US2153323A - Telephone system - Google Patents

Description

April 4, 1939. M. LANGER ET AL TELEPHONE SYSTEM Filed Nov. 50, 1956 2 Shets-Sheet 2 mm v R m Y ORWW. E TE L N GMM R ENOU O W w XW A A MU D E Patented Apr. 4, 1939 1 UNITED STATES TELEPHONE SYSTEM Max Langcr, Berlin-Hermsdorl,

inger, Berlin, and Jose! Kuchley,

Eduardv Wooll- Berlin-Siemensstadt, Germany, assignors to Siemens & Halske Aktiengesellschait oi Wernerwerk, Siemensstadt, near Berlin, Germany Application November 30, 1936, Serial No. 113,504

15 Claims.

Germany November 29, 1935 (Granted under the provisions of sec. 14, act of March 2, 1927;

The present invention relates to a circuit arrangement for busy metering in automatic remote communication systems and more especially in automatic telephone systems.

In telephone systems of the automatic type wherein automatic switches are used for the purpose of setting up connections between various lines of the system, situations arise where all of the switches of a particular group or groups are busy at the same time so that a subscriber attempting to route a connection by way of one of the group of busy switches is precluded from completifig the desired connection. In order to record this condition so that the operating engineers may be apprised thereof, it has been the practice in the past to provide, in association with a group of switches to be observed, a metering device which is operated when a call arrives and the all switch busy condition prevails, which device is held operated so long as the calling line, responsible for the operation of the metering device, is maintained in a calling condition. This arrangement is open to the objection that more than one overflow call cannot be handled at any one time, and hence only one of simultaneous or substantially simultaneous overflow calls is susceptible of being recorded.

The present invention overcomes this difficulty and permits of the registration of simultaneously or approximately simultaneously occurring calling impulses in that when all the lines of a group are busy and an impulse for taking a line of this group into use becomes operative switching means are transitorily operated to influence a F busy metering device independently of the duration of this impulse.

- Embodiments of the invention are shown in Figs. 1-6.

Fig. 1 shows a finder switch system including one means for metering calls when the finder switchesare all busy.

Fig. 2 shows a modified form of the metering arrangement shown within the dotted lines in Fig. 1.

Fig. 3 is a further modification of said metering means.

Fig. 4 is also a modified form of the metering arrangement.

Fig. 5 comprises a further form of metering arrangement using a glow. lamp.

For the purpose of clarity only those switching means are shown which are absolutely necessary to enable the invention to be understood.

The operations taking place in connection with the arrangement according to Fig. 1 are as follows:

when subscriber Tn removes his receiver for the purpose of initiating a call the subscriber's loop is closed and the following circuit is set up: earth, contact it, subscriber's loop, contact 2t,

winding I of relay R, battery and earth. Relay R operates its contacts, connects up winding 11 of relay R and relay '1 to the lead passing to wiper c oi the call finder AS by closing contacts 31' and 41' and at contact Ir establishes the following circuit for relay E for starting up the'call finder AS: earth resistance Wil, contacts 61:, ET, i501) and H1), winding of relay E, battery and earth. Relay E closes its contact "e and thereby completes the following circuit for the stepping magnet D of the call finder AS: earth, battery, magnet D', contacts lie and l8p, relay interrupter UR and earth. Under the influence of the relay interrupter the stepping magnet D receives impulses which promote the stepping of the wipers a, b, c of the call finder AS. when the call finder AS has reached the line leading to the calling substation Tn, i. e., when the wiper c has reached the contact over which the second winding of relay R and relay '1 are connected the following testing circuit is established: earth, battery, winding of relay T, contact 41', (and parallel therewith St) winding 11 of relay R, contact 31', wiper c of the call finder AS, windings I and II of relay P, contact llle and to earth in the followingconnecting device. In this circuit relays T and P energize while relay R is maintained energized. By closing contact Hp, the high resistance winding II of relay P is short circuited and the calling subscriber accordingly guarded against seizure on the part of another call finder. By the opening of contact l8p the stepping circuit for the rotary magnet D is cut oil and the call finder is thereby brought to rest. The switching through of the speaking leads to the following connecting device takes place at contacts 8p and 99. At contact l2pthe circuit for relay E is broken so that contact '36 is closed and accordingly the start chain AN is switched through to the relay E of another free call finder so that if a call is promoted by another subscriber the free call finder connected up over the start chain is started up. The energizing of relay T causes contact lit to open. Relays T and R are, however, as already described, maintained energized since relay R remains connected up over its winding II at contacts Br. and 41'. By the opening of contacts It and 2t, earth and battery and simultaneously winding I of relay R are disconnected from the speaking leads. Finally by the opening of contact St the starting earth is disconnected over resistance Wil. After the switching through of the speaking leads at contacts 8p and Op the following circuit is set up for relays A and B in the connecting device subsequent to the call finder AS: earth, battery, winding I of relay A, 'upper speaking lead, contact 8p, wiper a of the call finder AS, subscribers loop, call finder wiper b, contact 9p, winding I of relay B, and earth. The switching operations indicated by the energizing of relays A and B in'the following connecting device are of no significance for the present invention so that a detaileddescription will not be given. It: will merely be mentioned that a calling signal AZ is connected to windings II of relays A and B over I contacts which are not shown, which signal is induced in the windings I of these relays so that it can be perceived by the calling subscriber. Only after this calling signal has been received does the subscribed establishing the call operate his dial switch for the purpose of transmitting impulse trains. The calling signal or dial tone" is disconnected after the first digit has been dialled (in a manner not shown). The setting up of the call takes place in the known way with which we are not further concerned.

