US2173675A

US2173675A - Telephone system

Info

Publication number: US2173675A
Application number: US166940A
Authority: US
Inventors: Langford J Bowne
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1937-10-02
Filing date: 1937-10-02
Publication date: 1939-09-19
Anticipated expiration: 1956-09-19

Description

Sept. 19, 1939. L. J.BOWNE 2,173,675

TELEPHONE SYSTEM Filed Oct. 2, 1937 .3 Sheets-Sheet l INVENTOR .LJ. BOW/V5 ATTORNEY 5 Sheets-Sheet 2 lNl/ENTOR L..J BOWNE ATTORNEY L. J. BOWNE TELEPHONE SYSTEM Filed Oct. 2, 1937 FIG. 2

Sept. 19, 1939.

Sept. 19, 1939. 9 L J, BOWNE 2,173,675

- TELEPHONE SYSTEM Filed Oct. 2, 1937 3 Sheets-Sheet 3 FIG. 3

M /3/ wo INVENTOR, LJ BOWNE ATTORNEY Patented Sept. 19, 1939 UNITED STATES PATENT OFFICE TELEPHONE SYSTEM York Application October 2,

18 Claims.

- This invention relates to telephone systems and particularly to toll party line telephone systems.

" It is the object of this invention to improve the telephone service accorded to small "communities served by a single toll line from a toll center.

The invention is embodied in a toll party line circuit and associated subscribers station connecting circuits which cooperate to effect a system of telephone communication between a large toll center and widely scattered outlying communities, as well as between subscribers of the same community and neighboring communities.

"In accordance with the system of this invention, each of a plurality of outlying communities served by a toll line from a toll center is transformed into a switching center provided with automatically operating switching equipment in which a plurality of subscribers lines, either magneto or common battery, terminate and which is controlled over the two conductors of the toll line by means of a telephone dial of the type commonly employed in establishing automatic and semi-automatic telephone connections.

Each subscribers station, whether of the magneto or common battery type, on a party line is equipped with means for signaling an operator at a toll center by way of atoll line and for automatically rendering the toll line inaccessible to all other subscribers normally having access to the toll line. This lock-out feature is made possible by a relay, controlled over a circuit simplexed on the toll line, which operates as a consequence of the initiation of a call by a subscriber to remove ground potential from the line con .35 meeting relays at all other stations, thereby rendering them inoperative should a second subscriber attempt to use the toll line when in use by another subscriber.

In accordance with a feature of the invention, the look-out control relay, subsequent to its operation as the consequence of the initiation of a call by a subscriber, is placed under the control of the toll operator in such a manner that the withdrawal of an answering plug from the toll line subsequent to its insertion therein in response to an incoming call, and the reinsertion thereof results in all subscribers lines, including the calling line, being locked out from the toll line. This is a particularly desirable feature in that it furnishes a positive arrangement for number checking.

A further feature of the invention resides in the use of common signaling means at the toll ofiice which functions automatically in response to the initiation of a call at either a magneto or 1937, Serial No..166,940 (Cl. 179-27) common battery station to transmit a tone signal over the toll line as an indication to the call ing subscriber that the toll line is free for use.

These and other features of the invention not specifically identified, will be readily understood from the following detailed description made with Outgoing call from common battery subscriber In Fig. 3 there are illustrated two common bat- .tery stations A and B. For descriptive purposes it will be assumed that the subscriber at station A desires to communicate with the toll operator at the toll oflice indicated in Fig. 1 by the characters C. 0. When the subscriber at station A removes the receiver from the switchhook, in accordance with usual common battery practice, the resulting bridge across the tip and ring conductors of the line It causes the line relay II to operate in a circuit extending over the back contacts and the two upper armatures of relay l2.

Relay I i, operated, causes relay 13 to operate in a circuit extending from grounded battery l8, winding of relay i3, conductor M, normally closed back contacts of relay l5 to ground by way of the front contact and armature of relay H. At its lower armature relay l3 disconnects battery I8 from the windings of preceding relays, such as relays It and IT, in the chain in order to prevent the operation of such relays at this time. Had relay it been any other than the last relay in the chain, such as relay! 6 for example, it would look up under control of a relay 1 I. At its upper innermost armature and back contact, relay l6 would open the chain circuit H! to any succeeding relays in the chain to prevent, later on, the operation of other than the one connecting relay [2 associated with the first relay 53 of the chain operated. Relay l3 at its upper middle armature prepares an operating path from the lead 2| to the associated relay I5 which performs no function at this time. At its upper outermost armature and front contact, relay l3 connects the lead 22 to the start lead 23 causing start relay 24 to operate in a circuit extending from grounded battery, winding of relay 24, conductor 23, upper outermost armature and front contact of relay |3, conductor 22, conductor 25, lower normal makebefore-break contacts of relay 26, conductor 21 to ground at the right-hand normal make-beforebreak contacts of relay 28.

