US2431313A - Alternative routing telephone system - Google Patents

Description

Nov; 25, 1947. M. DEN HERTOG 2,431,313

LTERNATIVE ROUTING TELEPHONE SYSTEM l v Filed Jan. 28, 1943 12 Sheets-Sheet 1 .1. w END6'5 ya, '-9 HHIHHH I N VEN TOR.

MMT/Nus DEN HERTQG Nov. 25, 1947. M. DEN HERTOG ALTERNATIVE ROUTING TELEPHONE SYTEM Filed Jan. 28, 1943 12 Sheets-Sheet 2 hma- IN VEN TOR HART/Nus DEN Hm roc Nov. l25, 1947. M. DEN HERTOG 2,431,313

ALTERNATIVE ROUTINGTELEPHONE SYSTEM l Filed Jan, 28, 1945 12'sheetssneet s aus'busln IN VEN TOR. MART/Nus DEN HERTOG M. DEN HERTOG 2,431,313 AL'IIERNTIVE ROUTING TELEPHONE SYTEM Filed Jan. 28,1945 12 sheets-sheet 4 INV ENT OR. MART/NUS DE!! HE RTOG BY v 47m/wr Mmw Nov. 25, 1947.

Nox'r. 25, 1947. M. DEN HERToG 2,431,313

ALTERNATIVE ROUTING TELEPHONE SYSTEM Filed Jan, 28, 1945 12 Sheets-Sheet 5 l INVENTOR. NAR T/NUS DEN HERTOG Nov. 25, 1947.

M. DEN HERTOG ALTERNATIVE ROU'IING TELEPHONE SYSTEM Filed Jan. 28, 1945 12 sheets-sheep@ JNVENTOR. i NAR TINUS DEN H'KRTUG BY f 4@70E/VD Nov. 25, 1947. M. DEN HERTOG 2,431,313

ALTERNATIVE ROUTING TELEPHONE SYSTEM Filed Jan. 28, 1945 12 Sheets-Sheet '7 INVENTOR.

HART/NQS DEN HERTOG Nov. 25, 1947.

M. DEN HERTOG ALTERNATIVE ROUTING TELEPHONE SYSTEM Filed Jan. 28, 1943 12 Sheets-Sheet 8 @www INVENTOR. TMRT/NU1 DEN HERTUG Nov. 25, 1947.

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Nov. 25, 1947. M. DEN HERToG ALTERNATIVE ROUTING TELEPHONE SYSTEM Filed Jan. 28, 1943 12 Sheets-Sheet ll` la: o

IN VEN TOR MART/Nus DEN HERTOG Nov. 25, 1947. M. DEN HERTOG ALTERNATIVE ROUTING TELEPHONE SYSTEM Filed dan. 28, 1943 lz-sheets-sheet i2 was@ was@

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. M@ SMQ WE@ l NS@ MARTIN US DEN HERTOG Patented Nov. 25, 19347l ALTERNATIVE SR UTING TELEPHONE YSTEM `Martinus den Hertog, Antwerp, Belgium, assigner to International Standard Electric Corporation,

New York, N. Y., a corporation of Delaware Application January 2s, 1943,

In the Netherlands July 11,

21 Claims. (Cl. 179-18) The invention relates to new and useful -improvenients in a telephone system or similar system for establishing connections.

In such systems a selected line or group of lines is reached via more than one selection stage and connecting lines between each oi two consecutive stages of selectors, which may be either in the same or in different exchanges. More particularly, the inventionrelatcs to means for increasing the eiiiciency of the connecting lines and the selectors associated therewith.

It is known how one may obtain an increase of the efficiency of connecting ylines and of selectors by the application of the so-called overflow principle. For instance, arrangements are known in which a selection takes place in such a manner that rst a direct access is attempted to a predeterminal group of selector switches. 1f these are not accessible along a direct route, then one out of another group of selector switches is seized and non-numerically operated in response to a discriminating signal from a preceding stage. Thus along an indirect route access may be had to another selector in the desired group. In this system the setting of the selector is so controlled that a free outlet of only one predetermined group can be seized at any one time, and a selector cannot hunt for a free outlet in two vgroups o outlets simultaneously. This is accomplished by the expedient that depending on the seizure of an outlet leading directly or indirectly to its destination, the operation of the seized selector, numerically or non-numerically, is determined in the rst selector stage to which information must be conveyed whether a direct or an indirect outlet was found. According to said patent this is attained by permitting the first selector stage to hunt only in one group of outlets at a time and thus directly determine whether a direct or an indirect outlet is seized.

In my copending application No. 478,697, iiled on March 10, 1943, an arrangement is disclosed for allowing a group selector switch, after it has hunted without result over a certain group of outlets, to hunt over another group of outlets leading to bypass-selectors through which an outlet leading to the desired numerical group in another multiple split Vmay be found. According to said patent application, special selector circuits are so arranged that a relay determines whether an outlet of the iirst or of the second kind is seized. If the relay is operated, then it causes the seized by-pass-selector to be set by means of a special train of impulses sent from Serial No.3 473,883

2 the inst-mentioned selector or from an associated control circuit.