It has already been mentioned that the starting chain for the free call finders of a group is always switched on further to enable the establishment of calls over the call finders which are still free.

If it now so happens that all the call finders in a group are engaged it is not possible for the calling subscriber to establish a call. It is of considerable importance for supervisory purposes to know how often this case arises so that from the data thus obtained variations can be made in the arrangement of the connecting devices such as increasing the call finder groups or the like. For this purpose a metering device is provided which is operated each time a subscriber attempts to set up a call when all the call finders of a group are engaged. The criterion for all the call finders of a group having been taken into use and there being no longer one available is constituted by the energizingof a relay AB. The operation of this relay can most simply be eil'ected by extending the circuit for this relay through the contacts controlled by the testing relays P of the individual call finders. If all the call finders of the group are engaged and thus all the P relays of these call finders are energized a circuit for relay AB is set up over the p-contacts of these relays.

If under these conditions i. e., when relay AB is energized a subscriber takes up his receiver in order to set up a call the following circuit is closed over contact Ir by relay R (which is energized in the manner described above) earth, resistance Wil, contacts 6t, Ir and lGab, primary winding of the transformer Tr, battery and earth. The

impulse impresed in this manner on the primary side of the transformer is transmitted to the secondary winding and influences relay S associated with the secondary winding so that this relay is. energied for a short time and then releases. As a result the contact s is opened, contact Us is closed for a short time and contact 20s is again closed. During the interval when the contact Us is closed, the relay W is energied over the following circuit: earth, contact I93, winding I of relay W, contact 222:, resistance Wi3, battery and earth. Relay W closes its contacts 2310 and 24w and opens its contact 26w. At contact 23w a short-circuit is set up over winding 11 of relay W which has the effect of making this relay slowto-release. When shortly afterwards contact 20s is again closed the following circuit is completed for relay X over contact 24w which is still closed: earth, contacts 208, and 24:0, winding of relay X, battery and earth. Relay X opens its contact 22:: which has no particular effect, and closes contact 251.. A short time later relay W falls back and at contact 2410 breaks the circuit for relay X. Relay X is a slow-to-release relay so that its contacts remain in the operated position for a short time. The metering device Z is now connected up over contact 2620 in its normal position in the following circuit: earth,. contacts 25x, 26w, and 211 winding of meter Z, battery and earth. The meter is thus advanced one step forward. The operating time of-the meter is determined by the release period of relay X, which shortly afterwards releases and opens the circuit for the meter once more at contact 251:. Subscriber Tn who is informed by the continuance of the dial tone that he cannot set up a call for the moment thereupon replaces his receiver. Relay R is accordingly deenergied and inter alia opens contact 11'. The disconnecting impulse now operates on the primary of transformer T is transmitted to the secondary winding, and in a manner similar to that just described for the switching on impulse, produces a brief energizing of relay S. The operations already described now take place for influencing meter Z. Thus when a call is initiated by a subscriber when all the call finders of a groupare engaged the meter is advanced by two steps. Hence, it may be seen that for determining the number of unsuccessful calls the position of the meter must be divided by two.

