US2153574A - Automatic switching system and apparatus - Google Patents

Description

April 11, 1939.

E. E. KLEINSCHMIDT ET AL AUTOMATIC SWITCHING SYSTEM AND APPARATUS Original Filed Dec. 15, 1929 l0 Sheets-Sheet 1 INVENTOR I 5 iawi ATTO 6' April 1939- E. E. KLEINSCHMIDT El AL 2,153,574

AUTOMATiC SWITCHING SYSTEM AND APPARATUS Original Filed Dec. 13, 1929 10 Sheets-Sheet 2 April 11, 1939. E. E. KLEINSCHMIDT ET AL 2,153,574

AUTOMATIC SWITCHING SYSTEM AND APPARATUS gbri inal Filed Dec. 13, 1929 10 Shegts-Sheet 5 April 11, 1939. E. E. KLEVINSCHMIDT ET AL" I ,1

AUTOMATIC SWITCHING SYSTEM AND APPARATUS Original Filed Dec. 13, 1929 10 Shets-Sheet'4 NV Tow 8 Z1 zksc/zgza April 1939- E. E. KLEINSCHMIDT ET AL 2,153,574

AUTOMATIC SWITCHING SYSTEM AND APPARATUS Original Filed Dec 15, 1929 10 Sheets-Sheet 5 INVENTORJ J13. wand/22x02 2 iffy/ 95i April 1939. E. E. KLEINSCHMIDT ET AL 2,153,574

AUTOMATIC SWITCHING SYSTEM AND APPARATUS Original Filed Dec. 13, 1929 10 Sheets-Sheet 6 INVENTORS Z2? KZeZ/IJM/JZIQ'Z m A TTORN April 11, 1939. E, E. KLEINSCHMIDT ET AL 2,153,574

AUTOMATIC SWITCHING SYSTEM AND APPARATUS Original Filed Dec. 13, 1929 '10 Sheets-Sheet 7 April 11, 1939.

E. E KLEINSCHMIDT El AL 2,153,574

AUTOMATIC SWITCHING SYSTEM AND APPARATUS Original Filed Dec. 15, 1929 10 Sheets-Sheet 8 *1 [III llflllllll llfl Illlllllllllllllllllllllllllllll [III llflllllflllll unuu lllllfllllllllll ll Hzf INVENTORS a llizwzscizzzzat J. dial/56k 9 A TTORNE p 1939- E. E. KLEINSCHMIDT ET AL 2,153,574

AUTOMATIC SWITCHING SYSTEM AND APPARATUS Original Filed Dec. 15, 1929- 10 Sheets-Sheet 9 INVENTOR Z1. ilez'zzscizzlzaz A TTO Ap 1939- i E. E. KLEINSCHMIDT ET AL 2,153,574

AUTOMATIC SWITCHING SYSTEM AND APPARATUS Original Filed Dec. 13, 1929 10 Sheets-Sheet 10 INV TOR 1. I ile zscjlzzzdz Patented Apr. ll, W3

UNITED STATES PATENT OFFICE AUTOMATIC swrrcnmc SYSTEM AND maaa'rns Delaware Application December 13, 1929,, Serial No. 413,838 Renewed July 25, 1932 79 Claims. (Cl. 179-4) Our invention relates to automatic switching systems and apparatus therefor. More particularly the invention relates to automatic switching systems and apparatus for combined tele- 5 graph and telephone or other combined signalling operations.

Due to the difference in characteristics between telegraph and telephone signals, the former being characterized by direct periodic current marking and spacing signal impulses and the latter by a continuous oscillating current of speech frequency, difliculty has been experienced in permitting both telephone and telegraph operation over the usual automatic telephone switch- 15. ing mechanism. As isv well known, automatic switching systems are operated by dialed direct current signal impulses to which switching equipment responds for selecting the called party line.

Release of the equipment is ordinarily accomplished by the disconnection ofthe direct current for a predetermined interval when the subscriber hangs up. It will be evident that in such a system, the automatic equipment would be normally unable to distinguish between the dialing 5 signalling impulses and the telegraph signalling impulses and the direct current telegraph signals would furthermore experience difllculties in passing over telephone lines designed primarily for the transmission of speech frequencies.

30 In general, the invention contemplates a sepa rate signalling number for each telephone and telegraph set even where a single subscriber is provided with both types of sets. The switching equipment is arranged to connect all telegraph numbers through translating and repeating equipment which after connection has been completed through to the called subscriber, translates at the calling end of the system direct current signals originating at the calling sub- 40 scribers apparatus into alternating current of substantially speech frequency and retranslates the alternating currents at the called subscribers end of the system into direct current signal impulses for operating the receiving appara- 45 tus. Provision is also made for permitting telegraph signalling in both directions following connection and for restoration of the switching equipment at the end of communication.

Although each subscriber is provided with a 50 single signalling circuit to the switching equipment, provision is made for distinguishing between a telegraph and telephone call by a difference in frequency of the ringing current in each case.

55 At each of the stations, sets are arranged to permit calling of any other set at any other station. When the station desired is equipped with both a telephone set and a telegraph set, the desired set, telephone or telegraph, is indicated and is selectively connected to the line at the s responding station by reason of the signals of the directory number which has been dialed by the calling station. Many or all of the automatic switches of the telephone central ofices may be used for either telephone or telegraph connec- 10 tions. The trunk lines connecting several oflices of an exchange may be used for either telephone or telegraph communications alternatively.

Similarly the metering for totalizing telephone and telegraph calls is selectively accomplished by 16 distinguishing between telephone and telegraph signalling.

Accordingly an object of our invention is to provide novel means for adapting standard and well known types of telephone exchange appara- 20 tus to the co-operative service of telephone and telegraphswitching.

' A further object of our invention is to provide novel exchange systems in which two telephone sets may communicate as in an exchange which is exclusively telephonic and without being in any way inconvenienced by the presence of telegraph apparatus and in which also two telegraph sets may communicate by telegraphy, the connections being set up in the manner of a telephone connection with the use of telephone types of calling dials.

A still further object of our invention is to provide standard switches and circuits to enable the owner of an automatic telephone exchange provided with no telegraph service to add a minimum equipment for producing an exchange suitable for both classes of service; namely, telephonic and telegraphic.

Still another objectof our invention is to provide an automatic exchange system in which telegraphic service is added without diminishing the telephonic value of the service.

Further objects of an invention are to provide metering means for totalizing the telegraph calls 'of a line separately from the telephonic calls of the same line and to provide signals on a set of apparatus for warning against an attempt to use the set at a time when an alternative set upon the same line may be in use. Alternate forms of 5 apparatus are shown and other objects will be clear from the drawings and description, and from the scope of the appended claims.

