US2170403A

US2170403A - Telephone system

Info

Publication number: US2170403A
Application number: US128148A
Authority: US
Inventors: Myron C Goddard
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1937-02-27
Filing date: 1937-02-27
Publication date: 1939-08-22
Anticipated expiration: 1956-08-22

Description

Au 22, 1939. M, c, GODDARD 2,170,403

TELEPHONE SYSTEM Filed Feb. 27, 1937 5 Sheets-Sheet 1 lNl/ENTOR By M C. GODDARD A TTORNE Y Aug. 22, 1939. M. c. GODDARD 2,170,403

TELEPHONE SYSTEM Filed Feb. 27, 1937 3 Sheets-Sheet 2 ALARM CIRCUIT mm QQ ll INVENTOR By M C. GODDARD A T TORNEY Aug. 22, 1939. M. c. GODDARD 2,170,403

TELEPHONE SYSTEM Filed Feb. 2'7, 193'! 5 Sheets-Sheet 3 ALARM CIRCUIT "R01: STEP I HI INVENTOR M C. GODDARD E 2 v ATTORNEY Patented Aug. 22, 1939 PATENT OFFICE TELEPHONE SYSTEM Myron C. Goddard, Garden City, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application February 27, 1937, Serial No. 128,148 10 Claims. (01. 179 -27) This invention relates to telephone systems and particularly to systems comprising automatic switches for use in establishing connections.

It is the object of the invention to increase the 5 efiiciency of automatic telephone systems, to minimize the amount of switching equipment required, and to improve the quality of the service rendered by such systems.

It is known in automatic telephone systems to release the switches used in establishing a connection between a calling and a called line under control of the calling subscriber, the called subscriber, or jointly by both the calling and the called subscribers. In systems in which the release of the connection is controlled by the calling subscriber, it is of course possible for the calling subscriber to hold the called subscribers line busy after the called subscriber has restored the receiver to normal and thereby prevent the subscriber at this called station from originating or receiving calls. It is usual, when such a permanent signal condition exists, to start a timing operation and, at the end of a measured interval of time, to operate an alarm. This. interval is 25 usually quite long, such as from 22 to 44 minutes,

in order that the number of such permanent signal alarms be minimized, and during this long interval the called subscribers station is deprived of both incoming and outgoing service. According to this invention, common timing equipment is provided for a group of connectors with means for connecting the timing equipment to a connector when either the calling or the called subscribers supervisory relay releases and the other of the two supervisory relays is not thereafter released within a short measured interval. The timing equipment thereupon measures ofi a further short interval of time and then effects partial operation of the release magnet of the con- 40 nector in question to free the called line, the timing equipment being at the same time released for use with any other of the connectors in the group.

The invention will be better understood by considering a telephone system in which the features of the invention are embodied. One such system is shown schematically in the drawings which form a part of this specification. The invention is, however, not limited in its application to the particular system or switches shown. The three figures of the drawings are to be placed one below the other in numerical order toform an operative arrangement.

Referring to the drawings:

Fig. 1 shows a calling subscribers station A, a line-finder switch LF and an associatedrfirst-selector switch SI, a connector switch Cl,

Fig. 2 shows a connector switch C2 and a called subscribers station D; and

Fig. '3 shows group timing units GI and G9, group alarm unit GA, a finder switch F, a timing switch TS, and associated control relays.

The subscribers stations are prvided with the usual station equipment used in automatic telephone systems, and include an impulse sender of the dial type for use in establishing connection with any other line of the system. The linefinder switch LF, first-selector switch SI and connector switches Cl and C2 are of the wellknown two-motion step-by-step type. For a description of the structure of such switches and their operation when used as selectors and connectors reference may be had to pages 53 to 67, inclusive, of the second edition of Automatic Telephony by Smith and Campbell. For adescription of the operation of such a switch when used as a line-finder reference may be had to Patent 1,7 99,654 granted to R. L. Stokely April 7, 1931. The line-finder switch LF is represented by one set of brushes and a. single set of' terminals and the associated first-selector switch SI is represented by a set of brushes and two sets of terminals, all magnets and associated relays being omitted.

The connector switches Cl and C2 are shown in detail, the connector Cl being a level-hunting connector and the connector 02 being a local rotary connector. The level-hunting connector CI is a modification of the one disclosed in Patent 1,747,169 granted to H; Hovland February 18, 1930; and the local rotary connector C2 is a modification of the one shown in Fig. 2 of Patent 2,014,232 granted to H. Hovland, September 10, 1935. By the modification, the two supervisory circuits (controlled by the calling and called subscribers) have been connected to a conductor leading to one of the group timing units shown in Fig. 3 and to a terminal in the bank of finder switch F; another conductor has been added for connecting the release magnet of the switch to another terminal in the bank of switch F; and contacts have been added to the release magnets, these contacts being actuated upon partial energization of the magnet under the control of the timing equipment. The partial energiation of the release magnet I34 of level-hunting connector CI closes a circuit for completing the energization of the magnet to release the switch; since in such a connector the cut-through relay is not slow in releasing, other linesare not disturbed while.

