US1461528A - Automatic switch - Google Patents

Description

M w, 1923; i I EA6L528 F. s. IRVINE AUTOMATIC SWITCH Filed Sept. 22, 1920 7 Sheets-Sheet 1 Wye/77thflan/r J /rwhe. Q

July 10, 1923. I 1,461,528

- F. s. IRVINE AUTOMATIC SWITCH Mvenfor.

July 10, 1923.

Filed Sept. 22 1920 F. S. IRVINE AUTOMATIC SWITCH 7 Sheets-Sheet 4 July 10, 1923.

' F. S. IRVINE AUTOMATIC SWITCH Filed Sept. 22 1920 7 Sheets-Sheet 5 July 10, 1923.

F. S. IRVINE AUTOMATIC SWITCH Filed Sept. 22 1920 7 Sheets-Sheet ,6

H I Q July 10; 1923.

F. S. IRVINE AUTOMATIC SWITCH Filed Sept. 22 1920 '7 Sheets-Sheet '7 Patented July 10, 1923.

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FRANK S. IRVINE, OF HUNTINGTON, NEW YORK, ASSIGNOBTO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEVT YORK.

AUTOMATIC SWITCH.

Application filed September 22, 1920. Serial No. 411,880.

To all whom it may concern:

Be it known that I, F RANK S. IRVINE, a citizen of the United States, residing at Huntington, in the county of Suffolk, State of New York, have invented certain new and useful Improvements in Automatic Switches, of which the following is a full, clear, concise, and exact description.

This invention relates to automatic switching devices and more particularly to switches of the type used in telephone systems foreX- tending talking connections.

Where nonnumerical or finder switches are employed for seizing and extending subscribers lines either to succeeding selective switches or to operators positions, a convenient method of handling incoming calls is to divide the subscribers lines into groups and to assign the requisite number of finder switches to serve each of such groups of lines. It the capacity of the finders is large it is desirable to providethe finders with a plurality of sets of brushes, each brush set having access to a group of lines. By this arrangement only the particular brush set having access to thegroup of lines containing the calling line need be taken for use. Accordingly the finder is not required to move over the entire group of lines it serves, but only over a smaller group individual to a set of brushes in hunting and seizing a calling line. a

It is imperative that the period'consumcd by the finder switch in seizing a calling line be made as short as possible, especially where the lines are extended to switches or register mechanisms that are to be controlled by impulses sent from the substation. To materially reduce the hunting time it is proposed to divide each brush group into two subgroups and to connect the lines to the terminal banks such that one subgroup of lines appear as first choice lines to the brushes of half of the finders and as second choice lines to the brushes of the remaining finders. Likewise the second subgroup of lines appear as first choice lines to the second half of the finders and as second choice lines to the first half of the finders. Normally, when a call originates in one of the subgroups a finder having first choice access to this subgroup is taken for use. Hence, the finder is only required to move over the first half of a brush group. hen all finders, having aecess to a subgroup as first choice, are engaged and a call originates in that subgroup, i

one of the finders having second choice access to the subgroup is utilized, it anyof these be idle at the time.

As above stated a plurality of finders are provided-for servingeach of the subgroups. The first group of finders, for example, normally serve as firstchoice the first subgroup of lines of all brush groups appearing in those particular finders. The second group of finders normally serve as first choice the remaining subgroup of all brush groups. Since both groups of finders consist of a plurality of equivalent switches'meaus is necessarily provided to select an idle one for use in handling an incoming call. This is accomplished by the use of a series starter wire. To equalize the distribution of wear on the several finders of each group it is proposed to arrange the circuits such that the preferred order in which the finders of a group are taken for operation is shifted at each call.

Accordingly, the object of the present invention is to provide means, in a system of the foregoing character, whereby the order of preference, in which the finders or" either group are taken for use, is changed regardless 01": whether said finders are operated to serve one of their first choice lines or on of their second choice lines.

A feature of the invention relates to means operative each time a finder in either group is operated to extend a line to change the order in which the finders, of the group containing the operated finder, may betaken for use.

Other and further features contemplated by the invention will become more apparent from the following description.

Referring particularly, to the drawing, Figs. 1 to 7 inclusive, when arranged in the order illustrated in Fig. 8, disclose a portion of a telephone exchange system in which the principles of the invention are in- .corporated.

Fig. 1 shows two subscribers lines, one ineach subgroup of a group of lines, served by the same set of brushes of the finder switch. This figure also "shows the individual line relays and the group relays which control a series circuit for initiating the operation of the finder switches.

Fig. 2 illustrates diagrammatically a subscribers line in each of the two subgroups operation the proper one of a plurality of line finder switches in response to the initiation of a call. At the left of Fig. 3isillustrated one element of a preference SWltClr for determining the order in which the several corresponding subgroups of lines may gain access to the starter circuit. To the rlght of this figure is illustrated a switch for determining the preferred order in which the findersof a first group are taken for use. At the left of Fig. 4 is shown the second ele ment of the preference switch for determining the order in which the second subgroups of all brush groups may obtain access to the common starter circuit. At the right of Fig.

4'is shown another switch similar to the one illustrated at the right of Fig. 3 and serving to change the order in which the several finders of a second group are taken for use.

