US2105898A

US2105898A - Telephone exchange system

Info

Publication number: US2105898A
Application number: US65032A
Authority: US
Inventors: Whitney Wiley
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1936-02-21
Filing date: 1936-02-21
Publication date: 1938-01-18
Anticipated expiration: 1955-01-18

Description

Jan. 18, 1938. w. WHITNEY 2,105,898

I TELEPHONE EXCHANGE SYSTEM 7 Filed Feb. 21, 1936 4 Sheets-Sheet 1 g Q EEEEE lllllll IHHIHIIHHHHH & 9

1 INVENTOR m 9 By WWH/TNEV A 7'7'ORNEY Jan. 18, 1938. w. WHITNEY 2,105,893

TELEPHONE EXCHANGE SYSTEM Filed Feb. 21, 1936 4 Sheets-Sheet 2 IN 14 N TOR By W W/-// TNEV A T TORNE V Jan. 18, I938. w. WHITNEY 2,105,898

TELEPHONE EXCHANGE SYSTEM Filed Feb. 21, 1936 4 Sheets-Sheet 3 1' w H 8 I 0 o g N Q k L :1 u,,+ N sv WI 5 1 I ll i Hl .fi." H" m Qj k lNl ENTOR By W WH/TNEV exam A TTORNEV Jan. 18, 1938. w. WHITNEY TELEPHONE EXCHANGE SYSTEM Filed Feb. 21, 1936 4 Sheets-Sheet 4 w By NE V A TTORNEV Patented Jan. 18, 1938 UNITED STATES PATENT FlCE Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application February 21, 1936, Serial No. 65,032

6 Claims.

" This invention relates to automatic telephone exchange systems and more particularly to circuits for enabling an operator to intercept calls which have been extended toblank terminals of selector switches in the establishment of either local or toll connections.

The object of the invention is to simplify and improve the apparatus of an operators position in a system of this type whereby an operator may answer all types of intercepting calls with the same cord circuit equipment and receive a discriminating signal when she answers an intercepted call incoming over toll selectors.

In the installation of telephone exchanges in which mechanical switching mechanism is employed for extending connections between subscribers lines, it is the usual practice to divide the exchange area into a plurality of offices and to make provision in each ofiice for ultimately giving service to ten thousand subscribers lines. The number of oflices in the exchange area is so selected that at the outset no office is required to function to ultimate capacity, and therefore there must always be switching units which are not employed to their fullest extent. This is especially true of incoming selector switches which have access to small groups or divisions of trunk lines and to final selector switches which have access to the individual subscribers lines. Thus there will be a number of terminal sets in the banks of incoming selectors which are blank or not connected to working trunk lines extending to final selector switches and terminal sets in the banks of final selector switches which are blank or not connected to subscribers lines.

If an incoming selector switch in response to dialing is positioned to extend a connection into a division of an ofiice which has not been fully installed or a final selector is positioned upon a blank terminal to which no subscribers line has been connected, the attempted connection is routed to a trunk terminating at an operators position on a so-called A switchboard. This operator may also receive calls from subscribers who desire assistance and dial zero and may also receive calls from subscribers who desire to obtain toll connections.

It may occur that in an attempt to terminate a toll connection over a toll incoming selector and-final selector, such selectors may inadvertently be set upon a blank terminal. In this case also the attempted connection will be routed to a trunk terminating at the operators position. Thus both local and toll calls intended for a particular subscribers line may be routed over a common group of trunks to an operator's position if either an incoming or final selector switch used in the establishment of such a connection is erroneously set upon a blank terminal.

In accordance with the present invention the operators position is equipped with cord circuits with which she may answer such intercepted calls and with which she may complete the calls which the subscribers failed to complete. When a call becomes routed to an intercepted trunk, the operator answers and ascertains from the calling subscriber the number of the desired subscriber. She then proceeds to complete the connection if possible. If, however, a connection with a subscribers line terminating in the ofiice has been.

attempted from a distant toll point and has become routed to an intercepting trunk terminating at the operators position, it becomes desirable to inform the operator of the character of the call when she answers it for the reason that it would; not be advisable for the operator to attempt to complete such a toll connection.

In order that the operator may receive this special information when she answers an inter cepted call from a toll point, the toll incoming selector used in establishing the connection is provided with a resistance in the ringing generator ground lead. Thus the tip talking conductor at the toll incoming. selector always provides a resistance to ground when being answered by an intercepting operator either through the generator lead resistance on immediate ringing calls or through the tip winding of the repeating coil of the incoming trunk on delayed ringing calls.

Since the tip will always be connected direct to.

generator ground on calls over other types of incoming selectors when being answered by the intercepting operator, a means of discrimination is thus provided.

At the operators position circuit a low resistance marginal relay is provided which becomes connected from ground, in parallel with a connection through a resistance to grounded battery, to the tip conductor of the answering end of the cord circuit as soon as the operator answers the call by plu ing up in the intercepting trunk jack and by operating the talking key of the cord.

. circuit. If direct ringing generator ground is present on the tip conductor, the marginal relay does not operate and the position circuit proceeds in the regular manner to trip the ringing and to cut the operators headset through to the calling subscribers line. If, however, generator ground through a resistance is present on the tip conductor, as on a call from a toll incoming selector, the I marginal relay operates and causes the operation of another relay which prepares a circuit for connecting a source of tone current to the operators headset. The position circuit then proceeds to trip ringing in the usual manner. When tripping is completed tone current is applied to the operators headset until the operator depresses a tone removal key, whereupon the tone source is disconnected and the operators headset is connected for talking. Other means for giving the operator 2. special signal might be provided such as a lamp or an alarm device.