In the drawings:

Figure 1 is a diagrammatic view of the teleu graph repeater circuits only, omitting switching connections.

Figure 3 is a circuit diagram of the line finder, first selector and telegraph repeater associated with the calling party.

Figure4 is a circuit diagram of the second selector and selector repeater associated with the calling party.

Figure 5 is a circuit diagram of the selectors associated with the called party.

Figure 6 is a circuit diagram of the repeater and connector associated with the called party.

Figure 7 shows a combination sub-station having both telephone and telegraph sets and assumed in the description following to be the callins party- Figure 8 shows an alternative form of substation assumed in the description following to be the called party.

Figure 9 is a circuit diagram showing the circuit connections between calling station and called station for telegraphic communication.

Figure 10 is a circuit diagram showing the circuit connections between calling station and called station for telephonic communication, the two stations shown being telephone stations without any telegraphic equipment.

Figures 11 and 12 areedgeand side views showing details of the control mechanism for the station omnigraph.

Figures 13 and 14 are fragmentary side and plan views showing details of the timing device.

Figure 15 is a sectional view showing a detail of Figure 14, the section being taken on lines l5-l5, Figure 14.

Figure 16 is a detafl sectional view of the remote-test device.

Figure 17 is a view disclosing a modified form of omnigraph disk.

Figure 18 is a circuit diagram showing the circuit connections for the metering devices.

Figure 19 is a circuit diagram showing a modified arrangement of circuit connections for the metering devices.

Figure 20 is a circuit diagram of a modified form of convertible selector.

Figure 21 shows a modified form of omnigraph disk to be used with the metering system shown in Figure 19.

Figure 22 is a circuit diagram of a modified form of repeater.

Figure 23 is a circuit diagram of a modified form of convertible final connector.

Figure 24 is a circuit diagram of the final connector shown in Figure 1.

Figure 25 is a detail view of a telephone ringer.

Figure 26 is a detail view of a ringing relay for telegraph purposes.

Figure 2'? is a detail view of a polar relay and its circuit connections.

Figure 28 is a circuit diagram of a modified form of repeater system with ground return and employing direct current relays, and

Figure 29 is a circuit diagram of another modified form of repeater system with the details of Figure 22 substituted in the system of Figure 28.

In Figure 1, two subscriber stations, I and I, remotely disposed from each other are shown, each station being provided with a telephone set and a telegraph set, as shown in detail in Figure 7. Extending from each of these sets are their individual signalling lines I. and 8,...

telephone equipment, isalso provided with two directory numbers for its single vl irnalling line, one-being a telephone number and the othe'ra telegraph number.

The signalling lines I and I extendto the usual form of rotary line switch I, shown diagrammatically in Figure land in detail in Figure 3. which is of well known construction and'operates in response to the lifting of the telephone hook at the station'l to find the first idle selector such as selector 8, the wipers of which are connected over conductor 9 to the third contact on the rotary switch 1. It will be understood that similarly each of the other contacts of the rotary switch 1 has associated therewith a similar selector 8 connected to a conductor such as 9. Selector 8, which is also of any well known construction commonly used in the telephone art and is shown in detail in Figure 3, operates in, response to the first dialing signal at the station I to move the wipers oi the selector to predetermined contacts. The selector 8 is merely shown diagrammatically in Figure 1. It comprises a plurality of contacts arranged in horizontal rows, there being a number of these rows disposed one above the other. In operation, after the wiper [8 has moved vertically to select a predetermined row of contacts it automatically rotates in a horizontal plane until it reaches a contact connected to an idle selector.

The conductor iii extending from conductor 9 is shown in dotted lines to illustrate diagrammatically that it is normally open and is closed when the selector completes its operation. If the first dialed signal is a telephone signal, the circuit over conductor 9 is extended over conductors ill and ii to a selector repeater l2. If on the other hand, the first dialed signal is a telegraph signal, the circuit over conductor 9 is extended over the conductors ill and ii to a repeater M, which, as will appear hereinafter more fully from the detailed description, is arranged to transmit the telegraph codes over the signalling lines after connections have been made with the remote or called subscriber's station.

Upon operation of the repeater ll, a rotary line switch l5 of construction similar to the rotary line switch 1, briefly described above, is operated until it finds an idle selector l6. Upon the dialing of the second telegraph selecting signal the selector Iii operates to select a, linesuch as I! connected in multiple with the conductor Ii and extending to the selector repeater l2. The repeater I2 is thereupon operated in accordance Each ofsuch stations.- as I or I, which isprovided'withtelegraph and with the next or third telegraph selecting signal areas 8855. These two numbers are dialed 8. 0.8644

and T. S. O.-8,855, respectively. It will be assumed that station I isthe calling station and station 2 is thecalled station.

For telephonic communication accordingly the subscriber at station I lifts the receiver and dials S. 0. 8644. Upon lifting the receiver, the rotary line switch I responds thereto in the well known manner and rotates until it finds the first idle selector which in the present case is the selector 8, the operation of which .will be described more fully hereinafter. Th'e'eflect of dialingthe letter S is to lift the brushes of the selector. seven steps and to connect'theconductor 3 and 4 of the, station I through the wipers-on the rotary line switch I on which it has stopped and conductor 9 through the wipers l8 to the conductor ll extending to the repeater l2. Dialing the letter lifts the brushes of the selector repeater l2, in a manner to be described, through six steps and extends the circuit traced above over the conductors2| and 22 to a third selector 28 at the remote exchange, selector 2! being of construction similar to selector I. Y

Before tracing the further operation of dialing the telephone number, the effect of dialing a telegraph number up to this point will be briefly described. For telegraphic communication, the party at station I operates a starting key of a telegraph set corresponding to the hook switch of the telephone set, as will appear in detail hereinafter, and dials T. S. 0.-8855.

Upon operation of the starting key, the line switch I responds, as described above, to select the first idle selector switch 8 over the conductor 9. Dialing the letter T lifts the brush I8 eight steps and connects the station I to the repeater l4 over the conductor l3. The relay 23 comprising part of the repeater I4 is operated over this circuit and at its armature 24 closes a circuit through the retardation coil 25 and through the rotary line switch l which is now operated in the same manner as rotary line switch I to find the first idle selector such as selector 6.

The switching dial impulses produced by dialing the letter S from the station I will now be repeated by the relay 23 of the repeater l4 and will move the wipers 2'8 of the selector l6 seven steps extending the circuit over conductor to the selector repeater l2 as in the case of the telephone selection. When now the letter 0 is dialed, the brush 21 is raised six steps extending the circuit over conductor 2| as in the case of the telephone communication.

At this point it will be noted that in the case of the telephone selection the operation of dialing the letter S operates the selector 8 to connect through directly to the selector repeater |2 whereas in the case of the telegraph selection the operation of dialing the letter T extends a circuit from the station I over conductor l3 through the telegraph repeater l4 which in turn causes operation of the rotary line switch l5, the rotary line switch thereupon operating to select the first idle selector l2.