The system described in said patent application uses, therefore, selector switches with or without associated control circuits, and having a circuit arrangement which differs from the normal circuit. Furthermore, additional means must be provided in the selector switch or in one of the associated control circuits to make 1possible the setting oi a seized by-pass-selector by means ci" these circuits. One of the resultant difficulties is that, if by-pass-selectors are not required lfrom the beginning but only at a later stage, then'either all the circuits must be equipped with unnecessary equipment, or part of the circuits must be radically modified.

These dimculties may be met by the use of a switching system, like the one disclosed in the application of S. Simon, J. Kruithof and M. den Hertog, Serial No. 472,623, led January 16, 1943, and the applications of J. Kruithof, L. Kozrna and M'. den Hertog, SerialNo. 473,278,1ed January 22, 1943, and Serial No. 472,624, filed January 16, 1943.

By using the selector switches described in the last two patent applications, a register controller maybe so arranged that a selecting and hunting selector switch will stop upon the receipt ci two diiierent kinds of signaling currents, i. e. oi the signaling current which is received from the desiredrgroup of outlets, and of another signaling current which is received from a group of outlets to which by-passselectors are connected. The register is then in a position to continue with the next selection, depending on the signal-received (i. e. if an outlet in the desired group was seized) or to insert an additional selection, which sets the seized by-pass-selector onto the group of desired outlets associated therewith. This eliminates special provisions in the selector switches or associated control circuits, and the normal group selector circuits may be used. All functions required for the seizure and setting'of a 'oy-passselector are controlled from the register controller. 1 One of the characteristic features of the invention consistsin providing for the possibility of permitting a selector to hunt for a free outlet in more than one group during the same selecting operation. The outlets of each group send characteristic signals to a preceding switching stage to indicate to which group the seized outlet belongs. This preceding switching stage may accordingly determine the way in which the seized selector has to be set. The arrangement may be lease a ment of the selector all the outlets are to ind only a free outlet of a desired group, and Y if such a free outlet is not available, then the functioning of the selector is modified to hunt for a free outlet in the desired group and in an alternative group during the same-selecting opera-A tion.

the selector, which was in a lets of two different groups, sends a signal from the seized outlet to a preceding stage indicate whether the seized outlet is of the desired or of the alternative route. In the preceding stage the signal will cause the performance of an additional selection to reach a selector of direction by an indirect route, if an outlet of the alternative route was seized. No additional operation takes place if an outlet of the desired route was seized.

A further characteristic feature of the invention is that, depending'upon the switching system chosen, the setting of the selector seized by the alternative way takes place in a non-numerical way, of the selector setting in the'preceding selector stage. l f v According to still another characteristic feature of the invention, means may be provided to reselector if it selects an alternative outlet which will not give access to the desired line, and

According to another featureof the invention position to seize out-,`

in order to the desired 4 In Fig. 1 four of these groups are shown. If a connection is desired to the second thousands group of lines, then the first group selector will hunt under the control of the register, with the purpose of iin-ding a free outlet in the secondr Y level. n n

Let us first assume that-at the commencement of the hunting the selector, under the control of the register, can seize a free outlet in the second as well as in the third level. The terminal banks 1 of the selector are, however, so divided that the terminals belonging to the same level `are all located one next to the other, and the terminals belonging to different levels follow one another in Y the normal order. Thus, rst all the terminals of level 2 will be tested before the first terminals or this selector may be set by a repetition v to operate it to seize another alternative outlet,

the associated selector of which will hunt for al* outlet in the desired direction. l

According to a further feature of the invention, when a-selector has tried all the available alternative outlets and none of thesegives access to an outlet in the desired direction, then it starts its function anew, and will in the desired direction along the direct route.

Six embodiments of the invention will be described in connection with the drawings in which Figs. 1-5 schematically represent different Ways `in which consecutive selector stages may be connected by junctions; Figs.16- 1O and 14 diagrammatically show details of a connecting circuit with an associated register; Figs. 11,Y 12 and 12m) show different ways of cross-connecting in the register, to be used as indicated in Fig, 18, 19 or 20; Fig. 13 shows a group selector of the Vtype described in the application Ser. No. 473,278; Figs. 6-14 must be put together for embodiments in the way indicated in Figs. 15-20.

All six embodiments are variations of the method of group selector setting described in applicafirst try to find an outletV the six different I tion Ser. No. 473,278. The main feature ofthe ments will be explained with reference to Figs.`

The group selectors shownin Figs; '1-5, are all of the type in which in Vone single Vcyclic movewiped over by one or more sets of brushes.A The contacts are divided in ten or more groups or levels corresponding to just as many different numerical groups of'second group selectors, each of which is assumed to have access to a certain thousands group 'f y .thousands group.

receives a signal from Youtlets of all levels may of level 3 are reached. In the same way, all terminals of level 3 must be tested before a terminal of level' 4 is reached, etc. When the rst group selector nds an outlet 4in the desired group, in this case in the second level, the register responds in the normalY Way, i. e.'it will numericallyset the second group selector in accordance with thek received hundreds digit, 1

If, however, the rst group selector does' not Vnd an outlet in level 2 but only in level 3, then the register will cause the performing of an additional selection and the seized second group selector of the third level will be non-numerically caused to select an outlet in its 11thV level. This 11th level has outlets connected to the second group selectors which have access to the second When one. of these second group selectors is seized, the register responds and sets this group selector according to the hundreds digit received fromthe calling party.

