US1306716A - powell - Google Patents

Description

w. T. POWE'LL.

SELECTIVE SIGNALIHG SYSTEM. APPLICATION FILED pue.2a.191a.

1,306,716. Patented June 17, 1919.

3 SHEETS-SHEET 1.

W. T. POWELL.

SELECTIVE SIGNALING SYSTEM.

APPLICATION FILED AUG-23.1916.

Patentd June 17, 1919.

3 SHEETSSHEET 2- W. T. POWELL.

SELECTIVE SIGNALING SYSTEM.

APPLICATION FILED AUG.23,1916.

1 ,306,716. Patented June 1?, 1919.

3 SHEETS-SHEET 3.

JILL/N6 mum 57' E Nut/552 A as UNITED sTA'rEs PATENT OFFICE.

WINFRED T. POWELL, OF CHICAGO, ILLINOIS, ASSIGNOR TO AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, CORPORATION OF ILLINOIS.

SELECTIVE SIGNALING SYSTEM.

Specification of Letters Patent. Patented June 17, 1919- Application filed Aug 'ust 23, 1916. Serial No. 116,482.

tems which are provided with so-called r1ngback apparatus by means of which a calling subscriber may signal a called subscriber on his own line. In the patent to Hovland, #1,158,22l, there is described a system of handling reverting calls in bridged automatic party line systems, in which the calling subscriber,'by' manipulating his dial in accordance with the proper digits, operates a frequency selecting switch at the exchange, which switch selects simultaneously the two frequencies of ringing current which correspond to the calling and called substations.

' The calling subscriber then hangs up his receiver, whereupon mechanism in the frequency selector is put into operation to effect the application-of the two selected ringing currents to the calling line alternately. The called subscriber is thus signaled as usual; while the calling subscriber is also signaled so that he may know that the operation is proceeding in the proper manner, and also that he may be apprised of the response of the called subscriber by the cessation of the ringing operation which occursas soon as the called subscriber removes his receiver. The calling subscriber will then remove his receiver also and converse as desired.

The Hovland system is adapted to handle calls from anyone of four bridged substations to any one of the remaining three, there being provided the usual four frequencies of ringing current. The ob]ect of the present invention is to provide a revert- 1 ing call signaling system in which the usual four frequencies of ringing current are used to selectively signal at the same time any two of eight substations on the same llne, the ringers being connected four from one side of the line to ground and four from the other side of the line to ground.

Because of the fact that the ringers are not bridged across the line and because furthermore there are on each line two substations which respond to each frequency 01 phone line and the necessary central oflice circuits and apparatus. Fig. 3 is a chart showing the telephone numbers corresponding to all possible two station combinations on an eight party line.

Referring to Fig. 1 of the drawings, I have indicated by reference characters 11 and 12 a party line provided with eight substations which are indicated by reference characters A. to A inclusive. Substation A, which is representive of the group, comprises essentially the receiver 2, transmitter 3, switch hook 4, ringer 5, and condenser 6. Being an automatic substation there is also provided a calling device comprising a pair of impulse springs 7 and 8 controlled by the impulse cam 9 through the medium of a finger hole dial (not shown). .A calling device of suitable design is shown and described in the British patent to S. G. S. Dicker, #29,654 of 1910. When the receiver is on the hook it will be seen that the ringer 5 is connected from the line conductor 12 to ground. The substation A is similar to substation A but the ringer 5' is connected from line conductor 11 to ground. In order to save space only the rin ers of the remaining six substations have een shown, three of which are connected from line conductor 11 to ground and the other three from line conductor 12 to ground.

It has been found desirable in practice to use ringing currents of frequencies approximating 16, 33, 50, and 66 cycles per second. In accordance with this plan the ringers at substations A and A. are adapted to respond to the 16 cycle ringing current, the ringers at substations A and A to 33 cycle ringing current, the ringers at substations A and A. to 50 cycle ringing current, and

the ringers at substations Aand A to the 66 cycle ringing current.

At the exchange the line conductors 11 and 12 are terminated in an individual line switch C, which is of the general type of line switch disclosed in British patent to James #26301 of 1906; being, however,

more nearly of the particular type disclosed in U. S. Letters Patent #1,078,690, granted Jan. 17, 1912, to Frank Newforth. Since line switches of the foregoing type are well known in the art no extended description will be given. It will suflice to say that through the medium of line switch C the party line shown is given access to a plurality of selector switches one of which 1s shown and is indicated by reference character E.