The conductors 2| and 22 are connected to a brush 32 moving over contacts of a selector 28 and the selector 28 will be operated as in the case of selector 8 to extend a circuit over conductors 2| and 22 and over conductor 34 to wiper 35 of a selector 31.

It will be noted upon referring to the telephone and telegraph numbers again that the'first numeral of both the telephone and telegraph code are alike, both being 8. In response to eight impulses, the brush 32 of the selector 28 is stepped over eight contacts to extend the circuit as stated above over'conductor 34 to the brush 3!. It now. the telephone number is being dialed and six impulses are received, brush 25 will move to the sixth contact extending a circuit over conductors ll to the connector switch 49. The connector I9 now will operate in response to the dialing of-the last two I numbers 4-4 to extend telephone circuits from conductor 28 over conductors 5 and 8 completing the circuit to the called station 2.

If on the other hand, the telegraph number is being dialed and eight impulses are received, the

brush 35 will be stepped to the eighth contact extending the circuit over conductor 34 and the conductor '4| to the telegraph repeater 42. The.

telegraph repeater 42 comprises a dialing impulse repeating relay 43, telegraph receiving relay 45, telegraph repeating relay 48 anda source of alternating current 46. Armature 41 of relay 48 is also part of repeater 42 and operates to repeat impulses in the opposite direction, as will appear more fully hereinafter. Relay 45 is operated in response to received telegraph signalling impulses to operate its armature SI for operating the called party's telegraph apparatus after connection has been completed in accordance with the next two dialed numbers 5-5. The armature 5| is connected to the wipers 52 of a connector 53. The

connector 53 operates in response to the last two When the connection to the called station 2 is.

made through the telegraph repeater 42 in the manner described above, ringing current is impressed over the conductors 5 and 6 to the called station 2 which will operate in a manner to be described to remove the telephone set from the line and connect the telegraph set to the line.

A polar relay at the called station 2 will be controlled by current of reversed polarity on the line, the current from the final connector 53 being reverse in direction as compared with current from the final connector 39 and will retain the telegraph set upon the line until the release of the connection, when current through this relay will release the telegraph set and will replace the telephone set and the signalling devices upon the line.

The calling station I is shown in detail in Figure 7, and, as will appear hereinafter, comprises a telephone set and a telegraph set.

Because the numerical selected impulses originated by the calling dial of the telegraph set must pass through the repeater |4,'the calling dial of the telegraph set may be adjusted to operate at a lower speed than the calling dial of the telephone set if desired. Should the feature of two adjustments be used, the telephone set calling dial is not restricted in any way since the numerical currents from the telephone set do not encounter any retardation such as 25 in the repeater l4.

Figure 7 shows the details of the calling station comprising a telephone and a telegraph set, a telephone receiver 6|, transmitter 62 and hook 63 therefor, all of well known construction and connected in the well known manner to the usual form ot'telephone dial ll. One terminal of the telephone dial ll is connected over the conductor II to the telephone equipment described above, the switch operating with two contacts, one of 5 which is connected to conductor 88 and the other to the conductor 81. Conductor 88 extends to the upper contact of a switch arm 88 which in I turn is connected to the conductor l extending to' the rotary line switch as shown in Figure 1,

The other conductor 81 extends to the upper contact of the switch arm 88 which in turn extends over the conductor 3 to the other side of the rotary line switch as shown in Figure 1. Switch arms 88, 88-, II, I2 and I3 are operated 18 controlled by the telegraph start lever II of any well known construction.

The switch arm 88 when in engagement with its lower contact, as will appear more fully here-- Dialing for telegraph communication In order to initiate telegraph communication, the operator at the calling station I, Figure '7, operates the starting key 15 which in turn moves the change-over switch 'Il moving the switch arms 88, 88, II, I2 and I3 to their lower position and a holding circuit is closed from ground, through battery, winding of the magnet 8 l switch I2 and its contact, switch 82 and its contact, conductor 83 to the lower contact and switch spring M of the telephone hookswitch, to ground. Magnet 8I, upon energization, holds the change-over switch H in the operated position. An obvious energizing circuit is also completed over the switch I3 for the normally. non-operating motor 8l' of the telegraph set which is now started into operation. A further result of the operation of change-over switch H is to complete a circuit for the signalling lamp 85 over the switch arm 'Il indicating that the telegraph apparatus is in operation so that the telephone user will not attempt to use the telephone set at this time. A 55 similar circuit may be completed over the hook switch spring 8l and conductor 80 to the signalling lamp 81 to indicate to the telegrah operator when the telephone user has seized the line associated therewith for communication. A further result of the operation of change-over switch N is to connect the conductors 3 and l over the switch arms 69 and 88, respectively, to the telegraph apparatus over the conductor 8| and the telegraph dialing equipment.

As a result of this latter operation an energizing circuit is completed for the slow-to-release line relay IOI shown in Figure 3, which relay is part of the rotary line switch 1,. the circuit extending from ground; through battery, winding 70 of line relay IN, the back contact and armature I08 of a cut-of! relay I08, over the conductor l, through the switch arm 68 ,in engagement with its lower contact, through the contact of the dial 82, contact 88, transmitter 81, through the printer 75 magnet 86, polar relay 85, contacts M and 83 in by the vertical arm of change-over switch 'Il' parallel, conductor 8|, switch arm 88 in engagement with its lower contact, conductor 8 and armature H2 and its back contact to ground.

The line relay III of the rotary line switch I is thus energized in response to the changeover operation of the telegraph starting key II at the calling station I.

The rotary line switch I comprises, in addition to the line relay III, a cut-oil relay I88 and a motor magnet ll3.which controls a set of wipers I ll causing them to pass step by step over a bank of contacts Ill. The construction of the wipers Ill and bank is such that the wipers will at all times be in engagement with a set of bank contacts III. To each of the bank contacts II! are connected the customary positive and negative trunk H8, Ill and release trunk 0, leading to the selectors such as selector 8.

If the rotary line switch wipers are resting on a busy trunk when the line relay IOI becomes energized, the cut-off relay I08 will be shunted out and a circuit will be completed from trunk II6 which is at this time grounded, as will appear hereinafter. and over contact .I I8, brush lIl, armature I3I of the cut-oi! relay I08 in engagement with its back contact, armature I32 oi the line relay I0l in engagement with its front contact, contact and armature I22 of the motor magnet Ill and through the winding of magnet II3, to battery and ground.