In a similar manner, the rst group selector level, if no free outletY level. When, e. g. level 3 mayoverow to the next is desired, an alternative Vroute may be found via level 4, and whenthe last level is desired, an found via the first level. Y.

The advantage of this arrangement is that, for each call, the number of available outlets in the first lection is made only via'a single level,rand thus the efliciency of the outlets is increased; Since during thefsame operation the selector may'hunt in two levels, if no alternative route may -be until an outlet'becomes freein'one ofthe two available levels.y During eachrnew cyclic movement of the selector, preference is given to the outlets of Ythe desired level. When the-register the group selector selects an outlet in the desired or the alternative level, the register will control the performance of the next selection, or it may control the setting of the so-calledroverow selector in the 11th level. In previous arrangements the selector could test only one level on one operation and if it found no free outlet then the connection could be built up only via the Yalternative i level, even if an outlet inthe desired level became ifree before an outlet in the alternative level had `been found. V

The circuit` diagrams for this system'are the ones indicated in Fig, 15. i Vf A second embodiment will'now be described with the aid of Fig. 1. Y Y The first group selector is only initially oper-V atedito seize an outlet intheY desired level. The

now be Vdistributed in any calls to any other level of Y is found inV the: desired f group selector is twice as large as when sefree outlet is formed in the second level then the hunting may-be continued the selected outlet, orY when V arbitrary way throughout the bank of the selector, as is customary in selectors of this type.

By distributing the outlets so that a few but not all'the terminals of all levels will be consecutively reached when the rst part of the bank is tested, then in most cases the short hunt over a small part of the arc will be sufficient.

If the wipers of the selectors move over all the contacts of the bank are, a signal is sent to the register to perform a change-over to operate the selector to hunt for outlets in two different levels.

During the second and possibly further rotations of the selector brushes, the outlets of the desired level, and also the outlets of the next level are tested until a free outlet is found in one of the two levels. Theregister circuit receives a signal, just as in the case described above, to indicate whether the selected outlet belongs to the one level or to the other.

The circuits should be put together as shown in Fig. 16.

lin Fig. 2 an embodiment is shown, whereby two consecutive levels are paired and calls directed to an odd numbered level may overiiow to the following even numbered level, while calls directed to an even numbered level, may overflow to the preceding odd numbered level, provided, of course, that no free outlet is found in the desired level.

This system operates according to the same principle as described for the second embodiment of Fig. l, and the circuitsfare used as shown in Fig. 17. Both embodiments offer the same advantages as described above for the first embodiment according to Fig. 1.

Fig. 3 illustrates a single group selector stage, e. g., a rst group selector, of which certain levels serve for the connection of local group selectors via local junction lines, whereas other levels are used for reaching distant group selectors via outgoing trunks or junction lines.

In order to increase the efliciency of the outgoing junctions, calls directed to each of the levels, may be rerouted via a number of overoW terminals common to these levels, special overiiow selectors OS are provided, which give access to other trunks in the same outgoing direction. As indicated in the drawing, the one hundred available contacts or terminals of the group selector arc are divided into 5 X 14 sets of contacts for local outlets, 5 x 5 sets of contacts for outgoing outlets, and the remaining ve sets of contacts serve for reaching a group of overflow selectors OS. The efficiency of the local outlets will be relatively high, because a group of fourteen instead of the customary group of ten outlets is used. At the same time, the efficiency of the outgoing outlets is also increased, because the total number of available outlets for each of the iive groups is twenty-five, i. e. five connected directly to the first group selectors and twentlr accessible via the overflow selectors. This is so because the arc of one hundred contacts in the overflow selector is divided into ve groups, each having twenty sets of contacts, corresponding to the five levels over which th-e traffic may be diverted via these selectors.

The selectors operate as follows:

The rst group selector is controlled from the start b-y the register circuit so that it can test either the outlets of the desired level or it can seize one of the outlets leading to the overflow selectors OS. Since these outlets are connected to the last sets of contacts of the arc, the first group selector can reach these only if none of the outlets in the desired direction is free.

` When a free outlet in the desired direction is found, the register circuit responds by controlling the next numerical selection. When one of the outlets to the overflow selectors OS is seized, the register circuit repeats the first group selector setting. The overflow selector will, therefore, be moved to a level corresponding to the desired first group selector level and will select the outlet in the desired direction connected thereto. The levels of the overflow selectors, although their number is smaller than that of the first group selectors, are selected in the same manner as the rst group selector level. When an outgoing trunkis seized over one of the levels of the overiiow selectors, the register will control the next numerical selection.

The circuits in this system are used as shown in Fig. 18.

Fig. 4 illustrates an arrangement like in Fig. 3, but in which the first group selector has two overflow levels, each serving for a part of the other levels. Thus, a call to one of the levels I-5, which may be used for local calls, will, if no free outlet is found, overflow to the overflow level 6, giving access to a group of overflow selectors OSi to which other local outlets are connected leading in the same direction as those connected to levels |-5 of the rst group selector. Calls to levels 1-l l, which may be used for outgoing junctions to other exchanges will, when no free outlet is found, overflow to level l2, which gives access to a second group of overflow selectors OS2 to which other outlets to the same distant exchangesy are connected. The operation is as follows:

When a selector is set to one of the levels I-5 under the control of the register, it may size an outlet either in the desired level or in level 6. The outlets of level 6 are connected in the arc in such a way that they can only be reached after all the outlets of the levels |5 have been tested. If one of the levels 'l-H is desired, then the register will operate the selector to seize an outlet either in the desired level or in level l2, the latter being accessible only after the rst five have been tested.

