US1694615A - Automatic telephone system - Google Patents

Description

Dec. 11, 1928.

- 1,694,615 J. I. BELLAMY AUTOMATIC TBLBFHONB SYSTEM Original Filed July 22- 2 2 Sheets-Sheet 1 =Inuan UT- J 11m I5 5115 my .Z. I 1

Dec. 11, 1928. 1,694,615

J. l. BELLAMY 1111101111110 TELEPHONE SYSTEM Original Filed July 2. 1921 2 Sheets-Sheet 2 ggw nnnn AA i atented Dec. fill, @280 entree srras JOHN I. BELLA-MY, OF CHICAGO, ILLINOIS, ASSIGNOR', BY MESNE ASSIGNMENTS, EG AUTOMATIC ELECTRIC} IN'G, OF CHICAGO, ILLINOIS, A GOREQRATIQN F JDEEEA= WARE.

AUTOMATIC TELEPHONE SYSTEM.

Application filed July 22, 1921, Serial No. 486,763. Renewed May 19, 1928.

The present invention relates to automatic telephone systems in general, but is concerned more particularly with large multi-otfice automatic systems; and theobject, briefly stated, is the provision of a new and im proved trunking arrangement in a multi-,

ofiice automatic system, whereby such switchcs as. are not actually needed in any particular office may be omitted without altering \0 the number of digits in the telephone numbers of the lines that terminate in that ofiice. The object above pointed out is not broadly new, being disclosed in the prior U. S. patent issuedto Martin on August 30, 1927, No.

1 1,640,551. The present invention, however,

providesa numberof new and desirable features as will be pointed out fully hereinafter. A special feature of the invention relates to improved operation in a so called drop back selector. Another feature relates to an improved test circuit, whereby a number of lines can be tested or rotated over selectively with much greater speed without sacrificing accuracy, 2 while another feature relates to improved means for controlling the test circuit so as to prevent any operation of the relays or variousparts of the mechanism of a selector. switch, when itis releasing, due to the test 0 Wiper passing over grounded test contacts. Another feature which may be pointed out briefly at this time relates to an improved circuiiarrangement whereby the release trunk conductor of a selector'switch is automatically grounded during the releasing operation so that in case the selector becomes mechan-.

ically stuck in an off normal position it is automatically cut out of service.

A still further feature of the invention relates to improved means for controllin the slow acting release relay so as to ren er it more positive in action and capable of carrying a larger spring combination than heretofore.

As to certain of the features, this application may be considered as being an improvement on the application of C. E. Lomax, S. N. 407,996, filed September 3, 1920. Referring now to the drawings, Fig. 1 shows a selector which mechanically is of the well known vertical and rotary type and accordingly has its bank contacts arranged in horizontal rows or levels. The circuits of this selector include various features of the lIlVGIltlOIl and will be explained fully here mafter.

Fig. 2, shows a selector similarto the one shown in Fig. 1 with the proposed digit absorbmg or drop back feature added and with a different arrangement for controlling the test circuit so as to render it inoperative during the releasing operation. 0

v Fig. 3, is a'schematic la out showing a trunking arrangement in which the proposed drop back selector may be used very profitablly v eferi ing now particularly to Fig. 3,

which shows a portion of the trunking system in an automatic telephone system having a capacity of 100,000 lines, the lines are. as-' sumed to terminate in ten difierent oifices which are so interconnected with trunk lines as to form an integral system. The oflice wh1ch is reached when the digit 2 is dialled as well as the other oflices in the system, with the exception of the one which'is reached when the digit 3 is dialled, may be equipped to their full capacity, while for the purpose of illustration" it will be assumed that the ofiice to which connection is extended when 39 the digit 3 is dialled has for the time'being no more than 1000 telephone lines terminatingm 1t.