For a clearer understanding of the invention reference may be had to the following detailed description thereof and the mode of its operation taken in connection with the accompanying drawings of which:

Fig. 1 shows a trunk incoming from a toll point and terminating in an incoming selector switch having access to final selector trunks and to intercepting trunks, the outgoing end of one such intercepting trunk being illustrated;

Fig. 2 shows in the left portion thereof the relay equipment at the incoming end of the intercepting trunk and in the right portion thereof the headset circuit and key-set of an intercepting operators position;

Fig. 3 shows the position equipment of the intercepting operators position; and

Fig. 4 shows one cord circuit of the intercepting operators position.

For a complete disclosure of the invention the several figures of the drawings should be placed end to end with Fig. l at the extreme left and Fig. 4 at the extreme right.

The incoming selector switch I00 of Fig. 1 is of the well-known power-driven panel type designed for extending connections from toll operators positions equipped with key pulsing equipment of the type disclosed, for example in Patent 1,780,906, granted November 11, 1930 to W. W. Carpenter et a1.

For the purpose of this discussion it will be assumed that the toll operator has plugged into a trunk jack at her position (not shown), has keyed a subscribers line number and that a key pulsing sender at the toll oflice has become connected over trunk conductors IM and I02 with the incomirg selector I00 and proceeds to set the selector to establish a connection toward the terminals of the called line, the designation of which the toll operator has set up on her position keyset. It will further be assumed that the number keyed is 2467.

Upon the association of the sender with the incoming selector a fundamental circuit is established from battery, winding of control relay I03, lower right and upper contacts of sequence switch cam I04, upper normal contacts of test jack I05, conductor IOI, through the winding of the stepping relay of the sender (not shown), returning over conductor I02, lower normal contacts of jack I05, left contacts of cam I00 to ground. Relay I03 operates and closes a circuit from battery through the lower winding of relay I01, left contact of cam I08, lower right contact of cam I09, contacts of relaly I 03, upper contacts of cam IIO to ground over the left contacts of cam I I I. Belay I01 operates and locks in a circuit from battery through its lower winding, left contact of cam I08, lower right contact of cam I09, contacts of relay I03, upper left contact of cam IIO, lower left contact of cam II2, to ground at the upper front contact of relay I 01 whereby it is maintained operated under the control of relay I03 after the sequence switch leaves position I. At its upper back contact relay I01 removes ground from the circuit extending over the contacts of cam II3 to conductor II4 to provide for the operation of the all-trunks-busy register if all trunks in the group to be selected are busy and at its lower front contact establishes a circuit for advancing the sequence switch of the selector out of position I into position 2. This circuit may be traced from battery, winding of sequence switch magnet I50, contacts of cam I I5, upper left contact of cam II6, lower front contact of relay I01 to ground over the upper right and lower left contacts of cam I l I. Following the advance of the sequence. switch to position 2, relay I01 is maintained operated over its locking circuit under the control of relay I03.

With the sequence switch in position 2 and relays I03 and I01 operated a circuit is established for the up-drive magnet I I1 which may be traced from battery through the winding of this magnet, the lower contacts of cam II2 to ground at the upper front contact of relay I01 and the brush rod of the selector switch I00 is thereby driven upwardly in a brush selection movement. During the upward travel of the brush rod the commutator brush I18 engages the segments of. the lower portion of commutator strip II 9 thereby intermittently establishing a circuit from ground over the lower left and upper right contacts of cam III, lower front contact of relay I01, lower left and upper right contacts of cam I20, brush II 8, conducting segments of strip I I9, left contacts of cam I2I to the tip trunk conductor IM and also as traced through the winding of relay I03. Relay I03 is held operated but each ap plication of ground to trunk conductor IOI shunts down the stepping relay of the sender in the wellknown manner.

When the sender has been satisfied with respect to its incoming brush registration or as assumed after two shunting impulses have been transmitted, the sender opens the fundamental circuit thereby releasing relay I03 which, in turn, releases relay I01. Relay I01 upon releasing opens the circuit of up-drive magnet II1 to arrest the further upward movement of the brush rod and closes a circuit for advancing the sequence switch into position 3. This circuit may be traced from battery, winding of sequence switch I50, contacts of cam I5, lower contact of cam I22, inner upper back contact of relay I01 to ground. The brush rod has now positioned the brush sets carried thereby in such a position that the second brush set will be tripped during the initial portion of the subsequent upward movement of the brush rod.

With the sequence switch in position 3 a circuit is established from battery through the winding of trip magnet I23, lower contact of cam I24 to ground at the lower left contact of cam III. The fundamental circuit is again closed and relay I03 reoperates thereover closing an operating circuit for relay I01 which now extends from battery, lower winding of relay I01, left contact of cam I08, lower right contact of cam I09, contacts of relay I03, lower contacts of cam I40, left contacts of cam III to ground. Relay I01 operates and locks in a circuit from battery through its lower winding, left contact of cam I08, lower right contact of cam I09, contacts of relay I 03, lower contacts of cam I40, upper right and lower left contacts of cam I20, lower front contact of relay I01 to ground over the upper right and lower left contacts of cam II I whereby it is maintained operated under the control of relay I 03 F grosses after the sequence switch leaves position 3,- and establishes a circuit for advancing the sequence switch out of position 3 into position 4. This circuit may be traced from battery through the winding of sequence switch magnet I50, contacts of cam II5, left contact of cam I22 to ground at the inner upper front contact of relay I01 When the sequence switch enters position 3-3/ the lower winding of relay I01 is connected over the left and upper right contacts of cam I08 to the commutator strip H9 and over the left contact of cam I08 and the upper right contact of I09 to commutator strip I 25 and commutator strip I26 is connected over the lower right and upper left contacts of cam I2I to the tipfundamental conductor I I. When the sequence switch reaches position 4 the previously traced circuit for the up-drive magnet H1 is established and the brush rod is again driven upwardly in a group selection movement. Since the trip magnet I23 is operated at this time the second set of brushes becomes tripped during the initial portion of the movement.

iflsthe brush rod continues its travel the brushes II8, I21 and I28 engage with the segments of commutator strips II9,- I26 and I25, respectively, and since these brushes are connected to ground over the upper right and lower left contacts of cam I20, the lower front contact of relay I01 and the upper right and lower left contacts of cam I I I, intermittent shunting impulses are applied overthe circuit traced from commutator strip I26 to the tip fundamental conductor IOI and relay I01 is held operated both under control of the sender through the operation of relay I03 and over the circuits previously traced to the commutator strips I25 and I26. The conducting segments of commutator strip I26 are sufiiciently low to send shunting impulses to the sender early enough to satisfy it before it becomes necessary to release the up-drive magnet I I1.

