US2444033A

US2444033A - Butt-in telephone system

Info

Publication number: US2444033A
Application number: US487196A
Authority: US
Inventors: Cohrt Eigil
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1940-08-22
Filing date: 1943-05-15
Publication date: 1948-06-29
Anticipated expiration: 1965-06-29

Description

June 29, 1948. E. COHRT- 2,444,033

BUTT-IN TELEPHONE SYSTEM Filed May 15, 1943 v v 2 Sheets-Sheet 1 INVENTOR 1576/4 coy/Pr AGENT June 29, 1948. E. COHRT BUTT-IN TELEPHONE SYSTEI J 2 Sheets-Sheet 2 Filed May 15, 1943 INVENTOR 516/1 (pa /e7- AGENT.

Patented June 29, 1948 UNITED STA-res BUTT-IN TELEEHONE SYSTEM Application May 15, 1943, Serial No. 487,195 in Denmark August 22, 1940 7 Claims. 1

The present invention relates to automatic private branch telephone exchanges in which conversational connections between subscribers take place through cord circuits and no busy tone is given when a subscriber is reached who is already connected to. a conversational circuit.

Ordinarily, a. caller selecting a busy subscriber is not admitted on this subscribers connection but receives a busy tone. In P. B. Xs for quite special purposes it is necessary, however, that a connection is always established immediately. In such case, it is desirable to send to the subscribers carrying on the original conversation or signal indicating that still another subscriber has joined the connection. It is thus possible for a comparatively great number of subscribers to simultaneously carry on a conversation with one another. P. B. Xs thus present problems which do not exist in ordinary systems.

.An object of the present invention is to provide a P. B. X circuit in which a subscriber can be released. without other subscribers, talking over the same cord circuit, being released.

Another object of the invention is to provide means whereby asubscri'ber can be released from the connection over which he originally talked and continue the conversation with a new :subscriber connected to his line.

In brief I accomplish these and-other objects of the present invention as will become more apparent hereinafter, in the following manner:

Thecord circuits according to the present invention include a device by means. of which a cord circuit at call from a subscriber, who wants to talk to subscriber who is engaged by a conversational connection through another cord circuit, is connected to this latter connection and moves to listening-in position. In the latter position, a warning tone is flashed to the busy subscribers, and the same is used to lock the original cord circuit as long as at least one of the subscribers who was originally connected to it, is engaged by a conversational connection.

The invention will be more readily understood from the following description thereof and the accompanying drawings which illustrate an embodiment of the invention, by way of example. In the drawings- Fig. 1 illustrates a subscriber line circuit and a starting circuit;

Fig. 2 illustrates a cord circuit according to the invention; and

Fig. v3 illustrates a circuit for unused lines.

In the subscriber line circuit and starting circuit shown in Fig. 1, each subscriber line is provided with a combined line and cut off-relayLr, whereas a pilot relay Sr and a test resistance are common. to a maximum of twenty line circuits.

Astarting relay Urr is common toall the subscriber lines of the unit. When a subscriber desires to make a call and lifts the telephone off the cradleat his station, .a line loop is closed, and relay Lrtis half. attracted and .closes its right middle front contact; it is not sufiiciently energized for breaking its other contacts.

Thepilot relay Sris enengizedfollowed by relay Urr which supplies ground connection to the starting relays in the cord circuits.

The calling line is characterized by testpotential on the contact c (Fig. .2) of the line finder arc. All idle line finders rotate, and when one of these has found the calling .line it stops, and direct ground connection isgiven from the cord circuit .to the 0 wire, whereby relay L1. is energized strongly, so that. it. is entirely energized and separates itself from the a and b wires, after which the relays Sr and U11 are released, and the other rotating line finders stop. The test battery is interrupted at the right innermost back contact of .relay Lr.

When a line selector at call to a subscriber is adjusted to a subscriber, direct ground is connected to the 0 wine, so that relay L7 .is energized entirely and is interrupted from the a and 1) wires.

The cord circuit shown in Fig. .2 consists of a 50 point line finder SIVDF, one, or possibly two line selectors SMSI and SMSZ, and a group of relays. The exchange has a capacity of '50 subscribers, when the line selector SMS] is applied alone, while a capacity of 99 subscribers is obtained when the extra line selector SMS2 is applied too.