The case may occur in which the subscriber impulses operate on the primary winding of the v transformer.

If the subscriber after taking up his receiver transmits, for example, one impulse without having received the dial tone contact Ir is opened and closed once. Accordingly, one connecting and one disconnecting impulse operates on .the primary winding of the transformer These two impulses are transmitted to the secondary winding and produce two brief operations of relay S. On the first operation of relay S and the consequent closing of contact His relay Wis energized in the circuit described above. Because of the release of relay S and the closing of contact 20s which occur shortly after the energization of relay W, the relay X is connected up as already described. Before relay W releases (its winding II is short-circuited by its own contact 23w) contact Ills is closed again. Accordingly, the following circuit is set up: earth, contact iils, winding I of relay W, winding of relay Y released from the short-circuit by contact 221:, resistance Wi3, battery and earth. Relay Y energizes in this circuit and establishes a locking circuit independently of contact Ms: earth, resistance Wi2, contact Zly,

winding of relay Y, resistance Wi3, battery and relay W first releases after the release period which is protracted cuiting winding 11. Thereupon at contact w the circuit for relay X is broken. After a short time this'falls back and at" contact 221: shortcircuits the winding of relay Y. Only now after a definite time has elapsed does relay Y release.

If the circuit for the meter is considered it can be seen that no operation of the meter can be produced by the transmission of impulses from the subscriber's station because before contact 26w is closed, that is before relay W has released, relay Y is energized and this at contact 211! disconnects the meter. Relay Y is the last of the three relays to deen'ergize at the end of the numerical impulses, so that contact 2111 is only closed when contact 253: is opened.

The case has been described in which the sub-- scriber only transmits one impulse. Operation of the meter is, however, prevented also when a number of impulses are transmitted since relay Y holds the circuit for the meter-open until after the termination of the last impulse transmitted. As ,may be seen from Fig. 1 only a very short time is necessary for registering an unsuccessful call, this time being determined by the release of relay W. Only if an attempt to set up a call by another station is made during this short time does the registration not take place,- a disadvantage which can be tolerated since the situation giving rise thereto only seldom occurs. If, however, relay W has released, another unsuccessful call will be registered independently of whether or not the subscriber Tn has replaced his receiver. 1

Fig. 2 indicates another solution of the problem according to the invention and possesses the advantage over the arrangement shown in Fig. l

that the devices eiiecting the registering of the unsuccessful calls consist of normal relays in contradistinction to Fig. l where slow-to-operate relays have to be used.

The arrangement according to Fig. 2 is to replace that part of Fig. l which is enclosed by dotted lines. The mode of operation of the arrangement according to Fig. 2 is as follows:

If when all the call finders are engaged the subscriber Tn takes up his receiver, the call receiving relay R is energized and closes contact 1'. In the manner already described the relay S, connected to the secondary side of the transformer, is energized by induced impulses which are produced on the removal and replacement of the receiver by means of contact lr. Thus on station contact 35s is closed for a short time "and then opened again. At thispoint it should be noted that in comparison with the arrangement according to Fig. i the present network is arranged so that relay S is only provided with the one operating contact 35s. This is an advantage insofar as contact 35s is easier to operate than is contact l9s in Fig. 1' which is constructed as a reciprocating contact for whose closing it is necessary to overcome a definite tension.

When contact 353 is closed the following circuit is established for relay W: earth, contact 353, windings I and II of relay W, contact 31:, battery and earth. In this circuit relay W operates, opens its contact 3m; and closes contact 34w, (make-before-break contact). Relay X cannot operate since winding Iof relay W has a very low resistance and practically constitutes a short-circuit for the higher resistance winding of relay X. When contact 35s opens shortly on account of the short-clr-.

afterwards, relay X operates in the following circuit: earth, contact 14w, winding of relay X, winding II of relay W, contact 311:, battery and earth. Relay X closes contact 36:: and thereby completes a short-circuit over winding II of relay W. At contact 361: the short-circuit over winding I of relay Y is removed. This relay can not however energize since the relative resistances of the individual relays are so adjusted that when relay X is connected up first the relay Y cannot energize. Contact 33:: is closed and the meter Z is thereby transitorily connected up. At the end of the delayed period for the release of relay W, determined by the short-circuit of contact 361:, contact 3lw is again closed before contact 3410 opens so that the following circuit is established for the meter Z: earth, contact 8 ha, 321/, and 33x, winding of meter Z, battery and earth. Shortly afterwards contact 34w opens the circuit for relay X. After the latter has released the starting condition is once more set up. When the subscriber on realizing that he cannot establish a call for the moment replaces his receiver relay S energizes again and influences the meter once more as just described. The setting of the meter must be divided by 2 in order to be able to determine the number of unsuccessful attempts to establish a call.

