US1677414A - Automatic telephone system - Google Patents

Description

Julyl 7, 1928,

. R. F. STEHLIK AUTOMATIC TELEPHONE SYSTEM 2 insets-sheet 1 Filled llMay 25, 1927 E'uciul 11E ET'ahlik July 17, 1928.

R. F. STEHLIK AUTOMATIC TELEPHONE SYSTEM luv-anion FudE Z Z-L F STEZ-dik ill! Patented July 17, 1928.

eairsu sures PATENT cl rics.

RUDbLPH STEE L K or on onso rnnrnors assrqnon 'ro REsE vn 10mm COMPANY, OF KANSAS CITY, MrssoURr, A CORPORATION or DELAWARE.

"AUTOMATIC newt-Hoes SYSTEM.

Application filed May 25,

The present invention relates in general to automatic telephone systems, and is concerned more particularly with such systems in which a line finder is employed to connect an idle selecting switch with the terminals of a calling line, and the principal object of the invention, briefly stated,is theprovision of a newand improved finder system, which is thoroughly reliable in its operation, and which can be manufactured and maintained at a reasonable cost.

. The presentinvention relates more particularly to finder switches of the full selective type, that is to such aisystem in which the finder switch is moved first in one direction in search of the level. containing the calling line, and then in a coordinatedirection in search of the contacts of that line in the selected level. In one embodiment of my invention Iv employ as a finder switch, the well known Strowger connector, which is that shownin the Patent 815,176 issued to Keith, Erickson and Erickson, with the circuits and mechanical structure altered in accordance with the objects of my invention. Thistype of switch has been used in such systems heretofore, in which systems the finder switches proper were controlled by and through a group of common control equipment. The successful operation .of such a system is dependent largely upon the operation of the common control equipment, and if that control equipment becomes defective or out of order, a relatively large group of finder switches, and consequently larger group of subscriber lines was thrown out of service temporarily. Accordingly, as f a further object of my invention I provide a new and improved selective finder system, in which the finder switches are self contained and self controlled, and in which the control equipment common to a group of finder switches is reduced in quantity and function to render the operation of the system more reliable.

In finder switch systems which have been devised heretofore, a large group of finder switches are available to pick-up calls from a group of subscribers lines, those switches being allotted for service one at a time by 1927. Serial no. 193.960.

means of afinder allotter. The finder a1- lotter so employed constitutes a common con-. trol equipment, and if that equipmentiS faulty a finder switch group is thrown out of service; In recognization of this fact, systems have been devised heretofore with duplicate or tandem finder allotters, which alternately function to allot a finder switch for service. Accordingly a further object of this invention is to provide a new and improved finder allotter of the tandem type, and to provide simplified circuitconnections therefor, the improvements tending to render the finder allotterequipment more reliable.

In selective finder systems which have been devised heretofore and of which I: 'am aware, the removal of the receiver from the switchhook of the. calling telephone operates the line equipment, to energize the level relay, to mark the level of the calling line in the finder switch bank. 'This level marking re,- lay .was used in commonwith all the lines of that particular level. Therefore in a finder switch system having finder switches of a 10-level-capacity, ten of, such 'relaysarere' I quired for each group. The usual plurality of level marking relays runs up the initial cost of the system, and increases thenumber of, contact springs employed, thereby increasing the likelihood of dirty contacts and con sequent higher maintenance cost. As afurther object of myinvention I provide a new and improved level markingarrange'ment, in which the number of level marking relays has been reduced to one, and the number of contact springs further reduced to render the system less expensive-and more reliable. I

Further. objects of. my invention, not sp'ecifically mentioned here, will be apparent from the detailedv description and claims which follow. The drawings comprising Figs. 1 and 2, when arranged with Fig. 1 above Fig. 2 with. correspondingly numbered lines in alignment, shows suflicient details to enable a clear understanding of my invention.

Referring now particularly to Fig. -1, I

show a calling subscribers line A, terminatcut-off relays 1 and 2, which are operated responsive to acall upon that line to mark its destination at the finder switch banks and to start the finder switch to connect with it.