the brushes are being restored to normal. The partial energization of the release magnet 2 I3 of the rotary connector C2, is effective through an added set of contacts to cause release of the ringing cut-off and cut-through relays and thereby release the called line without restoring the brushes to normal unless and until the connection is released by the calling subscriber. The partial operation of the release magnet of the rotary connector switch C2 is also effective through an added contact to prevent trunk hunting after the cut-through relay releases in case the brushes are in engagement with a trunk to a private branch exchange, other than the last in the group. Both of the connectors CI and C2 are further modified by adding another connection in place of the aforementioned superviory circuits whereby a permanent signal alarm is operated, at the end of an interval of from 22 to 44 minutes, in case the permanent signal condition continues for that length of time.

The finder switch F is also a two-motion stepby-step switch comprising three pairs of multiple brushes, 32I and 322, 323 and 324, and 325 and 1 326, a commutator brush 321 and commutator 328, a vertical-stepping magnet 33L rotary-stepping magnet 332 and release magnet 333. Two conductors from each of the connectors, to which the finder F is common, connect to terminals in the bank of this finder. For instance, conductors I51 and H58 from connector CI and conductors 251 and 258 from connector 02 are shown connected to terminals in the bank of switch F. One of these two conductors from each connector, for instance conductor I51 or 251 is also connected through an individual resistance, such as 36! or 392, to the winding of a group relay, there being a group timing unit comprising a group relay and a timing relay for the thirty jconnectors connected to the terminals of each level of the bank of switch F. Two of the ten group timing units are shown; the group GI comprising relays 383 and 304 is associated with the terminals in the first level of the bank of switch F; and the group GS comprising relays 305 and 366 is associated with the terminals in the ninth level. The operation of the group relays is under the control of common timing contacts 3 and 3I2 each of which is closed for six seconds once every thirty seconds. tacts 3I2 begins eighteen seconds after the closure of contacts 3H ends, so that there is a delay of from 18 to 48 seconds between the operation of one of relays 383, 365, et cetera, before the operation of the associated one of relays 3M, 3%, et cetera. Each of

relays

305, 306, et cetera, when operated, connects ground to conductor 320 to start the operation of the finder switch F. The timing switch TS is a singlemotion step-by-step switch comprising a stepping magnet 3553, brush and bank 35! and a release magnet 352. The operation of magnet 35%), after finder switch F connects with a connector switch, is effected under control of interrupter 340 so that the advance of brush 35I to the last terminal measures a desired interval, for instance two or three minutes.

The group alarm unit GA comprising relays 301 and 308 effects the operation of a maintenance alarm in case the finder switch F fails to find a connector and cause release of the group timing unit within an interval of from 22 to 44 minutes. The operation of relay 321 is under the control of timing contacts 3I3 and the operation of relay 308 is under the control of tim- The closing of coning contacts 3M. Both these contacts are closed for six seconds every 22 minutes, the closure of contacts 3I3 beginning just after the closure of contacts 3! ends, so that an interval of from 22 to 44 minutes elapses before relay 308 closes the alarm circuit.

Assume first that the calling subscribers station A and line IilD have been connected by operation of the line-finder switch LF and first selector switch Si and any intermediate selectors (none shown) to the connector CI. The line relay H4 of the connector CI is thereupon operated by the current in a circuit from battery throughthe lower winding of relay H4, inner lower back contact of relay I I5, terminal I I2 and middle brush of selector SI, middle brush of line-finder LF, over the lower conductor of line I and through the subscriber's instrument at station A, back over the upper conductor of line Hill, uppermost brushes of switches LF and SI, terminal III, inner upper back contact of relay H5, and upper winding of relay H4 to ground. Relay I it closes a circuit for operating relay I I1; and relay 5 I1 connects ground to terminal M3 to hold the line-finder and selector switches in usual manner.

When the subscriber at station A dials the next to the last digit of the number of the station B with which connection is desired, relay H4 releases at each interruption of its circuit by the dial. Relay H1 is slow to release and remains operated during dialing. Each release of relay H4 closes a circuit from ground through the back contact of relay II l, upper front contact of relay H1, uppermost back contact of relay I22, and through the winding of the stepping magnet H9 of the auxiliary, rotary, recording switch. Another circuit is closed from ground through these contacts of relays H4 and H1, the inner upper back contact of relay I22 and through the winding of relay I to battery. Relay IZB is slow in releasing and, once operated in response to the first impulse received by relay IM, remains'operated until all of the impulses in the series have been received. The stepping magnet H9 operates and releases in response to each impulse, the brushes I06 and I01 being thereby advanced a corresponding number of steps. The oif-normal contacts I2! and I48 of the recording switch are actuated as soon as the brushes of this switch are moved out of normal position and, when'relay I28 releases at the end of the train of impulses, a circuit is closed from battery through the winding of relay I22, offnormal contact I2l, upper back contact of relay I20, to ground at the lowermost front contact of relay H1. Relay I22 operates and closes a locking circuit through off-normal contact I2I, inner lower front contact of relay II1 to ground at the front contact of relay I22. The operation of relay I22 prevents the operation of relay I20 and stepping magnet H9 when relay I I4 responds to the impulses originated by the dialing of the last digit of the called subscribers number. The setting of the recording switch determines the first level in which the brushes of switch C! are to be advanced in search for an idle trunk to the called subscribers private branch exchange.