, Fig.v 5 shows in detail iiort ons of the structure and circuits of. one of the finder switches of the first group. Within the small broken rectangles inthe lower righthand part of the figure are shown ccrtaln elements of three finder switches belonging to the same group.

Fig. 6 illustrates in diagrammatic form certain parts of the structure and circuits of four different finder switches of the second group.

'Fig. 7 illustrates a district or first selector switch .to which calling lines are extended by the finder switch shown in detail in Fig. 5.

The line finder switches used in this system are of the well-known power driven panel type, The corresponding brushes of a plurality of finder switches serving the same group of subscribers lines are arranged to be tripped into active relation with the terminal bank by means of a com-- mon trip rod, such as shown and. described in the patent to McQuarrie, 1,17 7,044, issued March 28, 1916.

The'district selector switch illustrated diagrammatically in Fig. 7 may also be of the a es power driven panel type and is similar in construction to the switch disclosed in the patent to Craft. and Reynolds, 1,128,696, issued January 5, 1915.

--The preference switch shown atxthe left of Figs. 3 and 4 is an ordinary rotary stepby-step switch, the brushes 304 andv 404 of which cooperate with corresponding arcuate in their step-by-ste'pmovement by the stepping magnet 40 8, shown in Fig. 4. The two 1 preference switches, shown on'the righthand side of Figs. 3 and 4, arelikewise step- ;bystcp devices each comprising a pair of brushes and corresponding terminal arcs. The brushes of these'switches are driven by the steppingmagnets 307 and 407 respectively.

In order that a better understanding may be had of the purpose of the invention,a general description will first be given ofthe grouping arrangement of the subscribers lines in a system ofthis character. Itmay be assumed for the purposev of illustration that the subscribers lines, such as 100, 110, 200, 210, etc. are dividedin major groups. of300 lines each. Accordingly, the finder switches, in the terminal banksof which. the subscribers lines appear, each have. acapa-city of 300 lines. It may further-beconsidered that the finder switches are provided. with 15 sets of brushes, each set at brushes, consequently, havingaccess to 20 subscribers. lines... With the arrangement of trippingbrushes used in switches of this character, it. is only necessary for the finder to move a distance corresponding to a brush group of 20. lines to seize and make connection with any calling line. That is, when a subscriber initiates a call the particular set of'brushes, of. anidle tinder SWltCll' havlng access to the group containing his line 1s tripped and: moved over the terminals of the group in search'of. such belong to the A group of their respective brush groups, while lines 110, 210, 230 belong to the B groups of the same brush groups. In other words there are ten lines similar to 100 in the A subgroup, and ten linessimilar to in the B subgroup ofthe particular brush group of twenty lines illustrated. in Fig. 1. Similarlythe same appliesto the lines shown in Fig; 2 for all of the remaining brush groups which are not shown in the drawing. Conforming with the subdivision of a brush group of lines into the A and B sub-groups, the entire group-of line finder switches serving a major groupof 300 lines isdi-videdinto two groups designated, the

number of finders assi ned to serve ama'or .c. y

nee-recs group of 300 lines may be taken to suit the requirements and is governed largely by the volume of the tralfic. Whatever this number may be it is divided equally or otherwise, if desired, into two groups, one of which, the A group, normally serves subscribers lines in the several A subgroups, and the other, the B group of finders, normally serves the subscribers" lines in the B subgroups. The finders of the A group are illustrated in F 5, and those of the B group in Fig. 6.

Referring to Fig. 5, one brush set and the section of the terminal bank cooperating therewith is illustrated. This section of the terminal bank is shown divided into two sections, a'lower sectionand an upper section. The subscribers line 100, which belon s to the A sub rou terminates in ter:

minals 516, 517, 518 and 519 of the lower section of terminals in the finder switch. The subscribers line 110, located in the B subgroup, terminates in the terminals 526, 527, 528 and 529 of the upper section in the finder switch. In a similar manner the ten subscribers lines of the A subgroup appear in the lower sections of terminals served by the corresponding brushes of the remaining finders of the A group. The ten subscribers lines of the B subgroup appear in the upper sections of terminals of the corresponding brush sets of all finders in the ll. group.

T tuning to Fig. 6 it will be seen that the subscriber's line lO0,nwhich appears in the lower section of terminals in theA finder switc es, terminates in terminals 615, 616, 617 and 618 of the upper section of terminals served by the brush set 604 of finder 600 of the B group of finders. In a similar way line 100 and the remaining lines of the A subgroup are multipled to corresponding terminals in the upper section served by the corresponding brush sets of the remaining finder switches 601, 602 603, etc. of the B group. Conversely, the lines, such as 110 of the B group, which appear in the upper groups of terminals in the A finders, are seen to be multipled to terminals 620, 621', 622 and 623 of finder 600, terminals 624, 625, 626 and 627 of finder 601, and to corresponding terminals in the lower sections served by the brushes of the remaining finders 602, 603, etc.- of the B group. The ten lines, such as 200 of the subgroup of the second brush group, would appear in a similar'manner in the lower'half of the sections served by a second setof brushes of each of the A finders, and in the upper half of the sections served by corresponding brushes of the B finder switches. Similarly, lines, such as 210 of the B subgroup of this particular brush group, would appear in the upper half of the brush section at the A finders, and in the lower half at the B finders. The same may be said of the lines of all remaining brush groups.