' The finder switchF comprises a Stro'wgeri two-motion switch mechanism, actuated by vertical magnet 12, rotary magnet 13 and release magnet 17 and controlled by the tour control relays 3, 1, 5, and 6.v This finder is equipped with a vertical wiper 53 which engages the contacts of 'a vertical bank VB as the finder switch shaft (not shown) is stepped upward by the verticalmagnet. The

mechanical features of this vertical wiper and vertical bank are not new, and do not from an integral part of the present invention. Such a wiperv and banks applied to a Strowger connector, is shown on page 69, the 1925 edition of the book Principles of Automatic Telephony by Harry B. Mahoney, and'a description of its operation-is made in the ensuing pages' ot'that text. Finder switch F also carries the customary line wipers 31 and 33rand the p'rivate wiper 32, which are rotated into engagement with the'contacts of a particular level after that level has been selected by the finder through the agency of the vertical bankr In the circuit shown, the finder switch F is ar ranged to operate in a vertical direction until the vertical wiper 53- encounters a grounded contact, thatcontact being grounded by the line equipment of a calling line to level;

mark thelevel containing that line. WVhen the vertical Wiper 53 encounters this grounded contact, the control relays of the finder F are altered so that the vertical magnet is open circuited, and the rotary magnet impulsed to drive the wipers 31 to 33 into en.- gagement with the contacts of the selected The rotary action of the finder F, continues until the private -wiper;32 encounters an ungrounded contact, at which time the finder switches through .to establish a connection from the calling line to the selector switch S. The selector switch S, is a well known Strowger selector switch, whose wipers aremoved first in'a vertical direction under the control of the calling device at the subscriber s station, and then moved automatically in a horizontal direction to select the-first idletrunk in the selected level.

Referring now to Fig. 2 I show finder al lotters FA and FA", each co'mprising'the V double'ended wipers which sweep-over a row of contacts, and a motor magnet for driving the wipers; Mechanically these finder allotters are like the well known rotary lineswitch, whose wipers move in a forward di rection .only,hav1ng no normal position and particular line.

selected finder through the finder allotter FAR Similarly relay 103 is associated with the finder allotter 1iA .Relay 101 is associated with the vertical bank circuits, being energized whenever callis initiated in the group, regardless ot'thele'vel containing that v The" energiza'tion of relay 101 projects agrounded circuit through relays 102 and 103 inmultiple, one or the other of'those relays energizing over that circuit to start the finder switch which it has preselected. I v p In Fig. 2 I also show the supervisory relay104, which is energized in series with the release magnet of a finder to extend super visory circuits as willbe pointed out. The banks of finder allotters-FA andFA each have 25 contacts in a row, over which the re spective wipers are driven. Thus if it Were desired to do so, each finder allotter could 'establishcircuits with 25'-separate finder switches. IIowever, since thefinderF is of the100 line type, that is, there are 100 contactrsets available to its wipers 21 tor33, it is not necessary that finder allottersFA and FA each have access to 25' finders. Such 'anarrangement would give the line group containing line A 50 finder switches, which is more than is necessary. It hasbeen found that trafiic in anautomatic exchange, can

the number of'calls lost because all of the finders available to the lines are busy. In the system shown in the present application, I have provided 20 finders, accessible through both of the. finder allotters. In the finder allotter FA, the finder switches are accessible in a regularorder, that is, the wipers 110112 on rotating in the direction ofthe arrows, encounters finder. switches Nos.*1 to 20 in consecutive order; In finder allotter FA I have reversed the allotment of the finders, so that the wipers 113 to 1141, upon rotating in the direction of the arrows, encounters finder No.20 first, and then proceeds to the No. 1 contact last, as will be more clearly brought out hereinafter. Since there are 25 contacts in the switch banks, 21 of. which h'avebeen employed the remaining four are unusedand made permanently busy by ground connection, in the banks over which the wiper-i110 otthe finder new- 14.:

allotter- FA sweeps and the wiper 113 of the finder allotter FA sweeps. 'A number of finders accessible to;- the line group contai'ning' line A can be increased to 24 by. removing the permanent busy connections re ferred' to above and connecting the added four finders to the respective bank terminals.

