US2866853A - Rotary finder with graded multiple - Google Patents

Description

Dec. 30, 1958 C.EQLOMAX ROTARY FINDER WITH GRADED MULTIPLE Filed Nov. 18, 1953 4 Sheets-Sheet 1 CLARENCE E.LOMAX zur@ ATT!

Dec. 30, 1958 c. E. LoMAx ROTARY FINDER4 WITH GRADED MULTIPLE Filed Nov. 18. 1953 4 Sheets-Sheet 2 N .mi

Dec. 30, 1958 ck. E. LoMAx ROTARY FINDER WITH GRADED MULTIPLE 4 Sheets-Sheet 3 Filed Nov. 18, 1953 INVENTOR. CLARENCE E. LOMAX I BY l Dec. 30, 1958 c. E. LoMAx 2,866,853

ROTARY FINDER WITH GRADED MULTIPLE Filed Nov. 18. 19,53 4 sheets-sheet 4 INVENTOR. CLARENCE E. LOMAX AT TY.

United States Patent ROTARY FINDER WITH GRADED MULTIPLE Clarence E. Lomax, Chicago, Ill., assigner to Generai Telephone Laboratories, Incorporated, a corporation of Delaware Application November 18, 1953, Serial No. 392,891

14 Claims. (Cl. 179-18) This invention relates to telephone systems and more particularly to the arrangement of finder switches therein and means for allotting said finders for use.

In early systems utilizing finder switches, each finder had access to one group of lines and had a numerical switch individual thereto. These numerical switches (selectors in large systems) were expensive however, and demands for economy necessitated a search for reducing the number of these switches necessary in a given system to provide a predetermined grade of service.

One of the earlier steps taken was to provide finder switches of one capacity having access to a group of lines and switches of double that one capacity and having access to two groupsof lines. As a result, the number of numerical switches in a given system could be reduced without impairing the grade of service as is well known in the art. However this method had practical limitations with respect to the number of lines any one inder switch could serve.

Further development led to the utilization of inexpensive rotary finder switches all of the same size but some of which were multipled with other finder switches which served other groups of lines. This had the same effect as using finders of dierent capacities while eliminating the disadvantage associated therewith.

To further reduce the number of rst selector switches in larger systems, the finders were graded-i. e. those serving a smaller number of lines being taken into use first.

Each development gave rise to problems of allotting, especially since finder control circuits were arranged in the allotter common to a group of finders to gain economy, and allotter circuits became increasingly more complicated. Simplicity, fiexibility, economy, and technical and commercial feasibility all had tol be taken into account in order to design a practical operating system. In the copending application of Graybill et al., Serial No. 345,028, filed March 27, 1953, now Patent No. 2,769,863, a highly exible and economical straight graded multiple system was disclosed, which system was especially adaptable for smaller systems having for example 300 lines.

However said Graybill system would become more unwieldly if the size of the system were greatly increased-e. g. extending chain circuits to widely scattered rst selectors in a much larger exchange. One of those chain circuits of said Graybill system was used for the purpose of rendering a third choice finder unavailable to its allotter if, while it was available, a second choice finder became idle and available to said allotter. The other chain circuit of said Graybill system was an all trunks busy circuit which prevented further rotation of the allotter if all trunks available thereto by way of its finders were busy and which circuit permitted further rotation of the allotter as soon as one trunk became idle.

Also in the system of said copending Graybill application, wear on the selectors could be more evenly distributed by a slipped arrangement ot the multipled findice ers--i. e. a third choice finder accessible rst in priority of use within its group ot third choice hders could be multipled with a third choice finder second in priority of use within its group and with other finders third, fourth and fifth in priority of use Within their respective groups. However, if the entire multiple is extended to more than six groups, the possibility of a greater percentage oi groups having their peak loads simultaneously is minimized, a better grade of service thereby being rendered without an increase in the number of switches used.

