereupon moves into position 17, deenergizing relay 170 by the opening of spring 181 as it leaves position. 15, which circuit has maintained the relay 170 energized since in position 14 the locking circuit through spring 177 was opened.

The deenergization of the relay 170 removes the test guard or condition of lowered potential from the test conductor of the called subscriber-s line by opening at its right hand armature the circuit to the test brush through the right hand (low resistance) winding of the relay 167. The subscribers line which has in the connection described been the called line is now free to be tested and seized by some other. connection in course of establishment, or since its cut-off relay isno longer energized, to initiate a call.

- As the sequence switch is passing through position 16 it completes the necessary circuits for causing the charging operation in any message register or toll devicewhich may be associated with the calling line. The operation of the message register 63 shown in Fig. 1 is accomplished by the closure thereto of a circuit including the registering battery 179 which battery is of suilicient potential to insure the operation of such register. The circuit is from battery 179,

through the inner left hand armature of the self-locking relay 176, springs 180 and 02 terminal 403, brush i03 spring 95 top, brush 10 i and terminal 10st of the finder switch, back contacts of the bottom armatures of the relays 55 and 5 1, message register 63 to ground and back to battery. It should be noted that this circuit was pre' pared by the locking up in the 13th position of the final sequence switch of the locking relay 176. This relay" can only be energized in the thirteenth position of this sequence switch and then only if the called partys control or disconnecting relay 175 is energized. Having once been energized it is maintained locked up until the sequence switch has left its sixteenth position by a circuit through its right hand armature and front contact and spring'18d bottom. It will therefore be seen that while the message registering circuit is directly controlled. by the final sequence switch in its sixteenth position, such circuit is prepared only in case the called subscriber has answered. This is for the reason that it is obvious that the re lay 175 cannot be energized in the thirteenth position of the final selector sequence switch if the called line having been found busy the final selector had been restored to normal position in the eleventh position of such sequence switch (as will be hereinafter described) or if after connection had been extended to such line the subscriber had not closed the energizing circuit for such relay 175 by removing his receiver from the hook. Correspondingly the operation of a toll device associated with the calling line will be directly controlled by the final selector sequence at spring 163 bottom and spring 97 bottom, while the character of current trans mitted will be controlled by the locking relay'176. That is to say, if the call has been successful the relay 176 being locked up the sequence switch will apply positive operat ing current from the front contact of the outer left hand armature of the relay 176 to the circuit of the calling line to charge the call by means of the spring 163 bottom. If on the other hand the call has not been successful the current transmitted to the line will be negative operating current from the back contact of the outer left hand armature of the relay 176 (such relay not having been energized) and such current will cause the charge for the call to be rebated. Furthermore, if the calling line has both a message register and a toll device associated with it, both will be operated. as required in the sixteenth position of the seqiience switch precisely as described, the circuits being prepared by the locking relay 176 and closed by the sequence switch.

As the final selector sequence switch passes out of its position 16 it opens thesprings 97 bottom, 163 bottom and 92. This opens entirely at the final selector the circuit of the trunk line leading from the terminals of the group selector for purposes to be described hereafter.

lVhen the sequence switch arrives in position 17 it will find closed for its power magnet 505 a circuit over the left hand back contact of relay 170 and spring 150 top. It will therefore move into its eighteenth position.

lVhen the final selector sequence switch passes from position 17 to position 18 a circuit is closed for the power magnet 506 over spring 160 bottom, back contact of relay 167, and spring 181 bottom, and the brush carriage is causedto move to normal. When it reaches normal position a. circuit over interrupter 510, insulated segment 182, and spring 183 bottom energizes relay 107 its left hand winding which opens the circuit of the power magnet 506 and closes circuit to the holding magnet 508 over spring 162 bottom. The energization of relay 17 0 due to the energization of relay 107 also completes a circuit for the sequence switch 505 over spring 155 bottom, causing the sequence switch to move from its 18th to its first or normal po-' sition.

It was explained. above that when the se quence switch 505 moves into position 17, the

circuit leading to terminal 103 of the group position 11. In positions 10 and 11 an earth.

connection is closed to the terminal 101 of the line finder 100 at spring 83 bottom, and battery is connected with the terminal 102 over relay 80 and spring 84 top, the holding circuit-to the subscribers cut-oil relay 51 remaining closed at spring 90 top. If now the disconnect was originated by the called subscriber, as has been assumed, and the callmg subscribers telephone is still off its hook, relay 80 will be energized atposition 11 of the sequence switch 105, and will hold the calling subscribers line locked to the connection until he restores his receiver. lVhen the receiver isrestored, relay S0 is denergized, and a circuit is closed for sequence switch 105 over spring 92 top, whereupon

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