US2102953A - Automatic telephone system - Google Patents

Description

Dec. 21, 1937. A. HEYDUCK UTOMATC TELEPHONE SYSTEM Filed Nov. 23, 1935 N `larin- Pw e.

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Patented Dec. 21, 1937 AUTOMATIC TELEPHONE SYSTEM;v

Alfred Heyduck, Berlin-Neuenhagen, Germany, assigner to Mix & Genest Aktiengesellschaft, Berlin-Schoneberg, Germany, a company Y Application November 23, 1935, serial No. 51,251 In Germany November 27, `1934 16 Claims.

The invention refers to automatic telephone systemsr and more particularly to those arrangements for selectors thereof, by which the station of a favored subscriber, for instance, can be switched to busy lines, and it has for its object to speed up the operation of such arrangements. This is accomplished in the following 'mannerz the selector, after having been engaged, will automatically step on, in response to each energizami; tion given by the station, to the next busy line and' will stop there. VConsequently it is not first necessary for the subscriber to. listen whether a line with which he happens to be connected, is free or busy, but he has the assurance fromv the la; beginning that he will be connected only with busy lines; that is to say, he will be connected only with those lines over which conversations are then taking place. i

'Ihe energization can be given through loop @y interruptions or by pressing a key. Interruption of the loop has the advantage that the sub-z scriber is in a position to skip a certain number of lines at once by Vselecting a number corre-A spondingly higher than 1, a 0 for instance. Through test switching means the circuit of the selector magnet, established by the impulse receiving device, is automatically maintained until the next busy line has been reached. In order to prevent the selector from stepping on automatically as soon as a line on which the subscriber is just listening in becomes free, the test circuit is closed only temporarily.

The selector also steps on automatically over dead contacts, which can be accomplished, for instance, by connecting the dead contacts; in the test bank to the same potential (battery) as the free lines. If the station has stepped theselector over all the lines, it will receive a warning signal indicating that all the lines have been 49 passed. Appropriately, the signal is connected to the rest position of the selector, so that it will serve at onceas a selector signal and, after passing overv all the contacts, as a warning signal. This has the advantage that the listening selector can be used at the saine time as a traiiic meter device. That means that all the subscriber has to do is to count how many times he has to press the key or how many times he has to dial digit 1, respectively, in order to hear the acoustic signal again. The number of pressings of the key or the number of dialings, respectively, exceeds then by 1 the number of lines which are busy at that moment.

It may now be desirable that it should also be possible for the subscriber to switch over to a specific line, regardless of whether it is busy orfree. This happens, for instance, if the listen- -ing selector is connected directly to P. B. X.

subscribers lines and if the favored station wants' 5. to watch the traffic or the calls of a particular subscriber. For this purpose it is possible to provide switching means which, depending on switching measures of the favored station, permit of changing the listeningfoperation of the selector in such a manner that the movement of this selector will be brought exclusively under the favored control of the station, an automatic stepping up of the selector thus being prevented. The invention is by Way of example explained hereafter with reference to the accompanying single figure of the drawing, which is a schematic circuit of an incorporation involving private branch exchanges with selector operation. In this embodiment calls within the P. B. X. exchange are set up over local interconnecting trunks or links, whereask outside calls to the main exchange are connected to the outside trunk lines by separate outside trunk selectors which are associated with the outside trunks and which find the calling P., B. X. lines. The arrangement according to this incorporation operates in such a manner that, if a favored station calls a special number so as to drive the impulse receiver (i. e. the stepping switch of the local trunk) to a certain contact or to a certainv group of contacts, certain switching devices will be prepared which will upon the release of the local trunk connect the favored P. B. X. station with the listening selector. The outside trunk lines are connected to the listening selector.

vThe private branch exchange shown in the drawing consists of local .trunks such as AS-LW and an outside trunk line selector AW, associated with outside trunk lines such as AL. Only one local trunk vand one outside trunk line with its outside trunk selector have been shown. The drawing also shows a listening selector AH (operated by a magnet MhW), over whose speech switching arms the favored P. B. X. station, rep- 45 resented in the drawing, can step up to the outside trunk lines. The connection in this case goes over a monitoring coil MPL-Ue, which is of such dimensions that the existing outside call will be only slightly damped through the listening in. For this purpose the primary winding has a larger number of turns than the secondary winding; condensers C2 and C3 may amount, for

instance, to 0.5 mf.