As soon as the sender is satisfied with respect to its incoming group selection, or as assumed after'one shunting impulse has been transmitted, the fundamental circuit is opened and relay I03 releases and removes its control of relay I61. The segments of commutator strip II9 overlap the segments of strip I25 and thereby prevent the release of relay I01 until the brush rod has traveled high enough for the locking pawl to engage the rack on the lower end of the brush rod when the up-drive magnet H1 is released by the release of relay I01. When the brush I28 engages the next insulating segment of strip I25 at which time the brush I I8 will have already engaged an insulating segment of strip H9 and the fundamental circuit Will have been opened at the sender, relay I01 releases in turn releasing updrive magnet I I1 and arresting the second tripped brush set upon the lowermost terminal set of the second group of terminals in the terminal bank to which it has access. Relay I 01 upon releasing also establishes'a circuit for advancing the sequence switch from position 4 into position which may be traced from battery through the winding of magnet I50, contacts of cam II 5, lower contact of cani I22, inner upper back con-' tact of relay I01 to ground.

With the sequence switch in position 5 a circuit is established from battery through the non-inductive'winding I29 and upper winding of relay I01, upper contacts of cam- I30, lower left and upper right contacts of cam H0 to ground over the'left contacts of cam III. Relay I01 o'pe'r 3 ates and establishes attest circuit from battery through its lower winding, lower contacts of cam I20, lower front contact of relay I01, lower left contact of cam I 09, lower right contact'of cam I08 to test brush I3I, thiscircuit being maintained in

positions

5 and 6 of the sequence switch. Relay I01 also advances the sequence switch into position 6 over a circuit extending from battery through the winding of magnet I50, contacts of carn II5, the left contact of cam I22 to ground at the upper front contact of relay I01. If the first trunk of the group is idle no groundis encountered by test brush I3I on the test terminal thereof and relay I01 releases as soon as the sequence switch leaves position 5 and immediately connects ground over the lower left contactof cam I I I, leftcontact of cam I24, lower back con tact of relay I01, thence as traced over test brush I3I to the test terminal of the trunk and advances the sequence switch from position 6 into position 8 over a circuit extending from battery, winding of magnet I50, contacts of cam I I5, lower contact of cam I22, inner upper back contact of relay I01 to ground. Bus-y ground is now connected to test brush I3I over the lower contacts of cani I I I to hold the selected trunk busy as long as the incoming selector is connected thereto. I

It will be assumed that the first trunk is busy and thatrelay I 01 is therefore held operatedover the test brush I3I when the sequence switch reaches position 6. At this time a circuit is closed from battery through the non-inductive winding I29 and upper winding of relay I01, right contacts of cam I30 to commutator strip I25 and with relay I01 operated the previously traced circuit is established for the up-drive magnet I I1 which drives the brush rod'up'wardly in a trunk hunting movement. When the test brush I3'I engages the test terminal of an idle trunk for example, the terminal of the trunk disclosed, the circuit through the lower winding of relay I01 is opened but the circuit through the upper winding will extend to commutator strip I25 thence over brush I28, the right contact of cam IIO, the lower left contact of cam II2, to ground at the upper front contact of relay I01 until the brushes of the switch become centered on the terminals of the idle trunk at which time the commutator brush I28 will engage an insulatingsegment of strip I and the circuit through the upper winding of relay I01 will also be opened. Relay I01 will thereupon release opening the circuit of the up-drive magnet Ill and advancing the sequence switch into position 8 as previously described.

It will now be assumed that the bank terminals I36, I34 and I35 upon which the brushes I3I, I32 and I33 have been positioned are unequipped, that is, not connected with any final selector trunk and have for that reason been connected to an intercepting trunk disclosed in the left portion of Fig. 2, terminating in a jack at an intercepting position on an A switchboard. With the sequence switch in position 8 and the sender ready to control the final brush selection, relay I 03 again operates and establishes a' circuit from battery through the lower winding of relay m1, left contact of cam I08, lower right contact of cam I09, contacts of relay I03 to the lower left contact of cam I 40 and in parallel therewith from battery through the non-inductive winding I29 of relay I01, upper left and lower right contacts of cam I09, contacts of relay I03 to the lower left contact of mm I40thence over the upper right contact of cam I amup brush I32 and terni'inal I34, conductor I31, left back contact of relay 200, winding of relay 20I to ground at the back contact of relay 202. Relay 20I operates in this circuit but relay I01 does not operate and the sequence switch of the incoming selector therefore remains in position 8.