If in a system as herein disclosed-i. e. 36 groups of lines, 50 lines per group or 1800 lines--said two abovementioned chain circuits are not used because the first selectors are widely scattered, another means must be provided for preventing seizure and use of a third choice finder while a second choice finder is available for use, thereby to improve the grade of service in a given system; and a means for returning a busy signal to a calling party and for reducing unnecessary wear and tear on the allotter when all trunks are busy is necessary.

The applicant herein discloses new and novel means for accomplishing said two desired results. Applicant further provides for reducing unnecessary wear and tear on the allotter by providing means for applying busy tone to a calling line as soon as the allotter tests and finds all trunks busy so that a calling party will hang up and cause the allotter t0 stop. It will be noted that a means similar to that provided for reducing the hunting speed of the allotter could have been used to positively stop the allotter rather than to reduce its speed when all trunks were found busy. However this would have necessitated the use of a means for periodically retesting for an idle trunk in the event the call was not abandoned (or if several calls were simultaneously initiated). This periodic testing would have delayed calls under heavy traliic conditions.

It is an object of this invention to provide a new and novel means for allotting automatic switches for use.

A further object of this invention is the new and novel means for signalling a calling party and for reducing the hunting speed of an allotter when all trunks are busy.

A feature of this invention is grading of multipled finder switches without the use of chain circuits from the selectors.

A further feature of this invention is the provision for an all trunks busy signal without use of an all trunks busy chain circuit from the selectors.

Other featureswill be evident upon a perusal of the following description in which:

Fig. l shows a subscriber line, the line circuit associated therewith and a finder having access thereto;

Fig. 2 shows the allotter associated with said subscriber line and having access to said finder;

Fig. 3 shows part of the allotter bank wiring and the circuits associated therewith;

Fig. 4 shows the multipled arrangement of second choice finders; and l Fig. 5 shows the multipled arrangement of third choice finders.

As shown in Figs. 3, 4 and 5, these circuits are especially adapted to serve an 1800 line system, said lines arranged in six groups, each group consisting ofvsix'subgroups of fty lines each. One allotter is associated with each subgroup and available to each allotter are two first choice finders, two second choice finders multipled with other second choice finders, and five third choice finders multipled with a still greater number of other third choice finders. The multipled arrangement of finders is shown in Figs; 4 and 5. For example', in Fig. 5 the groups are numbered l-VI, lthe subgroups are lettered A-F, and the selectors each connectedin common to six third choice finders are numbered 1-30 across `the top and bottom. To determine the y'finders connected to selector 2, forexample, starting at the top we see that `in group 1I thesecondtinderA ofn subgroup A, the third finder of subgroup B,A the fourth finder of subgroup C, and the fifth finder of lsubgroup `D are con n ected'thereto. From `the bottom, we -see that, in group 1H, the iirst finder of subgroup E 4 and the second `iinder of subgroup F are connected thereto. e

Fig. 4 similarly shows the-multipled arrangement of three subgroups of second choice tinders in each of three groups and the sin` selectors serving said groups.

Fig. `3 shows the switching relays R13-0 and Rltla of the two first choice `finders available to allotter 200. Also-` shown `are the allotter group switching ielays "R205 and R210, busy -relay R220 andintermediaterelay R215 together with the contrll wipers associated with said relays and the wiring of `the a'llotteifbank contacts accessible to said wipers. lie bankpositionsassociated with the nine finders accessible to allotter '"200`hare -numbered, positions '1 and2 associated with two first choice finders 3 and -tivi/ith the two second choice iinders, 'and `5, 6, 7, S and 9 with theilvethird choice hilers.`

The `finders have two sets ofV single ended Wipers 'displaced 180 from eachother. The dfinder" control cir cuits have been put in "the allotter to 'achieve economy. Conductor .V164 Will nbe found 'only in one 'first choice inder as shown in Fig. `3. l e

The allotter has a `l'ciclr-`off feature, well known inthe art, for bylpassing faulty Enders. Timed impulses are received 'over conductors 297 and'208 (Fig. 2) from `a timing device (not shown). V'When R200 is operated after a call is received 'and `an 'idle`fi'nde`r is found, R265 `is operated by an impulse received over conductor 298 and locked operated over an obvious circuit. `If A`tl`1e`tinder taken into use 'does notlind the calling line 'within a predetermined time, "an impulse received over conductor `297 will operate R270. R270 operates contacts 273 to energize M275. M275 opens contacts 276 to restore R240, which is followed by the restoration of R260, R265 and R270. M275 thenrestoresto step the allotter wipers to the next finder.