A description will rst be given of local P. B. X. 55

connections and outgoing trunk line connections. Since known switching operations are here lnvolved, the details of the respective circuit arrangements are not shown.

The relays are denoted by capital letters, their contacts by the respective small letters.

A local P. B. X. connection is started simply by removing the receiver at the P. B. X. station N. Line relay R is energized over the followin circuit: i

-|-, RI, mhIV, tII, N; thence partly through tI, mhII, resistance (T) and partly through TI, TI,

Relay T can not operate in this circuit because it lies in shunt to the resistance (T). By the operation of relay R however common relay Anh is energized, this being the starting relay for the local trunks: ground, TV, tIII, Anh,

At rI the winding ,TI of relay T is definitely separated and at rII the test circuit for AS is prepared. By the pulling up of relay Ahh line finder AS of a free local trunk is started by well known means which are not shown in the drawing'. If the calling line is found, the following test circuit is established: ground, PHII, PHI, c-arm of AS, TII, thence through RII and TII in parallel,

Relay PH locks at phI over its low resistance winding I and thereby provides a busy indication by lowering the test wire potential to prevent the intrusion of other connections in known manner. At phII and phIII the speech path to the supply bridge A, X of the line finder is switched through. By the pulling up of T the calling potential of the subscriber line is removed at tI and tII.

The P. B. X. subscriber now receives dial tone and with the aid of his dial is in a position to set the line selector LW to the desired P. B. X. station by well known means not illustrated. When the call has been thus set up relay P serves as test relay and relay Y as supply relay for the called party.

If the P. B. X. station wishes to establish an outside trunk line connection, the P. B. X. subscriber will press the ground key n after lifting the receiver. Winding RI is thereby short-circuited, wl'iile on the other hand relay T can operate due to the amplification of current in its winding I. At contact tI the shunt eld for winding TI is eliminated and at contact tII relay R is switched off and the subscribers line wire is switched instead over rest contact rIII to common relay Amr., which serves as starting relay for outside trunk connections. The test circuit for the outside trunk selector is prepared at tv.

By the pulling up of relay Ana the outside rimk selector AW of a free outside trunk line AL is energized by means not specifically shown so as to hunt for the calling subscriber. If this connection is found, a test relay (not shown) pulls up over the cZ-path of the outside trunk selector in series with RII and TII. Relay R is also operated by the connection whereby the call potentials are removed from the line, namely at rI and TIII. At TII the test circuit over the dpath is broken, but the low test-wire potential is maintained in known manner over the c-path arm of AW and consequently relays R and T remain energized. The P. B. X. station N is now in connection with the outside trunk line and is in a position to call the desired outside exchange subscriber, as for example by dialing if the out-v side exchange is of the automatic type.

If line finder AS of a local trunk has already been set to the calling line before the grounding key is pressed, differential relay X of the line finder is caused to operate through the pressing of the key n and by opening the holding circuit oi the local trunk at contact :c it causes this trunk to be again released. Otherwise the switching operations are the same as `described in the preceding paragraph. v