Relay 20I upon operating closes an obvious circuit for relay 203 which looks over its left front contact to ground over sleeve conductor I38 and test terminal I36, establishes an obvious operating circuit for slow-to-operate relay 204, connects ground to the swinging contact of interrupter 205 and supplies operating ground for itself over its middle right front contact to replace ground supplied from the back contact of relay 202. Relay 204 upon operating closes an obvious circuit for slow-to-operate relay 202 and a circuit for relay 201 extending from battery through resistance 208, winding and normal contacts of relay 201, inner front contact of relay 204 to ground. A branch of this circuit also extends over the normal contacts of relay 201, winding of relay 209, resistance 2I0 to battery, but the wind ing of relay 209 being shunted over its own back contact, relay 209 does not operate at this time. Relay 201, however, operates and closes a looking circuit for itself extending over its alternate contacts to ground at the outer right front contact of relay 203. Relay 202 upon operating establishes a circuit from ground through the left winding of relay '2 to battery and a circuit from ground through the right winding of relay 2I I and the source of ringing current 2I2. Relay 2 now operates and releases in response to the ringing cycle.

With relay 20I operated each operation of relay 2I I closes a circuit from ground at the inner right contact of relay 203, outer right contact of relay 20I, contacts of relay 2, ring conductor I39, terminal I35, brush I33, right contacts of cam I4I, lower right and upper contacts of cam I04 to the tip fundamental conductor If. These ground impulses shunt down the sender stepping relay and hold relay I03 operated. When the sender is satisfied with respect to its final brush registration or as assumed after five shunting impulses have been transmitted, it opens the fundamental circuit releasing relay I03 which in turn opens the previously traced circuit of relay 20I which releases and in turn releases relays 204 and 202 and opens the path over which ground impulses were transmitted by the operation of relay 2. Relay 204 upon releasing opens the short circuit from the winding of relay 209-and relay 209 now operates in a circuit from battery through resistance 2I0, winding of relay 209, alternate contacts of relay 201 to ground at the outer right contact of relay 203. Relay 209 upon operating closes an operating circuit for relay 2I3 extending from battery through the winding of relay 2I3, back contact of relay 2I4, left contact of relay 209 to ground at the outer right contact of relay 203. Relay 2I3 upon operating locks in a circuit from battery through its winding, the winding of relay 2M, front contact of relay M3 to ground at the outer left contact of relay 203 but the winding of relay 2M being shunted over its own back contact so long as relay 209 remains operated does not operate at this time. The operation of relay 209 has thus registered the completion of the final brush selection. The release of relay 202 opens the operating circuits of relay 2 and at its back contact prepares the initial operating circuit of relay 20I,

When the fundamental'circuit is again closed at the sender relay I03 operates followed by the reoperation of

relays

20I, 204 and 202. Relay 204 upon operating establishes a circuit from ground over its inner front contact, right front contact of relay 209 to a point between the Winding of relay 201 and resistance 208 thereby shunting the winding of relay 201 which now releases. With relay 201 released relay 209 is now held operated over a circuit extending from battery through resistance 2I0, winding of relay 209, normal contacts of relay 201 to ground at the inner contact of relay 204. Relay 202 upon operating reestablishes the operating circuits through the windings of relay 2I I and this relay again intermittently connects ground over the circuit previously traced to the tip conductor IOI of the fundamental circuit for intermittently shunting down the sender stepping relay.

When the sender is satisfied with respect to its final brush or tens registration or as assumed after seven shunting impulses have been transmitted it opens the fundamental circuit releasing relay I03 and relays 20I, 204 and 202 in turn. The release of relay 20I opens the path over which ground impulses were transmitted to the sender. lhe release of relay 202 opens the circuits through the windings of relay 2I I and the release of relay 204 opens the locking circuit of relay 209 which now releases and removes the shunt from the winding of relay 2I4. Relay 2I4 operates in the locking circuit of relay 2I3 thereby registering the completion of final tens selection.

As soon as the fundamental circuit is again closed at the sender relay I 03 reoperates followed by the reoperation of

relays

20I, 204 and 202. Relay 2I I again intermittently operates to transmit impulses to the sender. As soon as relay 204 operates relay 201 is again operated in a circuit from battery through resistance 208, winding and normal contacts of relay 201 to ground at the inner contacts of relay 204 and locks over its alternate contacts to ground at the outer right contact of relay 203. As soon as the sender is satisfied with respect to its final units registration or as assumed after eight shunting impulses have been transmitted it opens the fundamental circuit releasing relay I03 and relays 20I, 204 and 202 in turn. The release of relay 20I opens the path over which ground impulses were transmitted to the sender. The release of relay 202 opens the circuits through the windings of relay 2II and the release of relay 204 opens the shunt around the winding of relay 209 and relay 209 now operates in a circuit from battery through resistance 2I0, winding of relay 209, alternate contacts of relay 201, to ground at the outer right contact of relay 203. The reoperation of relay 200 registers the completion of final units selection.

With relays 209 and 2I4 both operated a circuit is now established from ground at the outer right contact of relay 203, left contact of relay 209, front contact of relay 2M, conductor I39, terminal I35, brush I33, right contacts of cam I4I, winding of relay I 03 to battery operating relay I 03 which in turn causes the reoperation of relay 20I. When the swing contact of interrupter 205 next engages its left contact relay 206 is operated in a circuit from ground over the left front contacts of relay 20I, left contacts of interrupter 205, winding of relay 206 to battery and looks over its inner right contact to ground after the interrupter 205 closes its right contact a circuit is established from ground thereover, outer right contact of relay 206, winding of relay 200 to battery. Relay 200 upon operating looks over its outer right front contact to ground at the inner right contact of relay 203 and connects shunting ground over its inner right contact to the winding of relay 20I thereby causing its release. The release of relay 20I opens the locking circuit of relay 205 but with relay 200 operated relay 205 remains operated over a circuit from ground at the inner right contact of relay 203, outer right contact of relay 200, outer right contact of relay 205, right contact of interrupter 205, inner right front contact and winding of relay 205 to battery until the interrupter opens its right contact when relay 206 will release.