In order to point out the trunking arrangev ment more clearly, it will be assumed that the subscriber at substation A desires to call the subscriber at substation A With the assumption as noted, the connection may be extended as follows: From the substation A,

by way of the individual line switch C, first or ofiice selector 1), second or thousands selector E, third or hundreds selector F, and the connector H, to the substation A This,

it will be noted, isthe usual trunking arrangement. Assumin now that the subas scriber at substation calls the subscriber at substation A, the connection may be traced as follows: From'tlie substation A, by way of the individual line switch C, first or ofiice selector '1), third or hundreds se lei l'ector F, and the connector H, tothe substation A. This latter connection extends over a path similar to the one of the substation A with the exception that it does not pass through any second or thousands sea there is only one thousands group of lines terminating in that ofiice, that no thousands selector is needed. Now it is necessary only to introduce in the system an extra. digit so as to make the telephone nlunbers in this oflice have the same number of digits as the Ones in the other ofiices. As has been before intimated, this is accomplished in the system disclosed herein by arranging the selector F to drop back or restore to normal when the first digit is dialled, after connection is obtained with it, and to operate like a regular selector when the following digit is dialled.

It is desirable to be able not only to assign numbers having the desired number of digits but also to be able to assign numbers that may be retained even after the ofiice has reached its ultimate growth.

As is well known, a full 10,000 line office may consist of a main office in which part of the lines terminate and one or more suboflices of probably 1000 lines each. Assuming that when the office under discussion is first installed, most of the lines, owing to their relatively short length, logically terminate in the main oflicc but other lines owing to their great length will, together with still others to be cutin later, be terminated eventually in a sub-ofiicc of 1000 lines capacity, the lines that eventually will be terminated in the sub-ofii'Ce must necessarily be reached, after the sub-ofiice is installed, by dialling a. different second or thousands digit than is dialled to reach any thousands group of lines in the main oflice with which the suboflice is associated. This situation does not cause any difliculty to be encountered in the present system, however, for the reason, that with the drop back selectors arranged to absorb the thousands digit regardless of what that digit is the numbers may be assigned not only in any particular thousands group of lines but in each and every thousands group of lines.

The apparatus, having thus been described in a more or less general manner, will now be described in connection with a detailed description of its operation. For this purpose it will be assumed that the subscriber at substation A desires to obtain connection with the subscriber at substation A. When the receiver is removed at substation A the individual line switch C is operated to extend the connection to an idle first selector, and assuming that the first selector D is the one to which the connection is extended the line and release relays 17 and 18, Fig. 1, are energized in the usual manner. Release relay 18, upon energizing, opens a point .in the circuit of the release magnet at armature 30 at the same time preparing the circuit of the vertical magnet 23; disconnects the ofi normal contacts 26 from the release trunk conductor 15 at armature 28 and closes a point in the circuit of switching relay 21; and at armature 29 places ground on release trunk conductor 51 thus establishing the usual holding circuit for line switch C.

The calling subscriber now operates his calling device in accordance with the first digit of the desired number, whereupon the circuit of line relay 17 is interrupted a cor responding number of times. Each time line relay17 deenergizes in response to one of these interruptions it closes at armature 25 the following circuit: From ground, by way of the resting contact of armature 37 and said armature, armature 25 and its resting contact, relay 19, armature 30 and its working contact, and vertical magnet 23 to battery. By the operation of'the vertical magnet, the shaft and wipers are raised step by step until the latter stand opposite the desired level of contacts, which in this case is the level in which the selector F terminates. Relay 19 is energized in series with the vertical magnet and being slow acting retains its armatures attracted throughout the vertical movement. At armature 31 relay 19, upon energizing, places a shunt around the major part of the winding of release relay 18. This has two distinct effects. One effect is that there is an increased flow of current through the part of the winding which is not short circuited, and which is composed of larger wire than the remainder of the winding, each time the circuit of the release relay 18 is closed, thereby giving more lines of force, or in effectincreasing the slowness of the relay. Another effect is that the part of the winding which is short circuited has the same effect on the relay as placing an additional copper slug thereon, thereby further increasing the slowness of the relay. As a further result of the operation of slow acting relay 19 it disconnects the rotary magnet 24 from the upper Winding of stepping relay 20 and connects it to the lower winding of-the said relay at armature 32. Stepping relay 20 energizes but rotary magnet 24 does not energize at this time because of the high resistance of the lower winding of stepping relay 20. Upon energizing, stepping relay 20 prepares a circuit for the rotary magnet 24 at armature 33. I