Relay 24, operated, establishes an obvious operating circuit for relay 29. At its upper armature, relay 24 causes relay 30 to operate in a circuit extending from grounded battery, winding of relay 30, conductors 3| and 32, operated upper contacts of relay 24,

conductors

33 and 21 to ground at the normal right-hand contacts of relay 28. At its innermost lower armature and front contact, relay 24 establishes an obvious operating circuit for the interrupter relay 34 which relay operates. The interrupter 34 is a relay structure with a weighted reed 9 which is tuned to approximately 20 cycles. It has two

contacts

35 and 36 used for connecting the battery 44 to repeating coil 31 and has a self-shunting contact 38. Relay 29 is slow to operate to give the interrupter 34 a chance to fully operate before resistance 40 is connected in series therewith. Relay 29 causes relay 4| to operate in an obvious circuit, removes the shunt from resistance 40 which is then connected in series with the winding of the interrupter relay 34 and connects the mid-point between resistance 40 and the winding of the interrupter relay 34 to the shunting contact 38 on the interrupter. This causes the winding of the interrupter relay to be deenergized and the reed 9 swings back past normal because of the weight and closes contact 35. The interrupter continues to vibrate shunting itself each time contact 38 is closed until the relay 24 releases. Relay 30 is slow to release to prevent false operation of relay l5.

When relay 29 operated, it closed a circuit to relay 4|, as hereinbefore stated, which relay operates and locks under control of relay 43 and at its innermost and middle lower armatures and front contacts connects the interrupter contacts to the drop winding of repeating coil 31. C10- sure of interrupter contact 36 causes current to flow from battery 44 through the upper righthand winding of repeating coil 31, front contact and innermost lower armature of relay 4|, conductor 8, contact 36, reed 9, front contact and middle lower armature of relay 24, conductor 23, outermost upper armature and front contact of relay l3,

conductors

22 and 25, normal lower contacts of relay 26, conductor 21, to ground on the normal right-hand contacts of relay 28, which sends one-half cycle of ringing current out on the line toward the central ofiice by way of the lefthand winding of repeating coil 31 which is bridged across the conductors of the toll line L. Closure of the interrupter contact 35 causes current to flow through the lower right-hand Winding of repeating coil 31, front contact and middle lower armature of relay 4|, conductor 1, contact 35, reed 9 and thence over the circuit first traced to ground on the normal right-hand contacts of relay 28, causing one-half cycle of ringing current in the opposite direction to flow out on the line. The recurring alternate closures of

contacts

36 and 35 of the interrupter thus continue to send ringing current toward the central office.

In addition to the starting of the ringing current circuit, relay 24 connects condenser 46 across the tip and ring conductors of the line to prevent excessive clicks from ringing current reaching any other subscriber and operates relay 30 (as hereinbefore mentioned) which opens the path for conductor 2| to prevent the operation of relay |5 when relay 28 operates, as will appear from a later description.

Relay 4|, at this time, disconnects the talking circuit of station A from the line L to prevent the subscriber hearing the ringing current later when relays l2 and 43 operate. Relay 4| prepares the operating circuit for relay |2 associated 0 with the operated relays II and I3 through the back contact of relay 41, conductors 60 and I9 and the operated innermost upper contacts of the calling relay l3.

Signal received at central ofiice 15 Ringing current from the interrupter relay 34 which is transmitted to the central office by way of the repeating coil 31 causes relay 50, which is connected across the tip and ring of the line L 20 by way of lower outer armature and back contact of relay 5|, to operate. Operated, relay 50 causes relay 52 to operate in an obvious circuit and establish an obvious circuit for the drop signal 88 which operates to appraise the operator of the 1,5 incoming call. At its armature 54 and associated front contact, relay 52 looks up under control of relay 5|. At its lower armature and front contact relay 52 connects 24 volt battery 56 to the simplex leg 55 of the toll line L which causes relay $0 28 and all such relays at other concentrating points to operate. At its outermost upper armature, relay 52 establishes an obvious circuit for relay 51 which connnects the tone circuit, generally indicated by the numeral 58, to the line. 35 This tone is heard by the calling subscriber as an indication that the toll line L is free for use as will appear presently.

The operation of relay 28, at the concentrating point at which a call is being originated causes m relay l2 to operate in a circuit extending from grounded battery, winding of relay l2, conductor 59, front contact and innermost upper armature of relay I3, back contacts and innermost upper armatures of chain relays l6 and I1, conductor 5 68, back contact and aramture of relay 41, conductor 6|, outermost lower armature and front contact of relay 4| to ground at the right-hand armature and front contact of relay 28.

The function of other relays 28 at concentrat- 0 ing points other than the one at which a call is originated will be described later.

Relay l2 operated, connects the calling subscribers station A to the talking battery supply 62 through the tip and ring resistance lamps 63 55 and 64, windings of relay 65 and retard coil 66 and disconnects the station from the battery through the windings of relay Relay l2 locks up in circuit extending from grounded battery, winding of relay I2, front contact and lower armature of 50 relay l2,

conductors

12, 13, 14, 15 to ground at the right-hand armature and front contact of relay 28.

Relays

43 and 41 now operate to ground by way of conductor 10, contacts 68 and lower armature of relay I2 and thence by way of the lock- 65 ing circuit for relay l2 just traced.

Relay 41 operates fast and opens ground from conductor 68 preventing the operation of any relay l2 which may be connected to conductor 2| through the operation of an operated relay 7 such as l6 or H when relay |3 of the calling line releases and closes the lead 66, should the relay |3 be any but but the last relay in the chain.