When an outlet in the desired level is found, the register is notified thereof and responds by performing the regular numerical setting in the next selector. If, however, an outlet in an overflow level is seized, then the register repeats the first group selection to control the overflow selector. The different levels of the overflow selectors are reached by the same numerical operations as the corresponding levels of the first group selectors.

A total of twenty-nine outlets for each of the ten levels of the first group selectors maybe reached. Nine outlets are connected directly to the iirst group selectors themselves, and twenty outlets are accessible through the overflow selectors. Although the number of outlets per level is considerably higher than by the normal use of a one hundred point selector, and the einciency of all the outlets is considerably increased, this is attained by adding only the overflow selectors which are used only for traffic peaks.

The circuits for this arrangement are the ones indicated in Fig. 19.

Obviously, the wiring of the terminal banks of the different selectors, illustrated in Figs. 3 and 4, can be arranged in different ways. The numbers for the different groups of outlets shown in erations will be Vtioned primary iirst group selector; selector will leave the contact on which it was these iigures are mentioned only by Way of example. h Fig. represents a modification of Fig. 3. It

shows a number of primary iirst group selectors PGS, each having ten Vgroups of outlets, to which second group selecto-rs are connected. The number of second group selectors required for each level is so large that the'multiple of the primary iirst group selectors must be split into a number of parts. By way of example, it is assumed that the multiple for each of the levels is divided into four parts. The symbol for a single nrst group selector PGS in the figure represents all primary iirst group selectors which have a common multiple. By way of example, a number of second group selectors are shown as accessib-le over the first level.

The rst group selectors have an eleventh level, the contacts of which are connected to secondary rst group selectors SGS. These have access to.

other multiple splits than are accessible to the corresponding primary first group selectors. For

instance, the contacts of level eleven of the priy mary rst group selectors, which have the rst multiple split in common, give access to secondary first group selectors, which are connected in multiple to the second, third or fourth multiple splits. With this arrangement any arbitrary part of the outlets for each level may be reached. The operation is as follows:

When a primary group selector, giving access to the first multiple split, is set on the first level, then the setting takes place under the control of the register in such a way that the selector may during that operation hunt for a free outlet of the first level, or for a free outlet of the eleventh level. In case a free outlet in the rst level is found, this is communicated to the register, which responds by performing the normal second group selector setting. Y

When a free outlet is found in level eleven, this is also communicated to the register, which responds by repeating the first group selector setting to the seized secondary rst group selector through which another multiple split and, therefore, another group of second group selectors for the same direction, is reached. The contacts of level eleven are distributed over different secondary rst group selectors, which are connected to different multiple splits.

When a secondary lirst group selector, belonging to the second multiple split, has been seized, it is set to the rst level. The arrangement is such, that this selector can 'test this level and also level eleven during the same operation. If the selector does not find a free outlet in the first level, it will hunt until it finds a free outlet in level eleven. If the selector arrives on the last contact of the eleventh level, to which no secondary selector is connected, then the same opperformed as upon seizure of any contact set belonging to level eleven, that is to say, the selector will stop and a signal will be Vsent vtoY theV register to indicate that the brushes stopped on a contact of level eleven. The register will then signal the primary rstgroup Vselector, in the present case, the selector in the first multiple split, and cause the releaseof the group selectorjin the second multiple split. Then the register starts to set once more the first-men- 'Ihis group first set (the secondary first group selector in the secondY multiple n'split Y has not yet returned to the home position and is, therefore, inaccessible),

and will againstart to hunt for 'a freeoutlet. Preferably a secondary i'irst groupr selector will now be seized in the next multipleV split, whereby theY next group of'outlets leading to the desired vsecond group selectors will be tested. If all these outlets are busy then the above-described operation may be repeated, so that the primaryirst group selector in the rst multiple split may consecutively be connected to a secondary rst group selector in all other ,multiple splits, yuntila free outlet is found. When'iinally all multiple splits have been unsuccessfully tested, the first group selector returns'to the beginning of thearc on level one and starts testing again the outletsin the first level. Y

The circuits for the Larrangement just scribedare the ones indicatedin Fig. 20.

The different embodiments of the invention according to Figs. 1-5 will now be described by reference to Figs. 6-14. The circuit diagrams should be combined for the six modifications as indicated in Figs. 15-20. n

, SYSTEM or FIG. 1 (KEY SHEETVFIG. 15)k The upper part'of Fig. 6 shows a connecting circuit, one end of which is connected via one or more line nders and register link finders or the like, to the line of a calling subscriber and the other end to a first group selector shown in Fig. 13 viaJ register link iinders and connecting links. The connections are shown Vthrough which d uring the establishing of a connection, the connecting circuit is connected ythrough register finders to a register circuit, some of the details of which are shown in the lowerpart of Fig. 6 and in Figs. 7 and 8. i

(a) Receipt of the digits are dialed by the calling subscriber in the known way by means of his calling dial, which will cause Y Lbr and Lhr are energized. Relay Lbr is a slow releasing relay and remains operated during the sending of the impulses.