If the traflic in the group require more than 24 finders, ordinary principles of trunk grading can be employed, and the added finders provided as required. To do this certain portions of thefinders would be common to both finder al'lotters, and other find.- ers' individual to each of the finder allotters, a change of this'kind beingpossible without departing from the scope and spirit of this invention. i

Throughout the drawings I have shown a plurality of batteries, to avoid unnecessary complication of the figures. In an installation of the system of my invention. there would be but one battery, preferably with its positive pole grounded.

When the subscriber at station A raises his receiver to initiate a call, line relay 2 is operated over the loop including the calling station, and upon operating removes the ground potential from contact 29, thereby marking that line calling-to the finder F, so that switch can establish a connection to it. Since the finder bank number of substation A is assumed to be 85, line relay 2, upon energizing places a ground upon the eight vertical bank contacts over which the vertical wiper 53 sweeps. This ground. completes a circuit for the start relay 101 in. serice with resistance such as 82, to energize that relay to start the finder equipment in motion. It will be noted that normally the contacts of the vertical bank VB are connected to battery potential placed on them through their-respective resistances such as 81 and 82, and the start relay 101 in series. When the line A initiated the call the eighth vertical bank contact is changed to ground potential the remai'ning contacts of the bank being maintained at battery potential by the resistances. "By this arrangement the verti cal wiper 53 encounters battery potential upon all of the contacts except that associated with the level it is desired to select, that potential serving to short circuit the e hange-overrelay to prevent that relay from energiz1ng and causing the finder to cut-in upon the wrong level.

The energization of startrelay 101,v throws ground out over conductor 130, thence through the winding of relays 102fand-103 in parallel, the circuit of relay 102 being completed through thewinding of motor magnet 105 of the finder allotterFA and the circuit of relay 103 being completed through the motor magnet 106 of thefinder allotter' FA". One or the'other of theserelays will be energized, it being assumed that relay 102 is slightlyfaster than relay 103, that relay will energize first and upon-becomingenergized opens the circuit of 103 to prevent its energizing. ment is provided on relay 102 to make it taster to pull up than relay 103, since it is im-. possible to build two relaysihaving exactly the same time constants, as would be necessaryil both relays 102 and 103 were to become fully energized at the same time. -When relay 102 energizes in series with magnet 105, the re sistance of the winding of relay 102 prevents the energization of that magnet. Relay 102 closes a circuit for the start relay 4 of the preselector finder E-causing that relay to.

energize and start the finders stepping in a vertical direction in search of a marked level, that-is the level containing the'line A. In the finder F, the impulsing relay 5 is energized over circuits completed by the start relay 4. and upon energizing, delivers an impulse of current to the vertical magnet 12, that magnet operating to advance the shaft containing the Wipers 31 to 33 and53 one vertical step. Vhen the; vertical magnet 12 has completely energized, it opens in- No special adj'ustterrupter springs 49, thereby interrupting the circuit of relay 5, to permit that relay ,to fall back and op'enthe circuit of the vertical magnet. Wiper 53 upon being elevated onestep encounters battery potential, which is led over the finder circuits, to short circuit the change-over relay 6, to prevent that relay from. energizing and diverting the impulses from-"the, vertical to the, rotary magnet; I 7

"When the wiper 53 encounters the level containing: the line A, battery potential upon. it is changed to ground potential,- and relay 6- is energized, in series with relay 5, .the energizing circuitof the former serving to hold the latter relay ingits energized position. Relay 6 opens the circuit of vertical magnet and changesthe impulsing circuit to the rotary magnet, which =is, immediately energized to advance 1 the wipers one step into the selective level. This arrangement permits the change-over from vertical to rotary motion of the finder with aminimum loss of time, the action is positive, dependent upon the energization rather than upon the ideenergizationbf the change-overrelay, as