If a subscriber at the favoured P. B. X. station Y N wishes to listen in on the outside trunk lines,

he begins rst 4of all by lifting the receiver, whereby he causes a free line nder AS to be Set to his line, and he then dials the number 00. Winding VhI of a relay Vh is connected to the battery and is led to contact il@ of the c-path of line selector LW. As soon as the line selector is set to this contact, test relay P of the line selector operates and in series operates relay Vh. Furthermore, a. contact aI of impulse relay A oi the local trunk is connected to contact il@ of the rt-path of line selector LW. Consequently, supply relay Y of the line selector is energized at once over its winding I and the call current is thereby switched off by the usual means (not shown) which ordinarily takes effect when a called subscriber answers. After relay Y has pulled up, the following circuit is established: ground, YII, b-arm of LW, d-arm of AS, y, darm of LW, MhII, mhiV, MhlII,

Slow acting relay Mhl starts to operate in this circuit. As can be seen from the drawing, the cir- Cuit flows over switching arm d of the line finder. This gives the assurance that relay Mh! can be reached only by certain stations, that is to say by favored P. B. X. stations. The :i3-contacts of AS are not wired at the other P. B. X. stations.

Relay Mh! locks over the c-arm and its con,- tact mhlII, and at once opens its energizing circuit at mhlV. Relay Mh is energized at mhiI. At mhlIII the c-contact of the line finder is grounded and relay P of line finder AS is thereby caused to release through short-circuiting, so that the local trunk is released. Consequently, through interrupting the c-path of LW the holding circuit of relay Mhl is opened. After a delay interval relay Mhl therefore releases. However, relay Mh is maintained in the following manner: on releasing the local trunk relays R and T are released, so that contacts tI and tII return to their rest position. 'Ihe following circuit is thereby established: MAI, DI, mhII, tI, N, tII, mhIV, DII, MAII,

Relay MA operates and switches nits contacts. Relay Mh, which is slow acting, is consequently maintained energized in the following circuit: ground, b'pII, malI, mhI, Mh, resistance,

With a contact mhI it is possible to prevent the favored P. B. X. station from being engaged by a line selector LW over the monitoring coil MhUe during the listening in. If however that is to be permitted, contact mhIis short-circuited.

At contact mhV the energization of relay Vh. whose winding VhI was deenergized in releasing the local trunk, is prepared anew over winding VhII of this relay. As long as contact maIII is switched over, winding VhII is short-circuited, however. At mhIII the circuit for a hot wire relay Hz' is interrupted, whose function is explained further on. At mhVII and mhVIII the switching through of the speech path is prepared and at mhVI the circuit for the rotary magnet MhW of the listening selector is prepared. The switching arms of this selector remain for the present in rest position (i. The favoured subscriber receives the selector signal over line WZ,

whose source of current was started at maII over' the line an. The subscriber at the Vfavored P. B. X. station now dials digit l inorder to set the listening selector to thefirst busy outside trunk line. The switching operations are as follows: At the first release of relay Ma contact maIII returns to its rest position, whereby-the short circuit for winding VhII is removed, so that this relay will be energized during the series of impulses. By opening contacts vhI and 'DhIII anyv disturbance of the outside trunk lines that are to be rpassed is avoided. At maI-the rotary magnet MILW of the listening selector will receive current in the followi ing circuit: groundmhini, mar', mhvr, Mew,

-. At the endofr the impulse, that is to say after relay MA has again'been operated, magnet MhW deenergizes again and consequently the listening selector makes one step, so that' its switching arms reach position I. If the outside trunk line connected with this step of the listening selector is busy, then contact UI of this outside trunk line is open, so thatl busy test relay BP will receive no current. Consequently, the selector remains in position I and, dueto the continuous short circuit at mhIII, relay Vh is ycaused to release. At chi and at vhIII the switching through of Vthe speech path is effected, sothat therfavored subscriber can now listen in on the'first outside trunk line.