` g vention, onl

- The first digit is recorded'by a step-by-step switch SM1. At the rst interruptionby the dial, SM1 is operated in the circuit: ground, back contact of Isf, front contact of Lbrg'winding of Lmr, Y Din, winding ofA SM1, battery. Y

:back contact of Relay Lmr operatesV at the iirst pulse and revmains operated during the dialing ofY each digit. SM1 takes a step for each de-energization of relay Isr and nally stops in a position corre- Y sponding to the iirst digit sent.

During the dial interval between the rst and Ysecond digits, relay IsfY remains operated long enough to release relay Lmr, so that the brushes of step-by-step switch IM, which was energized `over a front contact of relay Lmr, move one step during the dial interval IM moves its brush a to position 1 andV relay Dim lay switchesV the irri-stepping circuit fromSMi 'to SM2, so that the second digit Will be received by SM2 in the same manner as the iirst digit by" SM1. At the end of'v the second digit IM again takes a step, thereby energizing relay Dz'rz. `All the following Vdigits are recorded consecutively in the same manner byY diierent step-by-stepY As this is no essential part of the in step-by-stepiswitches K Y switches.

vy three ofthese areshown.`

The digits of the desired lsubscribers number` L operates. This re- (b) Alternating current test It will now be assumed that the first digit was 2, so that the second level of the rst group selector must be selected. It will be clear from the description of Fig. 1, that in this case means must be provided to hunt for an `outlet in the third level if all the outlets of the second level are busy.

As soon as the rst pulse of the first digit is reco-rded by SM1, the rst group selecto-r leaves its home position and starts the selection of a free second group selector in the group determined by the position of SM1.` As is usual for this type of group selectors, the outlets of level one are connected to terminal or contact sets so spaced from the ho-me position that, if the first digit is not 1, then a second pulse may be received by the register and SM1 take a second step, before the group selector can reach the rst contact set of level one. Similarly, the group selector can reach the first contact set of level two only after more than two pulses have been received, in case the rst digit is not 2, etc. In the case under consideration, SM1 stops in position 2 and only after that will the group selector arrive at the first set cf contacts belonging to level two.

Relay Ar in the first group selector is operated in the following circuit, .as soon as theregister is seized: ground, brush and home contact a of SM1. front contact of Lhr, b wire, back contact of Br, back contact of Ar, winding of Ar, battery.

Relay Ar remains operated over the d wire to ground via a front contact of relay Lhr.

The power magnet of the selector is energized when the register takes one step and the brush carriage starts to rotate, the circuit being: ground, brush and contact I in arc a of SM1, contact N and brush c of OM, back contacts of Vir,

Vt1r, Fir and Vrr, a wire, back contact of Br, front contact of Ar. power magnet P, battery.

The selector setting takes place in the manner described in the application Ser. No. 473,278, by comparing the phase angle of an alternating current of a free outlet over which the group selector wipes with the phase angle of a reference current in the register. The `phase angle of the reference current is dependent on the number dialed and only when a selector brush wipes over an outlet to which an alternating current of the same phase angle is connected will a signal receiver in the register operate and stop the selector.

In the present case the group selector must be able to stop o-n outlets of two different levels to which, therefore, alternating currents having two different phase angles are connected. Means are provided in the register to compare these two phase angles with those of two different reference currents. Ihese means are the two signal receivers I and II in Fig. 8. The reference currents for these two signal receivers are determined by the dialed number.

The reference current for signal receiver I is supplied through the following circuit: from an alternating current source having the required phase angle to contact 2 in arc b of SM1, contact N in arc d of OM, back contact of Or, primary winding of the transformer T1 in signal receiver I to ground.

The circuit for the second reference current is: from alternating current source with required phase angle to contact 2 in arc c of SM1, contact N in arc e of OM, primary winding of transformer T2 in signal receiver II to ground.

The connections to the arcs .b .and c of the different step-by-step switches SM1, SM2, etc., are so arranged that the current sources to the contacts of arc b are shifted one step with respect to arc c. In this way reference currents with phase angles of two consecutive values are connected to the two signal receivers enabling them to control selection in two consecutive levels of the group selector.

The circuit for the signaling currents received from the tested outlets of the first group selector 'is as follows: alternating current source, resistance of ohms in the tested second group se-` lector (same as first group selector), home contact of group selector, busy jack BJ, back contact of Ar, d wire, d brush .of the first group selector (Fig. 13), back contact of Br, front contact Ar, c wire, back contact of Str, and then in parallel the primary windings of the transformers HC1 and HG2 in the two signal receivers to ground.

The reference currents are So selected that the signal receiver I will respond when the desired level is hunted over by the selector, in the present case level two, and signal receiver II when the next level is tested by the selector;

If a free outlet is found in level two, signal receiver I will respond in the known manner by the ionization of tube B1, whereupon relay Vtr operates and the selector'stops.

Relay Vir energizes relay Fir in the circuit:

l ground, brush and contacts I and 2 in are a of SM1, home contact N and brush c of OM, front contact of Vtr, back contact `of Vtzr and Fhr, winding of Fir, battery.