.has been the custom heretofore. The r0- tary magnet energizes, advancing the switch wlpers, wiper 32 encountering ground potential as long as it. is standing upon the contacts of, an uncalling or a busy line. Wiper 32 encounters ground, switching relay 3 is short circuited, to prevent its premature operation. When .the contacts of the calling line are encountered, wiper 32 moves-its ground potential, and relay 3 energizes to switch the finder through to seize the calling line. The calling subscriber then hears dial tone which is conducted to his telephone over iso line conductors and 65, that tone being applied to the lowerwinding of the line relay 7 of the selector S. The subscriber upon hearing this dial tone operates his calling device in the well known manner, to operate the selector Sin accordance with the first digit of the number of the wanted telehone. The operation of selector S is famillar to those skilled in the art, and since it does-not form an integral part of this invention will not be enumerated in detail at this time.

Having thus described my invention in general I will now proceed with a. detailed description of its operation.

Line-A calls. I When the subscriber at substation A removes his receiver to initiate a call, line relay 2 is energized over a circuit traceable from ground through springs 25, line conductor 20, through the calling device, transmitter, receiver and switch-hookof the substation A, negative line conductor 21, springs 23, through the upper winding of relay 2 to battery. Upon energ1z1ng, rclay 2, at springs 26 and 27 removesground potential from the private contact 29 in the finder bank, thereby rendering the line A in a calling condition and accessible to the finder switch F. SpringBO at its make contact closes a circuit from gq'ound through springs 24, conductor 54, resistance 82, conductor' 83, through the winding of start relay 101 to battery, energizing that relay preparator to starting the finder switch in motion. round upon the conductor 54, places ground potential on the eighth contact in the vertical bank VB, thereby marking that'level to subsequently cause the-finder F to stop opposite'it and to rotate into it in search of the contact group 28 -30." The operation of springs 26, in addition to removing ground potential from the bank of contact 29, extends the release trunk conductor 22 to the normal release conductor 22, thereby preparing circuits over which the line A is subsequently marked busy in the banks of the connector switch.

,Startz'hg the finder The energization of start relay 101, closes a circuit from ground through springs 128, conductor [130, through the winding of relav'102,'conductor 136, springs 123, conductor 131," through springs 126, through the V winding of motor-magnet 105 to battery,

with a parallel circuit from conductor 130, through relay 103, conductor 134,-' springs I18, conduct-M135, through springs137, through the winding of magnet 106to battery. -Relays 102 and 103 will both start to energize over the circuit. It is assumed that relay 102 is slightly faster to pull up than relay '103,'that relay energizing first, operinafter explaine'chand at springs 117 and 18 opens points in the control circuit for finder allotter FA', to prevent that finder allotter from operating atthis time. At springs 119, relay 102 prepares a further point in the finder allotter kick ofl' circuit, and at springs 1.20, closes a circuit, from ground through these springs, conductor 137, through wiper 112, now assumed to be in engagement with its 20th bank'contact, conductor 71, through the winding of start relay 4, of t-hefinder F, to battery. -Relay 4 energizes over this circuit to start the finder. v

Vertical impulsz'ng.

' The energization of relay 4, closes a cir cuit for pulsing relay 5, traceable from ground through spring 40 and its make'contact, vertical interrupter springs 49, .conductor 67, spring 48 and its break contact, springs 41, conductor 68, through rotary interrupter springs 50, through the Winding of Relay 5 energizes over this circuit and at springs 42closes a clrcult relay 5 to battery.

mittingtha't magnet to fall back and'close springs 49, again establish the circuit for the pulsing relay 5. The first operation of the vertical magnet 12 elevates the vertical wiper 53 into engagement with the lower most contact of the bank VB; The energization of relay 4, at springs 41 prepares a point of circuit of switch-over relay 6, that circuit being traceable from battery through relay 5, throughrotary interrupter springs 50.