The allotter is of the nonlhoming, post-selecting type and has an escapement drive. When a 'call is received, ground on the guard leade. g. 161`of a busy finder causes the motor magnet M275`to step theallotter wipers to the next accessible finder. Ground 'oh Wiper 281- i. e. when a second choicetinder is encountered 'upon the `initiation of a call-Qwill cause M2745 lto move the `allotter wipers kone step if the second choice group switching relay R210 Yis not operated-45e. when a first choice Iindcr'is idle. When upon the initiation of a call a third choice finder is encountered, ground on wiper 283 will cause 'M3275 to move the allotter wipers one step unless third choice group switching relay R205 is operated. If all -finders are tested and `found busy, rrelay R220 will be operatedtocomplete a circuitfor operating `R225 then M275, `restoring R22'5`then M275, said "sequence of operations and restorations repeating 'itself until a tinderisltaken into use orntil `ground is removed from theallotter start lead to cause the allotter to restore 1to"nor`rnal. This sequence of operation results in the allotter operating at a reduced speed.

Any one of `several selectors well known in the arth cfg. that shown in the Newstedt Patent No. 2,529,409--4- may be used with the circuits shown in the attached drawings.

Extending-amcllingfline to a first numerical switch Operation of the equipment will now be described in detail. When ajcall' is initiated at 'substation 100,' line relay R120 operates over a circuit including c'ontacts 112,"the calling `loop and ycontacts 111. At `contacts "121R120 lconnectsbattery `over cut-off relay R110 'to the private contact 151; `at contacts 122, grounds "conductor 152 to busy mark the line circuit in the connector banks; and, at contacts 124, completes 'a circuit extending over start lead 153 and contacts 232 to operate the allotter start relay R235.

Allotter 200 is a post-selecting allotter. Assume that the wipers of said allotter are standing on the contacts terminating in finder 102 yand that said finder and the selector associated Vtherewith are both idle `and available for use. When start relay R235 operates, it closes contacts -2'36` prior to its other contacts'to .assure stepping over finder 102 if it is busy or not `available `for `use as will be explained later; but this is of no effect-now. Cou tacts 237 `close Vto complete a circuit including` contacts 276 and 224 to operate relay R240 in series with motor magnet M275. Said magnet willlnotoperate in series with R240. R240 operating opens at contacts 245 the operating circuit of M275; at contacts 241, extends ground over conductor 154 to operate the line relay of the selector associated with finder 102, Vthe selector returning ground back over private conductor 156; at contacts 242 and 247 completes an obvious circuit for preenergizing nterrupter relay R250 through a high resistance 4291; at contacts 248, completes an obvious circuit for operating sloW-toperate relay R260; and at contacts H249, prepares the operating circuit of the finder 'motor magnet M140.

`If,`when R240 operates, the wipers of the non-homing finder 102 are standing on the contacts terminating in line circuit 101, battery over R110, contacts 121, con tact 1.51,'co'nducto`r 157, R250 and contacts 247 to ground will rapidly operate 'R250 but the high resistance of R250 will .prevent 'the operation or R110. nase opens the operating circuit of M 140 at contacts 251 'before R250 can operate t'o 'close 'saido'pe'ratin'g circuit. :R250 closes contacts 25`2`to complete 'a circuitihclu'ding contacts 249 for operating relay R255. :R255 operating again opens the `iincler magnet operating circuit ttt'co'ntacts 257; at contacts 256, R255 'completes a circuit over conductor `1'5`8'fo`r operating thetinder switching 'relay F5130; and at contacts 258, which operate faster than contacts 256 and 257, Rzsslocks itself operated.