Relay l2 operated, releases relay II which in turn causes the release of relay |3. The re- 75 lease of relay !3 opens the circuit to the start relay 24 in order to stop the outgoing ring toward the central oliice. Relay 43 operated from the contacts 68 of relay l2, closes the talking circuit from the subscriber at station A to the tip and ring condensers H and '58 of the line concentrating circuit. At its innermost lower armature, relay 43 opens the locking circuit for relay M which relay, however, is held operated by way of its operating circuit under control of relay 29. At its middle and outermost lower armatures and front contacts, relay 3 prepares operating circuits for relays l9 and 89, respectively. If relay 65 had already operated, relay ill will operate in a circuit extending from grounded battery, front contact and middle lower armature of relay 43, conductor 8i, resistance 82, winding of relay '19, closed contacts of relay 8E conductor 83, front contact and armature of relay 55, conductors I l and 15 to ground at the right-hand armature and front contact of relay 28. At its upper inner armature and front contact relay l9 locks to ground under control of relay 28. At its lower armature and front contact relay l9 prepares its own releasing path which includes the outermost lower armature and front contact of relay 4! and resistance 82. Relay i9 may buzz until relay 4i releases. At its middle lower armature and front contact relay 13 establishes an obvious energizing circuit for relay 2% which relay operates and at its upper armature and front contact connects ground to lead 21 to cause the operation of any relay, such as relays l5 and 84 which may be connected to lead 2i at this time. At its lower armature relay 25 prevents the continued operation of relay 31! which otherwise might occur due to the existence of a circuit extending from grounded battery, winding of relay 3U, conductors 3! and 32, upper alternate contacts of relay 24, conductor 3-3, lower normal contacts of relay 26, conductor 25, conductor 22, the outermost upper front contact and armature of any operated chain relay such as l3, it or H, conductor 23, conductor 85,1eft-hand armature and front contact of relay 253, conductor 86, armature and front contact of relay 3B, conductors l4 and 75 to ground at the right-hand armature and front contact of relay 28. This locking circuit for relay 36 is therefore broken at the lower contacts of relay 26.

Relay in releasing, opens the circuit for relay 24 which was established by the operation of relay 23 and also removes ground from the contact of relay 3-. which stops the ringing current from going out on the line.

Relay 2% released, disconnects ground from the windings of

relays

34 and 29, opens the circuit to the vibrating contact or reed 9 of relay 3 opens th operating path under this condition for relay 3 3 and disconnects condenser 46 from across the line. Relay 29 in releasing, restores the starting circuit for vibrating relay as, opens the circuit to relay which releases, disconnecting the repeating coil 3'! from the vibrating circuit, opens the path to cause relay is to buzz, connects the tip and ring of the line to the subscribers talking circuit and opens its own locking circuit.

If the central omce line is not busy, tone from the tone circui 58 will be heard by calling subscriber on the release of relay 4!.

Operator answers In response to the actuation of the drop signal 88 at the central ofiice, the operator thereat inserts the plug of a cord circuit (not shown) into the talk jack 9!] associated with the signal. Ground from the contact on the jack operates relay 5| in an obvious circuit. At its inner lower armature, relay 5| connects the 24 volt battery 9| to the simplex lead 55 in multiple with the battery 56 from relay 52. At its outer upper armature, relay 5| opens the locking circuit for relay 52 which relay releases, deenergizing the drop signal 88 and releasing relay 5'! which in turn, disconnects the tone circuit 58 from the toll line. At its outer lower armature it disconnects the winding of relay from across the line to prevent its operation when the operator rings.

Relay 51 operates only when the tip spring contact closes and at its inner upper armature locks up to the ring spring contact of the jack 9!) thereby preventing the possibility of a false release of the calling party when the operator answers. The operator is now in connection with the station A and may complete the call in the usual manner or by the number checking method.

Number checking If the call is to be completed to a point which requires that the operator number check the calling party, she requests the calling subscriber to wait and removes the plug from the jack 9!). This permits relay 5! to release, to disconnect the 24 volt battery 9! from the simplex lead which releases all the simplex relays, such as 28, at all the station connecting circuits and releases the connected subscribers cut-through relays 43 and i2. Relay 26, which was held operated by the operation of relay 43, is slow to release so that when relay 43 releases, ground is momentarily maintained on the lead 2| for a purpose to be presently described.

When relay l2 released as a consequence of the release of relay 28, the subscribers line relay II is reconnected to the subscribers line and operates over the closed subscribers line loop. In operating, relay ll causes the operation of relay I3 which, at its middle upper armature and front contact connects the winding of relay l5 to the conductor 2| which, as mentioned in the preceding paragraph is still grounded at the upper armature and front contact of relay 2E. Relay I 5 therefore, operates and locks to ground at the armature and front contact of relay II. In operating, relay l5 also opens the circuit to relay !3 which releases its armatures, opening the grounded lead 2|. The release of relay 26 now is without eifect, as the relay I5 is operated and locked to the line relay I I. The subscriber therefore would be disconnected from the toll line when the operator reinserts the plug in jack 9!] at the central oflice.

The operator now dials the calling party code and if the correct number has been given, she completes the call.