Connections to idle subscribers are established in the ordinary way, but no busy tone is given in case of a call to a busy subscriber. In this event, the connection is established immediately after the warning tone has. been sent which indicates to the talking subscribers that a third party has just joined the connection.

The cord circuit, over which the original conversation was established, is thereupon lockedso long as a conversation is carried on with the originally calling or originally called subscriber, or possibly both. The other cord circuits, over which connection is established to a busy line, move to listening-in position, so that microphone feeding current is supplied from the original cord circuit-only. I

When a calling subscriber lifts the telephone off the cradle, the line relay is energized and gives starting potential to the starting relays Lsr of the cord circuit, which relays energize over a jack Ba and battery on the outermost left back contact of relay Ar. The line finder SMF rotates by means of the following circuit: battery, a resistance, the magnet SMFM, the interrupter of this magnet, back contact of relay Dr, a front contact on relay Lsr, a back contact on relay Pbr, a back contact on relay Ltr, a normal contact on a selector SMSZ, normal contact on the selector SMSI, the a are of selector SM in normal position, back contact on relay Ar, back contact on relay Asr and ground.

The line finders SMF in all idle cord circuits rotate and hunt for the calling subscriber who is characterized by test potential on the e contact of the line finder arc, to which the test relay Ltr is connected over the outermost left front contact of relay Lsr.

When the line finder reaches the contact corresponding to the calling subscriber, the test relay is energized and interrupts the circuit for the line finder magnet, so that the selector SMF stops. Via the front contact of relay Ltr and the back contact of relay Tcr as well as the innermost right front contact of relay Lsr ground connection is established through an 1800 ohms resistance on relay Bar to relay Br, which is energized slowly in order to prevent two cord circuits from being connected simultaneously to the same subscriber, relay Pbr being energized via the outermost right front contact of relay Lsr. Relay Pbr connects ground to the 6 ohms winding of relay Ltr, whereby double connection is prevented in known way, because two relays Ltr cannot be energized simultaneously when their 6 ohms windings are inserted.

When relay Br closes its front contact, a circult is closed for relay Dr, which is attracted and through-connects the a and 1: wires to a feeding relay Asr which is energized, while at the same time ground is connected to the wire of the subscriber line via the 0 brush of the line finder, whereby the line relay is entirely energized and switches off the subscriber line and interrupts the starting ground and the test battery. All the other rotating finders stop and from a front contact on relay Dr a circuit is closed for relay Ar which is energized. Relay Ar interrupts the battery from relay Lsr, which, however, is already released, so that it can no longer be energized; relay Ltr was released together with relay Pbr when the test battery was interrupted, whereas relay Br is kept energized through a resistance of 2000 ohms on relay Har from the front contacts of relay Asr. Relay Cbr is energized over the outermost left front contact of relay Har from ground through a pilot relay in the ringingand tone-circuit; the starting of the tone signal is obtained via the front contact of relay Tor.

The following circuit is closed for relay I-Isr: battery, left outermost front contact on relay Ar, front contact on relay Cbr, a resistance, winding on relay Hsr, back contact on relay Ftr, back contact on relayOtr, back contact on relay Rcr, right innermost front contact on relay Ar and ground.

Relay Cbr is then kept energized over the innermost left front contact of relay I-llsr from ground in the ringingand tone-circuit in parallel connection with relay Tor, which is energized over another front contact or relay Hsr. The 2000 ohms resistance on relay Har is Short-circuited over the right innermost front contact of relay Hsr, so that relay Br is locked direct from the front contact on relay Asr, whereby it is saturated and hence slow in releasing.

Dialing tone is sent to the calling subscriber in the following circuit: dialing tone generator, left front contact on relay Br, Te M1 condenser, the b are of the selector SM in normal position, left middle front contact on relay Ar, uppermost back contact on relay Ftr, a condenser and the a wire of the subscriber line.

The subscriber dials the first digit of the wanted number and relay Asr transmits the impulses via its back contact to the magnet SM in the following circuit: ground, back contact on relay Asr, left innermost front contact on relay Hsr winding on relay Lmr, back contact on relay Tcr, winding on the magnet SMM, a resistance, battery.

Whenthe selector SM has made the first step the dialing tone is interrupted.