If, when the allouer 's'tacrlay R240 operated, the finder wipersy had been 'standing 'on contacts other than those terminating in 'line' circuit 101, R250 would not operate because therew'ould be no battery potential on the private conta'cupon which one of the control Wipers was standing. After a shorttime delay, R260 would operate to complete a circuit extending 'over contacts 249, 257, 251'and 261, "conductor 7.59, self-interrupting contacts 141 and motor'm'agn'et M140 'to operate said magnet. M140=w11 operate 'over this circuit to step the wipers until'wipe'r 160 encounters Contact '151 with battery thereon 'to 4rapidly Voperate the `pre-energized interrupter relay 'R250 which opens contacts 251 `to 'pre- 'vent `further operation of 4M140. As previously -described, R255 willoperate and lock in response to thc operation of"R250.

WhenRiS'Scompletes the circuittfor operating switching relay R'130,'as.previously described, R130 operates contacts 131 and 132 to extend the calling line to the `selector by way `of lconductors 154- and E55; operates contacts 133 to short circuit R250, thereby to restore R250, and to extend the f'ground on `conductor i561 to cut-ct relay R by"way of wiper 160 to operate R110; operates contacts '134 Vto lock itself operated; operates contacts 135to'place ground on guard lead 1to1 to mark the iinder busy, an'cl operates contacts 136 to complete a circuitfextending over conductor1162 and contacts 244 for operating theallott'er restoring 'relay R230.

R110*operating opensicontacts .111 and 112. to restore R `which inturn-removesgroundlfrom the start lead 153;'R1-10'c1oses contacts 1'1'3 to 'maintain itself operated 'when R120 opens 'its original operating circuit at contacts 121; and the ground extended to R110 is fur- 'alertness ther extended to conductor 152 when contacts 123 are restored thereby to maintain a busy marking thereon.

In case that another cali iswaiting when R230 is operated in response to the operation of switching relay R130, R230 will open contacts 232 to restore the start relay R235, which in turn vwill open contacts 237 to restore R240, which relay in turn will open contacts 240 to restore R255 and R260 and open contacts 244 to restore R230. Contacts 231 are provided to prevent a false operation of M275 should contacts 245 reclose before contacts 236 open. When R230 restores, start relay R235 can reoperate over a circuit similar to that previously described. When contacts 236 operate, ground is extended from the guard lead 161, over wiper 282, contacts 231, 236, 245, 276 and 224 to magnet l 275 to energize said magnet. Since R260 will be the last relay to restore, contacts 264 are provided thereon to short circuit self-interrupting contacts 276 thereby to prevent a de-energization of M275 until after R260 restores to open contacts 264. M275 advances the allotter wipers one step upon the de-energization thereof. If the next accessible finder is busy or not available, M275 will reoperate (as will be explained hereafter) to again advance the wipers. step the wipers until an idle, available finder is encoun- I tered and taken into use.

Finder group selection 1t will be noted that the guard leads-e g. 161-o finders, which are connected in multiple to a single selector, are tied together so that, if one of the finders is busy and marked busy by ground on its guard lead, all finders multipled therewith will be busy marked. y

Further it will be noted that M275 has four alternate operating circuits for stepping over busy or unavailable finders namely: (l) from grounded wiper 282 as previously described, (2) from grounded wiper`281 over contacts 211, 243, 236, 245, 276 and 224 to M275, (3) from grounded wiper 283 over contacts 206, 243, 236, 245, 276 and 224i to M275 and (4) from grounded contacts 226 to M275.