conductor 68, through springs 41, springs-48 and: its break contact, over conductor'67 to the upper terminal of relay 6.. When wiper 53 engages the first contact'of the bank VB, battery potential is applied to the lower terminal of switch-over relay 6 over .circuits conductor 83, resistance 81, first contact and wiper 53, conductor 63, spring 36 and its traceable frombattery through relay 101,

I through resistance 82 and relay 101. How

ever relay 6 was not operate over this circuit because ofthe relatively high resistance of 82 and relay 101. The operation ofrelay and the vertical magnet 12 continues, along as wiper 3 encounters battery potentiahin this case for seven steps. 7

Last "vertical impulse.

\Vhen the vertical magnet andfrelay have completed seven cycles of operation as above described, they again energize for. the

, eighth time, the magnet 12 advancingthe wiper 53 into engagement with the'eighth bank contact ofthe bank VB to which conductor 54 is connected. Since the calling line A terminates in this eighthlevel, and has placed ground on conductor 54, wiper 53:encountersground. potential instead of battery "potential. ,As soon asthe vertical magnet 4 has completely. energizedzand opens springs 49, relay 6 energizes over a circuit traceable from ground, spring '27 and its make contact, springs 24, conductor 54, eighth bank contact and vertical wiper 5.3, conductor .63, spring 36 and'its break contact, conductor 64, springs 47 lower winding of relay 6, conductor 67, spring 48and its break contact, springs 41, conductor 68, rotary interrupter springs 50, through the windingv of relay 5 to battery.- Relay 6 is energized over this circuit and relay 5 being in an energized position at the moment the circuit was completed, remains in an energized position. Relay 6 upon energizing locks itself through spring 46 audits upper winding to ground at spring and its make contact,th ereby maintaining itselfenergized independent of the circuit .just traced through its lower winding. v

. Rotary impulsiag.

relay 6 opens the circuit of vertical mag.- net 12, permittingthat magnet to fallback, Spring makes contact with its make contact, a; circuit is closed for rotary magnet 13,

causing ,that magnet to. become energized immediately since relay 5 is held energized,

as explained,- above and contacts 42 are therefore closed. The energization of rotary magnet 13 advances wiper-s31 and 33 one rotary step into the selected level, and operateszspring 5t) at the end of the step to open the circuit of interrupter relay ,5, that relay falling back to terminate the pulse thereby, permittingthe rotary magnet 13 to deenergizeand at springs reclose the circuit of: relay 5. Sincethe calling line is assumed to have the finder bankdesignation of 85, contact set 28 to 30, inclusive, is the fifth set in the eighth level, therefore the first four contacts of the level willbe grounded, since it isalsoassumed that the other lines in that level are not calling at the moment. A circuit may now be traced from ground through springs 26 and27 in multiple, re-

lease trunk conductors 22'andcontact 29 of the first line in the level, wiper 32, conductor 6 3, spring 36 and its break contact con ductor 64, spring 48 and its make Contact, spring 41,. conductor 68, rotary interrupter spring 50, through the winding of relay 5 to battery. Relay 5 energizes over this; circuit,

at springs 42, closes a circuit through spring 45 andits make contact, through the winding. of the rotary magnet 13 to battery, energizing that magnet which advances the wipers 31 to 33 another step and at springs 50opens the. circuit of impulsing relay 5. Thisaction continuesfor four-steps, that is as long as wiper 32 encounters grounded contacts. When switch-over relay 6 is energlzed, it closes springs 44, places-ground upon release trunk conductor 61, that ground potential upon the upper terminal of switchthrough relay 3. As long as wiper 32 encounters ground; potential, switch-through relay 3 is short circuited, since ground from the wiper 32 through conductor 63, and is placed on the lower terminal over a circuit, springs 36 and its break contact. When the rotary magnet has energized for the fifth time, and advancedthe wipers 31-to 33, in'- elusive, into engagement with contacts 28 to 30, inclusive, of calling line A, wiper 32 loses ground,-relay 3 being no longer short circuited energizes over a'circuit traceable from grounded release trunk conductor 61, through the winding of relay 3, conductor 64, spring48 and its make contact, springs 41, rotary. interrupter spring 50, through the winding of relay 5 to battery. Relay 3 is of high resistance, and relay 5 is of low resistance, relay'3 theretore energizes over this c1rcu1t but relay 5 is prevented from energizmg by the lllglll'GSlStlIlCG of relay 3. Relay 3 upon energizlng closes spr1ngs'34 to Hit) 39, to switch through the ne ative and positive line conductors of the nder to trunks V 60 and 65, respectivel so that theselector switch S is seized in t e usual manner; Re-