The line switch C, together with a plurality of similar line switches, is controlled in its selective operation by means of the master switch D, which is-of the general type of line switch disclosed in the above mentioned patent to James; being, however, more nearly of the particular type disclosed in British patent to Martin, #1419 of 1910.

,The function of the master switch, as is well known, is to maintain the plungers of all the idle line switches which it controls in position before the terminals of an idle trunk line.

The selector switch E is of the general type of selector switch disclosed in U. S. Letters Patent #815,321, granted March 13, 1906, to Keith, Erickson, and Erlckson; being, however of the particular type disclosed in the British patent to the Automatic Telephone Mfg. Co., #2543 of 1914. A selector switch of the foregoing type is operable in response to the first digit of a called number to select one of a plurality of groups of trunk lines, after which the selector operates automatically to select an idle trunk line in the selected group and eX- tend connection thereto.

The selector switch E, in common with similar selectors, has access through certain of its bank levels to other selectors (not shown) by means of which connections may be extended toward the lines of other subscribers in the exchange, and it also has access through a separate bank level to a group of so-called frequency selectors, one of which is shown at F (Fig. 2).

The frequency selector F is a vertical and rotary directively controlled switch and is similar in mechanical construction to the switch shown in U. S. Letters Patent #815,176, granted March 13, 1906, to Keith, Erickson, and'Erickson. The circuits are modified, however, to adapt the switch to the two-wire system of control as shown in the Newforth U. S. Patent #13,901, reissued April 13, 1915, and are further modified to provide for the more comprehensive ringing operations which have to be performed. A still further modification lies in the provision of four wipers instead of three and the omission of the upper or private bank. The wipers are mounted on the shaft in two sets which are spaced apart a distance equal to the space between five bank levels.

It follows that when the lower set of wipers is in engagement with a set of bank contacts in the first level the upper set of wipers will be in engagement with the corresponding set in the sixth level, and when the lower set of wipers is in engagement with a set of bank contacts in the second level the upper set of wipers will be in engagement with the corresponding set in the seventh level, etc. From these considerations it will be seen that the frequency selector bank is for practical purposes divided horizontally into two sections, that the switch shaft is operable for five vertical steps instead of ten, and that when the shaft is rotated corresponding contacts in the upper and lower halves of the bank will be selected simultaneously.

The lower five levels of the frequency selector bank have certain of their contacts connected in suitable manner to the four ringing current generators R, R R and R, whereby selection of the proper ringing currents may be accomplished through the medium of the wipers 123 and 124. The three interrupters I, I and 1 which are mounted on a common shaft, are suitably connected to the proper bank contacts in the upper five levels, thereby providing means for controlling via the wipers 121 and 122 the application of the selected ringing current, or currents, to the calling line.

The necessity for the simultaneous selection of ringing currents and controlling circuits therefor may be seen from a more detailed consideration of the functions the frequency selector has to perform. In broad language the frequency selector must be provided with means whereby any one of the eight subscribers on a calling line, the line 1112 for example, may ring his own bell and the bell of any other subscriber on the same line alternately. Because of the arrangement of the substation ringers, two to each ringing current frequency connected on opposite sides'of the line to ground, there arises four different conditions under which thesignaling must be accomplished. The chart Fig. 3 shows every possible combination with the necessary telephone numbers and these different combinations are arranged in four groups accordin to the signaling operation required. Brie y stated, the first group includes all calls in which only one ringing current generator is' selected and which is applied to, the two sides of the calling line alternately; the second group includes all calls in which two generators are selected and applied alternately to one side of the calling line; the third group is similar to group twoexcept that it relates to the other side of the calling line; while the fourth group includes all calls in which two generators are selected and applied alternately one to one side of the calling line and the means other to the other side. Means are provided in the frequency selector F for reversing the incoming line and for switching from one selected generator to the other, which means comprise the relays 114 and 115. These relays together with a ringing relay 113 are controlled by the three ringing interrupters II inclusive, to produce the desired results, all in a manner which will be fully explained hereinafter. For the purposes of this explanation, it will first be assumed that the subscriber at substation A desires to signal the subscriber at substation A this being the connection illustrated in the drawings. Afterward connections representative of the other ringing conditions will be briefly described. Inasmuch as a large portion of the automatic equipment used is old and well known in the art, having been fully described in the publications referred to, the operation will be described in a more or less general manner except where it has to do with the principles of the invention.