Referring to Fig. 3 it will be seen that, when the two first choice finders are busy, their switching relays R130 and R130a will operate contacts 137 and 137a to complete an obvious circuit for operating second choice group switching relay R210. With R210 in a restored position, M275 would be operated each time wiper 281 encounters a grounded contact-i. e. when second choice finders 3 and 4 are encountered. When R210 operates to open wiper 281 at contacts 211, M275 will not operate when wiper 281 encounters a grounded contact and second choice finders will be available for use. Similarly, only when third choice group switching reay R205 operates to open wiper 283 at contacts 206, are third choice finders made available for use.

Assume that a call is initiated from substation 100 and, as previously described, the allotter start relay Y switching relay R210 has operated over a circuit including contacts 137i: and 137 and conductor 164. Assume further that the last finder taken into use was the last accessible to the two first choice finders and that the allotter wipers are camped on the third bank' positionmarked 2 in Fig. 3-whicl1 position has said finder, last taken into use, connected thereto. Ground over the guard lead corresponding to lead 161 will as previously described prevent the operation of R240 and will operate M275 to advance the wipers to the next position, to which conductor 296 is connected. Ground from wiper 28d over conductor 296 and operated contacts 212 of R210 to group switching relay R205 will operate R205. R205 operates contacts 208 to complete a circuit including contacts 213 and 238 for maintaining itself operated. At the same time, ground over wiper 202 and M275 will in this manner Ycontacts' 231', 236, 24s, 276 and 224m magnet M275 will operate said magnet to advance the wipers tothe next bank positionmarked 3 in Fig. 3. Both the second and third cho-ice finders are now available to the allotter because both R205 and R210 are operated. However, as shown in Fig. 3, the second choice finders are connected to the positions marked 3 and 4 which positions immediately follow the position to which conductor 296 is connected. It will be noted that said second choice finders are also connected to the positions immediately following the other bank position to which conductor 296 is connected. As a result thereof, the allotter must test second choice finders before third choice finders for an idle one thereof when both R210 and R205 are operated to make both second and third choice finders available simultaneously.

Assuming that the second choice finder connected to the fifth bank position, to which the allotter wipers have been advanced, is idle. As previously described with re- 'spect to finder 102, R240 and R260 will operate, said finder will find the calling line, R250 and R255 will operate, the finder switching relaycorresponding to R-will operate its contacts corresponding to 136 to operate R230. R235 restores in response to the operation of R230, its contacts 238 opening to restore R205.

If another call is waiting the allotter will restore to normal, then reoperate to select the second choice finder, connected to the sixth bank position, for extending said call. (If a first choice finder had become idle, R210 would have restored to cause the allotter to advanceover said last-mentioned second choice nder to take the idle first choice finder into use.)

If still another call is Waiting, the allotter must advance over the first choice finders, which are busy, and over the third choice finders, which are not accessible since R205 has restored, until the wipers encounter a position to which conductor 296 is connected. R205 will again operate, the wipers will be advanced tov second choice finders and if all these are busy then to a third choice finder which will be taken into use to extend the call. Again R205 will be restored as previously described.

It is apparent therefore that no third choice finder may be taken into use while a first or second choice finder is idle and that no second choice finder may be taken into use while a first choice finder is idle.

All trunks busyallotter speed reduced vallotter start relay will operate as previously described.

R210 will be in an operated position since first choice nders are busy, The wipers, regardless of the position on which they are camped, will be advanced until they reach a position to which conductor 296 is connected. As previously described R205 will operate and lock itself operated. The wipers will continue to be advanced until they reach the first banky position, to which position conductor 295 is connected. Then ground from wiper 284 over conductor 295 and operated contacts 207 to intermediate relay R215 will operate R215. R215 operates contacts 216 to maintain itself operated over a circuit including contacts 213 and 238. The wipers Vwill be advanced over all bank positions to again test for an idle finder; and, if none are found, the wipers will reach the last bank position, to which position conductor 294 is connected. t f

Then ground from wiper 284 over conductor 294 and operated contacts 217 to busy relay R220 will operate R220. R220 locks itself operated over a circuit extending over contacts 222, 213 and 23S. R220 will close contacts 221 to extend busy tone from busy tone equipment (not shown) over conductor and contacts on the line relay associated with the calling linev to the calling line. At contacts 223, R220 will connect interrupter relay R225 to the guard wiper 282 by way of a circuit including rcontacts 276,245, 236 and 231; and at contacts `normal speedof the allotter. on theallotter.