During the time that relays 200 and 206 are both operated a circuit is established from ground at the inner right contact of relay 200, left front contact of relay 206, tip conductor I31, terminal I 34, brush I 32, upper right and lower left contacts of cam I40, and thence as traced through the non-inductive winding I29 to battery and the lower winding of relay I01 to battery. Relay I01 now operates and locks in a circuit from battery through its non-inductive winding I29 and upper winding, upper contacts of cam I30, lower contact of cam H0, lower left contact of cam I I2 to ground at the upper front contact of relay I01 and closes a circuit for advancing the sequence switch into position 9. This circuit may be traced from battery, winding of sequence switch magnet I50, contacts of cam H5, upper left contact of cam II 6, lower front contact of relay I01, upper right and lower left contacts of cam III to ground. When the sequence switch advances out of position 9 relays I03 and I01 release.

With the sequence switch in position 9 ground is connected to the tip fundamental conductor IOI over the left contacts of cam I04 and battery is connected to the ring fundamental conductor I02 over the upper left and lower right contacts of cam I06 through the winding of relay I03 so that when the sender again closes the fundamental circuit relay I03 and sender relays operate and a reverse battery signal is given for controlling the dismissal of the sender. Relay I03 upon operating closes a circuit from battery through the lower winding of relay I01, left contact of cam I03, lower right contact of cam I09, contacts of relay H03, upper contacts of cam III] to ground over the left contacts of cam III.

Relay I01 operates and establishes a circuit from battery, winding of sequence switch magnet I50, contacts of cam H5, left contact of cam I22, upper front contact of relay I01 to ground whereby the sequence switch advances through position I0 into position II. When the sequence switch leaves position I0 relay I03 releases and while passing through positions 9-I/4 to I0 a charging circuit is established for condenser I42 extending from battery, lower winding of relay I44, contacts of cam I45, upper back contact of relay I43, through condenser I42, lower back contact of relay I43, upper contacts of cam I46 to ground in preparation for trunk closure.

When the sequence switch reaches position II a circuit is established from battery through the lower winding of relay I44, contacts of cam I45, upper back contact of relay I43, upper left winding of repeating coil I41, upper contacts of cam 82d, conductor IfiI through the winding of a supervisory relay (not shown) at the toll office,

returning over conductor I02, upper contacts of cam I06, lower left winding of coil I41, lower back contact of relay I43, upper winding of relay I44 to ground over the upper left and lower contacts of cam I48. Relay I44 operates closing a circuit for slow-to-release relay I49 and slowto-release relay I52 extending from battery through the winding of relay I52, back contact of relay I49, and in parallel from battery through the winding of relay I49, right contacts of cam I51, front contact of relay I44 to ground over the lower right and upper left contacts of cam I46. Relays I49 and I52 operate, relay I49 opening the initial operating circuit of relay I52 and closing a new operating circuit therefor over its upper front contact. At its upper front contact relay I52 supplies operating ground for relay I44 to replace operating ground supplied thereto over contacts of cam I48 after the sequence switch leaves position II and establishes a circuit for advancing the sequence switch into position I2 which circuit may be traced from battery, winding of sequence switch magnet I50, contacts of cam II5, the upper left contact of cam H6, left contacts of cam I20, lower front contacts of relay I52 to ground. The incoming selector circuit is now in condition for ringing.

When ringing current is applied at the toll office end of the trunk it flows over conductor IOI, upper contacts of cam. I2I, upper left wind ing of coil I41, through condenser I53 and the winding of ringing relay I54, lower left winding of coil I41, upper contacts of cam I06, back over conductor I02 thereby operating relay I54 which in turn causes the operation of relay I43. Relay I43 extends its operating ground over its upper front contact to battery through the upper winding of relay I55 which also operates. Relay I43 also opens the circuit of relay I44 but relay I44 is held operated in a circuit extending from battery through the lower winding thereof, contacts of cam I45, lower front contact of relay I43,

upper winding of relay I44 to ground at the upper contact of relay I52. Relay I55 upon operating locks in a circuit extending from battery through its lower winding, upper back contact of relay I56, upper back contact of relay I51, lower front contact of relay I55, contacts of cam I58 to ground at the lower contacts of relay I52 and at its upper front contact establishes an obvious circuit for relay I59. A ringing circuit is now established from the source I60 of ringing current, contacts of cam I6I, upper back contact of relay I01, winding of ringing trip relay I56, lower back contact of relay I51, lower front contact of relay I59, lower contacts of cam I4I, brush I33, terminal I35, conductor I39, inner left front contact of relay 200, left winding of relay '2I5, condenser 2I6, outer left front contact of relay 200, conductor I31, terminal I34, brush I32,

upper contacts of cam I40, upper front contact of relay I69, through resistance I62 to ground. Relay I56 does not operate in response to this ringing current but relay 2I5 operates, locks in a circuit from battery through its right winding and right front contact, back contact of relay 2I1, to ground at the inner right contact of relay 203 and establishes a circuit from battery over its left contact and conductor 2I8 to ground through the calling lamp 450.

The operator at the A switchboard upon seeing the lighted lamp knows that an intercepted call is awaiting her attention and inserts the plug 40I of an idle cord circuit into the trunk jack 400 whereupon a circuit is established from battery through the windings of marginal relay 403 and relay 402 in series and from battery through the non-inductive winding 404 of relay 403 in parallel thence over the sleeves of plug 40I and jack 400, conductor 2I9, winding of trunk sleeve relay 2H to ground. Relays 2H and 402 both operate but relay 403 being marginal does not receive sufficient current because of the high resistance of sleeve relay 2I I. Relay 2|! upon operating opens the locking circuit of relay H and prepares a disconnect signaling circuit.