The device according to Fig. 2 prevents the metering arrangement being influenced by impulses which the subscriber may transmit although he does not receive dial tone. Should the subscriber thus transmit impulses relay S is operated a plurality of times in succession. On transmitting each impulse contact 35s is closed, opened and then again closed and opened. When the contact 35s first closes W is caused to energize as above described. When the contact opens refor a short period. This delayed release, however, sufiices to bridge over the impulse, i. e. the contact 35s is closed for the second time while relay W still holds its contact 34w operated. The following circuit now obtains: earth, contact 35s, winding I of relay W, contact 360:, winding 1- of relay Y, battery and earth. Relay Y can now energize since the low resistance winding I of relay W is already connected up. Relay Y operates its contacts i. e., it opens contact 32y thereby opening a point in the metering circuit and establishes the following locking circuit for itself at contact 38y: earth, contacts 39:2, 38y, winding II of relay Y, battery and earth. If the subscriber has transmitted a number of impulses the condition just described is maintained namely, the energizing of all the relays W, X, and Y,

until after the last impulse contact 35s isopened I for a prolonged period. Relay W then releases. It opens its contact 34w and thereby breaks the circuit for relay X. The locking circuit for relay Y is only opened after relay X has released by the opening of contact 391:. Considering the circuit in which the meter Z is arranged it may be seen that on trar'ismitting impulses contacts 3| w shown in Figs. 1 and .2 in that the short connecting and disconnecting impulses do not operate directly on the relay Wbut through the intermediary of an auxiliary relay H. Since the induced impulse is only of a very short duration it may happen that the brief closing of the operated contact of relay S does not have the desired effect, i. e., the energizing of relay W. Consequently, the operating contact of relay S indicated by the reference character is in Fig. 3 operates on a relay H which is quick-to-energize over the circuit: earth, contacts is, 4 no, winding of relay H, battery and earth. The winding I of relay W is only connected up through the closing of contact 4371 whereupon the operations described above take place. Relay H remains energized in the circuit passing over contacts 42h and w until relay W has definitely energized. Relay II is then disconnected again by contact w.

Fig. 4 represents a further modification of the arrangements in Figs. 1 and 2, this figure replacing that portion of Fig. 1 enclosed by dotted lines. The arrangement according to Fig; 4 differs from that of Figs. 1 and 2 in particular in that the relay S is not a normal relay as in Figs. 1 and 2 but is assumed to be a polarized relay having two windings of which one, which is not shown (winding I), is arranged in the secondary circuit of the transformer Tr. This arrangement enables a single registration to be effected for the unsuccessful calls, so that the position of the meter indicates directly the number of these unsuccessful calls. Relay S on account of its construction as a polarized relay is only influenced by the switching on impulse on the removal of the receiver at the calling station, but not by the disconnecting impulse taking place when the receiver is replaced.

The detailed operation of the arrangement according to Fig. 4 is as follows: When all of the call finders of the group are engaged, the winding I (not shown) of the polarized relay S is influenced by the impulse induced in the transformer and earth. In this circuit relay W operates and by opening its contact 50W opens a point in the metering circuit. ,It also closes its contact 38w and thereby energizes the opposing winding II of the polarized relay S in the following circuit: earth, contacts 46s and 48w, winding II of relay S, battery and earth. Relay S disconnects itself in this way so that contact 41s again closes. Because of its slow-to-release characteristic, relay .W continues to hold its contacts in the operated position. The'following circuit is set up for relay X: earth, contacts "s, 49w, winding of relay X, battery and earth. Relay X opens its contact 45s, this being of no significance, and closes transitorily the circuit for the meter Z at contact 52x. When relay W releases shortly thereafter the circuit for the meter is completed as follows: earth. contacts 50w, Sly, and 52x, winding of meter Z, battery and earth. The meter accordingly takes one step forward. 'The circuit for the meter is maintained until the end of the release period of relay X whose circuit was opened at contact 49w. The meter is then disconnected at contact 521:. On the replacement of the receiver at the calling station no .further influencing of the relay takes place since the polarized relay remains uninfiuenced by the disconnecting impulse, which isin the opposite direction.