`224, `will `open the self-interrupting operating circuit of M275.` `R225 will bew operated byground `encountered `by theuguard wiper `282 `and will complete at contacts `226 `an obvious circuit for energizing M275. Contacts 276 willtopen to restore R225. `Contacts 226 will open to restofe'M275, `M275 restoring closes contacts 276 `and advances the wipers one step.

If the calling party does not abandon 'the call when the busy tone is extended to'his substation, AR225 and M275 will alternately operate and restoreto cause the `wipers to `search for an idle trunk at a speed much less than the This will reduce the wear As previously described, when aniidle finderis found and taken-into use, `R230 will operate in response to the operation of the finder switching relay. 1

R235 will restore-in responseto-the operation of `R230 and will open contacts 238 to Arestore relays 205, R215 Iand R220. Any `further operation of nthetallotterrnagnet will beover its normal operating circuit.

i If the calling partyabandonsthe callythe start trelay R235 will restore to open contacts 238 therebyito restore relays R205, `R215 and R220.` If another Call is :then initiated, thelmagnet M275 will be` operated over its nori mal i operating lcircuit.

It will be understoodithatV various modifcations=in the preferred embodiment may befrnade, and itis contemplated to covertthe appended claims a1l-such modifications as fall within the true `spirit andscopeof thenvention.

What is claimed is:

1. In anautomatic switch-having -access bywayftof wipers associated therewith to a pluralityoflines terminating in bank contacts of the switch, magnet means for advancing said wipers -overusaid contacts, meanstincluding saidwipers for-testing thesidle orbusycondition-of t said lines, means normally operated` responsive tot-said 2. A switch as claimed in claim `1 wherein said fifth means comprises contactsonone relay and wherein said last means comprises said one relay, -a first and a `last bank contact accessible `to said wipers before and after said lines respectively, another relay"having contacts, a,

circuit complctedwhen said wipersencounter"thefirst banktcontact foropera'ting said other relay to operate its contacts, a circuit including said contacts on said other relay completed tooperate said`one"relay if said wipers encounter thelast bank fcontactwhen said other relay.` is operated,'and meansresponsiveto said wipers encountering anidleone of saidlines'for restoring said other relay` 3. In a telephone system .having a` plurality of finders,

an allotter having access to-said finders by way of wipersj,

integraltto said allotter, said` allotter comprising ymeans -for advancing said wipers to test said finders, a magnet for operating said'means, acir'cu`it"including one of said wipers normally completed when'a 'busy'inder is vencountered for operating said magnet, an 'inte'rrupterrelay,` i a `circuit including said one wiper and contacts` on -fsaid magnctfor operating said `relay whenevertabusy `finder `is encountered, means for completing saidisecond-mentioncd'circuit andforiopening said lfirst-mentioned circuit,

means whereby tsaid` last meansiis `operatedupon `said;` allotter `finding all ofsaid finders busy, circuit means including t-contactsfon said` relay `operated'twhen` tsaid relay `is'ltoperated `to operate ysaid-jmagnet,contacts-cn saidmagnet operating to` open -said second-mentioned circuit thereby to restore said relay, `said `relay contacts restoring to restore said Amagnet to cause said first means to `advance `the Wipers one step, said magnet contacts restoring totagain complete said second-mentioned circuit, said wipersithereby-being advanced at a reduced speed when all `finders have been found busy for the purpose of reducing unnecessary wear on the allotter.

-4. In a telephone system as claimed in claim 3, said allotteralso comprising means whereby said second means is operated responsive to said allotter finding and taking into use an idle finder to again complete said firstmen tioned circuit and to open said second-mentioned circuit.