Dialing In order to determine whether or not the correct number has been given, the operator dials the code given to her by the calling subscriber, using the dial 93, jack 94 and the plug 92 of dial cord 95. The selectors S used at the station connecting circuits or concentrating points are of the polarized type and have an armature which is movable into three positions, that is, when the selector is normal and there is no current on the line the armature is in a neutral position. With a positive line current, the armature is attracted toward one pole-piece and with a negative line current, it is attracted toward the other polepiece. Movements of the armature toward either pole-piece advance a contact wheel by means of a ratchet wheel under the control of'the armature and a slow moving pawl. Alternate movements of the armature first toward one pole face and then toward the other pole face advance the selector wheel step by step following the dial at the central office. At selected points on the wheel, corresponding to its code, holding pins are located which engage with a holding spring before the retaining pawl releases the ratchet wheel associated with the contact wheel. The selector or selectors which has a pin at the periphery of the contact wheel in line with the holding spring remains in its operated position and selectors which do not have a holding pin at this point restore to normal. On the second and third digits the selectors advance in accordance with the code and the selector which has pins in accordance with the code sent from the dial closes the selected contact. The selectors just described do not, in themselves, form any part of the present invention and are well known in the art of train dispatching.

The current reversals for moving the selectors are generated by means of relays in the sending circuit which reverse the sending battery to the repeating coil at the central office once for each pulse of the dial. The combination of relays I00, IOI, I02 and I03 convert the open period of each pulse into one-half cycle of line current, thus with digit 2 a complete cycle is sent out on the line, moving the selectors two steps; with the code 5, two and one-half cycles of line current would be sent which causes the selector wheels to move five steps.

When the operator inserts the dial plug 92 into the dial jack 94, ground on the sleeve of the jack 90 through the sleeve contacts of jack 94 and plug 92, dial pulsing contact 90 and the tip of the cord plug 92, lower armature and back contact of relay 9?, conductor 98, back contact and inner armature of relay 99, conductor I00, winding of relay I05 to grounded battery causes relay I05 to operate and transfer the toll line L from the talk jack 00 to the sending circuit. Relay I00 also operates at this time in an obvious circuit direct from the dial. The function of relay I00 is described later.

Relay 505, at its inner upper armature connects ground from the jack contacts by way of conductor 97 to the upper winding of relay I08 to cause this relay to operate. At its innermost upper armature and front contact relay I08 establishes an obvious circuit for relay 99. Relay I08, at its middle upper armature and front contact, holds relay I05 operated while relay 99 transfers the operating path of relay I05 from jack ground to a lock ground on its inner armature and front contact. At its lower armature and front contact relay I08 also prepares a locking path to the contact of relay I09 and, at its outermost upper armature and front contact, connects negative sending battery M0 to the filter circuit F. Relay 99 operated, connects positive sending battery I i I to the filter F and at its inner armature connects ground to hold relay I05 operated. The purpose of this sequence of operation of relays I05, I08 and 99 is to prevent the transmission of a click to a station which may be connected to the line during the plugging in of the dial plug 92.

The remaining contact on the dial jack 94, when closed, causes relay 91 to operate in an obvious circuit, which in turn causes the operation of relay I09. Relay I09 in operating completes a locking circuit for relay I08 by way of conductor 90 and the lower winding of relay I08 and closes the operating circuit for relay I02 which circuit extends from grounded battery, winding of relay I00, armature and back contact of relay IOI, front contact and lower armature of relay I00, conductor H0, upper winding of relay I02 to ground at the front contact and armature of relay I09. Relay I02, being shunted by the dial contacts does not operate at this time. The circuit is now in condition for the dial to operate the sending circuit.

The sending circuit consists of relay 503, retardation coil H4, condensers IE5, H0 and Ill, resistances IIS and H9 and retardation coil I20 which function to convert the reversals of current from relay I03 into a line current which is practically a sine wave so that, if a station is connected to the line during the signaling period, there will be no objectionable clicks.

On the first opening of the dial pulsing contact, relay I00 remains operated and relay I02, due to the removal of the shunt, operates and connects the pulsing contact circuit through its lower winding to relay IOI. On the closure of the pulsing contact after the first open pulse,

relay I02 remains operated on its lower winding and relay I0! operates opening the circuit to relay I00, which relay releases. Relay I00 released, opens the circuit to relay I03 which releases and reverses the line connections to sending batteries H0 and III, thereby reversing the current on the line corresponding to one-half cycle, which causes all selectors S associated with the line to advance one step.

On the second opening of the dial contacts 90,

relays IM and I02 release, closing the pulsing circuit to relay 500. At the closure, at the end of the second open interval, relay I00 operates, closing the circuit to relay I03 which again operates and reverses the line current, completing the second half of the first cycle and advancing the selectors S to the second step. Further opens and closures of the dial operate relays I02 and I0!, release relays I0! and 902 and reoperate relay I00 as follows: On the odd opens, relay I02 operates in series with relay I00 holding it operated. On the closure following an odd open, relay It! operates in series with relay I02 holding relay I02 operated and releasing relay I00. On the even opens, relays IOI and E02 release and all pulsing relays are normal. At the end of a digit, relay I00 may be operated, or relays IOI and I02 may be operated according to whether it was an odd or even pulse that had been last sent.

Assuming that the subscriber at station A gave the correct code to the operator and the operator in turn actuated the dial 93 in accordance with this code, the current reversals sent out by the pulsing circuit just described would cause the selectors S to advance and the selector having a contact, such as I22 corresponding to the calling line would remain in its operated position and all other selectors would restore to normal.