Relay Ftr prepares a locking circuit for itself through the winding of relay Fhr and opens the circuit in which relay Chr was energized upon the energization of Dz`r1. Chr disconnects the potential that was applied to the tube B1, this tube becomes extinguished and relay Vtr releases. The circuit for the power magnet of the group selector was opened at the back contact of relay Fir. The release of relay Vir `does not, therefore, Cause the group selector brushes to move again, but relay Fhr operates in series with relay Fir via a front contact of relay Ftr and a back contact of relay Vrr to ground on a front contact of relay Lhr. Relay Fhr again closes the circuit for relay Chr, so that the signal receiver can again respond when comparing the signaling current received with the selected reference current. The tube B1 is .now ionized for the second time and relay Vir is operated for the second time. This takes place before the slow operating relay Kir could be energized via the back contact of relay Vir and front contacts of the relays Ftr and Fhr. The operation of relay Vtr results in the closing of a circuit for relay Str via a front contact of relay Fhr.

(c) Direct current test and switching through of register to following selecting position The operating of relay Str indicates that the alternating current test is completed and that the register circuit will now apply the direct current test to the found outlet. Reference is made to the description in the above-mentioned application Ser. No. 473,278, in which a similar circuit is described. When the direct current test passes successfully, the relays Tr and Dtr operate and connect ground to relay Sar over the following circuit: ground, front contact of Dir, back contacts of Vtgr and Vtzr, winding of Sar, battery. Relay Sar remains operated via the interrupter of OM and closes a circuit through the winding of this switch. Relay Sar cannot release until it the selected outlet, relay Sar` releases and OM Y signal receiver II receives signaling and reference moves yone step into position 1, in which it can control the next selecting operation according to the second digit that was dialed'. Relay Sar operates also relay Vrr, whereby the locking circuit for relays Fhr and Ftr is opened. These two relays are released. The relays Str and Vrr release after relayrSar is de-energized.

The release of relay Vrr closes again the circuit for relay Chr, so that the register is now ready to control thenext selector setting.

(d) No free outlet available in the desired level If no free outlet is available in the desired level,

then the selector continues its hunting operation and its brushes Will Wipe over the outlets of the next level. If one of these outlets is free, the signal'receiver II in the register responds, because the alternating current at this outlethas the same phase angle as thereference current which is connected to the signal receiver II.

- The tube Bz is therefore ionizedV and the relay Vt1r operates. This stops' the selector on the selected outlet. Relay Vtzr is now operated in the circuit: ground, brush a of SM1, contacts l and 2 in a arc, contact N and brush c of OM, back contact of Vtr, front contact of Vtir, backcontact of Vtzr, winding of this relay, battery. Y Relay Vtzr remains operated, under the control of a back contact of relay Vrr, to ground on a front contact of relay Lhr and switches the ground on,

the front contact of `relay Vtir through to the winding of relay Ftr. Y

Relay Ftr has the same functions as mentioned in chapter b, so that a second test of the received alternating current takes place, upon the successful termination of which relay Str operates.

(e) Direct current test The *direct` current test now takes place in the known manner and the relays Tr and Dtr operate. The ground on the front contact of relay Dtr is now switched over a front contact of relayY Vtzr to operate relay Vtsr, which locks up inde pendent of relay Vtzr direct to the front contact of relay Dtr.

(f) Register controls the adjustment of the by- :Dass-selector on the eleventh level The energization of relay Vtar results in the energization of relay Vrr, whereupon relays Ftr, Fhr, Vtzr and Chr release, Also, the tube B2 of the signal receiver is extinguished. A second result of the operation of relay Vtsr is, that relay Or is operated and locks up over the interrupter contact of OM.

When the rst group selector is connected through and the direct current test potential of the seized second group selector is removed, the relays "Ir and Dtr release, whereupon the relays Vtsr, Vrr and Str also release.

The register is now in a position to control the next selection, although the brushes of switch OM have not taken an additional step. The reference current for signalreceiver I is now no more obtained via arc b of step-by-step switchV SM1, but via the right hand outer front contact of relay Or which connects the primary Winding of T1 direct to an alternating current source having a phase angle corresponding to that existing on the outlets of the eleventh level. Signal receiver II is rendered inoperative because 12 the battery for 'the contrai electrode of tube B2 is disconnectedand replaced kby ground. This tubecan, therefore, not respond, not even `if currents having the same phase angle.

The seized second group selector can now select only an outlet in the eleventh level, to which the desired thousands outlets are connected. When` The register is now in condition to controlY selection in accordance with the second digit which the subscriber dials.

' (y) Further operations` For further operations of the register circuit in casesy where the selected outlet has no free direct current potential, or where hunting is performed by theselector during the receipt of the dialed number, reference is made to the description of said application Ser. No. 478,278.

SYSTEM orV FIG. 1 (KEY SHEET FIG. 16)

The circuits used are the same as in the first case, with the exceptionthat Fig. Y10, as comparedto Fig. 8, has three relays Epr, Ehr and Tlr added, which alter the operation of the register circuit, in case no free outlet is available in the desired level, as follows:

(a) )Seizure of outlet in eleventh level of first Y group selector The primary winding of transformer T2 of signal receiver II is connected via a back contact of Tlr to an alternating current source, which has the same phase angle as the alternating current connected to level eleven. Therefore, if no free outlet is found in the desired level, the first GS will test an outlet of level eleven.' This level eleven consists in this case ofa single contact set, the last contact in the arc, to which alternating current of the Vabove-mentioned phase angle is connected, but to which no second group selector is connected. Alternatively, instead of using a contact set in the arc, this eleventh'phase may be connected by closing a contact by means -of the brush carriage, just before it returns to its home position. This alternating current will actuate signal receiverV II and thus cause the energizing of relay Vtzr, which in turn'energizes relay E271'. Relay Epr prepares a locking circuit `for itself to ground on the interrupter contact of OM, and opens the circuit for relay Chr, via a back contact for relay Chr, whereupon tube B2 extinguishes and relay Vtlr is released. Relay Ehr is operated in series with the locking circuitV of relay Epr, and relay TZr is energized via a front contact of relay Ehr.