5. In a telephone system wherein the wipers of an allotter are normally advanced at a first speed as the allotter searches for an idle finder in a plurality of groups of finders, said allotter comprising magnet means for advancing said wipers to test said nders, circuit means in cluding one of said `wipers normally effective forioperat- `ing `said magnet means when a busy finder is encountered, atgroup switching relay, circuit means for operating said relaywhenall finders in one group are busy, a second `group switching relay, circuit means including contacts onthefirst group switching relay for operating said second t groupswitching relay, an intermediate relay, circuit means -includingcontacts on said second group switching relay for operating saidintermediate relay, an all trunks busy relay, circuit means including contacts on said intermediate relay for operating said all trunks busy relay upon all finders having been tested and found busy, an interrupter lrelay, circuit means including said one wiper for operating said interrupter relay, contacts on said all trunks 4busy'relay operatedwhen said busy relay is operated to render said` last circuit means effective and said first circuit means ineffective, contacts on said interrupter relay operatedwhen said interrupter relay is operated to operate said magnetmeans, and contacts on said magnet operated to restore said interrupter relay, whereby the 'wipers will be advanced at a second slower speed when all the finders are busy, said second speed thereby reducing wear on the allotter.

6. lIn a telephone system as claimed in claim 5, a group of bank contacts in said allotter accessible to another one cluding said other wiper and one of said bank contacts,

`said fourth-mentioned circuit means including said other 'wiper and` afsecond one of said bank contacts, and said fifth-mentioned circuit means including said other wiper anda third `one of said bank contacts.

' 7. ilnra'itelephone"system having a plurality of groups tof=finderswtchesfinder. switches in one of said groups multipled with :finder switches in other groups, an alllotterassociated with said one group for taking into use -each nderv switch by way of wipers integral to the Vallotter, means for 'busy-marking each finder switch and all findersmultipled therewith when said finder switch is taken into use, means in said allotter normally `effect1ve `for moving said wipers at one speed to test the findersaccessible thereto, means in said allotter for moving said wipers at a slower speed toreduce un- 60 t necessary wear `on the allotter, means whereby saidl third means is rendered veffective Aand said second means is rendered ineffective whenthe allotter tests and `finds all finders accessible thereto busy-marked, and means whereby said third means is rendered ineffective `and said second `means-is again rendered effective `when a finder'in said one `group thereafter'becomes idle and is taken into use. 8. In a telephone system, an allotter having wipers,

groups of first, second, and third choice finders terminatingin bank contacts accessible to said, wipers, control contacts accessible to' one of said Wipers, said contacts arranged such thatfthe contactstterminating first choice by contacts terminating third choice finders, magnet means for advancing said wipers over said contacts to test the finders, a circuit in the allotter normally completed for operating said magnet means to advance the wipers over the contacts terminating second choice finders when such finders are encountered, another circuit in the allotter normally completed for operating said magnet means to advance the wipers over the contacts terminating third choice finders when such finders are encountered, a group switching relay, means whereby said relay is operated while all first choice finders are busy, contacts on said relay operated when said relay operates to open said first circuit to make second choice nders available for use, another group switching relay, a circuit completed if said one wiper encounters said one control contact while said first group switching relay is operated for operating said other group switching relay, contacts on said other group switching relay operated when said other group switching relay operates to open said other circuit to make third choice finders available for use, means for restoring said other group switching relay when a finder is taken into use, means for restoring both of said relays if, after they are operated, a first choice finder becomes idle.

9. In a combination as claimed in claim 8, a circuit normally effective for operating said magnet means to advance said wipers over contacts terminating busy finders, an interrupter relay, a circuit for operating said interrupter relay, means operated upon the allotter finding all of said finders busy for rendering said fourth circuit ineffective and for rendering said fifth circuit effective to operate said interrupter relay when a busy finder is encountered, contacts on said interrupter relay operated when said interrupter relay operates to operate said magnet means, and contacts on said magnet operated to restore said interrupter relay, whereby the allotter wipers will be advanced rnore slowly when all finders are busy for the purpose of reducing wear on the allotter.