The aforementioned release of relay I20 also closes a circuit for operating relay I21; this circuit is traced from battery through the lower winding of relay I21, outer back contact of the rotary-stepping magnet E26 of switch CI, back contact of the vertical-stepping magnet I of switch Cl, inner lower back contact of relay I28,

normally closed contact I54 of the vertical offnormal springs of switch CI, lowermost back contact-of relay I20, back contact of the release magnet I34 of switch CI, lower back contact of relay I23, off-normal contact I2I of the recording switch, and through the upper back contact of relay I20 to ground at the lowermost front contact of relay H1. The operation of relay I21 closes a circuit for operating the vertical-stepping magnet I25; this circuit is traced from battery through the winding of magnet I25, inner upper back contact of relay I28, upper front contact of relay I21, contact I24 of the 10th rotary step springs of switch CI, through the back contact of release magnet I34 and thence to ground at relay II1 as hereinbefore traced. The operation of magnet I 25 steps the brushes I 0|, I02 and I03 of switch CI up to the first level of its terminal bank. As soon as the shaft of switch CI is moved out of normal position, the vertical off-normal springs VON are actuated and the circuit through the lower winding of relay I21 is traced through the front contact of spring I54 instead of through the back contact of this spring and the inner lower back contact of relay I28. If the terminal with which brush I01 of the recording switch is in engagement is not connected to the first ofl-normal segment of the vertical commutator I05 of switch CI, relay I21 releases when magnet I25 operates; the release of relay I21 causes the release of magnet I25; and the release of magnet I25 closes the circuit for operating relay I21. This cycle of operations of relay I21 and magnet I 25 is repeated, the brushes being raised one step by each operation of the magnet, until the level is reached which corresponds to the setting of the recording switch; at which time relay I21 is held operated by a circuit which includes brush I01 of the recording switch. Assuming that the terminals of bank I01 of the recording switch are cross-connected tothe terminals of the vertical commutator of switch CI as shown in the drawings and that the brushes of the recording switch have been advanced to the third off-normal position, the circuit for holding relay I21 operated is traced from battery through the'lower winding of relay I21, outer back contact of magnet I26, upper winding of relay I28, brush I04 and'third off-normal terminal of the vertical commutator I05 of switch CI, brush I01 of the recording switch, the front contact of the off-normal spring I54 and thence to ground at relay I I1 as hereinbefore described. Relay I21 holds the vertical-stepping magnet I25 operated until relay I28 operates, thereby preventing the further vertical advance of the brushes of switch CI. Relay I28 is operated by the current through its upper winding and closes a locking circuit through its lower Winding and lower front contact, the front contact of olfnorrnal spring I54, and thence to ground at relay II1 as hereinbefore traced. Relay I28 is, however, somewhat slow in operating sothat rotary. stepping will not begin until the brushes have been properly centered opposite the first level in which the brushes are tohunt for an idle trunk. With relay I28 operated, a circuit is closed from battery through the winding of the rotary-stepping magnet I26, upper front contact of relay I28, upper front contact of relay I 21 and thence to ground at relay I IT as hereinbefore traced. The operation of magnet I 26 advances the brushes IOI, I02 and I63 into engagement with the first set of terminals in the third level of the bank. The idle or busy condition of this set is tested through sleeve brush I03, busy trunks being characterized by a ground potential on the sleeve terminal and idle trunks by a battery potential. The operation of magnet I26 causes the release of relay I21 and the release of relay I21 causes the release of magnet I26. If the first set of terminals is busy, the release of magnet I 26 again closes the circuit for op upper back contact and upper winding of relay, I21, upper winding and upper back contact of' relay I 23, to ground at the front contact of relay I22. When magnet I26 releases, relay I21 cannot reoperate since the current through its upper winding electromagnetically opposes the current through its lower winding. Relay I 23 is sufficiently energized by the current through its upper winding to close a locking circuit from battery through its lower winding and inner lower front contact, thence through off-normal spring I2I of the recording switch to ground as hereinbefore described. After closing its locking circuit, relay I23 opens its operating circuit, opens the locking circuit of relay I28 to cause the release of relay I28, and opens the operating circuit of relay I21 to prevent its reoperation. The release of relay I20 closes the ringing circuit from ringing source I35, through the uppermost front contact of relay I23, upper winding and lower back contact of ringing cut-off relay I36, lowermost back contact of relay I28, lowermost front contact of relay I 23, brush I02, over line II 0 and through the ringer (not shown) at station B, back through brush IOI, middle upper front contact of relay I 23, uppermost back contact of relay I28, and through the uppermost back contact of relay I 36 to ringing ground When the called subscriber answers the call, relay I36 is suificiently energized to close a circuit through its lower winding and inner lower front contact thence to ground through contact I2I to ground as hereinbefore described. Relay I 35, when fully operated, opens the ringing circuit and closes a circuit for operating supervisory relay I I5; this circuit is from battery through the upper winding of relay I I5, uppermost front contact of relay I36, uppermost back contact of relay I28, middle upper front contact of relay I23, brush IOI, over the called line H0 and through the telephone set at station B, back through brush I02, lowermost front contact of relay I23, lowermost back contact of relay I28, middle lower front contact of relay I36, and through the lower winding of relay II5 to ground. Relay H4 is held operated under control of the calling subscriber and relay I I5 is held operated under control of the called subscriber during conversation. The talking circuit between the calling and called stations includes condensers I 40 and MI. For a further description of the operation of connector 01 other than its release after a talking connection has been established, reference may be had to the aforementioned Hovland Patent 1,747,169.