The motor magnet II3 will now operate and advance the wipers Ill step by step as it is energized and deenergized by the operation of its armature I22. In this manner, the cut-off relay I08 remains shunted out so long as the wiper Ill engages a private busy bank contact H5. When, however, an idle trunk is reached, the shunt circuit mentioned above is absent, and the cut-oil relay I08 will be energized over a circuit from ground, through the armature I 2| of the line relay I 0| and its front contact, through the winding of the cut-oil relay I08, the back contact and armature I22, the winding of the motor magnet H3, and battery to ground. The motor magnet I I3 is so constructed that it will not energize when in series with the cut-off relay I08. Cut-oft relay I08 will, however, energize over the above traced circuit and operate to extend the connections from conductors l and 3 over armatures I08 and 2 respectively, in engagement now with their front contacts, over conductors I23 and I2l, respectively, wipers lIl, contacts 5 and trunks Ill and H8 to the selector.

When out-off relay I08 energizes, it opens the circuit of line relay IIII at armature I08 and moves armature I3I into engagement with its front contact. Relay IOI, being a slow acting relay, will not immediately deenergize, but will maintain ground on the release trunk until suflicient time has elapsed for the release relay of the selector 8 to provide a new holding ground on the release trunk, for the cut-off relay I08 from battery, through motor magnet I I3, armature I22 and its back contact, cut-oil! relay I08, front contact and armature I31, wiper Ill and conductor II8 which is grounded as will be described. Immediately after this holding circuit for cut-off relay I09 is established, the line relay IOI will be deenergized.

In this manner the rotary-line switch I operates in response to the operation of the starting key I5 at the calling station I to rotate its wipers until they find a group of trunks ll8 to 8 extending to an idle selector, such as selector 8. The conductors Ill and 8 now extend a circuit from the calling station I over armatures I33 and I34, respectively, and through the two windings of, the line feed relay I35.

The line feed relay I35 is energized and at its armature I36 completes an obvious energizing ircuit for the release relay I31 which is of the quick-to-operate type. Release relay I31, upon energization, moves its armature I38 into engagement with its front contact and extends ground to the trunk II6 connected to the bank contact II for locking the relay I09 as described above and also to provide ground for any other wiper II4 of any other rotary line switch moving over this contact for shunting its associated cut-ofi relay and continuing the operation of its associated motor magnet as described in connection with the rotary line switch 1. When the upper wiper II4 engaged the upper private contact II5 no ground appeared on this trunk inasmuch as the selector 8 in the above was assumed to be in an idle condition.

The operations thus far described are those which take place automatically in response to the original operation of the starting key 15, the first idle selector 8 having been selected. It is assumed, as state dabove, that the telegraph code T. S. O. 8855 is being dialed and that at this time the letter T is dialed. As the letter T is dialed, the line feed relay I35 is periodically deenergized and reenergized. At the first deenergization of the line feed relay I35 in the dialing operation, a circuit is completed from ground, through armature I36 in engagement with its back contact, back contact and armature I4I, armature I42 in engagement with its front contact, through the winding of the slow-to-release series relay I43 and through the winding of the vertical magnet I 44, to ground.

The slow relay I43 is energized and will remain energized until the last of the group of impulses representing the letter T is dialed, inasmuch as the deenergizing intervals between the impulses are too short to deenergize relay I43. The vertical magnet I44 is energized to step the wipers I8 from one level of contacts I50 to the succeeding level of contacts I50. At the first step of the wipers by the vertical magnet I44 the off-normal switch I53 closes its contacts.

As is well known in the art, the release relay I31, the circuit of which is periodically opened as the armature I36 moves to its back contact, is not deenergized during'these intervals, its construction being such that insufficient time is provided during the ordinary impulsing interval to permit relay I31. to become deenergized. In the present case, it is assumed that eight such impulses are transmitted and the vertical magnet I44 is accordingly energized eight times moving its brushes I8 step by step until they reach the eighth row of selector contacts on the selector 8 as shown in Figure 1.

Energization of the slow relay I43, operates its armature I45 to engage its front contact, and the ground at armature I38 is extended over armature I45 and its front contact and over the back contact and armature I46 of the rotary magnet I41 and then over conductor I48, to relay I6I, but this has no eifect at this time due to the ground obtained at the opposite terminal of relay I6I. A circuit is also completed from the ground, over armature I45 and its front contact, over conductor I5I to the contact I52 of the off-normal switch I53, and through the windin of the private relay I54 to battery and ground. Relay I54 energizes and closes a locking circuit connected is busy,

for itself from ground and battery, through the winding of the relay I54, contact I52 of ofl-normal switch I53, conductor I5I, back contact and armature I46, armature of relay I54 to ground.

At the end of the dialing impulsing, relay I35 remains energized sufllciently long to in turn deenergize relay I43 which moves its armature I45 into engagement with its back contact establishing a circuit for rotary magnetI4-1'from ground, through battery, through the winding of the rotary magnet I41, front contact and armature I56, back contact and armature I45, armature I38 and its front contact to ground. Rotary magnet I41, upon energization, prepares the wipers I8 for stepping over the contacts I50 and moves its armature I46 out of engagement with its back contact thereby breaking the locking circult of private relay I54 and de-energizng this relay. De-energization of private relay I54 opens the circuit of rotary magnet I41 at armature I56. De-energization of rotary magnet I41 rotates the vlvslpers I8 into engagement with a set of contacts If the repeater to which these contacts are conductor I50 will have ground on it, as will appear hereinafter, and a circuit will be completed from grounded conductor I50, contact I50, wiper I8, conductor I39,

armature I40 in engagement with its back contact, conductor I48, armature I46 in engagement with its back contact, conductor I5I, off-normal contact I52, winding of private relay I54 to battery and ground. Private relay I54 will be energized, moving armature I56 into engagement with its front contact, again energizing rotary magnet I41. This magnet will then rotate the wipers I8 into engagement with the succeeding set of contacts I50 on the same level. If the repeater to which these contacts are connected is busy, the above-described operation will be repeated.

It will now be assumed that the wipers I8 have reached a set of contacts I50 which lead to an idle repeater. The conductor I50 leading from this idle repeater will be open instead of being grounded. Accordingly, a circuit will be completed from ground through battery, winding of the private relay I54, closed off-normal contacts I52, back contact and armature I46, conductor I48, winding of the cut-through relay I6I, con ductor H6 and armature I38 and its front contact to ground. Relay I54 is not operated, as the current flow is not suiilcient therefor, but relay I6I is so constructed as to operate over this circuit. Upon energization of relay I6I, the circuit from the calling station I is extended over conductors H1 and H8, armatures I33 and I34 in engagement with their front contacts, and over wipers I8 and contacts I50 to the feed relay 23 of the repeater I4.