When the calling subscriber at substation A removes his receiver to initiate the call, an energizing circuit is completed over the line conductors 11 and 12 for the line relay 14 of the line switch C. Upon attracting its armature, the line relay 14 closes a, circuit for the pull-in winding 18. Upon energizing, the pull-in winding operates both the plunger arm 15 and the cut-off armature 16; the former through the medium of its plunge (not shown) forcing the bank springs 3033,' inclusive, into engagement, respectively, with contacts 3437, inclusive; and the latter disconnecting the line conductors 11 and 12, respectively, from ground and from the line relay 14. By the engagement of bank springs 30 and 33 with contacts 34 and 37, respectively, the line conductors 12 and 11 are extended through normally closed contacts of the switching relay 63 to the double-wound line relay 50 of the selector E.

The line relay 50 is accordingly energized over the loop circuit including substation A and, upon attracting its armature, closes a circuit for the slow-acting release relay 51. Upon energizing, the release relay closes a holding circuit for the line switch C which maybe traced from ground G by Way of contact springs 65, contact 35, bank spring a 31 and the holding winding 17 to battery B. Since the line relay 14 is slow-acting, it retains its armature to maintain. the pull-in winding 18 energized until after the above holding circuit has. been established. A

branch of the holding circuit extends by way of conductor 20 to multiple test contacts in the banks of connector switches having access to the line of substation A where by a ground potential on these test contacts the said line is made busy. By the engagement of bank spring 32 with contact 36 a circuit is closed whereby the master switch D is opnow manipulate his dial in accordance with the first digit 0 of the desired number, thereby separatmg momentarily the impulse springs 7 and 8 ten times and interrupting each time the circuit of line relay 50 of selector E. As a result of these interruptions of its circuit the line relay 50 is deenergized a corresponding number of times, sending an impulse at each deenergization from ground at Gr to the slow-acting relay 62 and the vertical magnet 65 in series. The verticalmagnet, in response to these impulses, steps up the switch shaft until the wipers 70, 71, and 72 stand opposite the horizontal level in which are located contacts which are terminals of the group of frequency selectors The relay 62, being slow-acting, retains its armature during the series of impulses and closes a circuit for the test relay 64, which latter relay prepares a circuit for the rotary magnet 66 and locks itself to ground at G At the end of the series of impulses the relay 62 deenergizes, thereby completing the aforementioned circuit of the rotary magnet 66, whereupon the wipers 70, 71, and 72 start rotating in search of an idle trunk line. As is well known, the rotary magnet interrupts its own circuit and also the locking circuit of the test relay at every energization, the contacts in the latter circuit, however, being short-circuited by the test or private wiper 71 while passing over grounded busy contacts. As soon, therefore, as the test wiper 71 arrives at an under-. ground test contact the test relay 64 deenergizes and opens the rotary magnet circuit, thereby bringing the wipers to rest upon the terminals of an idle trunk line, assumed to be in this case the contacts 73, 74, and 75. As a further result of the. deenergization of the test relay 64, a circuit is completed for the line switching relay 63 which relay, upon energizing, disconnects the extended line conductors 12 and 11 from the windings of the line relay 50 and further extends them by way of wipers and 72, bank contacts 73 and 75, and trunk line con-- ductors 180 and 181 to the double-wound line relay 100 of the frequency selector F.

The line relay 100 thereupon energizes over the line circuit extending back through substation A and completes an energizing circuit for the slow-acting relay'101. Re-

lay 101, upon attracting its armature, prepares a circuit for the vertical and rotary magnets 104 and 105 and also completes a new holding circuit as follows: ground at G, contact springs 119, bank contact 74 and wiper 71 to wire junction 80, where the circuit divides, one branch extending by way of a back contact of relay 64 through the winding of line switching relay 63 to battery 13, and the other branch extending by way of off-normal contact 67 and interrupter contact 81 to wire junction 82 where it joins the previously described holding circuit extending back to the line switch C.