The arrangement illustrated in Fig. 4 also prevents the meter from being operated when the subscriber transmits numerical impulses when all the call finders are engaged. If,for example, two impulses are transmitted, a circuit is completed for relay W by the closing of contact 46:: when the first impulse is transmitted, this taking place in the manner already described. Through the closing of contact 48w the opposing winding ll of the polarized relay S is connected up so that this relay is caused to release. Relay X is thereby caused to energize as described above. The slowto-release characteristic of relay W is such that the impulses are bridged over by this relay. Contact 46s is thus closed the second time before relay W has released. Relay S is again caused to release by means of its opposing winding II. When contact 46s closes for the second time the following circuit is established for relay Y: earth, contact 46s, winding of-relay W, winding of relay Y (whose short-circuit is removed by contact 45x), battery and earth. Relay Y locks up in the following circuit: earth, resistance Wi5, contact '11, winding of relay Y, battery and earth. At contact ly the circuit for the meter is broken. Some time after the second opening of contact 468 relay W. falls back (it cannot remain energized over resistance W t and earth) and opens contact 4910, thereby to break the circuit for relay X. Through the closing of contact 45:1: a short-circuit is established over relay Y so that this circuit also releases. The circuit for the meter cannot be set up since relay Y remains energized and contact 5lz/ remains opened until another point in the metering circuit is opened at contact 521'.

The arrangement according to Fig. 4 has one disadvantage and that is, if the subscriber transmits only one impulse a circuit is established for the meter which is therefore advanced one step since the polarized relay S is only once influenced on the transmission of one impulse and thus contact 46s is closed only once.

Fig. 5 represents an improvement in the secondary circuit of the transformer T1, the improvement residing in the provision of a condenser Ko and a glow lamp GI for separating the secondary winding of the transformer from the relay S. This arrangement is for the purpose of insuring a satisfactory operation of relay S. If, in the arrangement according to Fig. 1, the relay included in the secondary circuit of the transformer is made of low resistance to insure a ready response, the induced impulse must necessarily only attain a small maximum potential so that in certain circumstances the energizing of relay S is doubtful. If, however, the relay is made of high resistance and the peak potential is accordingly greater the relay energizes with more difficulty. In the arrangement according to Fig. 5 in which the secondary circuit is practically open the peak potential is very great and this insures the striking of the glow lamp and the energizing of relay S. As frequently mentioned in the foregoing description the arrangements according to Figs. 1*5 possess certain disadvantages in that the reg istration of unsuccessful calls is not always efiected with certaintyand that in special cases false registering can take place.

In Fig. 6 an arrangement is shown which obviates all these disadvantages and insures a satisfactory registration of all unsuccessful calls in further operation of scriber Tn removes his receiver in order to set up a call the call receiving relay ZR. energizes in the following circuit: earth, contact 55t, subscribers loop, contact 5'It, winding I of relay R, battery and earth. Relay R operates its contacts and at contact 581' connects the testing lead of the call finder to battery over winding II of relay R, contacts 601' and Sit and winding I of relay T. At the same time the following circuit is set up for relay E by the closing of contact 631': earth, contacts 62t, 831', ab and 64p, winding relay E, battery and earth. In this circuit relay E energizes, closes its contact lie and thereby completes the following 'circuit for the rotary magnet D of the call finder: earth, battery, rotary magnet D, contacts 'l'le, 18p, relay interrupter UR and earth. The-wipers of the call finder are stepped forward under the influence of the relay interrupter until they have reached the calling subscriber's line. The following circuit is then established: earth, battery, winding I of relay T, contacts 601' or Git, winding II of relay R, contact 581, wiper c of the call finder AS, windings I and 11 of relay P, contact 15c and to earth in' the following connecting device. In this circuit relays P and T energize and the energizing of relay R is maintained. Relay P switches the speaking leads through at contacts 13p and 14p, short circuits its high resistance winding II at contact 1611, guards the calling line against being seized by a further call finder, brings the call finder to rest by opening contact 18p, and at contact 64p breaks the circuit for relay E. Relay E releases and closes contact G'le so that the start chain An is switched through to therelay E of another free call finder. Relay T which likewise energizes as already mentioned opens its contacts 55t and Sit and thereby disconnects battery and earth and winding .I of relay R. from the speaking leads. Through contact 63t earthpotential is disconnected from the start chain. The further establishment of the call and the setting of the subsequent connecting devices is of no interest in the present case.