The feed relay 23 is now energized over the circuit to the calling station apparatus and at its armature 24 completes a circuit to the bypass resistance 25, the circuit extending from ground to battery through the winding of the relay I62 to the back contact and. armature I64 of the cutof! relay I65 to armature 24 in engagement with its front contact, resistance and armature I66 in engagement with its back contact to ground.

Line relay I62, cut-cit relay I65 and motor magnet I68 control a rotary line switch I5 similar in construction to the rotary line switch 1 ground is placed on the conductor I68 leading to the motor magnet I68 from the brush I'll ii this brush is in engagement with a busy contact I12. It will be understood that ground is applied to the segment I12 as long as it is busy, or in other Words, has been seized by some other rotary line switch. As in the previous case, the rotary line switch I5, is individual to the telegraph repeater relay 23.

In the event that ground is applied to the conductor I88 when brush I'll is on a busy segment I12, the rotary magnet I68 is energized and its armature opens its own circuit at the same time stepping the brushes I'll and I" and I15 to the succeeding steps of contacts I 12, I16 and I11. As soon, however, as the brushes "I, I" and I15 engage a set of contacts I12, I16 and I11 which are not busy, ground will no longer be obtained at I12 and an energizing circuit is then completed from ground, through armature I18 of line relay I62, in engagement with its front contact, through the winding of the out-oil relay I65 and to the motor magnet I68 to battery and ground. The motor magnet I68 is so constructed that it does not respond to this circuit, but the relay I65 is energized. As in the previous case, it will be noted, as long as ground is obtained on the conductor I68 from the bank contact I 12, relay I65 will be shunted and not energized. Energization of relay I65 extends a circuit from the armature 2l of the repeater relay 23 over armatures I6l and I66, in engagement with their front contacts, to the wipers I" and I15 on bank con .tacts I16 and I11 extending as will now appear to the next selector.

This circuit now extends over conductors I8I and I82 to armatures I83 and I (Figure 4), re-

spectively, and their back contacts of a cutthrough relay I85 and to the windings of a line feed relay I 86 of a second selector I6. The second selector I6, it will be noted, is similar in construction to the selector 8 described in detail above. As in that case, there is provided a line feed relay I86 which is periodically energized and deenergized in accordance with the impulses received over the lines I8I and I82.

The line feed relay I86 is energized and at its armature I88 completes an obvious energizing circuit for the release relay I81 which is of the slow--to-release type. Release relay I81, upon energization, moves its armature I into engagement with its front contact and extends ground to the trunk I80 connected to the bank contact I12, so that any other wiper ill of any other rotary line switch moving over this contact I12 will find ground thereon shunting its associated cut-off relay I65 and continuing the operation of its associated motor magnet I68.

The letter S will now be dialed. As the letter S is dialed, the line feed relay I86 is periodically deenergized and energized. At the first deenergization of the line feed relay I88 in the dialing operation, a circuit is completed through the windings of the slow relay I8I and vertical magnet I82. The slow relay I8I is energized and will remain energized until the last of the group of impulses representing the letter S is dialed. The vertical magnet I82 is energized to step the wiper I84 from one contact I81 to the succeeding contact I81. At the first step of the wipers by the vertical magnet I 82 the oil-normal switch I88 closes its contacts.

It is assumed that seven impulses are transmitted when the letter S is dialed. Accordingly, the vertical magnet I82 is energized seven times,

moving the wipers I 8l step-by-step until they reach the seventh row of selector contacts on the selector I6.

Energization of the slow relay I8I operates its armature I83 to engage its front contact and a circuit is completed through the winding of the private relay I88. Private relay I88 is energized and completes a locking circuit for itself.

At the end of the impulsing, relay I86 remains energized sumciently long to in turn deenergize slow relay I8I. Deenergization of slow relay I8I completes a circuit for energizing rotary magnet 202. Energization of rotary magnet 202 prepares the wipers I8l for stepping over the contacts I81 and breaks the locking circuit of private relay I88, deenergizing this relay. Deenergization 01! private relay I88, opens the energizing circuit of rotary magnet 202. Deenergization of rotary magnet 202 rotates the wipers into engagement with a contact I81. If the repeater to which this contact is connected is busy, the rotary magnet 202 will be energized to rotate the wipers into engagement with the succeeding contact, as described in connection with selector 8. If, however, the repeater is idle, the cutthrough relay I85 will be energized and the circuit from conductor I8I and I82 will be extended over armatures I83 and I84, and their respective front contacts, over wipers I85 and I86, and the contacts engaged therewith to repeater I2. The selector repeater I2 combines the function of the selectors such as selector 8 and selector I6 and that of a repeater for repeating the next dial impulses over two conductors to a set of selector switches at the distant switching office. It will be noted that up to this point connections between the rotary line switches and the selectors at various steps have been made over three conductors. Inasmuch as the apparatus thus far described, including the selector repeater, is all located at one station, the use of three wires between the various apparatus is not objectionable. It will be clear, however, that in making connections to a remote station, the use of three wires would render the system entirely too costly. The selector repeater is therefore arranged to repeat the next dialed impulses over a two wire system as will appear from the following description.

As will be clear from a. comparison, the selector part of the selector repeater I2 is essentially the same as the selectors 8 and I6. As in each of the previous selectors, there is the usual line relay 2I I, similar to the line relay I86 of selector I6, release relay 2I2 similar to the release relay I81, slow relay 2I3 similar to the slow relay I8I, cut-through relay 2Il similar to the relay I89, stepping magnet 2I5 similar to the vertical stepping magnet I82 and a rotary magnet 2I6 similar to the rotary magnet 202, for rotating-the wipers to engage the contacts opposite which they have been positioned. The repeater which makes up the remaining portion of the apparatus is provided with a tone relay 22I, condenser cut-off relay 222, electro-polarized relay 223, and the bridging relay 224 which has two independent windings. I

Upon the connection of the brushes I85 and I86 with the contacts I81, the circuit from armature 2l of the repeater relay 23 is extended over the make before break contacts 23I and 232 to the windings of the line feed relay 2I I. Upon energization of line feed relay 2, relay 2I2 is energized which at its armature 233 places ground on the release trunk I81 leading to the wiper I8l.

The subscriber now dials the letter 0 comprising six impulses. As the letter 0 is dialed, the line feed relay 2| I is periodically deenergized and reenergized. At the first deenergization of the line feed relay 2 in the dialing operation a circuit is established from ground over armature 234 in engagement with its back contact, armature 235 in engagement with its front contact, armature 236 and its back contact, armature 236 and its back contact and through the windings of the slow relay H3 and the vertical stepping magnet 2I5 to batteryand ground.

The slow relay H3 is energized and will remain energized until the last impulse of the group of impulses representing the letter O is dialed. The vertical magnet 2l5 is energized to step the wipers 2, 242 and 243 from one level of contacts to the succeeding level of contacts. At the first step of. the wipers by the vertical magnet 215 the oil-normal switch 246 closes its contacts.