Relay 402 upon operating establishes a circuit for supervisory lamp 405 extending from battery over the inner contacts of relay 402, resistance 406, back contact of relay 401, back contact of relay 408 to ground through lamp 405 and in parallel therewith from battery over the inner contacts of relay 402, resistance 406, back contact of relay 401, back contact of relay 408, middle lower back contact of relay 409, inner normal contacts and winding of relay M0 to ground at the lower right normal contacts of key 4! I. Relay 4I0 locks in a circuit from battery at the inner contact of relay 402, inner upper alternate contacts and winding of relay M0 to ground at key 4| I.

When the operator throws her listening key 4 to the right or talking position, relay 4I0 releases and a circuit is established from ground at the left back contact of relay 30I, conductor 4| 2, upper right contacts of key MI to battery through the winding of relay All which operates and establishes a circuit from battery at the inner contact of relay 402, inner lower contact of relay 4, conductor 4I5, winding of relay 302 to ground. Relay 302 operates and connects battery through resistance 303 over its outer left contact to conductor 304 and ground over its inner left contact and the back contact of relay 305 through the winding of test relay 300 to conductor 304, thence over the lower contact of relay 4I'I, back contact of relay 45L upper normal contacts of key 4I4, tips of plug 40I and jack 400, conductor 220, outer left front contact of relay 200, conductor I31, terminal I34, brush I32, upper contacts of cam I40, upper front contact of relay I59 to generator ground through resistance I02. Test relay 306 now tests to determine if the connection has been extended to the operators position from a toll incoming selector such as the selector I00 or from a regular incoming selector. In all regular incoming selectors no resistance, such as I62 is supplied in the ringing generator ground lead and when the previously traced test circuit is established the test relay 300 is shunted by the direct ground at the incoming selector and does not operate. All toll incoming selectors, however, are equipped with a resistance in the ringing generator ground lead, as disclosed at I02 in selector I00, and when the test circuit is established the test relay 306 operates in a circuit from battery through resistance 303, outer left contact of relay 302, winding of test relay 306, back contact of-relay 305, to ground at the inner left contact of relay 302. Thus test relay 306 operates to give the operator a special signal only when an intercepted call is incoming to that position from a toll point.

When relay 306 operates, it establishes an obvious circuit for relay 301 which locks over its inner left contact, the back contact of relay 308 to ground at the inner left contact of relay 302. At its outer right contact it establishes a circuit from the tone source lead 309 through the primary winding of tone coil 3I0 and over its inner right and outer left contacts connects the secondary winding of tone coil 3I0 to the talking conductors 420 and 42I extending to the operators telephone circuit preparatory to applying tone current to the operators telephone set. At the time the test circuit was established ringing current from the ringing source I60 in the incoming selector was also transmitted over the circuit previously traced to trunk conductor I39 thence over the inner left front contact of relay 200, conductor 22I, rings of jack 400 and plug 40I, lower normal contacts of key 4, lower left winding of repeating coil 4I3, inner lower back contact of relay 403, inner lower back contact of relay 409, middle lower front contact of relay 4I'I, conductor 3, right back contact of relay 30I to ground through the winding of ringing trip relay 3I2. Ringing current or silent interval battery operates relay 3I2 which establishes a circuit from ground at the inner left contact of relay 302, contacts of relay 3| 2, winding of relay 3I3 to battery. Relay 3I3 operates locking directly to ground over the inner left contact of relay 302 and establishes a circuit from battery through the winding of relay 3I4, back contact of relay 3I5, right contacts of relays 3| 3 and 302 to ground as soon thereafter as interrupter 3|! makes its contacts. Relay 3I4 upon operating locks in a circuit through its winding, the winding of relay 3I5, contacts of relay 3| 4 to ground at theinner left contact of relay 302 and as soon as the interrupter 3I1 opens its contacts relay 3I5 operates in this locking circuit. Upon the next closure of the interrupter contacts relay 305 operates in a circuit extending from battery through its winding, back contact of relay 3I6, front contacts of relays 3I5, 3I3 and 302 to ground at the interrupter contacts and locks in a circuit through its winding and the winding of relay 3I6, right contact of relay 305 to ground at the inner left contact of relay 302, but the winding of relay 3I6 being shunted, relay 3I6 does not operate in this locking circuit until the interrupter again opens its contacts.

When relay 305 operates battery is connected through resistance 3I8 over the left contact of relay 305, right back contact of relay 30I to conductor 3H and thence as traced through the winding of the ringing trip relay I56 of the incoming selector to the source of ringing current I60 and relay I56 now operates, releasing relay I55 which in turn releases relay I59 to disconnect the source of ringing current and ground through resistance I62 from the intercepting trunk thereby releasing relay 3| 2 at the position circuit. With relay I59 released the tip and ring talking conductors at the incoming selector are extended from the right windings of repeating coil I4! trol of interrupter 3I'I has measured off a time interval following the operation of relay 3I2 by the ringing current before the ringing is tripped at the incoming selector. When following the operation of relay 3I6 the interrupter 3I'I again closes its contacts the circuit from ground at the contacts of the interrupter is extended as traced over the front contacts of relay 3I5, thence over the front contacts of relay 3I6 to battery through the winding of relay 30I and in parallel therewith over conductor 4I8, inner upper front contact of relay 4I'I, winding of relay 45I to battery at the inner front contact of relay 402. Relays 30I and 45I both operate, relay 45I looking to ground. over its inner front contact, at its lower back contact opening the test circuit from the tip of plug 40I to conductor 384 as previously traced and closing a talking circuit from the left windings of the repeating coil 4I3 of the cord circuit to the right windings of the repeating coil at the incoming selector. This circuit may be traced from ground through resistance I63, upper wind ing of supervisory relay I54, upper right winding of repeating coil I41, upper back contact of relay I59, upper contacts of cam I40, brush I32, terminal I34, conductor I31, outer left front contact of relay 208, conductor 222, tips of jack 490 and plug 4III, upper normal contacts of key 4H3, lower front contact of relay 45I, upper left winding of repeating coil 4I3, upper back contact of relay 403, lower'winding of relay 4E8, lower back contact of relay 4%, resistance 439 to battery and from battery through resistance I65, lower winding of relay I64, lower right winding of coil I41, lower back contact of relay I59, lower contacts of cam I4I, brush I33, terminal I35, conductor I39,

inner left front contact of relay 200, conductor 22I, rings of jack 4M and plug 40I, lower normal contacts of key 4I4, lower left winding of repeating coil 4I3, inner lower back contact of relay 403, inner lower back contact of relay 439 to ground through resistance 438.