Briefly stated, by this grouping arrangeis used.

inent the lines of the A subgroup of each of the fifteen brush groups of lines appear as first choice lines in the A. finder switches,and as second choice lines in the B finder switches. The lines of the B subgroups of each of the fifteen brush groups, in a like manner, appear as first choice lines in the,

B finderswitches and as second choice lines in the A finder switches. Consequently, whenever a call is initiated in one of the A subgroups, an A finder switch, if one be idle, is set in operation to find the calling line and in'so doing need traverse only a maximum of ten terminals. When a line in one of the B subgroups initiates a call, one of the B finder switches, which has first choice access to such line, is started in operation. Should a line originate a call in the A group when all of the A finders are busy, then, by means hereinafter to be explained, one of "the B finder switches is taken for use and must first traverse the lower section of ten terminals before it can enter the upper section to search for the calling line. In a similar fashion should a line in the B group initiate a call when all B finders are busy, then an A finder is taken for use, if one be id e at this time, to extend the calling line.

Where the series starter wire is employed for controlling the starting of an idle finder switch of a plurality of switches, experience shows that anunequal distribution of wear on the switches is certain to result. If all finders be idle and a call comes in, the first finder in the series is taken for use. If during the busy period of the first finder another call occurs, the second finder in order Only when a large number of simultaneous calls occur will the switches toward the latter end of the series be utilized. Hence, it is, obvious that the switches in the first of the series will bear the greater part of the work. To overcome this undesirable condition .a preferenceswitch is provided, the function of which is to shift, from time to time, theorder in which the finders of a group are taken for use. The switch indicated at the right of Fig. 3 performs this function with respect to the finders of the. A. group shown in Fig. 5. The preference switch shown to the right in Fig. 4: cooperates similarly with the several finders of the B group. Whenever a finder switch in. either group is taken for use the preference switch, serving such group is advanced one step whereby a new" order of preference in the appropriation of an idle switch is established. In this way the number of times that any particular switch is operated is substantially equal to the number of operations made by each of the other switches of the group. f

It is desirable that the orderin which the finders of either the AorB groups are taken for use may be shifted after the operation of any finderin such groups, regardless of whether such finder serves a l ne in the A subgroup or a" line in the B subgroup; Ac,-

cordingly, it is the purpose of this invention to provide a circuit arrangement whereby the pretercnceswitch governing the order in which :1 group of finders are taken for use may be advanced whenever one of such finders is operatedeither to serve a line to which. it s normally allotted'or to serve one of its second choiceiines as in the case when all thefinders in the other group are engaged.

. Havin iren. a general explanation of the i system, Jb iS'HOWlthOUght that a detailed description of the operations involved in the extension of a, calling line will be helpful W n'obtaining understanding of the 111- 2 nection. Upon removing his receiver from vention. I v It will be assumed that the subscriber to line 100wishes to obtain a telephone conthe switch hook a circuit is established from hand} armature, conductor 115., group relay battery through the winding of'line relay 104, inner left-hand armature and contact of cut-off relay 103, line conductor 1 102, through the loop of the calling substation, line conductor 101, contact and right-hand armature of relay103 to ground. Relay 1.04 becomes energized and completes a circuit from. ground through its contact left 105, common to the ten lines. of the .A group to battery and ground. 'Re].a.y105 becomes energized and completes a circuit from ground through its contact and arma ure, contact and armature of relay 106, lefthand armature and back contact of relay I i 107. left-hand, winding oi. relay 108, conductor 116.," outer left-hand armature and con.-

t-act of relay 302, outer left-hand armature p and contact of relay 402, contact. and arma- I first preference is. given to lines in the A and B subgroups of the first brush group shown in Fig. v1. In the event that a call,

should originate in this brush group simul taneously with the initiation of acall in any of the. other brush groups, such as those shown in Fig: 2, first preference is givento thatparticular brush group Whose relay,

such as relay 108 or 1.18, may obtain a locking; circuit through its righteha-nd Winding directly through-thewiper 804 or 404 without first passing throughthe back contacts and armatures of relayscorrespondingwto relays 108 and 118 in other brush groups. l Vith the preference: switch in the position indicated in the drawing, the holding circuit tor the righthandwinding of relay 108 is seen to lead directly through-the ter- 1nina1-309 and brush 304, thus giving first choice to lines in the A, grou'p of the'first brush group. I