lay 3 opens at springs 35 a point in the release-circuit of the finder F, and at springs Finder allotter seeks another fiadr. 2

At springs 38, relay 3, closes a circuit from und through those springs, conductor 72,

t rough the 20th bank contactand wiper 111 of the finder allotter FA conductor 138, springs 119, conductor 136, springs 123, springs 122,conductor 132, spring 116 and its make contact, through the winding of motor magnet 105 to the'finder allotter FA to battery, with a parallel path from spring 123 through conductor 131, interrupter springs 126, through the winding of the magnet 105 to battery. Magnet 105 energizes, prepares to advance the wipers 110 to 112, inclusive, one step. When the finder F switched through to the line A, the circuit of relay 101 was opened, permitting that relay to deenergize and at sprin 128 removethe ground from the start con uctor 130. The

. removal of ground from the start conductor 130 permits relay 102 to fall back, and at springs 116 and 119 opens the circuit just traced for allotter motor magnet 112, permitting that magnet to fall back and advance the wipers 110 and 112, inclusive, one step. Sincecontacts 21 to 24 of the bank overwhich wiper 110 rotates are grounded,

. motor magnet 105 is again energized over the circuit traceable from that ground through wiper 110, spring 116 and its break contact, conductor 132, springs 122, conductor 131, interrupter springs. 126, through the winding of magnet 105 to battery. Magnet 105 energizes, preparing to advance the wipers. anot 1er step, and opening springs 126, to permit itself to fall back. Magnet 105 therefore operates in a buzzer like fashion, advancing the wipers step-by-step until wiper 110 fails to pick-up ground potential.

All finders busy.

Assuming now that the finder F was the last idle finder of the group. When the finder is elevated off-normal by the vertical ated, removing ground from the busy common conductor 70, and placing ground upon the conductor 69 to guard the finder and prevent its hein picked up by one of the finder allotters. I the finder F was the last idle finder, conductor 70 no longer has ground potential on it, since all the 'ofi-normal springs of the group are operated. Therefore when Wiper 110 of the finder allotter FA encounters the 25th bank contact, it fails to pick-up ground. Consequently the finder allotter FA comes to rest on contact sets 25, of its bank, remaining there until a finder becomes idle, at which time wiper 110 .will again pick up ground from conductor 70, and the finder allotterwill move on in search of that'idle finder.

Since finder F was assumed to be'the last idle finder of the group, finder allotter FA would also bestanding on it, since the test wiper 113 of that finder would pick up ground potential on all other contacts of its banks. When the-oif-normal springs 52'are operated, conductor 69 is placed on ground potential, wiper 113, which is then standing on its sixth bank contact, would pick up that ground, closing a circuit from that ground through that wiper, springs 121, through conductor 133, to the break contact of spring 117 of the relay 112. When the relay'3of the finder F switches through and opens the circuit of relay 2, as explained above, permitting that relay to fall back, the circuit from conductor 133 is completed through springs 117, conductor 135, interrupter springs 127, magnet 106 to battery. This magnet energizes, interrupting its own circuit at springs 127, and acts in a buzzer like fashion to advance the wipers of finder allotter FA. Since all'of the other finders of the group are busy, the wiper 113 will encounter ground on all the contacts between six and twenty-five, inclusive, when it moves Sir;

into connection with its bank contact 1, to

which conductor 70 is connected, it will lose its ground potential and the wiper-s will come to rest on that contact. Thus it will be seen that both of the finder allotters are alined upon the resting contact, pending the unbusying of one of the finders of the roup. If some subscriber in the group shofid attempt to call, he will energize the relay 101 as before, throwing the ground upon the start conductor 130, that ground serving to energize relay 102 or relay 103 as before.