At the end of the vertical movement slow acting relay 19 deenergizes, removes the short circuit from around the lower part of the Winding of release relay 18 at armature 31, and at armature 32 shifts the circuit of rotary magnet 24 from the lower winding of step ping relay 20 to the upper Winding of the said stepping relay. Rotary magnet 24 now energizes and stepping relay 20 is maintained energized over the following circuit: From ground by way of 011' normal contacts 26, armature 28 and its working cont-act. working contact of armature 33 and said armature, resting contact of the armature of rotary magnet 24 and said armature, upper gsisbra contacts controlled by armaturei32,la1 1 d ro tary magnet 24'to battery; 1 Upon'energizing,

24 steps the shaft'a nd wip'ersj rotary magnet 47, I inclusive, into engagement with the first set of contacts in the level opposite which they are raised, at the same time opening its own circuit and that of stepping re.- lay 20, whereupon they both deenergize. Stepping relay 20,- upon deenergizing,-opens another point'in the initial circuitof its own upper winding and consequently in the circuit of the rotary magnet 24 at armature 33, and rotary magnet 24, upon deen'ergizing, closes again a point in its. own circuit and that of the upper winding of stepping relay 20. From this point the operation depends upon whether the trunkline terminating in,

the first set of contacts is busy or idle. Kit is busy, there is a ground potential on the test contact thereof and the stepping relay and the rotary magnet energize again over the-follows ing circuit: From ground by way of the busy test contact, test wiper 46, armature 36 and its resting contact, and thence by way of a previously traced circuit through the upper winding of stepping relay 20 and rotary magnet 24 to battery. Stepping relay 20, upon energizing, closes the previously traced local circuit for itself and for the rotary magnet at armature 33, and rotary magnet 24,

upon energizing, advances the wipers intov engagement with the next set of contacts and again opens its own circuit and'that of the stepping relay, whereupon the stepping relay and rotary magnet deenergize again. This cycle of operation is repeated over and over untilan idle or ungrounded test contact is reached.

WVhen an idle set of contacts is reached, or one in which the test contact is not grounded, switching relay 21, being no longer short circuited, energizes over the following circuit: From ground by way of off normal contacts 26, armature 28 and its working contact, switching relay 21 and thence by way of a previously traced circuit to battery by way of the upper winding of stepping relay 20' and rotary magnet 24. Neither stepping relay 20 nor rotary magnet 24 are energized over this circuit because of the high resistance of switching relay 21 but the latter relay is energized and at armature 37 removes ground from the armature of the line relay; grounds the test'wiper 46. so as to make the seized trunk busy immediately, at armature 36; connects up the release trunk conductor 15 with the test wiper 46 at armature 35; and at armature 34 an d 38 disconnects the line conductors 14 and 16 from the upper and lower windings of line relay 17 and extends them byway of armatnres 34 and 38 and their working contacts, line wipers 45 and 47, and from-thence (assuming that the trunk line terminating in the bank contacts 48-50 inclusive, is the'one selected) by way of bank contacts-48 and 5,0,

trunk conductors 51 and 53, and armatures 84. and88 and their resting contacts, to the upper andlower windings of line relay 60 of the drop back selector F. Line relay 60, upon energizing, closes the circuit of release relay 61 at armature 69. Release relay 61, upon energizing, opens a point in the circuit of 're-" lease magnet 66 at armature 75, at the same time preparing a circuit for the vertical magnet 67 disconnect the on normal contacts 70 from the release trunk conductor 52 and closes a point in the circuit of switching relay 65 at armature 73; co'nnectsupthe test wiper at armature 72; andv at armature 7 4 placesground on release trunk conductor 52, thereby closing a holding circuit for the'selector D and line switch C before the slowfacting release relay 18 of the selector Dhas had time 8;

to deenergize.