Relay Lmr is energized during the impulsing, and closes via its front contact the following circuit for relay Har: battery, winding on relay Har, front contact on relay Lmr, back contact on relay Tcr, back contact on relay Lsr, innermost left front contact on relay Har and to ground.

Relay I-Iar is energized and locked to ground on relay Dr over its middle left front contact,

after which it interrupts its own magnetizing circuit at its innermost back contact.

Relay Ltr is energized after the release of relays Lsr and Pbr in the following circuit: ground, a winding on relay Ltr, back contact on relay Pbr, front contact on relay I-Isr, marking line l, are c of selector SM in normal position, a resistance, and battery.

When the first impulse has been received and the selector SM has made one step, relay Har is energized as already mentioned, and the following circuit is closed for the magnet SMSIM: battery, a resistance, the magnet SMSIM, its interrupter, right innermost back contact on relay Sdr, outermost right front contact on relay Har, outermost right back contact on relay Tcr, back contact on relay Ltr. 'I-Iowever, inasmuch as relay Ltr is energized, as already mentioned, the selector SMSI rotates only if the first digit consists of two or more impulses.

As soon as the selector SM releases the marking lin No. 1, the circuit for the magnet SMSlM is closed, whereby the selector SMSI rotates. When the first digit is received, relay Asr remains energized, whereas relay Lmr is released.

When the selector SMSI reaches the marking line on which the selector SM is standing, a circuit is closed for relay Ltr via the e are and e brush of the selector SMSI, and this relay is energized and stops the selector. The following circuit is closed for relay Tcr after the release of relay Lmr: ground, right middle front contact on relay Ar, front contact on relay Ltr, back contact on relay Tcr, back contact on relay Imr, front contact on relay Har, winding on relay Tcr and battery.

Relay Tcr is energized and locked via its outermost left front contact to ground on relay Ar and opens at its outermost right front contact the circult for the selector SMSI, so that the finder SSI cannot rotate any more.

If the capacity of the exchange exceeds 50 lines, relay Sdr is energized by the tenth digits 6, 7, 8, 9, 0 via the d arc of the selector SM and chan es over from the line selector SMSI to SMSZ.

ascr bes Thesubscriber. now selects the units digit and relay Asr operates in accordance with the dial. The: impulses are transmitted direct to the magnet of the line selector viathe following circuit: ground, back contact on relay Asr, front contact onrelay'Hsr, winding on relay Imr, front contact on relay Tcr, contact on relay Sdr, winding on the magnet SMSIM, 48 ohms resistance and battery. -Relay Lmr is energized during the .impulsing and closes the following circuit for relay Pbr: battery, winding on relay Pbr, left innermost front contact on relay Tcr, front contact onrelay Lmr, left middle front contact on relay Har, frontcontact on relay Dr and to ground.

Relay Pbrcloses the following circuitfor relay Rcrtbattery; winding on relay Rcr, left middle front contact on relay Pbr, back contact on relay Ftr, back contact on relay Otr, back contact onrelay Rcr, right innermost front contact on relay Ar and to ground.

Relay Rcr is locked via its own front contact to ground via the back contacts of relays Otr and Ftr and interrupts its own magnetizing circuit. Relay Ltr is released when the selector SMS'l leaves the marking line.

When the units digit has been received, the selector SMSI is adjusted to the line of the wanted subscriber, and relay Asr remains energized, whereas relay Lmr is released.

When relay Lmr is released after the last digit has been received, relay Pbr is released (which was locked'over the front contact of relay Lmr) and the following circuit is closed between the line of the called subscriber and relay Ftr: battery, winding on relay LT (line circuit), 0 line, the 0 brush of the line selector, front contact on relay H winding on relay Fir, front contact on relay 'Icr, left front contact on relay Cbr, right innermost back contact on relay Pbr, back contact cnrelay Ltr, right middle front contact on relay A and to ground.

It should be noted that when relay R0?" was energized, the energizing circuit for relay Hsr was interrupted, this relay re-mains, however, energized via the left middle front contact of relay Pbr in parallel connection with relay Tcr during the impulsi-ng. After the release of' relay Pbr, the circuit for relay I-Isr is interrupted,

but since this relay releases slowly, it allows relay Ftr to energize in case of connection to an idle subscriber via its innermost right front contact. When relay Ftr closes its uppermost front contact it is locked in following circuit: battery, winding on relay Fir, front contact on relay Fir, winding on relay Ftr, front contact on relay Tor, front contact on relay Cbr, back contact on relay Pbr, back contact on relay Lit, right middle front contact on relay Ar and ground.