Relay I64 now operates establishing a circuit from battery through the winding of relay I51 to the upper left contact of cam I I2 and in parallel therewith from battery through the lower winding of relay I43 to the upper right contact of cam IIZ, thence over the lower contact of cam III], contacts of relay I54 to ground at the lower contacts of relay I49. Relay I43 upon operating disconnects battery and ground through the windings of relay I44 from conductors NH and I02 of the trunk circuit thereby extinguishing the calling supervisory lamp at the toll operators cord circuit to apprise her that the call has been answered. Relay I43 also establishes the previously traced circuit for holding relay I44 operated.

When relay 3M operated at the time relay 45I operated it looked over its inner right contact to ground at the inner left contact of relay 382, opened the ringing trip circuit at its right back contact and closed a circuit from ground over its left front contact and conductor 3M to batterl through the upper winding of relay 222 thereby operating relay 222. At its left back contact relay 30I also removes direct ground from conductor 4I2 by which the initial operating circuit of relay M1 was completed. Relay II? is now held operated over the previously traced circuit to conductor 4 I 2 and then to ground through resistance 32!). Relay 4 I l of another cord circuit of the position will not operate in this circuit through resistance 320 in case a talking key of such cord circuit should at this time be operated to the talking position. This is for the purpose of preventing two cord circuits from being connected to the operators telephone set circuit at the same time.

With

relays

222 and 321 both operated tone current impressed on the secondary winding of tone coil 3 I Ii from source 339, flows over conductor 42 I,

upper contact ofrelay 222, left windings of repeating coil 223, condenser 22$, lower contacts of relay 222, back over conductor 42 I, and tone current thus flows through the operators headset receiver through the upper left winding of coil 223, inner back contact of relay 224, through the receiver 225 and lower back contact of relay 224. The operator upon hearing the tone then knows that a call from a toll point has been intercepted.

To discontinue this tone she then operates key 32I thus operating relay 308 which locks over its front contact to ground at the inner left contact of relay 302 and at its back contact opens the locking circuit of relay 331 which now releases. Relay 3291 upon releasing completely opens the circuits through the windings of tone coil 3I0.

Since the operators transmitter 221 is inductively connected to the talking conductors 420 and 42 I through the windings of repeating coil 223 and a talking loop between conductors 428 and 42I is completed at the cord circuit from conductor 42%, inner lower right alternate contacts of key III I, right windings of repeating coil 4I3, inner upper right alternate contacts of key M I to conductor 42L the operator is enabled to converse with the toll operator to give her any necessary information for reaching the subscribers line to which a connection has been attempted.

Should the intercepting operator desire to recall the toll operator after the toll operator has disconnected her headset from the toll cord circuit she may do so by depressing key 4 I 4. The operation of key 4 I 4 opens the circuit of supervisory relay I64 which in turn releases relay I43. Relay I43 upon releasing reconnects battery and ground through the windings of relay I 44 to the trunk conductors III! and I02 and thereby causes the lighting of the calling supervisory lamp at the toll operators cord circuit. When key 4I4 is released relays IE4 and I43 again operate and the cord circuit lamp is extinguished. Thus by intermittently operating key M4 the toll cordcircuit supervisory lamp may be flashed to signal the toll operator.

After having given the necessary information the intercepting operator removes plug 4IJI from jack 49!] thereby releasing all operated relays of her cord circuit and position circuit, releasing relay 227 of the intercepting trunk circuit and supervisory relay I84 of the incoming selector. Relay I54 upon releasing in turn releases relay I43 which reconnects relay I44 to conductors IIII and I92 and thereby causes the relighting of the calling supervisory lamp as a disconnect signal. The toll operator noting the signal withdraws her cord circuit plug from the jack of trunk IIlI, I62 thereby releasing relay I44 which, in turn, releases relays I49 and IE2. Relay I52 upon releasing closes a circuit from battery, winding of sequence switch magnet I50, contacts of cam I I5, upper right contact of cam I22 to ground at the back contact of relay I52, for advancing the sequence switch out of position I2 into position It. In position It a circuit is established for the down-drive magnet I25, over the upper right contact of cam I24 to ground at the lower left contact of cam I I I for driving the incoming selector brush rod into normal position. To prevent the snagging of the brushes during this downward movement the trip magnet I23 is operated over the lower contact of cam I24 and the lower left contact of cam III. Upon reaching normal a circuit is established from ground over the left contacts of cam III, brush I28, normal commutator segment I61, lower right contact of cam lit, contacts of cam H to battery through the winding of sequence switch magnet I50 thereby advancing the sequence switch into position H.

In position I? a circuit is established from battery, winding of sequence switch magnet I 59, contacts of cam IIS, upper left contact of cam 22 to ground over the left contacts of cam I46 advancing the sequence switch into position I 8 .in which position the circuit of sequence switch magnet I50 is extended over the lower contact of cam I22 and the inner upper back contact of relay I01 to ground thereby advancing the sequence switch into normal position I. The incoming selector is now fully restored.

When the sequence switch leaves position I4- I /4 ground is removed from test brush I3I at the lower contacts of cam III, thus releasing relay 203 of the intercepting trunk circuit. Relay 203 upon releasing releases relays 200, 201, 209, 2I3 and 2 I4. The intercepting trunk is now in normal condition.