In the present case, it is assumed that six impulses are transmitted in the dialing of the letter 0 and accordingly the vertical magnet 2l5 is energized six times, moving the wipers six times until they reach the sixth level of contacts.

Energization of the slow relay 2" operates its armature 244 to engage its front contact and establishes a circuit from ground to the front contact and armature 233, armature 244 and its front contact to the contact of 'the off-normal switch 246, through the winding of, the private relay 245, battery and ground. The private relay 245 upon energization will form a locking circuit for itself from ground through battery and the winding of the relay 245, through the closed contact of the off-normal switch 246, the front contact and armature 245' of the relay 245, armature 241 and the back contact of the rotary magnet H6 and over the armature 233 and its front contact to ground.

At the end of the impulsing, line feed relay 2 remains energized long enough to deenergize slow relay 2|3 which moves its armature 244 into engagement with its back contact and completes a circuit for rotary magnet 2|6 from ground to battery, through the winding of the rotary magnet 2l6, front contact and armature 25l, back contact and armature 244 and front contact and armature 233 to ground. Rotary magnet 2l6 will energize over this circuit and operate to prepare the wipers for stepping over the contacts in the sixth level. In addition, the rotary magnet 2| 6 moves its armature 241 away from its back contact and thereby opens the locking circuit of the relay 245 and deenergizing this relay. Deenergization of relay 245 opens the circuit of the rotary magnet H6 at armature 245'. Deenergization of rotary magnet 2|6 rotates the wipers into engagement with a set of contacts.

If the first bank contact is idle a circuit will be established from ground, through battery, through the winding of the relay 245, through the closed contacts of the off-normal switch 246 back contact and armat ure 253, through the winding of the relay 2l4, through armature 233 and front contact to ground. The relay 245 is not energized over this circuit but relay 2 is energized and operates its armature 238 to prepare the repeater circuit.

Relay 2 l4 upon energization opens the energizing circuit of the slow relay 2l3 and completes an energizing circuit for the slow relay 222 from ground to battery to the winding of relay 222, front contact and armature 238, back contact and armature 236, front contact and armature 235, back contact and armature 234 to ground.

As soon as the wipers 2 to 243 engage their contacts, a circuit is established over the two trunk conductors 26! and 262 to the line relay 263, Figure 5, at the remote station selector 26. This circuit extends from ground, through battery at the remote selector, to the upper winding of the relay 263, back contact and armature 264 of the break relay 265, conductor 262, wiper 242, armature 266 of relay 2 in engagement with its front contact, armature 261 and its back contact, lower winding of the relay 223, make-before-break contact 263, lower winding of the relay 224, over armature 269 and its front contact, over the wiper 24I, conductor 26L armature 2', and its back contact and through the lower winding of the relay 263 to ground. The line relay 263 at the selector 28 will energize over this circuit and stand in readiness to receive the impulses which will be sent in by the repeater.

When the relay 224 energized, a circuit was established from ground, to battery, through the upper winding of the relay 223 and over the armature 212 in engagement with its front contact, to

ground. The current now flows in both windings of relay 223, but these windings are opposed that the relay is not operated.

When the subscriber dials the next character which in thepresent case is assumed to be nu meral 8, the line feed relay 2 will momentarily release its armature 234 each time. Each-time the line feed relay 2 deenergizes, a circuit is closed from ground through armature 234 in engage'ment with its back contact, armature 235 in engagement with its front contact, armature 236 and its back contact, armature 236 and its front contact, through the relay 222 to battery and ground. The relay 222 will energize over this circuit and since it is a slow acting relay, will maintain its armature in an operative position as long as the line relay 2 is responding to the dial impulses. When the relay 222 energizes, the upper condenser 2'I5-is disconnected from the trunk, and at the same time the circuit to the lower winding 'of relay 223 and the lower winding of the relay 224 will be opened at armature 261. The circuit for the relay 263 now extends from the wiper 242 to armature 266 and its front contact, armature 261 and its front contact, armature 269 and its front contact, and the wiper 2. Each time the line relay 2 deenergizes, it will open the circuit of the line relay 263 at armature 263 and in-this way, the dialing impulses are repeated over the trunk to the switches at the remote exchange which will respond to the repeated impulses and complete the connection in the usual manner.

If the trunk tested had been busy, the selector repeater would have started rotating in an .attempt to find an idle trunk in the same manner as explained in connection with the selectors 6 and i6. The selector repeaters carry a private bank which is multipled among all switches. This bank is not connected with the trunk but is used only to protect a trunk from intrusion after a selected repeater has seized it. The private bank contact is made busy over the circuit from the private wiper 243 on which ground is applied as soon as the trunk is busy and which thereupon shunts the private relay such as relay 245 preventing it from operating and permitting periodic energization of the rotary magnet as explained in connection with selectors 8 and IS.

The distinction of telephone selection over tel- &

egraph selection in the operation thus far described would be merely in the omission of the telegraph repeater apparatus l4, the rotary line switch l and second selector IS, the first selector 8 being directly connected to the repeater selector l2 in the case of a telephone selection and the telephone dialing impulses being directly applied to the repeater relay 2| I which in turn repeats the impulses over the conductors 26i and 262.

The difference in the effect between telegraphic and telephonic connections on the selector re peater will be described following the complete description of a selection to a called party.

From this point, all impulses transmitted from the transmitting station by the dialing operation are applied directly to the telegraph repeater relay 28 which in turn repeats these impulses to the line feed relay 2, the line feed relay MI in turn again repeating impulses over the conductors 26l and 262.

It is now assumed that the next dialing operation transmits, as stated, eight impulses and the line relay 288, Figure 5, at the selector 28 in the remote exchange is energized eight successive times.

The selector 28, it will be noted, is an exact duplicate of the selectors 8 and I6. It comprises the line relay 268 which operates in response to the initial current over conductors 26l and 262 to energize the release relay 28l. The release relay 28I upon energization operates its armatures 282 and 288 to engage their front contacts. Upon each deenergization of relay 268, a circuit is completed over armatures 284 and 286 through the slow relay 286 and the vertical stepping magnet 281. Both the slow relay 286 and the vertical stepping magnet 281 are thus energized, the stepping magnet 281 functioning to step the brushes 281, 288 and 288 from level to level.

Upon receipt of the last of these impulses, the armature 284 remains on its front contact sufficiently long to permit relay 286 to deenergize, it being understood that during the impulsing,

however, the intervals are not sufficient to permit such deenergization of relay 286. Upon deenergization of relay 286 an energizing circuit is completed for the private relay 286 over the contact of the closed of! normal switch 288, the front contact and armature 288 of the relay 286 and the armature 282 and its front contact, to ground. Relay 286 upon energization, locks itself over armature 281 of the rotary magnet 282. Upon deenergization now of relay 286 as traced above, the rotary magnet 282 is energized to move the wipers 281, 288, 288 to engage the first contacts on the eighth level.