When the calling subscriber releases the connection relay II4 releases, causing the release of relay I I1. When the called subscriber releases the connection, relay I I5 releases. The release of .ing of start relay 330.

all three of these relays causes the release of relays I22, -!3!5 and !23; disconnects holding ground from terminal !!3, thereby causing release of the preceding switches in usual manner; and. closes a circuit for operating the release magnet I41 of the recording switch; this circuit is traced from ground at the back contact of relay H4, through the upper back contact of relay II'l, uppermost back contact of relay !!5, oil-normal contact I48 of the recording switch, and through the winding of magnet I41 to battery. The operation of magnet !41 effects the return of the recording switch to normal. The release of relay !22 closes a circuit for operating release magnet !34 of connector switch CI; this circuit is traced from ground at the back contact of relay !!4, through back contacts of relays !I'! and !!5, lowermost back contact of relay I22, off-normal contact I33 of switch Cl, and through the winding of magnet I34 to battery. The connector switch and auxiliary recording switch are thereby both restored to normal.

If one of the two connected subscribers releases the connection in advance of the other, ground is connected to conductor !51 to call in the common timing equipment. If relay H4 releases and relay !!5 is held operated, conductor !51 is connected through the uppermost front contact of relay !!5 and the upper back contact of relay !!1, to ground at the back contact of relay H4. If relay !!5 releases and relay H4 is held operated, conductor I51 is connected through the inner upper front contact of relay I36 to ground at the lowermost back contact of relay H5. In either case, if this condition continues until the interrupter contact 3!! next connects battery to the winding of relay 335 of group timing unit G9, relay 335 is operated through the individual resistor 33! over conductor I51 to ground at relay H4 or at relay !!5. Relay 335 looks through its left front contact and remains operated until ground is disconnected from conductor I51. If the condition continues after relay 355 operates until the next closure of interrupter contacts 3I2, relay 336 operates, the operating circuit being traced through the right front contact of relay 335. Relay 333 looks, through its inner left front contact, under control of relay 3G5, connects ground to the ninth-level terminal of the commutator bank 328 of switch F, and connects ground through conductor 326, the inner upper back contact of relay 34!, normally closed contact of the vertical off-normal springs VON, to the wind- Relay 33il operates and closes a locking circuit through its inner upper front contact to the same ground independent of the vertical oif-normal springs VON. Relay 330 closes a circuit for operating relay 334; this circuit is traced from battery through the winding of relay 335, back contacts of rotary-stepping magnet 332 and vertical stepping magnet 33!, back contact of relay 333, uppermost back contacts of

relays

338, 331, 336 and 3M, to ground at the uppermost front contact of relay 333. Relay 334 closes a circuit, for operating the vertical stepping magnet 33 from battery through the winding of this magnet, inner lower back Contact of relay 335, front contact of relay 334, back contact of relay 339 and thence to ground at relay 33!! as hereinbefore traced The operation of magnet 33! steps the brushes 32! to 321, inclusive, up tothe first level of the terminal bank and opens the circuit through the winding of relay 334. Relay 334 releases when magnet 33! operates unless'the terminals of the connector to which the timing equipment is to be connected are located in the first level of the bank. Since in the case being described the terminals of connector C! are located in the ninth level, relay 334 and magnet 33! are alternately operated and released to raise the brushes step by step until commutator brush 321 engages the ninth commutator segment. Relay 334 is then held operated to prevent further vertical movement, the circuit for holding relay 334 being traced through the back contact of rotary stepping magnet 332, lower winding of relay 335, brush 321 and ninthlevel commutator segment, to ground at the inner' right front contact of relay 306. Relay 335, operated by the energization of its lower winding, opens the operating circuit of the verticalstepping magnet 33!, and closes a circuit from battery through the winding of magnet 33 I upper winding and upper front contact of relay 335 to ground at the upper front contact of relay 330. The current in this circuit is sufficient tohold relay 335 operated but is insuflicient to hold the magnet 33! operated. With relay 335 operated, the stepping relay 334 assumes control of the rotary-stepping magnet 332. Since relay 335 is slow in operating, the brushes are properly centered before rotary motion is started by the operation of magnet 332. The operation of magnet 332 steps the brushes 32! to 326, inclusive, of switch F into engagement with the first set of terminals in the ninth level of the bank and moves the commutator brush 321 out of engagement with the commutator segment. Relay 334 releases when magnet 332 operates, and the release of relay 334 causes the release of magnet 332. Upon release of magnet 332 after its initial operation, the circuit for operating relay 334 is again closed through the back contacts of both of magnets 33! and 332. Relay 334 and magnet 332 are thereupon alternately operated and released to step the brushes from one set of terminals to the next until one of the three pairs of brushes encounters the set of terminals to which the connection in question is connected. When, in the case herein described, the