However, if the first outside trunk line is free, then contact vil of the rst outside trunk line has been closed and the following circuitA is established: y

dI, cI .of the rst outside trunk line, c-arrn' of MhW, BP; '12h11, shaft-controlled rest contact'wO (which closes `after leaving the rest position),

Relay BP operates in this circuit and again energizes magnet MhW at contact bpI. At the same time the short-circuiting of relay Vh is further prevented, so that Vh will not release for the present. The circuit of test relay BP will now loe opened again at self-interruptor contact of the selector magnet. Due to this, magnet MhW is again deenergized at bpI, so that the selector will step up its switching arms `one step and consequently'steps on to position 2. If the second line is free, too,`as has been assumed in the drawv i trunk line is connected. Relay BP cannot now operate again. Consequently, the selector stops at position 3, relay WLY releases and at its contacts ohI and 'UhIII it switches the monitoring coil Mlzle to outside trunk line 3.

The favored subscriber can now listen in on the conversation going on over this line. Ii the conversation is of no interest to him or if he wishes'to listen in on still another outsidel trunk line,fhe will again dial digit l and will thereby ,l step up the listening selector to the next following busy outside trunk line, this being line 5. It should be mentioned that contact 11h11 always closes only temporarily the energizing circuit for the test relay. Consequently, if the selector stands on a busy outside trunk line, that is to say if the subscriber is listening in, and if this line after a little while becomes free again, the listening selector will be prevented from turning automatically to the next busy line to the annoyance of the subscriber. However, if one wishes to permit this automatic stepping up, then contact ULII wouldl have to be short-circuited as shown by a dotted line in the drawing.

In the drawing it has been assumed that only rive outside trunk lines are connected to the selector, for instance because the private branch outside trunk is only equipped for five outside trunk lines. Therefore, positions 6 and 1 of the listening selector are dead. It will now be assumed that the subscriber again ydials digit l, on the presumption that' there are vstillY other busy Voutside trunk lines.` In that case, thelistening selector will, to begin with, make one step in the described manner, so that its switching arms reach position ii. To the dead positions 6 and 'l of arm c battery has been connected directly, so that relay BP can operate in these two positions and that the selector will step automatically into rest position 1li. At this point the subscriber again receives v the exchange signal, whose source of current has started anew over SO, maII, and the line an, and he knows thereby that the selector has passed overall the lines. If the subscriber has taken notice of the number of dialing operations which were required to receive the selector signal again, he will know the number of outside trunk lines busy at that particular moment.

In some instances it may be required that the favored subscriber be enabled to switch in on any desired line with the aid of the listening selector, therefore also to free lines, especially if the listening selector is connected directly to the P. B. X. subscriber lines instead of to the outside trunk line. Consequently, the listening selector must be prevented from passingautomatically over the free lines. For this purpose diierential relay D has been provided. If the 'favored subscriber presses the grounding key at his-station at any time after engaging theY listening selector, differential relay D operates and is caused to hold itself over maIV and dII and its winding DIII. At contact dI the battery potential is switched from contact ci and the operation vof relay BP is thereby prevented. Accordingly, magnet MhW of the listening selector is now exclusively under the control of contact mal, that is to say under the exclusive control of the subscribers dial,.so that he can control the listening selector and set it to any desired line, for instance also by dialing a higher digit than 1.

The arrangement can also be such that the listening selector can be reached by means of different indicator digits, for instance 'by means of indicator @Sin addition to mi. On dialing indicator 09, for instance, a discriminating relay will operate only in this case but will not ope-rate if indicator il!) is dialed. This relay could take the place of differential relay D, which is energized by Vpressing the grounding, key, and the functions of which it could take over.

If the subscriber at P.- B. X. station N replaces this receiver at any time, relay MA is released, so

` that relay Mh is continuously short-circuited.

Mh therefore releases and at mhVl closes a selfinterrupting circuit for magnet MLW. The latter is stepped up with the aid of its self-interrupting contact until it reaches the rest position, consequently where contact 'wO opens.

If indicator @il is dialed by an unauthorized P. B. X. station, relay Vh will pull up over its winding I but relay MhI can not operate because, as already explained before its circuit is opened in contact bank of arm d' of the line iinder. However, hot wire relay Hi is heated over mhIII,

vhIV. Therefore, if the subscriber does not replace the receiver at once, the hot wire relay has time to switch its contact, thus causing relays P and VhI to be short-circuted. Through the release of relay P the line selector is busied and the subscriber receives the busy signal.