Relay Lr of the subscriber line is energized in series with relay Ftr, and when relay Hsr closes its right innermost back contact it remains energized from direct ground connected to the 0 line in following circuit: battery, a wmding on relay LT (line circuit), the c brush of the line selector, right innermost back contact on relay Hsr, lowest front contact on relay Fir, right front contact on relay Cbr and to ground.

After the release of relay Hsr relay Chi is un der control of relay Rcr via the lowest front contact of this latter'relay.

Ringing signal is sent to the called subscriber via following circuit: ringing generator, front contact on relay Rc'r, winding on relay Csr, right innermost back contact on relay Otr, lowest front 15 contact onrelay Ftr, biline, thesubscrlber apparatus, a line, uppermost front contact on relay Fir, lowest front contact on relay R01, innermost right front contact on relay Ar and ground.

The 750 ohms' winding of relay Csr is shunted by a winding on relay Rcr, whereas itsother winding is sh-ort-circuited by ground on the a wire, so that relay Csr is made slow in becoming energized.

Callback toneis sent to the calling subscriber from the left outermost back contact of relay PM 'via' a front contact on relay R011 and the 17 wire.

When the called subscriber lifts the telephone off the cradle, the line loop is closed, whereby relay Csr receives sufiicient current through its right winding for energization, and since relay Rcr is locked via a back contact on relay Csr, this relay is; released immediately and interrupts the ringing and the call back tone and throughconnects the conversational connection viatw condensers.

Relay Cs'r remains attracted via the a and b wires in series with the called subscriber apparatus and provides microphone feeding current. The conversational circuit is now closed between the calling and the called subscriber.

Relay Cbr, the magnetization circuit of which is to be interrupted by relay Bar, is then kept energized from the left front contact of relay Csr. When relay Bar is released the connection to theringingand tone-circuit is interrupted by relay Rcr. and this circuit stops. 1

During the conversation the cord circuit is under control of the calling as well as the called subscriber. If the calling subscriber restores the telephone handset to the cradle at his station, thereby normally disconnecting or d sengaging the station, the cord circuit is released, and the calling as well as the called subscriber are released immediately. In. case th called subscriber restores his telephone first. he releases himself immediately. whereas the cord circuit is not released until the calling subscriber restores his telephone.

When the calling subscriber restores his telephone relay Asr is released so that relay Br, which after the release of relay Hsr was looked through a 2000 ohms resistance on relayHar, is released and interrupts the ground connection on relay Dr which is released and interrupts the sub- .scriber line from the cord circuit. Relay Dr interrupts the locking circuit for relay Ar which is released and interrupts the locking circuit for relay Tor which also releases. Relay Fir is released together with all the other relays in the circuit.

The selector SM rotates to normal position by a circuit Via its contact arc a and its interrupter. When it reaches normal position a circuit is closed for the line selector via its home contact and interrupter, and the line selector moves to normal position, after which the cord circuit is I released and ready for new calls.

When the called subscriber is released. relay Csr is released, the line loop is interrupted, and the circuit for relay Clir is interruptedso that this relay is released slowly. Ground on the 0 wire, which kept the line relay energized, is in terru-pted and the line becomes idle. At the same time the locking circuit for relay Ft-r is opened bythe left frontcontact of relay CM, and relay Ftr is released and disconnects the called subscriber from :the cord circuit. The cord.- circuit itself is not released until the calling subscriber restores the telephone as explained above.

In case of a call to a busy subscriber, relay Ftr cannot attract the armature when the wire is being tested, a direct ground connection being found from the cord circuit, over which the original conversation was established.

Relay Ftr then remains in normal position after the units digit has been sent, and relay Hsr is released. Relay Tor is released slowly after the release of relay I-Isr and a warning tone is sent during the releasing time'of relay T01- to the talking subscriber via the following circuit: dialing tone generator Sg, left front contact on relay Br, condenser right outermost back contact on relay Hsr; left front contact on relay Tor and the bbrush of the line selector.