brushes

325 and 326 engage the terminals to which connector C! is connected, a circuit is closed for operating relay 338; this circuit is traced from battery through the winding of relay 338, middle upper back contact of relay 331, inner upper contact of relay 336, brush 326, over conductor I51 toground at either relay !!4 or relay !!5 of connector Ci. Were the connector in question connected to terminals with which brushes 32! and 322 engage, relay 336 would be operated instead of relay 338; and if the connector in question were connected to terminals with which brushes 323 and 324 engage, relay 331 would be operated instead of relay 338. The operation of any one of relays 336, 33'! or 338 prevents further operation of stepping relay 334 and closes a circuit for operating relay 339; this circuit is traced from ground at the upper front contact of relay 333, uppermost back contact of relay 34!, and upper front contact of relay 335 if'relay 333 is operated, or through the uppermost back contact of relay 335 and the upper front contact of relay 331, if relay 33'! is operated, or through the uppermost back contacts of relays 336 and 331 and the upper front contacts of relay 338 if relay 338 is operated. At its upper front contact, relay 339 connects interrupter 340 to the winding of the rotary-stepping magnet 350 of magnet I34.

1 and I36.

of the timing switchTS, and at its lower front contact relay 339 connects its winding in series With the winding of relay 34I to ground at the lower front contact of relay 330. As long as the operating circuit for relay 339 remains closed, the winding of relay MI is short-circuited and this relay cannot operate. Each closure of ground through interrupter 340 operates magnet 350 and advances the brush of switch TS one step. The number of steps taken before brush 35I encounters a grounded terminal and the frequency with which the interrupter closes its ground connection may be varied to measure any desired interval of time. Since the same supervisory condition exists in the connector on calls routed to an intercepting operator as when only one of the calling and called stations releases as above described, the common timing equipment is called in on intercepting calls and the switch TS should measure ofi a period longer than that required for the disposal of a call by an intercepting operator. Under such circumstances an interrupter which closes once every eighteen seconds will give an ample delay of three minutes before brush 35I engages terminal III at which time a circuit is closed from ground through brush 35I, winding of relay 343, inner lower back contact of relay 34I, lower front contact of relay 338, brush 325, conductor I58, thence through contacts I48 and the winding of release magnet I41 of the recording switch. Relay 343 and release magnet I4! operate,- the recording switch being thereby restored to normal. The opening of ofi-normal contact I2I causes the release of relays I22, I23 When relay I22 releases, the ground on conductor I58 is connected to the winding of release magnet I34, but the resistance of the winding of relay 343 of the timing equipment is high enough to permit only the partial operation Magnet I34 closes at its inner right front contact, a circuit through ofi-normal contact I33 for completing its energization and thereby causing the brushes and shaft of switch CI to be restored to normal. With both the recording and connector switches restored to normal, the circuit over conductor I58 is opened and relay 343 releases.

If the timing equipment was called in because the called station was holding the connection, the forced release of relays I36 and I23 causes the release of relay I I5 thereby disconnecting holding ground potential from terminal H3 and the preceding selectors are also returned tonormal. In this case the called line; I I is connected to a first selector as for an originating call and a first-selector permanent-signal alarm will be operated after the lapse of a predetermined interval in usual manner. If, however, the timing equipment was called in because the calling station was holding the connection, relays H4 and II! remain operated, after the called line 'has been freed by returning the switch CI to normal, and ground is connected from the lowermost front contact of relay I I1, through the upper back con,- tact of relay I20, inner lower front contactof relay III, inner lower back contacts of relays I22 and I20, to an alarm circuit; whereby, after" an interval of from 22 to 44 minutes, a permanent-signal alarm is operated in the same 'manner as in the case of a first-selector perman'en't-signal condition. In either case the ground potential is disconnected from conductor I 51 thereby causing the successive release of group relays 305 and 306 and the release of the operated one of

relays

336, 331 and 338. The release of relay 306 disconnects ground from conductor 320 thereby opening the circuit through the winding of relay 330. Relay 330 releases unless some other group timing unit relay, such as relay 304, were operated, in which case relay 330 would be held operated. In any case, with all of

relays

336, 331 and 338 released, the short circuit for the winding of relay MI is opened; and relay 330, if not held operated, is slow in releasing, so that relay 34I is operated and relay 339 held operated to ground at the lower contact of relay 330. The operation of relay 34I causes the release of relay 330, if not already released, and the release of relay 330 causes the release of relay 335. The release of relay 330 closes a circuit through the normally open contact of the ofi-normal springs of switch TS, for operating the release magnet 352 of this switch, thereby restoring brush 35I to normal. The release of relay 335 and return of switch TS to normal, closes a circuit through its. lowermost back contact and the lower contact of the vertical off-normal springs of switch F, the normally closed contact of the ofi-normal springs of switch TS, to ground at the back contact of relay 330; and the resulting operationof magnet 333 returns the shaft and brushes of switch F to normal. When the vertical off-normal springs are restored to normal, start relay 330 can be reoperated to start search for the terminals of some other connector which has been released by one but not both of two interconnected subscribers.