The relay 302 becomes energized series" with the right-hand winding :01 relay 108,

and this latter relay remains energized. .Re'- lay 108,-at the same time, completes a circuit for the'trip magnet 5.05,;which governsthe tripping of the particular set of brushesin all finders of both A and '13 groups, which have access to the terminals oij'sthe; calling line 1.00. This circuit leads from ground through the inner left-hand armature and contact of relay 108, conductor 1'24, Winding of trip magnet 505 to battery and ground. llelay 302, at its outer left-hand armature and contact, opens the circuitto the conductor .116, thereby preventing the energization of the relay similar to relay 108 in any other brush group. Relay 802, at its inner right-hand armature and; contact, closes'a circuit from ground over conductor 312, through the Winding of stepping magnet 408, to battery and ground. Magnet 408 becomes energized preparatory to advancing the brushes 304 and 404 to their next position terminals. Relay 302' also completes a circuit from ground through its outer right-hand armature and contact, conductor 313, left-hand make-before-brealr contact of relay 303, brush" 306, terminal 314, conductor 31.5, inner left-.handarmature and back contact of relay 500, winding of 1 relay 504 t battery and ground. Relay 504 becomes energized and locks up in a circuit from battery through its winding and contact and inner left-hand armature, conductor 530, contact and armature of relay 522 to ground. Relay 504 completes a circuit from ground through its outer left hand armature and front contact, contact and outer right,-, handarmature of relay 500, conductor 316, right-handmake-before-break contact of relay 303, Winding of said relayto battery and ground. Relay 303 becomes energized and looks up in a circuit from battery through its windin rand "righthand armature and.

make-beforebrealr contact, conductor 313 toground at the outer right-hand armature or relay 302. Relay 303 completes a circuit from battery through'the windingrof stepping magnet 30?, brush '305, left-hand armature and contact of relay 303, conductor 318, contact and outer right-hand armature of relay 302 to ground. The magnet 307 becomes energized and prepares to advance the brushes305 and 306 forward one step when the circuit of said magnet is opened.

- Relay 504 also closes a circuit at its righthand armature and contact for the up-drive power magnet 506 of the finder switch shown in detail in the drawing. As will more fully be explained later, the selection of this finder switch for use is based on the assumption that the brush 306 of the preference switch is standing in the position shown and that said finder is idle at the time the call originates. The power magnet 506 causes the upward movement of the brush shaft 508. Since the, trip magnet 505 is energized in the circuit above described, the trip spindle 511, which is common to the brush sets of all finders in the A and B groups shown in Figs. 5 and 6, is rotated to its set'position. The first upward movement, therefore, of brush 508 causes the brushes 512, 513, 514 and 515 to be tripped so as to engage the terminalsof the bank. Shortly following the tripping of the set of brushes, the brush 520 encounters the metallicseglnent 531 and a circuit is closed from ground through" brush 520, segment 531, outer left-hand armature and contact of relay 523, conductor 317, back contact and inner left-hand armature of relay301, conductor 121, contact and outer left-hand armature of relay 108, winding of'relay 107 to battery and ground. Relay 107 becomes energized and locks ,up in a circuit from battery through its winding and front contact and left-hand armature, conductor 122, armature and contact of relay 106 to ground .at the armature and contact of relay 105. Relay 107, at its right-hand contact, opens the holding circuit. of relay 7 108, whereby this latter releases its armatures.

The deenergization of relay 108 causes the opening of the circuit of trip magnet 505 and the common brushtrip rod 511 restores to its normal position. Relay 108, furthermore, opens the circuit of relay 302, which becomes deenergized. Relay 302, at its outer left-hand armature and contact, closes the conductor 116 so that further calls in the same or other brush groups may now gain access to the common starter circuit. Relay 302, at itsv inner right-hand armature, opens the circuit of magnet 408, which becomes deenergized "and advances the brushes 304 and 404 of the preference switch to their next position terminals. Relay 302, atits outer right-hand armature, opens the circuits of relay 303 and magnet 307. Relay 303 releases its armatures while magnet 307 becomes deenergized to advance the brushes 305 and 306 forward one step. At

the time relay 107 becomes energized as the however, is non-inductively wound and does is closed from ground through the outer right-hand armature and contact of relay 523, windingof test relay 522, brush 512, terminal 516, conductor 123, right-hand armature and front contact of relay 104, contact and outer left-hand armature of relay 103, left-hand winding of relay 106 to battery and ground. The test relay 522 be comes energized in this circuit and opens the holding circuit of relay 504. Relay 504, however, is maintained energized in a circuit over conductor 530, commutator 521 and brush 520 to ground. When the brushes of the finder switch are accurately centered on the terminals of the calling line, brush520 engages an insulating segmentof commutator 521, and relay 504 releases its armatures. Relay 504 opens the circuit of the up -drive power magnet 506 andthe brush shaft 508 ceases its upward movement.

Belay 106, which also energizes in series with relay 522, opens the holding. circuit of relay 107. Relay 107, being of the slowto release type, does not retract its armatures immediately after its circuit is opened by 3 the energization of relay 106. Although the right-hand winding of relay 106 does not furnish suflicient magnetic flux to attract the armature, said winding will maintain the attraction of the armature, once it has been operated by the energization of the left-hand winding. Consequently, relay 106 will remain in its operated condition as long as relay 107 maintains its armature attracted to hold the circuit for the right-hand winding of said relay 106 closed.