What is claimed is:

l. In a telephone system a selector actuated by a magnet and adapted to connect a station of the system to busy lines, means at the said station for producing loop interruptions, an impulse receiving device responsive to said interruptions for causing the energization of the magnet of the selector and auxiliary means effective to continue the driving of said selector as long as said selector is connected to a non-busy line.

2. In a telephone system, a selector operated by a magnet and adapted to connect a station to busy lines, means for producing at the said station a variable number of loop interruptions, an impulse receiving device variably responsive to said interruptions in dependence on their number, means for transmitting a correspondingly variable energization to the magnet of the selector, and test switching means for continuing the energization of this magnet until the next following busy line is reached.

3. A telephone system, comprising a selector operated by a magnet and adapted to connect a station to busy lines, means for producing at the said station loop interruptions, an impulse receiving device adapted to energize said magnet responsive to said interruptions, test switching means for continuing the energization of this magnet until the next following busy line is reached, and means for rendering the said test switching means only temporarily effective, so as to prevent the automatic stepping up of the said selector if a busy line just being tested becomes free.

4. A telephone system according to claim 1 further comprising means for stepping the said selector over dead bank contacts thereof in response to an electrical condition of said contacts.

5. A telephone system according to claim 1 comprising means for giving a warning signal to the said station in response to the passage of the said selector over all the lines.

6. A telephone system according to claim 1 comprising means for giving a warning signal to the said station in response to the passage of said selector over all the lines, this signal being associated with the home position of this selector and being adapted to serve also as a dial tone.

'7. A telephone system according to claim 1, comprising means for changing the mode of operation of the said selector, such means being under the control of the said station.

8. In a private branch exchange system having local lines and outside lines, a selector adapted to switch a local line of this system to busy lines, means adapted to respond to control signals received over said local line for causing said selector to hunt for and connect tothe next busy line, a local trunk having a digit impulse receiver, switching mechanism adapted to release the said local trunk and to connect said local line tol the said selector, and means for operating said switching mechanism in response to a predetermined setting of said digit impulse IeCelVeI.

9. A system according to claim 8 further comprising means effective only with respect to one particular local line for giving the local line access to said selector.

10. A system according to claim 8, in which said selector makes connections to said outside lines.

11. In a system according to claim 8, a talking current supply relay in said local trunk and means for energizing this relay over the speech arms of this local trunk in response to a predetermined setting of the impulse receiver of said trunk.

12. A system according tol claim 8, wherein the said switching mechanism is included in the test circuit of the said selector.

13. A system accor-ding to claim 8, comprising a supply relay in said local trunk, a primary line switch for connecting said local trunk to said local line, a special relay adapted to be operated by current through this supply relay and over a switching arm of the said primary switch, said special relay being a member of the said switching devices which are adapted to release the said local trunk and to connect the said local line to said selector.

14. A system according to claim 8, in which said switching devices, which are adapted to release the said local trunk and to connect the said local line to the said selector comprise a relay associated with said local line for controlling the connection of the said local line with the said selector, said relay being adapted to hold itself after the release of said local trunk and also to protect said local line against other engagement.

15. In a system according to claim 8, means for completing the connection of said local line to said selector only if said local line is a predetermined one of the local lines of the system, and a timing switch for giving a signal to any one of the other local lines in response to an attempted connection of the latter to said selector.

16. In a system according to claim 8, meansfor giving the said local line access to said selector only if said local line is a predetermined one of the local lines of the system, a test relay for the said local trunk, a timing switch adapted to short-circuit this relay, means for energizing this timing switch in response to the reception over any other of the local lines of signals such as are used to connect the predetermined local line to the selector and means, controlled by said short-circuit, for transmitting a signal over said other local line.

ALFRED HEYDUCK.

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