If a connector switch causes the operation of a set of group relays GI, G9 and the group relays are not released, due to failure of the finder switch or for any other reason, the group alarm relays 301 and 308 measure an interval of from 22 to 44 minutes and then close an alarm circuit. To this endthe operation of any one of group relays 304, 306, et cetera connects ground to one side of the winding of relay 301 and, as soon thereafter as interrupter contacts 3I3 are closed, relay 30'! operates and locks independent of the interrupter. utes, relay 301 has not yet released, the closing of interrupter contacts 3I4 causes the operation of relay 308. Relay308 locks under control'of relay 301 and closes an alarm circuit to light lamp 309 or operate any other alarm as desired.-

line I00 have been extended by the operation of the line-finder LF and first selector SI through terminals I6I, I62 and I63tothe rotary connector C2. The line relay 20I of connector C2 is operated by the current in the circuit from battery through the lower winding of relay 20I, inner lower back contact ofrelay 204, through terminal I62, middle brushes of switches SI and LF, over the calling line I00 and through the telephone at station A, back through the upper brushes of switches LF and SI, terminal I6 I inner upper back contact of relay 204 and through the upper winding of relay 20I to ground. Relay 20I closes the circuit for operating relay 202; and relay 202 connects ground through its lowermost front contact, over sleeve conductor 220 to terminal I63 to hold the preceding switches in usual manner. When the subscriber at station A dials the next to the last digit of the number of a called station D, relay '20I is released by each interruption of the above traced circuit at the dial contacts. Relay 202 is slow in releasing and remains operated during the response of relay 20! to dial impulses.- The first release of relay 20I closes a circuit from ground at the back contact of relay 20I, upper front contact of relay 202, normally closed contact of the vertical off-normal springs 2M, winding of relay 203 and through the winding of vertical stepping magnet M to battery. Relay 20s and magnet 21! are operated by the current in this circuit, the brushes of switch 02 being stepped up to the first level of the terminal bank by the operation of magnet 2| I. The vertical off-normal springs 2H3 are actuated when the shaft and brushes move out of normal position, the circuit for magnet 29! and relay 203 being thereby closed through the lower normally open contact of springs 2M and the front contact of relay 203 instead of through the normally closed contact of springs 2 I4. Each succeeding release and reoperation of relay 20I causes a corresponding operation and release of magnet 2I I thereby advancing the brushes to the required level of the bank. Being slow in releasing, relay 203 remains operated until all of the impulses in the train have been received by relay 20L The release of relay 203 at the end of the train prepare the rotary-stepping magnet 2I2 for response to the next train of impulses received by relay 20I, which impulses are created by the dialing of the last digit of the number of the called station. The release of relay 20I, in response to each of these impulses, closes a circuit for operating relay 205 and rotary-stepping magnet 2I2; this circuit is traced from ground at the back contact of relay 20I, upper front contact of relay 202, lower normally open contact of springs 2I4, back contact of relay 203, upper back contact of relay 208, winding of relay 205, lower back, contact of relay 2I0, and through the winding of magnet 2I2 to battery. The first operationof magnet 2I2 rotates the brushes into engagement with the first set' of terminals in the selected level and each succeeding operation of this magnet advances the brushes one step, thereby selecting the set of terminals corresponding to the last digit of the called number. Being slow in releasing, relay 205 remains operated while the brushes are being advanced, the test brush 2I1 being connected through the lower front contact of relay 205 and inner upper back contact of relay 2 I 0 to the winding of busy test relay 208. The potential of the terminal with which brush 2I1 is in engagement indicates whether the line connected thereto is idle or busy; and, if busy, whether it is one of a group of trunks to a private branch exchange. If the line is idle, brush 2I1 encounters a battery potential; relay 208 does not operate; and, as soon as relay 205 releases, a circuit is closed for operating relay 2I0. The circuit for operating relay 2 I 0 is traced from the battery potential encountered by brush 2I1, through the inner lower back contact of relay 205, upper winding of relay 2I0, lower back contact of relay 208, to ground at the lowermost front contact of relay 202. Relay 2 I 0 is sufiiciently energized by its upper winding to close a circuit through its lower winding and inner lower front contact, thence through the outer back contact of release magnet 2I3, to

ground at the inner lower front contact of relay 202. Relay 2I0', completely operated by the energization of its lower winding, closes the ringing circuit from source 235, through the uppermost front contact of relay 2I0, upper Winding and lower back contact of relay 206, middle lower front contact of relay 2I0, brush 2I5, over the called subscribers line and through the ringer (not shown) at station D, back through brush 2I,5, inner upper front contact of relay 2I0, and through the uppermost back contact of relay 205 to ground.