10. In a telephone system, an allotter having wipers and bank contacts, groups of first, second and third choice finders accessible to said allotter, magnet means for advancing the wipers over said bank contacts to test the finders, a circuit in the allotter normally completed for operating said magnet means for advancing the wipers one step when a second choice finder is encountered, a circuit in the allotter normally completed for operating said magnet means for advancing the wipers one step when a third choice finder is encountered, means for opening said first mentioned circuit when all first choice finders are busy, means independent of the busy or idle condition of the second choice finders for opening said Second-mentioned circuit when all first choice finders are busy, said second choice finders arranged to be those first available to the allotter upon said second circuit being opened, means for again completing said second secondmentioned circuit upon a finder being taken into use, said arrangement of second choice finders and said last means preventing a third choice finder being taken into use while a second choice finder is idle.

11. In a telephone system having a plurality of subscriber lines, an allotter having wipers and a plurality of sets of bank contacts accessible to said wipers, a plurality of finder switches terminating in some of said contact sets and having access to said lines, magnet means in the allotter for moving said wipers over said contact sets to test for an idle finder, first and second of said sets of contacts arranged to respectively precede and follow the contact sets in which said finders terminate, an intermediate relay having contacts, circuit means for operating said relay to operate its contacts when said wipers encounter said first set of contacts, an all trunks busy relay having contacts, a circuit including said intermediate relay contacts completed to yoperate said busy relay if said wipers encounter said second set of contacts while said intermediate relay is operated, means operated responsive to said wipers encountering an idle finder for restoring said intermediate relay and its contacts, and means including said contacts on said al1 trunks busy relay for impressing a busy signal on a calling one of said lines.

12. In a telephone system having a line over which calls are initiated, an allotter associated therewith, a plu rality of sets of bank contacts and allotter wipers having access thereto, a plurality of trunks terminating in some of said contact sets, one of said contact sets arranged to precede and another of said contact sets arranged to follow those contact sets terminating said trunks, means operated responsive to the initiation of a call over said line for advancing the wipers over the contact sets, an intermediate relay, circuit means completed when said wipers encounter said one contact set for operating said relay, a busy relay with contacts for impressing a busy signal upon said calliing line, a circuit including contacts on said intermediate relay completed for operating the busy relay if said wipers encounter said other contact set while said intermediate relay is operated, and means operated responsive to said wipers encountering an idle trunk for restoring said intermediate relay thereby to prevent the operation of said busy relay.

13. A telephone system as claimed in claim 12 together with means controlled by the operation of the busy relay for advancing the wipers over the contact sets at a slower speed for reducing excessive wear on the allotter while all of said trunks are busy.

14. A system as claimed in claim 12 wherein said plurality of tmnks include first choice trunks, second choice trunks and third choice trunks, a control contact set arranged to follow the contact sets to which the first choice trunks are connected, said control contact set being followed by contact sets terminating second choice trunks, the latter contact sets being followed by contact sets terminating third choice trunks, one special circuit in the allotter normally completed for advancing the wipers over second choice trunks, a first group switching relay operated while all first choice trunks are busy for opening said special circuit to make said second choice trunks available for use, another special circuit in the allotter normally completed for advancing the wipers over third choice trunks, another group switching relay, a circuit completed if said wipers encounter said one control contact set while .said first group switching relay is operated for operating said other group switching relay, contacts on said other group switching relayV operated when said other group switching relay operates for opening said other special circuit to make third choice trunks available for use, means for restoring said other group switching relay when a trunk is taken into use and means for restoring both of said group switching relays if, after they are operated, a rst choice trunk becomes idle.

References Cited in the file of this patent UNITED STATES PATENTS 1,902,186 Saunders Mar. 21, 1933 1,972,199 Merk Sept. 4, 1934 1,999,104 Merk Apr. 23, 1935 2,113,119 Taylor et al. Apr. 5, 1938 2,115,320 Saunders Apr. 26, 1938

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