Y (b) Second hunting operation connected from the alternating current source having phase displacement II, and instead of this reference current, a reference current determined by the dialed number is now connected to signal receiver II via arc c of SM1 and a front contact of Tlv. This alternating current source corresponds to the level next to the desired level.

The brushes of the selector perform a second rotation in the same way as described for the arrangement of Fig. 15 for the rst rotation.

(c) No free outlet is found in the .desired level during the second rotation When, during the second rotation of the brushes, a free outlet is found in the level next to the desired level, signal receiver II will respond and relay Vtn will be operated. The following circuit is closed for relay Vtzr; ground, brush a and contacts in a arc of SM1, contact N and Ac brush of OM, back contact of Vtr, front Contact of Vt1r, front contact of Enr, back contact of Vtzr, winding of Vtz, battery.

The operation of relay Vtzr is the same as described for the case of Fig. 15 and, therefore, a second alternating current test will take place, as well as a direct current test of the selected outlet. The operation of the direct current test relays Tr and Dtv results in the next selector set ting without the necessity` of moving the switch OM an additional step.

(d) Register controls the wsly'ustment of luy-passselector on the eleventh level By the operation of relay Or the condition of the two signal receivers is` changed in the same way as described in connection with Fig. 15, so that the by-pass-selector will hunt -for an outlet in the eleventh level. This outlet leads to a second group selector in the desired thousandths group. After that the brushes of switch OM advance one step and the register is ready for the control of the second group selector according to the dialed second digit.

THE SYSTEM oF FIG. 2 (KEY SHEET FIG. 17)

This is a modification of Fig. 16, in that the connections of the arcs c of the different step-bystep switches SM1, SM2, etc., are wired different.

As explained in the general description of Fig. 2, if the desir-ed level number is odd, then dur ing the second rotation of the switch brushes, the next even numbered level may be seized whereas, if the desired level is even numbered, then during the second rotation oi the switch brushes the preceding odd numbered level may be selected. The circuits are the same as those of Fig. 16, with exception that in Fig. 9 the connections of the arcs c of the step-by-step switches SM1, etc., are adapted to the new requirements.

If the first digit is odd, then the reference current for signal receiver I, which is supplied via arc b of SM1 during the second rotation of the selector brushes, will have a phase angle correspending to the phase angle oi the alternating current connected to the outlet of the desired level. Signal receiver II operates in this case on a reference current supplied over arc c of SM1, which has a phase angle corresponding to that of the next level.

In the case of an even digit, the phase angle supplied over arc b again corresponds to that of the desired level, but that supplied ove1 are c corresponds to the phase an gle of the current supplied over the preceding level.

-number of levels, for

SYSTEM oF FIG.' 3 (KEY SHEET FIG. 18)-REoIsTER CONNECTIONS ACCORDING To FIG. 12m) The circuits are the same as those for Fig. 15, except that the reference currents are controlled in a somewhat different manner by the arcs c of the different step-by-step switches, on which the successive digits are registered.

(a) Hunting condition of jirst group selector The first group selector is so controlled by the register that an outlet in the desired level may be selected by signal receiver I, the reference current `to transformer T1 being supplied over arc b of the step-by-step switch or, if no free outlet is found in this level, the selector may hunt for an outlet in level eleven. To this end, the signal receiver II is connected over arc c of the step-bystep switch to the alternating current source with the corresponding phase angle. In accordance with Fig. 3 the connections in Fig. 14 are so modified (Fig. 11) that the alternative seizure of an outlet in level eleven takes place only in case the selected level is one of the levels i-Ii. This is accomplished by the connection ofthe reference current for signal receiver II only in the aboveindicated positions of SM1. The other terminals of SM1 are connected to an alternating current source having characteristics which do not representany level in the group selector arc. The purpose of this is to keep the signal receiver by means of this reference current continuously in the inoperative position, because in the absence of reference current, response would take place immediately.

For the digits, for which the selector setting takes place without alternative selection ci the eleventh level, the signal receiver II remains inoperative because the ground supplied over the corresponding contacts in the f arc of OM, will keep the potential on the controlling electrode of tube B2 so low that it will not respond. i

Other modifications are possible by suitably wiring the register. Thus, one may vary the which level eleven must serve as. alternative, and the successive digits, for which this alternative operation must be performed.

(b) VOperation of the register, if .outlet in level eleven has been seized As a result of the operation of relay Vtir upon the functioning of signal receiver II, the relay Or is operated at the moment the selected out-v let is deiinitely seized and the register will then control the subsequent selecto-r setting, without moving the brushes of step-by-step switch OM. This takes vplace in the same way as was described in connection with Fig. 15. This second selector setting is so controlled by Or that the signal receiver II is rendered inoperative because direct ground is supplied to the controlling electrode of the tube B2. The overflow selector OS will, therefore, be sent in accordance with the rst digit, i. e. in accordance with the position of SM1, without any alternative operation.