Energization of rotary magnet 282'will also open the locking circuit of the relay 286 which upon deenergization in turn opens the circuit of the rotary magnet 282 at its armature I88. The usual circuits including the relay 286 and 265 in series will now be established, relay 286, however, not energizing over this circuit. This is the condition obtained if the contact over which the wipers 281, 288 and 288 engage is not busy; that is, there is no ground on the trunk with which the wiper 281 engages. If there is such a busy condition there is ground on this trunk and this ground extends over the wiper 281 shunting out the relay 265 at armature 284 and preparing another energizing circuit for the relay 286 which upon energization reenergizes the rotary magnet 282 to step the wipers to the,

next set of contacts on the eighth level and this operation continues until the wipers reach a set release relay 882, the slow relay 888, vertical magnet 884, rotary magnet 886, private relay 888, release magnet 881 and the cut through relay 888. As in the previous case, by operation of these relays, the wipers 8ll, 8I2 and M8 are stepped up eight level in response to the eight impulses comprising the dialing code assumed in the present case and the wipers 8 to 8l8 are raised to the eighth level. At this time, the rotary magnet 886 is energized once, causing the wipers to engage the first set of contacts on this level. If the contacts are not busy the wipers will remain in. engagement therewith. If they are busy, the wipers continue .to the next set of contacts and so on in the same level until a set of contacts which are not busy are reached. The relay 888 thereupon is energized, extending the circuit from wipers 288 and 288 through to the wipers M2 and 8i 8 and over conductors 8| 6 and 8|6 to the line feed relay 48.

The numeral 5 will now be dialed. During this operation the line relay 48 (Figure 6) will be deenergized and reenergized five times. Prior to this dialing operation the relay 48 will be energized, moving its armature 821 into engagement with its front contact. This closes a circuit from ground to battery through the winding of relay 826, front contact and armature 821 to ground. Relay 826 is energized moving its armature 828 into engagement with its front contact and extending ground over line 8" and moving its armature 828 into engagement with its front contact. Relay 828, being of the slow type, will remain energized during the transmission of the five dialing impulses. The flrst signal transmitted in the dialing operation will deenergize line relay 48, establishingi a circuit from ground over armature 821 in engagement with its back contact, armature 828 in engagement with its front contact, contact 88i of the off-normal switch 882, through the winding of the slow relay 888 and the vertical magnet 884, through battery to ground. The vertical magnet 884 will now be energized, stepping the wipers 888, 881 and 888 vertically,

This operation will be repeated five times, one for each impulse, and the wipers will be stepped to the fifth level. After the fifth impulse. the line feed relay 48 will remain energized for a period long enough to permit relay 888 to become deenergized. Relay 888 when deenergized, moves its armature 885 into engagement with its back contact and a circuit will be prepared from ground over armature 821 if and when in engagement with its back contact, armature 828 in engagement with its front contact, switch contact 8 of the oil-normal switch 882,'armature 885 in engagement with its back contact, armature 481 in engagement with its back contact, armature 848 in engagement with its back contact, through the winding of rotary magnet 844, through battery to ground. Simultaneously with the first energization of the rotary magnet 844, the slow relay 845 will be energized over a circuit which is in parallel with the rotary magnet 844. The slow relay 846, when energized, will move its armature 3" into engagement with its front contact, closing a shunt circuit around the armature 431 and making the energizing circuit and 6. The line feed relay 43 remains energized at the end of the impulsing and the rotary magnet 344 is deenergized. Similarly the energizing circuit forthe slow rotary relay 345 is also opened lit prepared for relay 342.

at armature 321 of the line feed relay 43 and relay 345 deenergizes after an interval of time permitting its armatures to drop to their back position. An energizing circuit is thereupon completed from ground, to battery, through the winding of the cut-oil relay 36l, contact and wiper 336, make-before-break contact 353, armature 354 in engagement with its track contact, through the upper winding of the private relay 362, back contact and armature 363, front contact and armature 323 to ground.

Relay 362 energizes and at armature 366 completes a locking circuit for itself from ground through battery lower winding of relay 362, front contact and armature 365, front-contact and armature 323 to ground. At armature 343, the circuit of the rotary magnet 344 is opened. This has no effect as the circuit of the rotary magnet was already open. At armature 366 a ground is established for the wiper 336 from ground over the armature 366 and its front contact 353 and wiper 336. The movement of armature 366 into engagement with its front contact operates the contact 353 to open the original energizing circult of relay 362, which extended through its upper winding. At armature 336, a circuit is At armature 351, the circuit leading from busy relay 333 is opened so as to prevent energization of the busy relay 333. At armature 313 a ringing circuit is established from ground through ringing generator 311, back contact and armature 312, front contact and armature 313, wiper 333, conductor 6, arm 338 of change over switch 316, Figure 8, condenser 313, selective ringing relay 313, back'contact and armature 33l to ground. The selective ringing relay 313 is energized and its armature completes an obvious energizing circuit for the relay 332 which in turn at its armature completes an energizing circuit for the magnet 333. Magnet 333 up'on energization operates the armature 334 and the change over switch 316 to switch the circuits extending over the lines and 6 to the local telegraph equipment.

As a result of the operation of the change over switch 316 an energizing circuit is completed for the detector relay 342 from ground through battery and the upper winding of the detector relay 342, back contact and armature 335, front contact and armature 386, wiper 331, conductor 5, switch 333 in engagement with its lower contact, contact 332, polar relay 333, printer magnet 334, transmitter 335, switch 336, switch 331, switch member 333 in engagement with itslower con- "tact, conductor 6, wiper 333, armature 313 and its front contact,'armature 312 and its back contact, through the source 31 I, to ground. Detector lay 435.

relay 342 is energized over this circuit and operates its armature: to engage their front contacts. At armature 331 a locking circuit is completed for the relay 342 from ground, through battery, lower winding of relay 342, armature 331 and its front contact, front contact and armature 323 to ground. At armatures 312 and 335 and their front contacts, the upper and lower windings of relay 43 are extended over conductors 5 and 3 in series with the receiving printing magnet 334 and telegraph transmitter 335. At armature 312, the ringingcircuit is opened.