If the selected line is busy, the busy ground potential encountered by brush 2I1 causes the operation of test relay 208. Relay 208 is held operated, after relay 205 releases, through the inner upper back contact of relay 2I0, inner upper front contact of relay 208, upper back contact of relay 209, and the test brush 2I1. If the line to which the brushes connect is an individual line or the last trunk of a private branch exchange group, the terminal with which brush 2I1 engages is not strapped to the terminal which brush 2I8 engage-s; and the release of relay 205 closes a circuit from battery through the winding of relay 201, back contact of rotarystepping magnet 2I2, back contact of relay 201, lowermost front contact of relay 208, lowermost back contact of relay 205, winding and upper back contact of relay 209, and through brush 2I1 to the busy potential. Relay 201, being marginal, does not operate, but relay 209 operates and closes a locking circuit through its inner upper front contact to ground atrelay 202. With relay 209 operated, the locking circuit of' relay 208 is traced through the inner upper front contact of relay 209 toground at relay 202, instead of through the upper back contact of relay 209 to the test brush 2E1. At its uppermost front contact, relay 209 connects the busy tone source 23I over conductor 230, to the lower winding of relay 204, a busy tone being transmitted through condenser 2 52 to thecalling station. The connection of ground through the lower winding of relay 20a to the busy tone conductor 23I also operates relay 232 to start the measurement of an interval of from 22 to 44 minutes; so that, if the connector C2 is not released by the callingsubscriber within the measured interval, an alarm is operated. a

If the selected line is one of a group of trunks to a private branch exchange and not the last one of the group, the terminals with which brushes 2I1 and 2I8 are in engagement are strapped together and the winding of relay 209 is short-circuited, by a connection which includes its lower back contact, the inner lower front contact of relay 208, the inner back contact of release magnet 2I3, and brush 2I0. In this case relay 209 does not operate; but the marginal relay 201 operates and closes a locking circuit through its inner upper front contact to ground at relay 202. Relay 201 closes, at its outer upper front contact, a circuit for reoperating the rotary stepping magnet 2I2, thereby advancing the brushes to the next trunk in the group. The operation of magnet 2I2 releases relay 201. If the next trunk is idle, relay 208 releases and relay 2I0 operates as hereinbefore described; but if this trunk is busy and isnot the last of the group relay 200 remains operated and relay 201 reoperates to cause the reoperation of magnet 2I2. When the brushes reach the last trunk in the group, relay 201 cannot again reoperate; if this trunk is busy, relay 208 remains operated and relay 209 operates to transmit a busy tone; or if this trunk is idle, relay 208 releases andrelay 2! 0 operates to close the ringing circuit as hereinbefore described. I

When the called line is found idle and the ringing circuit closed, the energization of the upper Winding of relay 200 is increased whenthe call is answered at the called station. Relay 206 thereupon closes at its inner lower front contact, a circuit for energizing its; lower winding and thereby, causing its complete operation. This circuit includes the outer back contact of release magnet 2!3 and the inner lower front contact of relay 202. At its outer front contacts, relay 206 connects the windings of supervisory relay 204 to the brushes 2!5 and 2!6, the talking current being transmitted through condensers 24! and 242. Relay 204 operates, to interchange the connections between terminals !0! and !62 and the windings of relay and remains operated as long as the called line loop is closed at station D.

When the instrument at station A is restored to normal relay 20! releases and when the instrument at station D is restored to normal relay 204 releases. The release of relay 20! causes the release of relay 202; and the release of relay 204 restores the normal connections between terminals l6! and !62 and the windings of relay 20!. With both of relays 20! and 204 released, relays 206 and 2 !0 release closing a circuit from battery through the winding of release magnet 2!3, up permost back contact of relay 2l0, upper contact of off-normal springs 2! 4, uppermost back contact of relay 204, and back contacts of relays 202 and 20! to ground. Release magnet 2!3 operates thereby restoring the switch to normal in usual manner.

When either one of relays 20! and 204 are released and the other is held operated, conductor is connected to ground to start the operation of the group timing relays 305 and 306. If relay 204 is held operated, this connection is traced through the upper outer front contact of relay 204 and the upper back contacts of relays 20! and 202; if relay 20! is held operated, this connection is traced through the inner upper front contact of relay 206, to ground at the lowermost back contact of relay 204. This supervisory ground is connected through conductor 25! and through individual resistor 302 to the winding of relay 305. If the operated one of relays 20! and 204 does not release before relay 306 operates, the finder'F is started. When the brushes of switch F find the terminals of connector C2, relay 33'! operates; and, when the timing switch TS has measured an interval of three minutes, ground is connected through brush 35!, winding of relay 343, inner lower back contact of relay 34!, lower front contact of relay 331, and brush 323, over conductor 258 to cause the partial operation of release magnet 2 !3 of connector C2. The partial operation of magnet 2!3 actuates its contacts to cause the release of