ductor 137, that ground going through wiper 112 now resting on its twenty-fifth bank contact, over conductor 141 to an overflow meter, registering the call as lost because all the finders of the group were busy at the time it was made. When one of the finders become idle, assume that the finder F is that magnet 12, ofl'-normal springs 52 are operfinder, both finder allotters FA and FA As soon as relay 102 pulls up, it will at springs 120 place the ground on conwill position-their wipers upon it, finder FA rotating from contacts 1 to- 6 and finder FA from contacts through 1 to 20.

Simultaneous calls.

. winding of relay 103, conductor 134, springs 11 8, conductor 135, through interrupter springs 127, through the winding of magnet 106 to battery. The energization of relay 103, opens the circuit over which finder allotter FA seeks another idle finder, this circuit having been traced hereinbefore. Re lay 103 closes at springs 125 a finder start circuit for the start relay 4 of the finder which it has preselected, energizing that relay to start its operation of the finder in the manner above described. WVh'en the finder has switched through, relay 103 is short.- circuited, having ground from conductor 130 upon its lower terminals and ground from wiper 114 through springs 124 to its upper terminal. Relay 108 therefore falls back, and since relay 102 is already back both finder allotters FA? and FA start looking for an idle finder. If another call is pending, relays 102 and 103 will be prevented from energizing by the actuation of the interrupter springs 126 and 127, respectively, by the operation of the magnets of the finderallotters in searching for an idle finder. -As soon as one or the other of the 'allotters findsan' idle finder, the relaycorrespon'ding thereto will energize, stopping both of the finder allotters in the manner hereinbefore described. Thus it will be seen that in the case of two simultaneous calls, the one is handled by a finder controlled through the finder allotter FA? and the other by finder controlled through the allotter FA", and if another call is pendingat. the time it is controlled through the finder allotter which finds an 'idle'finder first.

The above embodiment of my invention has been shown and described by Way of example only and I am not to be limited by the specific disclosure shown, as there are many modifications and adaptations appar ent to one skilled in the art, which can be madewithout departing from the scope of my invention. V

.Having thus described my invention, what I consider new and desire to have protected by Letters Patent is pointed out in the appended claims: 1

What isclaimed is:

1. In an automatic switch mechanism, two

driving magnets e'achcontrollingan'interrupter-spring, an interrupter relay commonto said magnets, a circuit for said relay including said interrupter springs in series, wipers on said switch, contactsaccessible to said wipers, means for energizingsaid relay over said circuit to operate the first of said magnets'under the control of a certain one of said wipers and interrupter springs, means operatedthrough said certain wiper to shunt said certain interrupter spring and to render mary contact to mark saidline calling, wip

ers on said finder having access tos'aid contacts, and means in said finder controlled through said wipers to select said marked contacts and to line. 4

3. In an automatic telephone systenl, a subscribers line, a fi'nderhaving access thereto,-a primary test contact associated with said line and normally maintained at establish a connection to said battery potential, at secondary test contact. 2

associated with said line and normally maintained at ground potential, means responsive to the initiation of a call on said line to remove ground from said secondary contact and to apply ground potential to said primary contact to mark said line calling,

wipers on said finder having access to said contacts, means in said finder controlled through said wipers to select said marked contacts and to establish a connection to said line, and means responsive to the establishment of said connection to remove said.

for removing the potential from one of said contacts and applying that potential to the other to mark the line calling, and means in said finder including wipers engaging said contacts for moving said finder to select said each level through a resistance individualto that contact, acalling line, means associated therewithfor marking the contact associated with the level containing that line and for energizing said relay through said resistance, finder switch started through the energization of said relay, and means in said switch for stopping it when said marked contact is engaged.