After the overflow selector has found a free outlet, OM will take a step and the register will be ready to perform the setting of the second group selector in accordance with the second digit.

SYSTEM or FIG. 4 (CIRCUITS ACCORDING To FIG. 19)

This case differs from the foregoing only in 1 that for part of the levels one alternative level is present, and for another p-art of the levelsa second alternative level. The first alternative level is characterized by the presence of alternating current with a determined phase angle, e. g. Pl l, and the second alternative level by another alternating current with a phase angle of e. g. p l2. The desired result is attained by connecting signal receiver I via the b brush .of step-by-step switch SM1 with the reference current corresponding to the signaling currents in the desired level. Signal receiver II is connected to a reference current pil or cl2, under the controlv of arc c of the same step-by-step switch, depending on the selection of the first or the second level as the alternative to the desired level. The circuits are, therefore, like the one described in connection with Fig 18, with'exception of the jumpering and the provision in the glOup SeleotOr are a second alternative level characterized by alternating current cl2,

SYSTEM ACCORDING To FIG. 5 (KEY FIG. 20)

When a group selector tests in an alternative level, the last selector setting will be repeated in the seized b-y-pass-selector. If this by-pass-selector hunts also in an alternative level, then the register circuit takes care of it, that the by-passselector be released, and that the rst group Selector start hunting again under the same conditions as the first time. The result may be that either another by-pass-selector will be seized, in which case the preceding operation is repeated, or that the rst group selector will find a free outlet in the desired level. This will be signaled to the register as soon as it can respond by the setting of the next digit.

All these operations are already known from the foregoing description, with exception of the way in which a group selector releases a by-passselector and starts hunting again. In order to make this clear, the preceding operations will i also be briey described.

(a) First selector setting During the rst selector setting signal receiver I is connected to the reference current corresponding to the desired level, i. e. via arc b of the step-by-step switch on which the digit is registered. Signal receiver II receives a reference current corresponding to the signaling current which is present in the alternative level eleven. When an outlet in level elevenk is seized. signal receiver II responds and relay Vtn is operated, as are also the relays Vtar and Ftr. Tube Bz is extinguished,

relay Vtlr releases and relay Fhr is operated in series with relay Ftr. The second alternating current test is then made and relay Vtir operates once more, relay Str is energized, and the direct current test starts. Relays Tr and Dtr operate and the latter energizes relay Vtsr via the change over contact of relay Vtzr. Relay Vtsr applies ground for operating of relay On and this relay prepares a holding circuit for itself via the interrupter contact of OM.

As soon as the by-pass-selector is definitely seized, the circuit. to the direct current potential 16 for the setting of the by-pass-selector without OM being moved, so that the by-pass-selector is set according to the rst digit, since the connections to the reference currents of the two signal receivers are not changed. Y

(b) By-pass-selector tests in the alternative level eleven for the second time and relay Vtlr operates for' the second time; this circuit is as follows: ground, brush and a arc contacts of SM1, contact N and brush c of OM, back contact of Vtr, front`contacts of Vtir, Vtzr and Fhr, back contact of Bd?, front contact of Orz, winding of Bclr, to battery.

Relay Bdr operates and remains energized over make-before-break pendent of relay Orz to ground via the front contact of relay Vtir. It opens also the temporary operating circuit for the relays Ori and 0T2 so that these relays release, and closes a ground to wire c of the rst group selector, which wire leads to the point where the locking winding of relay Br is connected in the rvst group selector to the series resistance of 600 ohms.V The relay Br is, therefore, short-circuited and opens the circuit through which signaling current is supplied to the signal receivers. The release of relay Br causes the rst group selector to return to the condition in which the hunting for a freeoutlet may takeplace (only relay Ar operated).

When relay Ori is released, it closes a ground via a back contact and a front contact of relay Bdr for the operating of relay Vrr. This relay opens the circuit for relay Chr (which extinguishes the tube B2 and releases relay Vtir) and the circuit for the power magnet of the rst group selector over two back contacts. It opens the locking circuit for the relays Vt2r, Ftr and Fhr via a third back contact, whereby relay Bdr also releases. After this relay is released, which takes place somewhat slowly to assureY that the preceding relays have released, relay Vrr also releases and closes the circuit for relay Chr and for the operation of the power magnet.

The register circuit is now again in condition to control the setting of the ilrst group selector, because switch OM is still in the home position.

The register will again start the setting of the rst group selector. This selector is on a ycontact set belonging to one of the by-pass-selectors which, of course, is not in the home position because it had just hunted in the eleventh level. The first group selector will, therefore, leave this contact set.` The first free by-pass-selector will be given preference because the contact sets of the different by-pass-selectors are consecutively connected in the contact arc. The normal course will therefore be that when all desired outlets are found busy, all free by-pass-selectors will be occupied consecutively, and when the last one has tried without success to nd an outlet in the desired direction, the first group selector will start v again at the beginning of its arc and can start.

In other words, the rst hunt is for a free outlet in the first group selector arc itself.

Obviously, different variations are possible. For` instance, the selectors may be tested in the out-u closed for operating relay,VV

contact combinations, inde-

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