As soon as the finder switch leaves its normal position the off normal contact 525 is closed and relay 524 becomes energized. Relay 524 completes a circuit from battery through the left hand winding of relay 500 to ground at the contact and inner left-hand armature of relay 524. Relay 500 serves to indicatethat the finder switch is busy and to extend the starter wire 315 forward to the armature of the corresponding relay 501 at the next finder switch, as will be more fully explained hereinafter. The operation of relay 524 causes the energization of-relay 707 at the district selector switch by means of a circuit from battery through the winding of relay 707, conductor 715, contact and inner right-hand armature of relay 524,- conductor 716, contact 702 (1 to 10) of sequence switch 700, to ground. Relay 707 being energized, a circuit is established for relay 706 as soon as relay 504 releasesits armatures at the end ofthe movement of the finder switch. This circuit may be traced fro-n'i ground through the outer left-hand armature and back contact'of relay 504, conductor 53-2, contact and outer right-hand arma ture of relay-524, conductor 717, Windingot relay 706, contact 705 (1 to 15), front contact and left-hand armature of relay 707, conductor 718, to battery and ground at the left-hand normal contact of relay 523. Re-

lay 700becon-1es energized and closes a circuit for drivingisequence switch 700 out of position 1 and into position 2. This circult leads from battery through the winding of sequence switch 700, contact 701 (1), contact iand -leitt-hand armature of relay 706' to ground.

Re'la'y706 also'closes a circuit for the operation of the cut-E relay 103 of the calling subscribers line 100. This circuit leads terval following the operation of relay 5.- tjonsequently, relays 10-7 and 106 maintain v105 rele'ases its armature.

from battery through the right-hand arma ture and front contact of relay 706, conductor.71-9 brush 513, terminal 517 conductor 125-, \vindinglot relay 1'03 to ground. Relay 1'03 opens the circuit above traced for the line relay 104, permitting the latter to release-its arn'iatures. The release of the lefthand armature of relay 104 removes ground from conductor 115, and permits the dcen- "ergiza tion of relay 105, provided no other line relay corresponding to relay 104 in the A group is'ene'rgized at this time. Relay The time re quired for the deenergization of the slow to release relay 107 is so taken that said relay maintains its armatu-res attracted for an'inrelay 108 become d'eenergized, the conductor 122 is open at the armature and contact of relay 105', and relay 108 cannot be reoperateddue to the same call to start a second finder switch hunting.

i The calling subscribers line has th usbeen extended over brushes 51.5 and-514 ot a finderswitc'h in the A group, conductors 533 and 534 to sequence switch contacts 710 and- 711 at the district selector switch. By

' means of the usual sender selector switch (not shown) the subscribers line may be .turthe'r extended over conductors 720 and 721 to'an idle register sender; A district selector switch substantially of the character as the one employed herein, having an indivi'chial sender selector for associating v "the ,subscribers line with an idle register thepatentto Steam and Scudder, No.

sender, is shown and described in detail in 1,395,977 granted November 1, 1921. The

calling line having been extended to a register sender, the calling subscriber may pro ceed to transmit impulses by means oii his dial 126 to set up the designation of the called line on the registers of the sender. Following the registration of the desired number the sender operates to control the selective movement of the switch shown in Fig. 7 to set the brushes 712, 713. and 714 on a trunk leading to the proper succeeding switch, and thereafter to control such switch and as many other switches, as may be involved in the particular connection being extended. During the time that the switches are being positioned under the control of the sender, the se'quence'swrtch 700- is ad'- vanced from position to posltion in the manner-fully described in the above mentionc'iil Patent No. 1,395,977, grant-ed November 1, 1921, until it reaches position 12, which sequence switch 700 leaves position 9%, conductors 720 and 721 are disconnected from the calling subscri-hers line. As. sequence switch 700 reaches position 9%}, the right-= hand contacts 710 and 711-a're closed to ex tion 10, contact 702 is opened and the origi nal energizing circuit of relay 707 is i-ntere rupted, but this relay remains operated in a circu t from battery through the Winding inner .right h-and armature and contact of relay 707, contact 703" to18 l) to ground.

At the end'of the conversation the calling subscriber replaceshis receiver to the switchhook and relay 7 08 releases its armature.

Relay 708 opens the circuit of relay 707, which also becomes deener'gized The, 'se quence switch 700 is their driven into position 18' as by means of. the following circuit: battery, through the winding of the magnetof said. seqi'rence'switch, lower-contact 701 (10 to 17)", contact and outer right-- hand armature-Jot relay'707to ground. In.

this position of sequence switch 700, the relay 523, individual to the finder switch, is energized in a circuit from battery through the left-hand normal contact of said relay, conductor 718, left-hand; armature and back contact of relay 707, contact 704 (17 to 18),

conductor 722. winding of relay. 5'23, and

contact and outer left-hand armature of reflay 524 to: ground. Relay 523 becomes energized and. locks up in a circuit from battery over its ma-ke before-break contact and inner left-hand armature, winding of said relay to ground at the. outer left-hand armature of relay. 524. In anysuitable manner,

such as that described in the above mentioned. Patent No. 1,395,977, vgranted N0- 1'00 thereof, armature and contact of relay 708,

85 may be taken as the talking position. When j vembcr 1, 1921, the district switch shown the winding of downdrive power magnet 507, contact and inner right-hand armature of relay 523 to ground. Power magnet 507 causes the brush shaft 508 to move downwardly. On reaching the; normal position the brush shaft 508 opens the 011' normal contact 525, causing thereby the deenergization of relay 524. Relay 524 opens the holding circuits of-relays 500' and 523. Relay 523 causes the deenergization of the downdrive power magnet. and relay 500 renders the finder switch available for further calls.