The subscriber at substation A may now operate his dial in accordance with the second digit 2 of the desired number, resulting now in deenergizations of the line relay 100 of the frequency selector F. At each dccncrgization the line relay 100 sends an impulse from ground at G to the slow-acting relay 107 and the vertical magnet 104 in series, side switch wiper 115 being in its first position. The vertical magnet, in response to these impulses, steps up the shaft until the upper and lower sets ofwipers stand opposite, respectively, the seventh and the second horizontal levels of bank contacts. Relay 107, being slow-acting, retains its armature during the series of impulses and maintains a circuit from ground at G for the private magnet 108. At the end of the series of impulses, the relay 107 denergizes and breaks the circuit of the private magnet, which latter controls the side switch wiper 115 in the usual manner to advance it to its second position.

The subscriber at substation A may now operate his dial in accordance with the third and final digit 1 of the desired number, resulting now in asingle deenergization of the line relay 100. Side switch wiper 115 being in its second position, the line relay in response thereto sends an impulse to the slowacting relay 107 in series with the rotary magnet 105. The rotary magnet operates in response to this impulse to rotate the upper wipers 121 and 122 and the lower wipers 123 and 124 until they engage the f rst sets of bank contacts in the respective levels to which they have been raised. The relay 107 and the private magnet 108 are energized during the last series of impulses as before, the latter upon deenergizing, again controlling the side switch wiper 115 to advance it to its third position.

The foregoing operations of the frequency selector are practically identical with the operation of the connector described in the above mentioned Newforth patent. The remaining operations will be described with considerable more detail. Having opera-ted his calling device to perform the necessary selective operations at the exchange, the calling subscriber at substation A will now hang up his receiver, thereby again breaking the circuit of the line relay 100. Upon deenergizing, the line relay completes a circuit for the switching relay 112 over the following path: ground at G, closed contacts of line relay 100, contact springs 120, winding of relay 107, contact springs 131, winding of relay 112, and side switch wiper 115 (in third position) to battery B. Relay 107 is not energized. Relay 112, upon attracting its armature, first completes a circuit by which the slow-acting release relay 101 may be kept energized independent of the -line relay 100 and which may be traced as follows: ground at G, contact springs 132, and winding of relay 101 to battery B. As a further result of the energization of relay 112 the incoming trunk line conductors 180 and 181 are disconnected from the windings of the line relay 100 at contact springs 146 and 149, respectively, and are connected instead by way of contact springs 144 and 147 to the contact springs 135 and 138 of the ringing relay 113. Finally, assuming that the interrupter I is in the position shown, a circuit is completed for the ringing relay 113 as follows: ground at G, interrupter I, conductor 150, contact springs 1.33, and winding of relay 113 to battery B.

Upon the energization of the ringing relay 113, a circuit for the generator R is com pleted as follows: ground at G", generator R, upper contact 2 up and 1 in, wiper 123, contact springs 161 and 162, contact springs 166 and 165, contact springs 137 and 138, contact springs 147 and 148, trunk line conductor 181 to bank contact 75, thence by Way of wiper 72, contact springs of switching relay 63,bank contact 37, spring 33, line conductor 11, and ringers of substation A A A and A in parallel to ground, and thence back to ground G", the starting point. Upon the closure of the above circuit, the ringer at substation A which is the ringer corresponding to the frequency of generator R, responds to thereby notify the subscriber that he is wanted. After a brief interval the ringing relay circuit is broken by the rotation of the interrupter I and the said ringing relay deenergizes. It will be observed that the interrupter I has two live segments, providing for two ringing periods at each complete revolution, while the interrupters l and I have but one live segment each. It follows, therefore, that in the second half of the revolution of the interrupter shaft the circuit of the ringing relay 113 will again be completed. Also at the same time or an instant before the following circuit is completed by interrupter I ground at G, interrupter I conductor 152, upper bank contact 7 up and 1 in, wiper 121, contact springs 171 and 170, and winding of relay 114 to battery B. As has been previously mentioned the relay 114 is a reversing relay which now, upon energizing, operates to complete the circuit of generator R over the trunk line conductor 180 instead of the conductor 181. Beginning at contact spring 162 of relay 115 the generator circuit extends as follows: contact spring 162, contact springs 167 and 168, contact springs 134 and 135, contact springs 144 and 145, trunk line conductor 180 to bank contact 73, thence by way of wiper 70, contacts of the switching relay 63, bank contact 34, spring 30, line conductor 12, and the ringers at substations A, A A and A in parallel to ground. The ringer at substation A now responds, thereby notifying the calling subscriber that the operation is proceeding satisfactorily.