In the system disclosed, all the stations are normally disconnected from the line and are' selectively connected to the line by means of a selector S which has four contacts any one of which may be closed without affecting the relays connected to the other contacts. Any number of such selectors may be connected tothe line and any one of the four contacts on one selector can be selected and closed without closing a contact on any other selector on the same line. The code wheels of these selectors are set so that the same total number of steps is necessary to advance the code wheel to the first selected contact on all selectors that are to be used on the same line. In the system disclosed, the selectors will be set preferably for a total of 17 steps to the first code contact. The second, third and fourth code contacts require 19, 21 and 23 steps, respectively. In order to prevent the various selectors on the same line all stepping'up to the first contact the 17 pulses are sent. These impulses are broken into three sets of pulses totalling 17 in number. For example, in a selector having a selector number 7-6-4, the code to be dialed to select a station on the first contact would be 764; for a station on the second contact the code would be 766; for a station on*the third contact the code would be 768 and for the fourth contact the code would be 760. In like manner a second selector on the line having a number 7-73 would cause the four station contacts to be selected when the codes 773, 775, 777 and 779, respectively, are dialed.

In the case chosen for descriptive purposes, we may assume the selector individual to the group of common battery lines is numbered 764. With contact I22 as the first contact, the station A associated therewith would have assigned thereto the code 764, whereas the fourth contact, associated with subscribers station B would be reached by dialing 760.

When the code is comprised of a set of impulses totalling 19, 21 or 23, the selector contact passes over the intermediate contacts and causes current to flow for a short time through the connecting relay, such as I2, connected to that contact point. This relay is prevented from operating by means of the selector relay I29 and retardation coil I4I. The relay I23 is connected to the code wheel and the retardation coil MI is connected to the holding spring. During the pass-by time, relays I23 and the connecting relay, such as I2, are in multiple and the combination is in series with retardation coil MI. The connecting relay, such as I2, cannot operate under this condition as it does not receive sufficient current and relay I23 will not operate fast enough to short circuit the retardation coil I 4|. When the wheel comes to rest on a called terminal, relay I23 operates and short-circuits the retardation coil MI and allows the associated relay, such as I2 associated with the engaged contact to operate.

From the foregoing it will be apparent that when the operator dials 764, the contact I22 will be selected and relay I2 operated from grounded battery, winding of relay I2, conductor I29, contact I22 and selector brush to ground at the front contact and armature of selector relay I23. The operation of relay I2 connects the subscribers line I to the toll line and releases relay II which in turn causes the release of relay I 5. The operator removes the dial plug to verbally check the given number.

If the correct code had not been given, some other relay such as relay I25, H2 or I29, for example, would have been operated and the operator finding no party on the line would know that an incorrect code had been given.

At the end of a normal code the operator removes the dial plug from the dial jack 94 allowing relays 91, I09, I98, 99 and I95 to release in the Order named. The normal code combinations are such as to leave relay I99 normal when the plug is removed from the jack. Relay 9'! releases slowly, in turn, releasing relay I09. The

releasing time of relay 91 is sufficient to allow. the selector armatures to restore to their neutral position- When relay 9'! restores to normal it connects the pulsing circuit, that is, the Winding of relay I00 to the operated contact of relay I99 causing relay I00 to operate, in turn, operating relay I99 which sends a surge of current out on the line to move any operated selector from its holding position so that it will restore to normal. Relay I09 is slow to release in order to hold relays I08, 99 and I05 operated while this surge of current is sent out on the line. When relay I99 releases it opens the locking circuit for relay I 99 which relay releases fast and disconnects the negative sending battery II!) from the sending circuit and opens the circuit for relay 99. Relay 99 releases slowly to allow condenser II? to discharge through resistance I26 and for the energy in the windings of repeating coil I20 to dissipate before the line is out back to the talk jack 90. Relay 99 released, releases relay I95 which disconnects the sending circuit and reconnects the line to the talk jack circuit.

Disconnection At the end of the call the subscriber at station A replaces the receiver on' the switchhook where upon relay 95, (Fig. 2) which is operated over erating circuit for relay 39 which relay operates armature and front Relay 24 operated, causes an obvious circuit and connects ground to the interrupter relay 94 causing the operation of the interrupter.

Relay 29 causes the operation of relay GI over an obvious circuit, removes the shunt from rethe mid-point between resistance 40 and the interrupter to the shunting contact 38 thereof. This sets the interrupter into operation. When relay 29 operated it caused relay 4| to operate as previously stated. Relay 4| connects the

contacts

35 and 36 of the interrupter to the repeating coil 31. Relay M also disconnects the subscribers line and the winding through resistance .82.. Relay 19 released, opens the circuit to relay I 28 which is slow in releasing and which, in turn, opens the leasing and disconnects ground from the interrupter and relay 24, the latter releasing and causing the release of relays 29 and M. Relay 4| releases to disconnect the ringing current from the line. The period that the ringing current is connected to the line during the operation and release of the above-mentioned relays is approximately one-half second which is sufficient to operate ringing relays in the operators cord (not shown) associated with the talking jack 90, which relays cause the operation of a cord signal. Upon 6 noting the signal the operator may challenge to make certain that the signal is for disconnect purposes and then remove the cord plug from the jack 96. This act causes relay 5I to release and disconnects battery Ell from the simplex lead 55 whereupon all simplex relays, such as 28, re- .lease which, in turn, causes the release of relay I2 and restores the circuit to normal.