relays

206 and 2!0 Without causing release of the shaft and brushes. Relay 204 then releases if not already released; in which case, relays 20! and 202 having been released, the circuit for causing complete operation of the release magnet is closed as hereinbefore described and the connector switch is restored to normal. If, however, the timing equipment was called in because the connection was being held by the calling subscriber, a circuit for operating relay 208 is closed through the front contact of release magnet 2!3, and relay 208 closes the circuit for operating relay 200. 'Relay 209 closes the busy tone circuit and causesthe operation of relay 232; so that, if relay 20! is not released within the measured interval, an alarm will be operated in usual manner.

W'hat is claimed is:

1. In a telephone system, subscribers lines, connector switches for interconnecting calling and called lines, timing means for measuring a predetermined interval of time,a finder switch, and means for operating said finder switch to connect said timing means to any one of said connectors upon release of the connection! by either one but not the other of two interconnected subscribers.

2. In a telephone system, subscribers lines, connector switches, each interconnecting a calling line and a called line, a finder switch, an individual set of terminals in the bank of said finder switch for each of said connectors, means eifective if one of two interconnected subscribers fails to replace the receiver within a predetermined interval of time after the other subscriber replaces the receiver for causing said finder switch to connect with the terminals of the connector switch through which the lines of said two subscribers are connected, and electromagnetic means effective if said one of the two subscribers fails to replace the receiver during a further predetermined interval of time for freeing the called line.

3. In a telephone system, a calling line, a called line, a numerical connector switch interconnecting said lines, and circuit means effective a predetermined interval of time after the release of the connection by either one but not both of the interconnected subscribers for freeing said called line from said connection.

4. In a telephone system, a calling line, a. called line, a connector switch interconnecting said lines, a first supervisory relay, said relay controlled by the calling subscriber, a second supervisory relay, said second relay controlled by the called subscriber, a third relay, said third relay having contacts for connecting said last-mentioned supervisory relay to and through the brushes of the connector switch to the called line, a release magnet for said switch, means controlled by said supervisory relaysand including a contact of said release magnet for holding said third relay operated, and circuit means effective a predetermined interval oi time after the release of either one but not the other of said supervisory relays for partially energizing said release magnet to open said contact and release said third relay.

5. In a telephone system, lines, connector switches for completing connections between calling and called lines, each of said connectors comprising a first supervisory relay, a second supervisory relay, a third relay and a release magnet, said first supervisory relay controlled by the calling subscriber, said second supervisory relay controlled by the called subscriber, said third relay having contacts for connecting the windings of said second relay to and through the brushes of the connector to the called line, circuit means controlled by said supervisory relays and including a contact of said release magnet for holding said third relay operated, control means for use in partially energizing the release magnet of any one of said connectors to cause release of the third relay, switching means for connecting said control means to any one of said connectors, timing means for operating said switch- 15 ing means in the event that both of the supervisory relays of one of the connectors have not released within a predetermined interval after one of these supervisory relays releases, and timing means for rendering said control means effective to partially energize the release magnet of a connector a predetermined interval of time after the connection of the control means. to said connector.

6. In a telephone system, subscribers lines, connector switches for use in completing connections between calling and called lines, each of said connectors comprising a supervisory relay controlled by the calling line and a supervisory relay controlled by the called line and a release magnet, a finder switch, a set of terminals for each connector in the bank of said finder switch, said terminals being divided into groups, a group relay for each group of terminals and the corresponding group of connectors, individual resistors for connecting each of said connectors to the'winding of the associated group relay, means in each of said connectors for operating the associated group relay in response to the release of one but not both of said supervisory relays, start relays, one for each of said group relays, for initiating the operation of said finder switch, means for operating any one of said start relays a predetermined interval of time after the operation of the associated group relay, means for stopping the operation of the finder switch when its brushes engage the terminals of a connector awaiting release of the second of its tWo supervisory relays, and circuit means effectivea predetermined interval of time after the brushes encounter the terminals of such a connector for partially energizing the release magnet of said connector to free'th'e called line.

'7. In a telephone system according to claim 6, a signal, and means comprising a relay common to said group relays for operating said signal in response to the continued operation of a group relay for a predetermined interval of time.

8. In a telephone system according to claim 6, means operatively responsive to the partial energization of the release magnet of a connector by said control means for freeing said control means for use with another of said connectors.

9. In a telephone system according to claim 6, means responsive to the partial energization of the release magnet of a connector by said circuit means for restoring said circuit means to normal, and means for operating an alarm if said circuit means is not restored to normal within a predetermined interval after it becomes effective to cause partial energization of the release magnet of a connector.

10. In a telephone system, a calling line, a called line, a. numerical connector switch interconnecting said lines and circuit means efiective' a predetermined interval of time after the release of the connection by either one but not both of the interconnected subscribers for returning said connector switch to normal.

MYRON C. GODDARD.