It will next be assumed that the sub-- scriber of a line, such as line 110 in the B subgroup of the brushgroup illustrated in Fig. 1, wishes to obtain a telephone connecrelay 113, left-hand armature and back con tact of relay 114, left-hand winding of re lay 118, conductor 116, outer left-hand armature and contact of relay 302, outer lefthand armature and contactof relay 402, contact and armature of stepping magnet 408 to battery and ground. Relay 118, which corresponds to relay 108, becomes energized in this circuit and locks up in a circuit as follows: ground, through the right-hand normal contact of relay 114, right-hand winding and front contact and lnnerr1ght hand armature of relay 118, conductor127, terminal 409, brush 404, assuming the preference switch to be standing in its first position, left-hand armature and back contact of relayv 400, conductor 410, back contact and right-hand armature of relay 301, conductor 318, winding of relay. 402 to battery and ground. Relay 118 operates in the same manner as explained in connection with .relay 108 to close a circuit for the trip magnet 505 controlling the sets of brushesof the A and B groups of finder switches having access to the terminals in which the lines of this particular b'rush group appear. This I 118, thence as above traced over conductor.

124 to thewinding of magnet 505. It will be observed that a call originating in the and, at the same time, a the-A subgroup of the second brush group B subgroup results in the operation of relocks up in "series with relay 402 of the common starter circuit, which corresponds to the relay 302 used in connection with calls originating in the A subgroups.

Relay 402 opens the conductor 116 to prevent'the cnergization of other relays similar to 108 and 118,and also closes a circuit at its inner right-hand armature and front contact for stepping magnet 408. Furthermore, relay 402 completes a circuit from ground through its outer righthand armature and contact. conductor 411, left-hand normal contact of relay 403, brush 406, terminal .412, assuming the preference switch to be standing in its first position, conductor 413, inner left-hand armature and back contact of relay 607, winding of relay 611' to battery-and ground. Relay 611 is individual to the finder switch indicated at 600 in the B group of finders and corresponds to the relay 504, shown in Fig. 5. The venergization, therefore. of relay 611 brings about the operation of the idle finder switch. 600, which advances its tripped set of brushes into engagement withterminals 620, 621, 622 and 623 of the calling subscribers line in the B subgroup. From this point on the establishment and releaseof the connection proceeds in the same man ner as the call discussed in detail above.

Considering the two calls above described, one occurring in the A subgroup and the other in the B subgroup of the brush group illustrated in 1', it was assumed that the lay 118 individual to this subgroup which brushes 304 and 404 were standing in both already stated, withthese brushes on their first position terminals preferenceis given to the first brush group shown in Fig 1 over allsucc'eeding brush groups inth'e event of simultaneous calls. F or example, assume that with the preference switch in its first position a call originates in the A subgroup of the first brush group shown in Fig. 1, call originates in illustrated in Fig. 2. As already explained, relay 108 and relay 208 become energized in response to these calls by means of circuits closed through their left-hand operative windings and conductor 116. Relay 108 islocked up over its right hand winding in a circuit including conductor 117, which leads directly through the'brush 304 of the preference switch to the winding of relay 302. Relay 208, however, of the second brush group has'a path completed as follows for its right-hand winding: ground,

through its right-hand winding and. front contact and inner rigl'it-hand armature, conductor 201 to the second term1nal319 of the preference switch. Since the preference switch brush 804 is standing in its I first position, the above traced path'for. the

i 5 ,right-handwindingof relay-208 fails to be completed through to the winding of relay 302. Another path is-closed as'follows: ground through the right handwinding and front contact and innerright hand armature of relay 208,conductor-202, and back contact and outer right-hand armature 'of l'elay 118 to the back contact ,and inner right hand armature of -1'elayjl0S., Since, relay 1081s energized, this 1c1rcu1t is also) opened -.-and, consequently, relayu208 ofthesecond brush group must release its armatures'as soon as relay 302 becomes energized iniseries with relay 108. Hence, where two-calls :originatein different brush groups simul- -tancously,-the one having the highest-order be seen that the other-brush 404E of-tlie preference switch governs in a similar manner the order inwhi-ch the different B subgroups.

Lmay 'obtain'access to the common starter fcircuit shown in Figs. 3 and 4.