The CZIllIIIgSUbSCI'lbBI now operates h s calling device in accordance, with the second digit of the desired number or'the digit which ordinarily picks out the thousands-group' of linesin a 100,000 line system. Inlthe present case the digit for which the calling device is turned is immaterial asfar as the final result 1 is concerned and will be determined by what thousands group thefcalled'line will be terminatedin after thenumber of lines has increased-to more than one thousand. Each time line relay 60'deene'rgizes" in'response to 11- the operation of the'calling device at the c'a'lling substation, it closesat armature 69 the following circuit: Fr'om ground by way of the resting contact of armature .87 and said armature, armature 69 and its resting contact, armature 7 5 and its" working contact, 'relay 63, and vertical magnet 67 to battery. By the operation of the vertical magnet,the shaft and wipers 8992, inclusive, of the selector F are raised step by step until the latter stand opposite the desiredlevel of contacts. Relay 63 is energized in series with the vertical mag net and being slow acting retains its armature and at armature 81 places a shunt around the I10 attracted throughout the vertical movement 1 lower part of the winding of releaserelay 61 1 while at armature 82 it shifts the circuit of the rotary magnet from the upper winding of stepping relay 64 to the lower winding of the said relay. Upon energizing, stepping relay 64 prepares a circuit for the rotary magnet at armature 83. i

At the end of the vertical movement, slow acting relay 63 deenergizes; removes the shunt from around the lower part of the winding of release relay 61 at armature 81, and at armature 82 disconnects the rotary magnet 68 from the lower winding of'stepping relay 64, whereupon stepping relay 64 deenergizes. With relay 63 deenergized', the following circuit may be traced: From ground by Way of the upper winding of relay 62, resistance R, normally closed contacts controlled by armature 77, working contact of ofi normal 86 and said spring, normally closed contacts controlled by armature 82, and rotary magnet 68 to battery. Rotary maget 68 is not energized over the above rracecl circuit on account or the high resistance of the upper winding of relay 6:2 and the resistance R. llelay 62, being marginally adjust-ed, operaitesits armatures only partway at this time and accordingly disconnects armature "56 from its resting contact but does not connect it with its working contact; places matures '77 and 78 into contact with their respective working contacts but does not open the normally closed contacts controlled by the said armatures; operates armature 7 9 suficienfly to bring it into engagement with its working contact. With relay 62 thus partly operated, the following circuit is closed for release magnet 66: From ground by way of release conductor 52, normally closed contacts controlled by armature '78, worhing contact of armature 7 8 and said armature, 06 normal contacts 2 1, anrl release magnet 66 to battery. By the operation of the release magnet, the shaft and wipers of the selector F are restored to normal position. the initial circuit of the release magnet being opened at the OE normal contacts 71 by the shaft when it reaches normal posi- -tion. Upon the 06 normal contacts 71 being separahed, a shunt is removed from around 'the lower of relay 62 whereupon the said relay energizes over the following circult: From ground by way of release trunk conductor 52, lower winding of relay 62, worhng contact of armature 79 and said armature, and release magnet 66 to battery. Belwse mawet 66 rleenergizes in series with the lower or relay 62 owing to the high resistance of the said lower winding but the relay 62 new pulls all the way up, thereby opening the normall closed contacts controlled by armatures 7 and 7 8 and placing armature 76 into engagement with its working contact. It be seen now that the net result of the dialling of the second digit in the number, or the first digit after the selector 1* has been reached, is that the said selector has operated in its vertical movement; restored itself to normal position, ancl relay 62 has become lockerl up.

The calling snhscrihcr now operates his calling device in accordance with the next digit of the desired number, whereupon the vertical magnet 67 is energized a corresponding number of times to step the switch shaft and wipers up to the desired level and slow acting relay 63 and stepping relay 64 are energized in a manner )reviously rlescribecl. At the end of the vertical movement, slow acting relay 63 (leenergizes and transfers the circuit of the rotary magnet from the lower to the upper winding of stepping relay 64. Stepping relay 64 is maintained energized eonora momentaril and rotary magnet 68 energizes over the fol owing circuit: From ground by way of 06 normal contacts 70, armature 73 and its working contact,'working contact of armature 83 and said armature, resting contact of the armature of rotary magnet 68, and said armature, upper winding of stepping relay 64, armature 76 and its working contact, normally closed contacts controlled by armature 82, and rotary magnet 68 to battery. Upon energizing, rotary magnet 68 opens its own circuit and also that of the upper winding of stepping relay 64. Stepping relay 64, upon deenergizing, opens another point in its own circuit and in that of rotary magnet 68, and rotary magnet 68, upon (leenergizing, closes the first mentioned point in its own circuit and that of the stepping relay 64.