This tone informs the talking subscribers that athird subscriber has joined the connection.

The following circuit is closed for relay Otr which is slow in getting energized: battery, winding on relay Otr, left innermost front contact on relay Tc'r, back contact on relay Tor, lowest back contact on rela Ftr, front contact on relay Cbr and to ground.

Relay Otr is energized and interrupts the locking circuit for relay Rcr, which is released and interrupts the feeding relay Csr from the a and b Wires. The calling subscriber is now through connected to the busy subscriber via the innermostfront contacts of relay 0151', so that the calling subscribers may now talk to the busy subscriber. Relay Cbr is kept energized via a front contact on relay Otr and a back'contact on relay Csr. Via the right outermost front contact of relay Otr ground is connected to the (1 brush of the line selector, and via the d multiple wire this ground is carried to the cord circuit, over which the original conversation was established, and maintains it, so that it cannot be released which must not happen, since the microphone current is fed from there.

When the calling subscriber is released the cord circuit is released as already mentioned, and rela Otr interrupts the ground connection from the d multiple wire, so that the busy cord circuit is released in normal way.

During a normal conversation with an idle sub scriber, the relays KOTl and KO'Iz are connected via the relays Dr and Ftr, respectively, to the d brushes of the line finder and the line selector. In case of a call to a, busy subscriber the cord circuit, which went to listening-in position, as explained above, connects ground to the d multiple wire, so that relay Kori is energized, in case the call is to a calling subscriber, and relay Ken is energized, in case the call is to a called subscriber.

At call to a callingsubscriber, relay Kori is energized as explained and. connects ground to the relays Ar and Dr, which are in this way under control of the cord circuit in listening-in position, and the cord circuit is, therefore, locked as long as conversation takes place to the calling subscriber.

- At call to 9. called subscriber, relay Korz is energized and connects ground to relay Ar, which is locked and locks the cord circuit.

At call to a calling subscriber, where the called subscriber is released, the cord circuit is locked via relay KOTI, and when the called'subscriber in the original conversation restores his telephone, relay Csr is released followed by relay Clrr.

.Relay Cbr interrupts the ground from the c line of the called subscriber, and relay Ftr is released, when relay C'b-r interrupts its left front contact, so that the called subscriber is free.

At call to a called subscriber, where the calling subscriber is released, relay Asr is released followed by relay Br. Relay Dr'is released and interrupts the calling subscriber from the cord circuit, whereas the cord circuit (as aforementioned) is locked from the front contact of relay KOTz. When the conversation is finished, relay KOTz is released and interrupts the connection to relay Ar, which isreleased and releases the cord circuit.

On simultaneous calls to the calling as well as the called subscriber, relay Kan as well as Korz are energized. If it is desired to interrupt the original conversation and the called as well as the calling subscriber want to continue with the new conversation, they may interrupt the existing connection by depressing the cradle for a moment. When the calling subscriber depresses the cradle relay Asr is released followed by relay Br, but, since relay Kori, is energized, relay Dr cannot be released. Via the back contact of relay Br and the front contact of relay K07). a circuit is closed for relay T'br, which is energized and locks. The relay Asr and Br are energized a moment later. The original conversation is now interrupted by relay Tbr, and feeding current is supplied from the relays Asr and Csr to the calling as well as the called subscriber.

When the called subscriber depresses the cradle, relay Csr is released, followed by relay Cbr. Relay Ftr is not released, since it is kept energized via the lowest front contact of relay KOTz. At the same time, relay K012 replaces the ground on the outermost right front contact of relay Cbr, so that the line relay is kept energized. The following circuit is closed for relay Tbr: battery, winding on relay Tbr, lowest front contact on relay Kor, left back contact on relay Cbr, back contact on relay Pbr, back contact on relay Ltr, middle right front contact on relay Ar and to ground.

Relay Tbr interrupts the talking circuit between the calling and the called subscriber. When relay Csr energizes again, it is followed by relay Cbr.

The cord circuit will not be able to be released until relay KOTI as well as Kora are released, i. e., when conversations are no longer taking place to the calling or called subscriber.

It should be noted that when the conversation to the calling or called subscriber is interrupted, he will be released from the cord circuit as above explained.