Outgoing call from magneto station In Fig. 3 there are shown two magneto stations C and D. For purpose of description it will be assumed that the subscriber at station C desires to establish a connection with the central office C. O. by way of the toll line L. In order to make such a call the subscriber operates the hand generator I39 in the usual manner for approximately one-half second. This causes the operation of relay I3I in an obvious circuit. If the toll line is not busy, relay 26 will be normal and providing no relay, on a common battery subscribers line is operated, due to a common battery subscriber originating a call, relay I25 will operate in a circuit extending from grounded battery I8, normal make-before-break contacts of chain relays I3, I6 and I1, conductor I32, upper Winding of relay I26, armature and front contact of relay I3i, conductors I33 and 25, lower normal make before-break contacts of relay i6 to ground at the normal make-before-break contacts of relay 28. Relay I25, at its two upper armatures bridges the subscribers line Hill across the toll line through condensers I34 and I35 and the ringing current from the hand generator I36 is thus connected from the subscribers line over the toll line L to the central ofiice. This current causes relay 56 to operate in the same manner as hereinbefore described in connection with a call to the central office originating at the common battery station A. The drop signal 88 is accordingly operated, tone connected to the toll line and 24 volt battery 56 connected to the simplex leg 55 in the same manner as previously described.

The connection of 24 volt battery 56 to the -implex leg 55 as in the previous case, causes elay 28 at the calling point, and all similar re- "tys at other points to operate to perform the functions hereinbefore described. Relay I26 in operating establishes a locking circuit for itself extending from grounded battery, lower winding of relay I26, lower front contact and armature of relay I26, conductors l3, M and E5 to ground on the right-hand armature and front contact of relay 28.

Relay 28 operated, opens up lead 21 to prevent any common battery line circuit operating the interrupter circuit ahd to prevent any relay, such as I44 in any other magneto subscriber line circuit at this point from operating its associated relay H2. The simplex relays, such as 28, at other concentrating points operate to open up the operating paths for other connecting relays such as I26 and i2, preventing stations at those points from connecting to the line in case they should try to originate a call. The call is answered in the manner already described.

Number checking such as relays I3, I6 or H,

given code. The apparatus functions in the same manner as already described in connection with number checking or a common battery line except that the selector S associated with the group of lines to which line Hill belongs would select contact I35 to cause the operation of relay I26 in an obvious circuit to connect the line tothe toll line L.

Disconnect After the conversation is completed in the case of a magneto subscriber, the subscriber rings off in the usual manner. This causes the supervisory lamp or signal associated with the operators cord (not shown) to be actuated.

Reuertive calls A calling subscriber, on either a common battery line or a magneto line calls the central office in the manner previously described and informs the operator that a connection with a second party is desired. When the operator learns that the called party is on the same line as the calling party, she instructs the calling subscriber to wait and removes the answering cord from the toll line jack to effect the release of all simplex relays such as 26 as well as the operated connecting relay, such as I2 or I26. The operator then reinserts the plug, dials the code of the called party and rings in the usual manner. When the called party answers, the operator informs the called party that she has a call, asks the called party to Wait and dials the calling party. When the connecting relay, such as I2 or I26 of the calling party operates as hereinbeiore described, the operator instructs the two parties to talk. No interruption to dialing will occur while the called subscribers receiver is oii the hook in the case of the common battery station because of the blocking condensers ii and I8 which prevent the shunt of the common battery supply circuits and the station subscribers set from interfering with the line circuits and because of the condensers i34 and I35 in the case of the magneto subscribers line circuit which prevent the shunt of relay I3I and the subscribers set from interiering with the line signals.

Lockout features Relay 28, one of which is connected to the simplex leg 55 at each concentrating point, prevents any station from connecting to the toll line as long as it is operated. All such relays operate when central office 24 volt battery is connected to the simplex leg as already described. When relay 26 operates, connecting relay I2, relay 43 and lockout-control relay 26 operate, the last placing ground on the lead 2| which, as will be noted, is included in the operating circuits for all relays such as i5 and 84 which circuit is completed when a corresponding relay, such as l6 or H operate in response to the initiation of a call by a subscriber at any station such as station A or B.

Any common battery station such as stations A and B which attempts to originate a call when the toll line is busy causes its associated line relay, such as relay II to operate which, in turn, operates the corresponding relay I3 to complete the circuit for relay I5 to ground on lead 2I at the upper armature and front contact of relay 26. The operation of relay l5, or relay 84 as the case may be, opens the operating circuit to relay I3, or IT, so that the energizing circuit to the connecting relay I2, or I25 cannot be completed.

The calling subscriber is accordingly locked out when attempting to seize the toll line when busy. Magneto subscribers are prevented from connecting to the line due to the fact that the lockout-control relay 26, which is operated, opens the lead 25 which controls the operation of the connecting relay I26, or H2, when their corresponding relay l3 or M4 is actuated in response to the initiation of a call at the station C, or D.

During the period after a common battery subscriber has initiated a call and before the central oilice circuit connects battery to the simplex lead, all other stations are prevented from connecting to the line at the same concentrating point by the two chain circuits through contacts of relays i3, I6 and ll. If the second call is originated by a line preceding the calling line, the relay, such as [6 or [7, in the preceding circuit is prevented from operating because battery is opened at the calling line relay, such as I3. If the second line is a succeeding line in the chain, lead 68 is opened at the preceding relay such as it or IT, thus preventing the connecting relay, such as 25. or l2 in the second calling line from operating when relay 28 operates.