The operation now depends upon whether the trunk line terminating in the first set of contacts is busy or idle. Ifit is busy there is a ground potential on the test contact thereof and steppmg relay 64 and rotary magnet 68,

energize again over the following circuit: From ground by way of the grounded test contact, test Wiper 90, armature 86 and its resting contact, armature 72 and its Working contact, resting contact of the armature of rotary magnet 68 and said armature, and thence by way of a. previously traced circuit through stepping relay 64 and rotary magnet 68 to battery. Upon'en'ergizing, stepping relay 64 closes again in the previously described local circuit for itself and the rotary magnet, and the rotary magnet, upon energizing, advances the shaft and Wipers 88-91, inclusive, into engagement with the next set oi contacts, at the same time opening its own circuit and that of stepping relay 64, whereupon'they both deenerglze. This same cycle of operations is repeated CV81 and over until an idle or ungrounded test contact is reached.

When an idle set of contacts is reached switching relay energizes over the following circuit: From ground by way of off normal contacts 70, armature '73 and its working contact, switching relay 65, and thence to battery by Way of previously traced circuit, through the upper wmding of stepping relay 64 and rotary magnet 68. Neither stepping relay 64 or rotary magnet 68 energizes over this circuit because of the highresistanco of switching relay 65. Upon energizing, switching relay 65-assuming that the trunk lino terminating in bank contacts 92-94, inclusive, is the first one found to be idleswitches the connection through by way of armatures 84 and 88 and their working contacts, wipers 88 and 91, bank contacts 92 and 94, line conductors 95 and 97,to the upper and lower windings of the line relay of (OllINLl'Ol H, Fig. 3. The line and release relays of connector H (not shown) now energize in the usual manner and the latter places ground on maining two digits of the desired number,

whereupon the connector H is operated in the usual manner to connect with the line of substation A, and when the connection is finally completed and the calling subscriber has answered, the calling and called -ibscribers may converse with each other as desired, the talking circuits that are shown being outlined by the heavy conductors.

When the conversation is completed the two subscribers replace their receivers.

When the receiver is replacd at substation A the circuit of the line relay of connector H is opened, whereupon the line and release relays of the said connector deenergize and the connector His at once restored to normal position in the usual manner. As soon as ground is removed from release trunk conductor 96 by the deenergization of the release relay of connector H, the circuit for switching relay 65 and relay 62 of selector F and switching relay 21 of selector D, as well as the circuit for the switching relay of the line switch C is opened, and the said relays immediately deenergize. In the selector F, relay 62, upon deenergizing, does notperform any particular function at this time but switching relay 65 upon deenergizing places ground on release trunk conductor 52 again by way of off normal contacts 70, and armature 73 and its resting contact, and the resting contact of armature 85 and said armature, This is done primarily to prevent the selector F from being taken for use again in case it becomes mechanically stuck in an off normal position. In the normal course of events,

however, the said selector does not become stuck and release magnet 66., upon energizing, in series with the resting contact of armature 87 and said armature, armature 69 and its resting contact, armature 75 and its resting contact, and off normal contacts 71, restores the switch shaft and wipers to normal position, ground being removed from release trunk conductor52 at ofl normal contacts and the circuit of the release magnet 66 being opened at off normal contacts 77 by the shaft when it reaches normal position.

It will be noted in connection with the test circuit of the selector F that the said circuit is closed at armature 72 and its working contact only while release relay 61 is energized and consequently is always open during the releasing operation, and accordingly there is no possible chance for either stepping relay 64 or rotary magnet 68 to become energized while test wiper 90 is passing over grounded test contacts during the releasing operation.