With the preference switchin a given position, assigning first preference to a pvrtlcular brush group, ifa call originatesin' any other brushgroup, it may succeed in gainlng access to the common starter circuit provided no call occurs simultaneously in ";-any group having a higher order of preferenceat that particular'time. For exan1-i ple', assurne that a'call s initiated on the line 230 ofthe B subgroup of thethird. brush group, while the preference switch is stand- 'ng initsfir'st pos1t1on,.namely,' nthe posi-v tion to which the first preference isawarded v tothe first brush group. Relay 288 becomes -.-the relays 108, 118,208 and 218, belonging energized in response to thecall-and locks up over its right-hand winding since none of to groups having a higherorder of-zprefen ence, are energized atthis time. The locking circuit for relay 238 maybe traced from ground through the right hand winding and Jfront contact and inner right-hand armature of relay 23S, conductor 203, back contact'and outermightz-hand armature of relay208, back contact and inner right-hand armature of relav 218, conductor 204-, back contact and outer right-hand armatureofrelay 108,"back conta ct and inner right-handarmature .ofrelay 118, 1 conductor 127, terminal 409, brush 404C, and thence, as above described, to battery andground, through the winding of relay 402. Relay 4:02' operates, as explained,

toiinitiatethe movemento'f an idle line find- I er" switch of the group to makecon-nection with the'calling subscribers line. Following the extension of each connection 'the preference switch-brushes 304: and 4.04am

.advancedby the stepping'magnet 408tozes GI'S.

finally reaches :an idle switch.

'tablish: a new order of preference among the :brushgroups. In this manneran equality vof serviceis given to all-subscribers lines and no particular group of lines will be favored by. reason of its'location in the finder switches, i p

ltwas describedhereinbefore how the preference switches, shown at the xright :of iF1gs.'3-and 4-, are advanced from position :to position ifollowing the operation, of (a I findersvvitch inthe A and groups. lVith the brush 3060f the switch shown in Fig.

'3 standing in its first position,'the starter wire is extended first to the armature of-relay 500, individual to the first finder in the A group, namely, the one shown in detail in'the drawing. Should thisiinderbe idle when a call originates, it will be taken for use in preference to allsucceeding fin'd- Following the operation of the first finder, the brush 306 advances to its second position terminal, whereby the starter wire is extended to a correspondingzarmature of relay 501, individual tothe second finder switch in the A grvoup, and this switch now becomes the first preference. .Correspondingly, following the operation of each finder switch the preference switch advances one position and gives the first choice of selection to anew finder-switch. If the particular finder to which the first preference is given by the switch arn1"306 be busy, then the starter wire will be extended over the armature and front: contact of th'e-relay, such-as 500, to the armature of the corresponding *relay of the next finder-switch in order. -This'Inanne1'..of,ex--" tending the starter wirefcan .be more :fully seen by referring: to the relays 607, 608,- 609 and 6100f the four finderxswitches of'the" 'B group, shown inl ig;16.' 'Considerf that the preference switch pertaining to the 'B group of finders is standing'with itsbrush 106 on the first position terniinal ilQQ .In

this position first preference is given to wire leads directly over conductor 413'to theinner left-handarmature 'ofrelay 607. Should the first finder switch 600, however," be engaged at thetimea call originates in one of theYJB subgroups,then the starter wireis extended by wayof brush" 4:06, terminal 4:12, conductor 413,.innerleft- 'handarmature and front contact ofrelay 607, conductor 628 inner "left-hand armature and backucontact ofrelay 608 assuming finder switch 601 to be idle, throughgthe winding of relay 612. 'Relay'612 thereupon serves to start the finder switch 60l .:into

operation to find the calling line. In a represent busy finder v switches until it similar manner the starterwirelmay be 0X- tended over'the armatures'and front contacts of all relays 607, 608, .009, etc., that 7 It will lastly be considered that a call is initiated on a line in the A subgroup, such as line 100, when all of the A finder switches having first choice access to such line are busy. Since all of the finders A are busy, relays 500, 501, 502, 503, etc., are all energized, consequently, a series circuit is closed from ground through the contacts and lefthand armatures of these relays, conductor 320, left-hand winding of relay 300 to battery and ground. Hence, when the group relay 108 is energized, its locking circuit is closed as follows: ground, through the right-hand normal contact of relay 107, right-hand winding and front contact and inner right-hand armature of relay 108, con- .ductor 117, terminal 309, brush 304, provided the preference switch is standing in its first position, left-hand armature and front contact of relay 300, winding of ,re-

" lay 301 to battery and ground. Relay 301 attracts its armatures and completes a circuit from battery through the winding of relay 402, conductor 318, right-hand armature and front contact of relay 301, conductor 321, contact and outer right-hand armature of relay 400 to ground. Relay 402 therefore becomes energized in response to the initiation of a call in the A subgroup. Relay 402, as already explained, causes the energization of stepping magnet 408, opens the circuit to conductor 116 to prevent the initiation of other calls, and closes the starter wire through brush 406 to .an idle line finder switch in the B group. The chosen finder switch is operated, moves over the first ten terminals and hunts for the terminals of the calling line inthe upper section of ten terminals, Since it is assumed line 100 is calling and provided the finder switch 600 happens to be the one taken for use, the set of brushes 604 are driven into engagement with the terminals 615, 616, 617 and 618 of the calling line. When the calling line has been found, relay 403 becomes energized in the manner similar to that explained in connection with relay 303 and causes the energization of stepping magnet 407. When later relay 402 deenergizes due to the energization of relay 107, relay 403 releases its armatures and stepping, magnet 407 advances the brushes 405 and 406 forward one position, thereby changing the order in which the finder switches of the B group are taken for use.