In case a tenth digit is dialed, which is not used for subscriber numbers, a busy tone is given via the b are of the selector SM to the calling subscriber.

Fig. 3 shows a circuit for unused lines. 7

In the usual telephone systems an unused line is characterized by an interrupted c line on the c are of the line selector, which causes the cord circuit to send a busy tone. In the P. B. X without test no busy tone is sent, for which reason it is necessary to connect a circuit for unused lines to the line selector arc and interrupt the normal line equipment belonging to unused lines.

When a call is made to an unused line, relay Cor is energized and starts the tone. The cord circuit moves to ringing position, but due to the presence of a 500 ohms induction coil, it instantly moves to talking position, after which the busy tone is sent via the front contact of relay Cor t0 the calling subscriber, who then restores the telephone and releases the cord circuit.

It will be clear that many changes may be made in the construction and arrangement described above without departing from the spirit and scope of the present invention. I therefore do not wish to be understood as limiting myself to the details of construction and arrangement set forth herein.

I claim 1. An automatic private branch telephone exchange of the type permitting a conversational connection between a first and second subscriber, and in which a third subscriber can be connected to the first or second subscriber without receiving a busy signal, being thus enabled to participate in the conversation, comprising in combination a plurality of cord circuits, a telephone subscribers station associated with each cord circuit, first means for interconnecting at least a pair of said stations over the respective cord circuits to establish a conversational connection, second means for interconnecting at least one of the remaining cord circuits to said conversational connection for participation in any conversation over said conversational connection, control means operatively connected to said second means for sending a Warning signal to the receivers connected to the original conversational connection when one of said remaining cord circuits is connected to said conversational connection, said contnol means also locking said original conversational connection as long as one of the stations of the original conversational connection remains connected, whereby the subscribers on the original conversational connection are advised by said warning signal when a new subscriber cuts himself in, and conversation with such new subscriber may be continued, due to said locking action, as long as one of the subscribers on the original conversational connection remains in the circuit, though the other cord circuits are interrupted.

2. The system claimed in claim 1, in which said control means includes coupling means actuated by said second means when one of said remaining cord circuits is connected to said conversational connection, whereby said conversational connection is looked as long as conversation takes place over said connected remaining cord circuit.

3. The system claimed in claim 1, in which said control means includes a relay actuated by said second means when one of said remaining cord circuits is connected to said conversational connection, whereby said conversational connection is looked as long as conversation takes place over said connected remaining cord circuit.

4. The system claimed in claim 1, comprising a relay connected to said conversational connection and actuated by manual disengagement of one of the subscribers stations thereof, said relay being adapted to release said disengaged station from its cord circuit.

5. The system claimed in claim 1, in which said conversational connection comprises two connected cord circuits, a first and second subscribers station associated with said two cord circuits, a first relay connected. to and actuated by said first receiver, said first relay being adapted to disconnect the cord circuit appertaining to said first subscribers station, when the latter is manually disconnected; a second relay connected to and actuated by said second subscribers station, said second relay being adapted to disconnect the cord circuit appertainin to said second subscribers station when the latter is manually disconnected.

6. The system claimed in claim 1, in which said control means includes a relay actuated by said second means when one of said remaining cord circuits is connected to said conversational connection, whereby said conversational connection is looked as long as conversation takes place over said connected remaining cord circuit and in which said conversational connection comprises two connected cord circuits, a first and. a second subscribers station associated with said two cord circuits, a first relay connected to and actuated by said first station, said first relay being adapted to disconnect the cord circuit appertaining to said first station, when the latter is manually disconnected; a second relay connected to and actuated by said second station, said second relay being adapted to disconnect the cord circuit appertaining to said second subscribers station when the latter is manually disconnected, all said relays being connected in such a way that upon a simultaneous call to said first and second stations, while the original conversational connection still subsists, the subscriber at said first or second stations may interrupt said original conversation and continue with the new one by momentarily disconnecting the respective station.

7. The system claimed in claim 1, comprising signalling means associated with said cord circuits, said signalling means bein adapted to send a busy signal over a cord circuit when a subscriber in said circuit selects a non-existing number.

EIGIL COHRT.

REFERENCES CITED FOREIGN PATENTS Country Date Denmark Aug. 2'7, 1945 Number