Contact 65ab is closed if there are call finders available for setting up a call. When all the call finders of the group are engaged the relay Ab (not shown) is energized so that contact Stab is closed. If under these conditions a subscriber,

' for example subscriber Tn, attempts to set up a call the call receiving relay R. is switched on when he removes the receiver and by closing contact 631 sets up the following circuit: earth, contacts 62t, 631', Stab, and 68g, magnet DI of a switch ZW, which is here indicated by the metering switch and which operates after the manner of a call finder, battery and earth. In this circuit the rotary magnet DI of the meter switch energizes and advances the wipers one step. The rotary magnet DI possesses a contact GSdl by the closing of which a circuit is established for the winding of relay G: earth, contact Gildl, winding of relay G, battery and earth. Through the opening of contact 68g the energizing circuit for the rotary magnet D is opened and at contact Bilyi the. circuit for relay D is broken again. The closing of contact 689 effects the the rotary magnet DI. The reciprocal play between the rotary magnet DI and the relay G continues until the wiper of the metering switch SW has reached the contact to which the calling subscriber is connected. The following testing circuit is then established: earth, battery, winding I of relay T, contact 60f or Glt, winding 11 of relay R, contact 581', wiper magnet of the rotary switch 1 distinction to relay T has of the meter switch ZW, windings I and II of the testing relay Pl, contacts Web, 631', Git and earth.- In this circuit relay PI of the metering switch energizes and by closing contacts lflpl short-circuits its high resistance winding. On account of the increase in current density thereby produced in the circuit set up above the relay T of the subscriber is also energized.

At the same time by the closing of contact 1 lpl the following circuit is set up for the busy meter: earth, contact 'llpi, winding of meter Z, battery and earth. Themeter thus registers the unsuccessful attempt to set up a call. The testing relay PI of the meter switch ZW canonly'operate when the wiper of the meter switch reaches a contact to which a subscriber is connected who has taken up his receiver while relay Ab is energized.' If the wiper of the meter switch zw reaches a contact to which is connected a subscriber who has already set up a call over a call finder the relay PI of the meter switch ZW cannot energizesince the testing relay P of the call finder is energized in series with the winding Tl of relay T, and by closing its contact 16;) has short-circuited its high resistance winding II. Because of the diversion of the current through the contacts 161? and the resulting lowvoltage drop across the low resistance winding Pi, it is not possible for relay Pl to energize in this case.

It has already. been mentioned that if the wiper of the meter switch ZW passes on to a contact corresponding to a subscriber unsuccessfully attempting to set up a call a circuit is established in which in addition to relay Pi of th meter switch, relay T at the subscribers station is also energized. The subscriber's relay '1' energizes and locks its contacts. nection at contact 62t the circuit for the rotary ZW is disconnected so that the meter switch is brought to res At the same time relay PI of the meter switch is caused to deenergize and thereby disconnect the meter Z. At contact Git the circuit for relays R and T is broken so that relay R which in contrano slow-to-release feature, falls back. Relay T, however, maintains its contacts in the operated position so that the following circuit is established: earth, contacts 531', and 542%, subscribers loop, contact 56t, winding II of relay T, contact 591', winding I of relay T, battery and earth. This circuit is maintained .until the calling subscriber replaces his receiver Because of the earth conplace, however, when the meter switch reaches the first subscriber Tn'since, due to the opening of contact 581' and Bit, it is impossible for relay Pl to energize when the contact-to which this subscriber is connected is reached. The meter switch thus passes over this contact and steps until the second calling subscriber is reached and then eflfects the registering irrespective of the number of subscriber's who take up their receivers at the same time and attempt to set up a call all the subscribers are sought out in succession by the meter switch and a registration is effected for each one.