What is claimed is 1 1. In a telephone system, subscribers lines arranged in a plurality of groups, automatic switches arranged in a plurality of groups for serving all of said lines, and arranged to be taken for use in a given order, each group of switches arranged to serve as first choice a different one of said groups of lines, means responsive to a call in any group of lines to operate an automatic switch in the group normally serving such group of lines as first choice, means for operating a switch in'another group when all the switches normally serving as first choice the group of lines containing the calling line are busy, a preference device for changing the order in which the switches of a group are to be taken for use, and means responsive to theoperation of a switch for operating said device whetherthe operated switch is taken to serve its first choice group of lines or-another group.

2. In a telephone system, subscribers lines arranged in a plurality of groups, automatic switches arranged in a plurality of groups for serving all of said lines, and arranged to be taken for use in a definite order, each group of switches arranged to serve as first choice a different one of said. groups of lines, means responsive to a call in any group of lines to operate an automatic switch in the group normally serving such group of lines as first choice, means for operating a switch in another group when all the switches nornally serving as first choice the, group 'of lines containing the calling line are busy, a

step-by-step preference switch for changing the order in which the automatic switches of a group are to be taken for use, and means responsive to the operation of an automate switch for advancing said preference switch whether the operated automatic switch is taken to serve its first choice group of lines or another group of lines.

3. In a telephone system, subscribers lines arranged in a plurality of groups, automatic switches arranged in a plurality of groups for serving all of said lines, and arranged to be taken for use in a given order, each group of switches arranged to serve as first choice a different one of said groups of lines, means responsive to a call in any group of lines to operate an auto. matic switch in the group normally serving such group of lines as first choice, means for operating a switch incanot-her group when all the switches normally serving as first choice the group of lines containing the calling line are busy, a preference device for each of said groups of switches for changing the order in which the automatic switches of such groups are to be taken for use, and means responsive to the operation of an automatic switch in any group for.

operating the preference device indvidual to serve as first choice a difierent one of saidgroups of lines, means responsive to a call in any group of lines to operate a finder switch in the group normally serving such group of lines as first choice, means for operating a finder in another group when all of the finders normally serving as first choice the group of lines containing the calling line are busy, a preference device for changing the order in which the finders of a group are. to be taken for use, and means responsive to the operation of a find- 1 er switch for operating said device whether the; operated finder is taken to serve his .first choice group ol lines or another group.

5. In a telephone system, subscribers lines arranged in two groups, a plurality of finder switches arranged in two groups, and ar ranged to be taken for use in a given order, each group of finders arranged to serve both groups of lines and to serve a different one of said groups of lines as first choice,

whetherthe operated finder is taken to serve a line in its first choice group or av line inthe other of said groups of lines. 7 I 6. In a telephone system, telephone lines divided into a plurality'ot groups, automatic switches arranged in a plurality of groups for serving all of said lines and arranged to be taken for use in a given order, each group of switches serving as first choice a different one of sa d groups of llnes, means foroperating normally the automatic swltch 1n the -group serving as first choice the group or lines containing a calling line, means for operating a switch in another group when all the switches normally serving the calling group are busy, means for changing the order in which the switches of a group are tovbe taken for use, and means rendered eifeotive upon the operation of a switch for operating said last mentioned means whether the operatedswitoh is taken to serve its first choice group of lines or another group.

7,, In a telephone system, telephone lines divided in a plurality of groups, automatic switches arranged in'a, plurality of groups for servingall of said lines and arranged to be taken for use 1n, a defimte ordenea'ch group of switches servmg as first choice a different one or said'groups of lines, means 7 responsive to a call inany group of lines to operate an automat c switch in the group normally serving the calling group as first choice, means for operating a switch in another group when all or the switches nor mally serving a calling group are busy, means for changing the order'in which the switches of a group are to be taken for use, and means responsive to the operation of a switch for rendering said last mentioned means effective whether the operatedswitch is taken tofserve its first choice'group of lines or another group.

8. In a telephone system, subscribers? lines arranged in a pluralityof groups, automatic switches arranged in a plurality of groups for serving all of said lines and, arranged to be taken for use in a given order, eachgroup of switches arranged to serve'as first choicea different one of said groups of lines,'means responsive to a call 111 any group oflmes to operate an automatlc' switch in the group normally serving said group of lines as first choice, means for o crating a switch in another group when a l the. switchesnormally serving as first choice a group of linescon taming thecalling lineare'busy, and a preference device for changing the order in which the switches of a group" are to be taken for use. p I

9] In a telephone system, subscribers lines arranged in a plurality of groups, automatic switches arranged in a plurality of groups forserving all ofsaid lines and arranged to.

be taken for use in a given order, each group of switches arranged to serve as first cholce a dl'fierent one of said groups of l nes, means responsive to acall in any groupoflin'es to operate ani automatic switch in the group normally serving saidgroup of l1nes as first choice, means for'operating a. switch in an other group when all the switches normally serving asfirst choice a group or lines con: taining the calling line are busy, and a .preference device for each of said groups of switches for changing theorder in which the switches otsaid groups are to be taken for use. I 1

In witness whereof, I hereunto subscribe my name this 15th day of September A. D., 1920.

FRANK s. ravine.

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