On number checking, as hereinbefore described, the operator removes her plug from the jack 90 causing the release of all simplex relays 28 which release the connecting relay I2, I25, !26 or H2 as the case may be, thus disconnecting the calling party from the toll line. Relays I2 and 43, in the case of a common battery station, would release the latter opening the circuit to slow-to-release lockout-control relay 26. However, this relay holds ground on lead 2! long enough to effect the operation of relay 55 when relay I 3 operates in response to the reconnection of relay H to the subscribers station when relay I2 is released.

telay 15 would accordingly operate and lock to the armature of relay H and open the circuit to relay is which relay releases, opening the operating circuit to connecting relay I2. This relay accordingly cannot operate and the calling subscriber is disconnected from the toll line.

If the calling party were a magneto subscriber, the removal of the plug from jack 9!! releases the relay 28 and the operated relay, such as relay I 25 would release.

Call originating at central office- It is believed unnecessary to describe the circuit operations incident to the extension of a call originating at the central oifice and intended for any of the subscribers stations A, B, C or D, since such operations have been covered in detail under the headings of number checking, dialing and revertive calls.

Recall A subscriber may recall the central office operator after the operator has removed the dial plug from the jack after dialing. The magneto station subscriber can recall by operating the hand generator in the usual manner and the common battery station subscriber may recall by holding down the switchhook for approximately two seconds and then releasing it. This signal is passed to the operator by means of ringing current in the same manner as the disconnect signal, the only difference being that when the operator answers the recall signal, the subscriber is on the line when the operator challenges.

What is claimed is:

1. In a telephone system, a central office, a

toll line extending therefrom to a switching cen ter and having a simplex leg, a station at the switching center normally having access to said toll line and connected thereto as the result of the initiation of a call at the station, and means controlled from said central office by Way of the simplex leg of said toll line for disconnecting said station from said toll line and rendering the toll line inaccessible to the station.

2. In a telephone system, a central ofiice, a 10 toll line extending therefrom to a switching center, and having a simplex leg, a plurality of stations at the switching center normally having access to said toll line and one of said stations being connected to said toll line as the result of the initiation of a call thereat, and means controlled from said central office by way of the simplex leg of the said toll line for disconnecting the connected station from the toll line and rendering the toll line inaccessible to all of said 20 stations.

3. In a telephone system, a central oflice, a toll line extending therefrom to a switching center,

a plurality of stations at said switching center normally having access to said toll line, a lock- 25 out relay individual to each of said stations, a connecting relay for each of said stations, a relay individual to said toll line, and means including said last-mentioned relay responsive to the initiation of a call at one of said stations 30 for actuating the connecting relay individual to the calling station to connect the calling station to the toll line, said means also being controlled from said central oifice to release the operated connecting relay, operate the lookout 35 relay associated with the calling station and prepare an operating circuit for all other lockout relays whereby the calling station is disconnected from said toll line and said toll line is rendered inaccessible to all stations including the calling r40 station.

4. In a telephone system, a central oiiice, a toll line extending therefrom to a switching center and having a simplex leg, a plurality of stations at the switching center normally hav- 5 ing access to said toll line, a lookout relay for each of said stations, a connecting relay for each of said stations, and means including a relay connected in the simplex leg of said toll line responsive to the initiation of a call at one of said :50 stations for actuating the connecting relay of the calling station to connect the calling station to said toll line, said means also being controlled from said central ofiice to release the operate-d connecting relay, operate the lockout;55 relay of the calling line and prepare an operating circuit for all other lockout relays whereby the calling station is disconnected from said toll line and said toll line is rendered inaccessible to all said stations including the calling station.

5. In a telephone system, a central ofiice, a toll line extending therefrom to a switching center and having a simplex leg, a plurality of stations at the switching center normally having access to said toll line, a lookout relay for easingof said stations, a connecting relay for each of said stations, a relay controlled over the simplex leg of said toll line, a source of current at said central ofiice, means responsive to the initiation of a. call at one of said stations for con-r necting said central ofiice source of current to the simplex leg of said toll line to effect the operation of the relay controlled thereover, and means responsive to the operation of said simplex relay for actuating the connecting relay of, they calling station to connect the calling station to said toll line, said simplex relay also being controlled from said central ofiice to release the operated connecting relay, operate the lockout relay of the calling line and to prepare an operating circuit for all other lockout relays Whereby all stations including the calling station are rendered inoperative to initiate a call over said toll line.

6. In a telephone system, a central office, a toll line extending therefrom to a switching center and having a simplex leg, a subscribers line normally having access to said toll line, means including a relay controlled over the simplex leg of said toll line, responsive to the initiation of a call on said subscribers line for connecting said subscribers line to said toll line, means at said central omce for controlling said relay over the simplex leg of said toll line to cause the release of said relay whereby said subscribers line is dis connected from said toll line, and means operating in response to the disconnection of said subscribers line from said toll line for rendering the toll line inaccessible to said subscribers line.

'7. In a telephone system, a central office, a toll line, extending therefrom to a switching center, a subscribers line normally having access to said toll line, means responsive to the initiation of a call on said subscribers line for connecting said subscribers line to said toll line, and means effective, subsequent to the connection of said subscribers line to said toll line and controlled from said central office for disconnecting said subscribers line from said toll line and rendering said toll line inaccessible to said subscribers line.