What is claimed is:

1. In a signalling system, a plurality of lines, a group of automatic switches adapted to be taken for use by calling ones of said lines and each operative to forward a connection from a -means, means operative only when calling line to a desired called line,

all of said switches are busy and responsive to an attempt otacallingoneotsaidlinestotake oneoisaid switches for use ior causing said registering means to register the call, and means whereby saidlast-namedmeanscausessaidregister means to register two substantially simultaneous calls originated'when all of said switches are busy.

2. In a system, a plurality of lines, agroup oi'callfinderseachhavingacccsstosaid 1ines,eachoisaidfinders, whenassignedtothe use of a calling line, being automatically operative to search for and seize the calling line, said flndersbeingadaptedtobe tosuccessive calling lines in a definite order, registering means, means operative only when all of said finders are busy and responsive to the initiation of a call on one of said lines for causing said registering means to register the call, and means whereby said last-named means causes said registering means to register two substantially simultaneous calls originated when all 0! said finders are busy.

3. In a signalling system, a plurality of lines, a group of call finders having access to said lines, each or said finders, when. assigned to the use 0! a calling line, being automatically operative to search for and seize the calling line, said finders being adapted to be assigned to successive calling lines in a definite order, a stepping ,switch having a plurality of positions each corresponding to one of said lines, means operative only when all of said finders are may and responsive to theinitiation of a call on one of said lines for causing said stepping switch to operate to the one position corresponding to the calling line, registering means, and means responsive to the operation of said switch to said one position for ccg-llising said registering means to register the 4. In a signalling system, a plurality of lines, a group of call finders having access to said lines, each of said finders, when assigned to the use or a calling line, being automatically operative to search for and seize the calling line, said finders being adapted to be assigned to successive calling lines in a definite order, a stepping switch having a plurality of positions each corresponding to one of said lines, means operative only when all 01' said finders are busy and responsive to the initiation of a call on one of said lines for causing said stepping switch to operate to the one position corresponding to the calling line, registering means, means responsive to the operation of said switch to said one position for causing said registering means to register the call, and means responsive to the operation of said switch to said one podtion for preventing said switch from again being operated to said one pofltion until said call is abandoned.

5. In a signalling system, a plurality of lines, a group oi call finders having access to said lines, each 01 said finders, when assigned to the use of a calling line, being automatically operative to search for and seize the calling line, said finders being adapted to be assigned to successive calling lines in a definite order, a stepping switch for causing said stepping switch to operate to the one position corresponding to the calling line, a testing circuit adapted to be completed when 75 said switch is operated to said one position, a

relay included in said testing circuit and energized in response to the completion thereof, registering means, and means responsive to the operation of said relay for causing said means to register the call.

6. In a. signalling system, a plurality of lines, a group of call finders having access to said lines, each of said finders, when assigned to the use of a calling line, being automatically operative to search for and seize the calling line, said finders being adapted to be assigned to successive calling lines in a definite order, a stepping switch having a plurality of positions each corresponding to one of said lines, means operative only when all of said finders are busy and responsive to the initiation of a call on one of said lines ior causing said stepping switch to operate to the one position corresponding to the calling line, a testing circuit adapted to be completed when said switch is operated to said one position, a

pair of relays included in said testing circuit,

each of said relays being energized when said circuit is completed, registering means means responsive to the energization of one of said relays for causing said registering means to register said call, and means responsive to the energization of the other of said relays for interrupting said testing circuit independently of said switch. A

7. In a signalling system, a plurality of lines,

a group of call finders having access to said lines,

each of said finders, when assigned to the use of a calling line-being automatically operative to search for and seize the calling line, said finders being adapted to be assigned to successive calling lines in a definite order, a stepping switch having a plurality of positions each corresponding to one of said lines, means operative only when all oi said finders are busy and responsive to the initiation of a call on one of said lines for causing said stepping switch to operate to the one position corresponding to the calling line, a testing circuit adapted to be completed when said switch is operated to said one position, a pair of relays included in said testing circuit, each of said relays being energized when said circuit is completed, registering means, means responsive to the energization of one of said relays tor causing said registering means to register said call, means responsive to the energization of the other of said relays for interrupting said testing circuit independently or said switch, and means including said other relay for holding said testing circuit open until said call is abandoned.