In the selector D, switching relay 21, upon deenergizing in response to the removal of the ground potential from release trunk conductor 52, closes at armature36 a circuit for rotary magnet 24 as follows: From-ground, which has been replaced on release trunk conductor 52 upon the falling back of switching relay 65 of selector F, by way of test contact 49, test wiper 46 and thence by way of a previously traced circuit to rotary magnet 24:. At the same time swithing relay 21 closes at armature 37 the following circuit.

for release magnet 22: From ground by way of the workingcontact of armature 37 and said armature, armature 25 and its resting contact, relay 19, armature 30 and its resting contact,off normal contacts 27, and release magnet 22 to battery. Rotary magnet 24, stepping relay 20, release magnet 22, and relay 19 now energize simultaneously. R0- tary magnet 24, upon energizing, steps the wipers forward one step in the usual manner and at the same time opens its own circuit including the upper winding of stepping relay 20 and falls back again; and relay 19 upon energizing shifts the circuit of the r0- tary magnet from the upper to the lower winding of stepping relay 22, thereby aintaining the stepping relay 2O energized. By the operation of the release magnet 22, the shaft andwipers of the selector D are restored to normal position in the usual manner, the circuit of the release magnet being opened at off normal contacts 27 by the switch shaft when it reaches normal position. Relay 19, upon deenergizing after the off normal contacts 27 have opened, shifts the circuit of the rotary magnet 24 from the lower to the upper winding of stepping relay 20, whereupon the said stepping relay deenergizes. It will be noted that a ground po- It may be pointed out here that in case it I is so desired the drop back selector F may be arranged to drop back only upon the calling of a particular digit, by merely changing the spring 80 from an 0H normal spring to a spring that operates only when the shaft is stepped up to a particular level. The circuits do not need to be altered when the change is'made but work equally well either way.

The various features of the invention, having been thus described, will now be pointed out more fully in the appended claims.

What I claim as my invention is:

1. In a telephone system, a subscribers line, means including a first selector, 2. second selector, and a connector for connecting the said first line with a second line, means including said first selector, another second selector, a third selector and another connector for connecting said first line with a third line, telephone numbers for said second and third lines having the same number of digits, and means for automatically releasing the first mentioned second selector whenever the said second line is called in order to cancel one of the digits in the number.

2. In a multi-otfice telephone system, two subscribers lines terminating in two different ofices, telephone numbers for saidlines having the same number of digits, a calling subscribers line terminating in a third otfice, means including a first selector-in the third office and a certain number of serially related switches in the first office for connecting said calling line with the said first line, means including said first selector and a series of switches in the second ofice for connecting said calling line with the said second line, said second series of switches being greater by one than for automatically releasing one of the said switches in the first oifice whenever said first line is called in order to cancel one of the digits in the number.

3. In a multi-otfice telephone system, a plurality of oifices each having the same ultimate capacity, blocks of telephone numbers assigned to said ofices, the numbers n each block having the same number of digits as the numbers in the other blocks, serially related groups of switches in each ofice, there being a lesser number of groups in some ofices than in the others, and means including drop-back second selectors in those oflices which. have less groups of switches than the others for making the numbering system conform to the number of groups in use.

i. In a multi-oifice telephone system, a plurality of oifices each having the same ultimate capacity, blocks of telephone numbers assi ned to said offices, the numbers in each blodk having the same number of digits as the numbers in the other blocks, serially related groups of switches in each ofiice, there being a lesser number of groups in some oflices than in the others, and means including drop-back selectors in those oifices which have less groups of switches than the others for cancelling the proper number of digits in the telephone numbers of lines terminating in such oflices in order to make the numbering of such lines conform to the number of groups in use.