8. In a telephone system, a cental office, a toll line extending therefrom to a switching center and having a simplex leg, a source of current at said central oiiice, a relay in the simplex leg of said toll line, means responsive to the initiation of a call at said station for connecting said central oihce source of current to said simplex leg to cause the operation of the relay therein, a connecting relay for said station operating in response to the operation of said simplex relay for connecting said station to said toll line, and means responsive to the seizure of the toll line at the central ofiice in response to an incoming call from said station for disconnecting said central oflice source of current from the simplex leg and substituting therefor another source of current whereupon said simplex relay remains operated, said means functioning upon the release of said toll line at said central office to release said connecting relay whereupon said station is disconnected from said toll line.

9. In a telephone system, a central ofiice, a toll line extending therefrom to a switching center and having a simplex leg, a source of current at said central office, a relay in the simplex leg of said toll line, means responsive to the initiation of a call at said station for connecting said central oflice source of current to said simplex leg to cause the operation of the relay therein, a connecting relay for said station operating in response to the operation of said simplex relay for connecting said station to said toll line, and means controlled by the operator at said central ofiice for efiecting the release of said connecting relay whereupon said station is disconnected from said toll line.

10. In a telephone system, a central office, a toll line extending therefrom to a switching center and having a simplex leg, a plurality of stations including a calling station at th switching center normally having access to said toll line, a connecting relay for each station for connecting its respective station to said toll line, a second relay for each station which operates in response to the initiation of a call at its respective station for preparing an operating circuit for its respective connecting relay, means controlled over the simplex leg of said toll line and operating in response to the initiation of a call at the calling station for completing the circuit to the connecting relay individual to the calling station, and means controlled by the operated second relay for rendering the second relays of all other stations unresponsive to the initiation of a call at its respective station whereby said toll line is rendered inaccessible to all other stations.

11. In a telephone system, a central office, a toll line extending therefrom to a switching center and having a simplex leg, a plurality of stations at said switching center normally having access to said toll line, a source of current at said central office, a relay controlled over the simplex leg of said toll line, a first relay for each of said stations, a connecting relay for each of said stations jointly controlled by its respective first relay and the relay controlled over the simplex leg, means responsive to the initiation of a call at one of said stations, for operating its respective first relay and connecting said source of current to said simplex leg to eifect the operation of the relay controlled thereover whereupon the connecting relay of the calling station operates to connect its respective station to the toll line, and means including armature contacts of the operated first relay for rendering the first relays of all other stations inoperative should an attempt to originate a call at any thereof be made.

12. In a telephone system, a central ofiice, a toll line extending from said central office to a switching center, a plurality of stations at said switching center, a source of tone at said central oflice normally disconnected from said toll line, means responsive to the initiation of a call at any of said stations for transmitting signaling current over said toll line to said central ofiice, and means at said central office responsive to the signaling current incoming over said line for connecting said source of tone to said toll line to produce an audible signal in the receiver at the calling station as an indication of the receipt of the call at the central ofiice.

13. In a telephone system, a central oiiice, a toll line extending therefrom to a switching center, a source of tone at said central ofiice normally disconnected from said toll line, connecting means at said central office for connecting said source of tone to said toll line, magneto and comrncn battery stations at the switching center having access to said toll line, and means responsive to the initiation of a call at any of said stations for efiecting the transmission of signaling current over said toll line to cause the operation of said connecting means whereby said tone source is connected to said toll line to advise the subscriber at the calling station of the idle condition of said toll line and that the call has been received at the central office.

14. In a telephone system, a central office, a toll line extending therefrom to a switching center, a source of tone at said central office normally disconnected from said toll line, connecting means at said central office for connecting said. tone source to said toll line, a common bat tery station at the switching center having access to said toll line, a source of signaling current at the switching center, and means responsive to the removal of the receiver at said station in initiating a call over said toll line for connecting said source of signaling current to the toll line to efiect the operation of said connecting means at said station of the idle condition of said toll line.

15. In a telephone system, a central ofiice, a toll line extending therefrom to a switching center, a source of tone at said central ofiice normally disconnected from said toll line, connecting means at said central ofiice for connecting said tone source to said toll line, a magneto station at said switching center having access to said toll line and having a hand-operated generator, and means responsive to the operation of the handoperated generator at said magneto station in initiating a call over said toll line for actuating said sponse to the initiation of a call at either of said stations for actuating said connecting means whereby said tone source is connected to said toll line to advise the subscriber at the calling station of the idle condition of the toll line.

17. In a telephone system, a central ofiice, a toll line extending therefrom to a switching center, a signal at said central office individual to said toll line, a source of tone at said central oflice normally disconnected from said toll line, a relay controlling the operation of said signal and of said tone source to said toll line, magneto and common battery stations at the switching center having access to said toll line, means at each of said stations effective in source connected to said toll line.

18. In a telephone system, a central office, a toll line extending therefrom to a switching center and having a simplex leg, a plurality of common battery and magneto stations at the switching center normally having access to said toll line, a relay in the simplex leg of said to-ll line, means including said relay responsive to the initiation of a call at any of said stations for connecting the calling station to the toll line and rendering the toll line inaccessible to all other of said stations, and means also including said relay and responsive to the seizure release and immediate reseizure of said toll line ofiice for rendering said toll line inaccessible to all of said stations including the calling station.

LAN GFORD J. BOWNE.