Armature 5| of relay 45 is in a circuit which extends from the line 5 to; the line 3 so that the movement of armature 5| into engagement with its front contact will shunt the receiving apparatus at the called station, At armature 436, a circuit is prepared for the secondary of the transformer 46. Over this circuit code signals of alternating current will be transmitted in acomnigraph signalling When the magnet 333 is energized, the change-, over switch 316 is moved to its lowermost position and a circuit for the motor 424 is closed. Simultaneously with the energization of the magnet 333, the notched omnigraph disk 421 is released for rotation as will be described in detail hereinaiter. As the disk 421 rotates, it alternately opens and closes the switch 336 thereby deenerg'lzing and energizing relay 43. Deenergization and energization of relay 43 will move its armature 41 back and forth to make and break the circuit which extends from the transformer 46 over the conductors M5 and 3 l6 to the relay 435, Figure 4, the circuit extending from the line over wiper 2, through the winding of the relay 435, over the back contact and armature 436, back contact and armature 261, front contact and armature 266, wiper 242 and back over the line. Energization of relay 435 moves its armature 431 into engagement with the front contact and closes an energizing circuit for relay 433 from ground, through battery and winding of relay 433, front contact and armature 431 to ground. Relay 433 closes a locking circuit for itself from ground, through battery and winding of relay 433, armature 433 and its front contact, armature 233 and its front contact to ground. Armature 236 of relay 433 opens the circuit which extends to relay 222. At armature 443, the relay 433 closes a circuit for shunting the armature 263 and its contact. This shunting circuit extends from the.

The notches in disk 421 are so cut that operation of this disk will transmit to the calling station the message TSO--8855. This message is sent immediately after the dialing of the last figure of the directory number and acts as a signal to the calling station and further as a check by which the calling station knows the identity of the station connected.

Transmission of telegraph signals In this case, transmission of telegraph signals is obtained by alternate intervals of current and no current. Such operations will now be described and may be understood by reference to either Figure 2 or Figure 9.

Normally when telegraphic signals are not being transmitted and the two lines are connected for telegraphic purposes relay 23 at repeater l4 and relay 48 at repeater 42 are both energized.-

Relay 23 is energized over a circuit extending from ground, through battery, upper winding of relay 23, printer magnet 33, transmitter 81, lower winding of relay 23, to ground. The circuit for relay 48 extends from ground, through battery, through the upper winding of relay 48, printer magnet 394, transmitter 395, lower winding of relay 43 to ground. When the transmitter 31 at station I is operated to open the first-described circuit, relay 23 will be deenergized, moving its armature 24 into engagement with its back contact and thereby completing an alternating current circuit for the relay 45 this circuit extending from the source 3|, over back contact and armature 24, over the line to armature 41 in engagement with its front contact through winding of relay 45 and back over the line to the source 3|. Relay 45 is energized, moving its armature 5| into engagement with its front contact and thereby shunting out the printing magnet 394 and transmitter 395 of the station 2. This deenergizes the printing magnet 394 and accordingly the said magnet registers a no current impulse. The no current" impulse transmitted from station I is thus registered as a no current impulse at station 2.

When the transmitter 31 at station I closes. the circuit to transmit a current impulse, relay 23 is energized, moving its armature 24 into engagement with its front contact thereby breaking the alternating current circuit above described. This deenergizes relay 45 causing its armature 5| to move away from its front contact thereby removing the shunt from printer magnet 394 and printer 395. Printer magnet 394 then becomes energized and registers a current impulse. In this manner a current" impulse transmitted from station I is registered as a "current impulse at station 2.

In a similar manner, "current impulse transmitted by transmitter 395 will be registered as current" impulses bythe printer magnet 33 and no current impulses transmitted from the transmitter 395 will be registered as no current impulses by the printer magnet 36.

Operation of transmitter 395 opens and closes the circuit of relay 48 which operates, whenever it is deenergized, to move its armature 41 into engagement with its back contact thereby estab-- lishing a circuit from the secondary of the transformer 43to energize the relay 4| The relay 4| whenever it is energized, moves its armature into engagement with its front contact to short circuit the line to calling station I thereby establishing a condition of no current on the line to the printer magnet 33 at station I.

It will be clear from the above description that direct current impulses transmitted from calling station I are translated into alternating current impulses at the repeater l4, retranslated into direct current impulses at the repeater 42 and received by the called station 2 in the form of direct current impulses. In the same manner, direct current impulses transmitted from called station 2 are translated into alternating current impulses at the repeater 42, retranslated into direct arcane current impulses at repeater 4 and received at calling station I in the form 01. direct current, impulses.

Busy signals In the above description it was assumed that the called party was not busy at the time when the calling party attempted to establish communication with it. It will now be assumed that the called party was busy.

Under this condition, as described above. the wiper 333 will have ground on it. A circuit will be established from grounded wiper 333, switch 353, armature 354 in engagement with its front contact (relay 345 not having had time to deenergize), back contact and armature 351, winding of busy. relay 339, battery and ground. Busy relay 339 energizes and upon the release of relay 345 it closes a locking circuit for itself at its armature 333. This locking circuit extends from ground through battery, winding of relay 339, armature 351 and its back contact, switch 355, front contact and armature 333, front contact and armature 328, to ground. At armature 401. the energizing circuit of the rotary magnet 344 is opened so as to prevent accidental energize.- tlon of this rotary magnet 344. At armature 409, a circuit is prepared for the secondary of the transformer 43. At armature 403 a busy circuit is established for the relay 43, from ground, through battery, switch 4, armature 408 and its front contact, lower winding of relay 48, to ground.

The busy device 0 is rotated in the direction of the arrow shown in Figure 6 and the switch 4 is alternately opened and closed thus alternately deenergizing and energizing the relay 43. As this relay 48 is alternately deenergized and energized, its armature 41 will move back and forth between its contacts. Whenever the arms.- ture 41 engages its back contact, telegraphic code signals of alternating current will flow from the secondary of the transformer 46 over armature H2 in engagement with its back contact (relay 345 being still deenergized), armature 409 in engagement with its front contact, armature 41 in engagement with its back contact, conductor 3|5, through the repeater apparatus |4, conductor 3|3 and back to the secondary of the transformer 43. The repeater M will translate these code currents into current-vs-shunt conditions in the line to the calling station to print the word busy" at the calling station to indicate that the'called station is busy. Restoration of the selectors will then take place in response to a release of the calling party's apparatus as will be described hereinafter.

It will be evident from the above description that the relay 23 of the repeater |4 responds to both dialing and telegraph codes transmitted from the calling station. During the transmission of dialing signals and before the circuit has been completed to the called party, relay 23 repeats only direct current signals to energize the relay 2 of the selector repeater |2. The circuit for these direct current signals extends from ground, through battery, the upper winding of relay 2 over the connections completed as shown in Figure9, armature 24 in engagement with its front contact, resistance 25, back over the completed circuits, lower winding of relay 2| to ground. While these direct current signals are being transmitted the alternating current signals from source 3| are transmitted also but are ineffective because the wire to armature 41 of relay 48 is open at armatures 403, 409 and

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