Had the call been incoming to the intercepting position from a regular incoming selector the intercepting operator would not have received the tone signal as previously described but the tripping of ringing and the establishment of the talking circuit between the calling subscriber and the operator would have been accomplished in the same manner. After ascertaining from the subscriber the designation of the line with which he attempted to obtain a connection the operator may then proceed to complete the connection by inserting plug 422 into the jack of an outgoing trunk, operating the dialing key 322 and then keying up the digits of the required line designation on the key-set 230. Since the manner in which the key-set and cord circuit apparatus function in the establishment of the connection does not directly concern the present invention it will not be described herein. Reference to Patent 1,916,760 granted July 4, 1933 to I. H. Henry may be had for a complete description.

In the foregoing discussion it was assumed that in attempting to establish a connection to the subscribers line whose directory number was 2467, the incoming selector I00 was set upon trunk terminals which were unequipped for a regular service connection and were connected to the intercepting trunk disclosed in Fig. 2. It will now be assumed that the terminals upon which the incoming selector was set are connected to a final selector and that in accordance with the final brush, final tens, and final units registrations set up in the sender at the toll position a final selector is set upon the terminals identified by the keyed designation 2467 but that this set of terminals is unequipped, the called subscriber's line, for example, having been disconnected or given a new directory number. In this case this set of terminals in the final selector would be connected to an intercepting trunk of the type disclosed in Patent 1,930,612 granted October 1'7, 1933 to E. L. Getz and upon the seizure of this trunk by the final selector a trunk lamp at the A switchboard would be lighted to signal an intercepting operator that an intercepted call is awaiting her attention.

The operator would answer the call in the manner previously described resulting in the operation of cord circuit relays 402 and 4I'I and the operation of relay 302 at the position circuit. With relays 4H and 302 operated the previously traced test circuit from the test relay 306 to the tip of plug 40I would be extended over the tip conductor of the intercepting trunk, tip brush of the final selector, tip brush I32 of incoming selector I00 over the upper contacts of cam I40, upper back contacts of relay I59, this relay being unoperated because of the delayed initiation of ringing, upper right winding of repeating coil I4'I, upper winding of relay I64, resistance I63 to ground. Test relay 30B operates in this case preparing the tone circuit at the operators position. As soon as ringing is initiated and relay I59 operates, ringing current is then transmitted from the incoming selector, is tripped at the operators position circuit and the circuits then function in the manner previously described.

Had the call been extended through a regular service incoming selector and final selector to the intercepting position then upon automatic ringing from the incoming selector direct ringing ground would be connected to the test circuit and relay 306 would not function. Thus test relay 305 determines in the manner previously described whether the intercepted call is incoming from a regular service connection or from a toll connection.

What is claimed is:

1. In a telephone system, an operators position, trunk lines extending to said position, a plurality of groups of selector switches having access to said trunk lines, a cord circuit at said operators position for connection with said trunk lines, signaling means at said operators position and a discriminating relay at said position for controlling said signaling means and operable only when a connection to said operators position is established over a selector switch of one of said groups.

2. In a telephone system, an operators position, trunk lines incoming to said position, a plurality of groups of selector switches having access to said trunk lines, a cord circuit at said operators position for connection with said trunk lines, a source of tone current and a telephone set at said operators position, and a discriminating relay at said position for controlling the connection of said source of tone current to the telephone set and operable only when a connection to said operators position is established over a selector switch of one of said groups.

3. In a telephone system, an operators position, trunk lines incoming to said position, a plurality of groups of selector switches having access to said trunk lines, a cord circuit at said operators position for connection with said trunk lines, signaling means at said operators position, a marginal relay at said position operable to control said signalling means and a circuit for said relay established either directly to ground when a connection is completed to said position over a selector switch of one of said groups or to ground through a resistance when a connection is completed to said position over a selector switch of another of said groups, said relay being operable only when a connection is established over a selector switch of the latter group.

4. In a telephone system, an operators position, trunk lines incoming to said position, a plurality of groups of selector switches having access to said trunk lines, a cord circuit at said operators position for connection with said trunk lines, a source of tone current and a telephone set at said operators position, a marginal relay at said position operable to control the connection of said source of tone current to said telephone set and a circuit for said relay established either directly to ground when a connection is completed to said position over a selector switch of one of said groups or to ground through a resistance when a connection is completed to said position over a selector switch of another of said groups, said relay being operable only when a connection is established over a selector switch of the latter group.

5. In a telephone system, an operators position, trunk lines incoming to said position, a selector switch having access to said trunk lines,

a cord circuit at said operator's position for connection with said trunk lines, means in said switch operable following the seizure of a trunk line for applying ground through a resistance and a source of ringing current over the tip and ring conductors respectively of said trunk line to said operators position, a source of tone current, a telephone set and a relay at said position, said relay operable upon the connection of said resistance ground to prepare a circuit for applying said source of tone current to said telephone set, means at said operators position for discontinuing the application of ringing current and means for thereafter completing said latter circuit.

6. In a telephone system, an operators position, trunk lines incoming to said position, a selector switch having access to said trunk lines, a cord circuit at said operators position for connection with said trunk lines, a relay in said cord circuit, a source of tone current, a telephone set and a test relay at said position, means in said switch operable following the seizure of a trunk line for establishing a test circuit from ground through a resistance at said switch over the tip conductor of said trunk line to said test relay and a ringing circuit from a source of ringing current at said switch over the ring conductor of said trunk line to said position, said test relay being responsive to the establishment of said test circuit to prepare a circuit for applying said source of tone current to said telephone set, means at said operator's position for discontinuing the application of ringing current and for operating said cord circuit relay to open said test circuit and to complete the talking circuit over said cord circuit, and means for thereafter completing said tone circuit.

WILEYWHITNEY.