5. In a multi-ofiice telephone system, a plurality of ofices each having the same ultimate capacity, blocks of telephone numbers assigned to said offices, the numbers in each block having the same number of digits as the said first series, and means ween e the numbers in the other blocks, serially re lated groups of switches in each ofiice, therc being a lesser number of groups in some offices than in the others, and means only in those offices which have less groups of switches than the others for making the numbering system conform to the number of groups in use, said means comprising circuit arrangements in a particular group of switches for causing such switches to automatically release the first time they are operated.

6. In a digit absorbing or drop back selector having primary and secondary movements, a release magnet, a relay, a circuit for partially energizing said relay at the completion of the primary movement, a circuit for said magnet closed by said relay, a circuit for completely energizing said relay as soon as the switch is restored, and contacts controlled by said relay for altering the switch circuit so that a subsequent primary move ment will be followed automatically by the secondary movement.

7. In a telephone system, an automatic switch for use in connecting calling and called lines, a quick acting line relay and a slow acting release relay for said switch, a circuit for said release relay closed by said line relay through normally open contacts thereon, means for momentarily deenergizmg said line relay to operate said switch, and means for increasing the current in the said circuit of said release relay while said switch is operating.

8 In a telephone system, an automatic sw tch for use in connecting calling and called lines, said switch having primary and secondary movements, a quick acting line relay and a slow acting release relay for said switch, a circuit for said slow acting relay closed by said quick acting relay, a second slow acting relay energized during the primary movement of said switch and deenergized at the end thereof, and contact springs actuated by said second slow acting relay for short circuiting a portion of the winding of said first slow acting relay.

9. In a telephone system, a selector switch for use 1 n connecting calling and called lines, said swltch having directive primary and automatic secondary movements, a stepping relay controlling the secondary movement, a pair of off normal contacts, a circuit for said relay including said pair of off normal contacts, means for releasing said switch, and a test circuit also including said pair of off normal contacts for rendering said switch busy while releasing.

10. In a telephone system, a selector switch for use in connecting calling and called lines, said switch having directive primary movement and automatic secondary movement, a secondary motor magnet and a stepping relay, a test wiper, a circuit for energizing said magnet and said relay including the said test 1 I o wiper, said magnet and relay being connected in the circuit in series, and contacts on said stepping rela for closing said circuit over a path exclu ing said test wiper.

11. In a telephone system, an automatic switch having wipers, said wipers having a normal position, means for moving said wipers from their normal position to eti'e'ct a connection, means for subsequently releasing said wipers to said normal position, a relay controlling the electrical connection of said wipers to said switch, a pair of off normal contacts, a test conductor for said switch, and a circuit extending through said OK normal contacts and contacts on said relay for applying a guarding potential to said test conductor during the restoration of said wipers to their normal position.

12. In an automatic switching device, a line relay, a release relay, contacts on said line relay through which current is supplied to said release relay, and means for increasing the amount of current supplied to said relay through said contacts while said line relay is being operated to control the device.

13. In a telephone system, a selector switch for use in connecting calling and called lines, said switch having directive primary movement and automatic secondary movement, a secondary motor magnet, a stepping relay and a switching relay, a. test wiper, a circuit for energizing said magnet and stepping relay including said testwiper, said magnet and stepping relay being connected in the circuit in series, contacts on said stepping relay for closing said circuit over a path excluding said test wiper, and means for energizing said switching relay in a circuit including said magnet, stepping relay and switching relay in series.

14. In a telephone system, a selector switch for use in connecting calling and called lines, said switch having directive primary movement and automatic secondary movement, a secondary motor magnet-,- a stepping relay and a switching relay, means for energizing said magnet and stepping relay .in series to control the automatic secondary movement, and means for energizing said switching relay in a circuit in series with said magnet and stepplng relay when the automatic secondary movement is completed.

15. In a digit absorbing device having an initial and a subsequent directive movement wherein said device automatically releases after the initial movement, a two-step relay, a circuit for operating said relay in its first step responsive to the initial movement to cause the release of said device, a circuit for operating said relay in its second step responsive to the device being restored, and means controlled by said relay to prevent a second automatic releasing operation after the subsequent dii'ective movement.

In witness whereof, I hereunto subscribe my name this 15th day of July, A. 1)., 1921.

JOHN I. BELLAMY.

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