8. In a signalling system, a plurality of lines, a group of automatic switches adapted to be seized by calling ones of said lines and each operative to forward a connection from a calling line to a desired called'line, a relay operable between two' positions, means. operative only when all of said switches are busy and responsive to an attempted seizure of one of said switches by a calling line for causing said relay momentarily to operate from one oi. its two positions torthe other, registering means, and means responsive to the operation of said relay to said other position for causing said registering means to register the operation of said relay.

9. In a signalling system, a plurality of lines, a group of call finders each having access to said lines, each of said finders, when assigned to the I between two positions, means operative only when all of said finders are busy and responsive to the initiation of a call on one of said lines for causing said relay momentarily to operate from one of its two positions tothe other, registering means,

and means responsive to the operation of said re- I when all of said finders are busy and responsive to the initiation of a call on one of said lines for causing said relay momentarily to operate from one of its two positions to the other, registering means, means responsive to the operation of said relay to said other. position for causing said registering means to register said call, and means for preventing impulses transmitted over said calling line from falsely operating said registering means. V

11. In a signalling system, a plurality of lines, a group of call finders each having access to said lines, each of said finders, when assigned to the use of a calling line, being automatically operative to search for and seize the calling line, said finders being adapted to be assigned to successive calling lines in a 'deflnite order, an impulse re-'- sponsive relay, means operative only when all of said finders are busy and responsive to the initiation of a call on one of said lines for momentarily energizing said relay, a metering device including an operating winding, a circuit for energizing said winding, and a plurality of relays responsive to the operation of said impulse responsive relays for controlling the condition of said circuit, said plurality of relays being so connected and arranged that said operating circuit is completed once for each operation of said impulse responsive relay provided successive impulses causing opera-.

tion of said impulse responsive relay are separated by more than a predetermined time interval and said operating winding is maintained interrupted if said impulses are separated by less than a predetermined time interval.

, 12. A metering network adapted to register current pulses transmitted thereto and comprising, in combination, an impulse responsive relay adapted to operate once during each pulse transmitted to said network, a metering device, means responsive to' each operation of said relay for causing said metering device to register the corresponding pulse, and means for preventing said metering device from operating when the rate on said pulse is greater than a predetermined value.

13. A metering network adapted to register current pulses transmitted thereto and comprising, in combination, a pulse responsive relay, a

metering device including an operating winding,

a circuit for energizing said winding, and a plurality of relays responsive to the operation of said pulse responsive relay for controlling the condition of said circuit, said relays being so connected and arranged that said operating circuit is completed once for each operation of said pulse responsive relay provided said pulses are separated by more than a predetermined time interval' and said circuit is maintained interrupted provided said'pulses are separated by less than said predetermined time interval.

14. A metering network adapted to register current pulses transmitted thereto and comprising, in combination, a pulse responsive relay adapted to respond to pulses transmitted to said network, a metering device including an operating winding, a circuit for energizing said winding,

a second relay operative in response to each operation of said pulse responsive relay only in the event said pulse responsive relay is not repeatedly operated at more than a predetermined rate of speed, said second relay, uponoperating, being effective to open a point in said circuit, a third relay operative in response to the operation 0! said first relay, said third relay, upon operating, beingeffective to prepare said circuit, and said second and third relays being so constructed that said second relay restores before said third relay at the end of a received pulse, whereby said circuit is momentarily completed once for each operation of said pulse responsive relay.

15. A metering network adapted to register pulses transmitted thereto and comprising, in combination a pulse responsive relay adapted to respond to pulses transmitted to said network, a

meteringdevice including an operating winding,

. at more than a predeterminedrate of speed, said second relay, upon operating, being 'eflective to open a point in said circuit, a third relay operative in response to the operation 01' said first relay, said third relay, upon operating, being eitective to prepare said circuit, said second and third relays being so constructed that said second relay restores before said third relay at the end of a received pulse, whereby said circuit is momentarily completed once for each operation of said pulse responsive relay, and a fourth relay controlled by said third relay and said pulse responsive relay, said fourth relay only being operative in response to the operation of said pulse responsive relay during an interval when said third relay is operated and being the last of said relays to restore following the restoration oil-said pulse responsive relay. and means controlled by said fourth relay for holding said circuit open so long as said fourth relay is operated.

" sxnmom.

EDUARD wocnmona. JOSEF

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