6. In a telephone system, a finder switch, a group of subscribers lines arranged in sub groups, a testing contact individual to each sub-group, a start relay commonto said group and connected to each of said contacts,

' means responsive to "a call on one of said lines to energize said relay and to mark only the: contact of the sub-groups containing the line, an'd means controlled by said .relay to start said finder to find said calling line.

7.,In a telephone system, a group of lines divided into a plurality of subgroups, a finder switch having a wiper, a group of contacts accessible to said wiper containing a contact for each of said subgroups, a relay common to said contact group and connected to the contacts thereinthrough resistances individual to each contact, means responsive to the initiation of a call on one of said lines to energize said relay through the resistance of the contact associated with the subgroup containing the line and to mark that contact selectable by said wiper, and means controlled by said relay to operate said finder to select said contact and to connect with said calling line. i

8. In an automatic switch, a pair of test wipers permanently connected together, contacts accessible to said wipers, relays in said switch controlled through said wipers and contacts over circuits, including means for rendering the first of said relays responsive to ground potential and for rendering the second of said relays responsive to zero potential on said wiper, and means operated by said relays to control the operation of said switch.

9. In a telephone system, a finder switch having wipers operable in primary and secondary motions, a primary test wiper and contacts engaged thereby to control the primary motion of said finder, said contacts normally carrying a potential placed thereon by battery through a high resistance, lines accessible to said finder, means responsive to the initiation of a call on one of said lines to mark one of said primary test contacts and to start said finder in its primary motion,.a change-over relay iI1"S2Lld finder operated when sa d primary test w per engages :said marked contact, and means controlled by said relay to stop the primary and start the secondary motion of said finder switch.

- 10. In a telephone system, a finder switch having primary and secondary stepping magnets, interrupter springs controlled by each of said magnets, an interrupter relay, a change-over relay, means for energizing said interrupter relay to start the operation of said finder, over: a circuit through said interrupter springs in series andrcontacts on said change-over relay, means including a primary test wiper and said change-over relay removing said interrupter relay from the control of said primary magnet interrupter springs and for subsequently placing it under the control ofsaid secondarymagnet interrupter springs to operate said finder in primary and secondary direction into a desired position. y

11.111 a telephone system, a group of finder. switches, a pair of distributor switches having banks of contacts and wipers which engage said contacts,connections from individual ones of said finder switches to the contacts oi the first of said distributor switches in consecutive order and extending to the contacts of the second of said distributor switches in reverse order, means for associating said distributors with idle ones of said finder switches, a line and means responsive to a call thereon to operate one or the other of said-distributors to start its associated finder to establish a connection with said line,

12. In, an automatic telephone system, a group of finder switches, two distributor switches having access to said finders, banks of contacts on said distributors, the bank contacts of one distributor being connected to the finder-sin vconsecutive. order and the bank contacts of the other connected in reverse order, means for seizingand operating idle ones of said finder switches through said distributors, means responsive to'the operation of the last idle finder of the group to stop said distributors on an over fiow contact, and means operated when one of said finders becomes idle to start said distributors from said over-flow contacts insearch of said finder.

13. In an automatic telephone systenna group of subscribers lines, a group of finder switches having access to said lines, two distributor switches including means for allotting said finders for use one at a time, a start relay associated with each distributor switch, means responsive to the initiation'of a call on one ofsaid lines to establish a start circuit to said distributors, said circuit ex tending through both of said relays in paral- 101 to energize one of them, and means controlled by said energized relay to open the circuit through the other relay and to start said allotted finder to connect with said calling' line. I r v 14. In an automatic switch, a pair ot test Wipers permanently connected together, a set of contacts accessible to each of said wipers, relays in said switch, circuits for said relays over which the first is caused to respond to and the second prevented from responding to a given potential on said 10 In witness whereof, I hereunto subscribe 15 my name this third day of May, A, D. 1927.

RUDOLPH F. sTEHLIK;

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