The operation continues as described until either the calling or called subscriber res moves his receiver, the ringing relay 113 being energized twice at every revolution of the interrupter shaft while the reversing relay 114 is energized at every other energization of the ringing relay, thereby ringing the bells at substations A and A alternately.

When the called subscriber at substation A removes his receiver to answer the call, a circuit for the ring cut-0E relay 106 is completed which, in case ringing relay 113 is not energized, extends as follows: ground at G, contact springs 139 and 138, and contact springs 147 and 148 to trunk line conductor 181, thence over previously traced path to line conductor 11, thence by way of the receiver and transmitter of substation A to line conductor 12, thence over previously traced circuit to trunk line conductor 180, thence by way of contact springs 145 and 1%, contact springs 135 and 136, and winding 109 of relay 106 to battery B. In case the ringing relay is energized the trunk line conductor 181 will be grounded at G" via the previously traced circuit of generator R Hence,in this instance, ground at G" will be substituted for ground (3 in the above traced circuit, and in addition the battery end of the circuit, instead of passing direct from contact springs 135 and 136- of the ringing relay to the winding 109, will extend as follows: contact springs 135 and 134, contact springs 168 and 169, and winding 109 of relay 106 to battery B. In case the reversing relay 114 is energized the circuit for the ring cut-off relay 106 will be the same as in the condition just/mentioned except that the trunk line conductors 180 and 181 are reversed as regards their connection to ground and battery, respectively.

In any case, it will be seen that when the receiver is removed at substation A, a circuit will be completed for the ring cut-off relay 106. Upon attracting its armature, relay 106 looks itself over the following circuit: ground at G, ofi-normal contact 140, contact springs 142, and winding 110 to battery 13. At the same time a circuit for the private magnet 108 is closed as follows: ground G ofl"-nor1nal contact 140, contact springs 141, and winding of private magnet 108 to battery B. The private magnet, upon energizing, disconnects the wipers 121 and 122, respectively, from relays 114 and 115. As a further result of the energization of the ring cut-ofi' relay 106 the circuit of the switching relay 112 is broken at contact springs 131. Upon denergizing, the switching relay 112 restores the original circuit by which the trunk line conductors 180 and 181 are again extended to the double-wound line relay 100. The line relay 100 accordingly energizes as before, except that the loop includes substation A instead of substation A, and upon attracting its armature, again completes the circuit of the slow-acting release relay 101 over the original path.

The ringing operation has now been stopped. Being apprised thereby of the fact that the wanted subscriber has ansnered," the subscriber at substation A will now remove his receiver also, and is then able to converse with the subscriber at substation A as desired. Current is supplied to the two transmitters in parallel from the windings of the line relay 100, while the voice currents take the path shown in.

heavy lines.

When the conversation is finished both subscribers will hang up their receivers. When the last receiver is replaced the circuit of the line relay 100 is broken, which relay therefore deenergizes to break the circuit of the slow-acting release relay 101. Upon deenergizing, the release relay 101 closes a circuit for the release magnet 111 in the usual manner, whereupon the frequency selector F is restored to normal therefore that the selector E and the line switch C are restored to normal position in the usual and well known manner, whereare brought into engagement with the fifth set of contacts in the fourth level and the nected to'the generator R, whichis the generator to which the ringer at substation A responds; while the upper bank contact 4 up and 5 in is connected to the generator R which is the generator to which the ringer at substation A corresponds. It will be observed, further, that the lower bank contact 9 up and 5 in, with whichthe wiper 122 is in engagement, is connected to conductor 152 extending to interrupter 1 And lastly it will be seen that since relay 114 is deenergized the middle spring 162 of relay 115 is connected via a path previously traced to the line conductor 11 from which the ringers at substations A and A are connected to ground. Now it will be clear that as the interrupter shaft revolves the ringer relay 113 will be energized twice for each revolution of the interrupter. I while the relay 115 will be energized at every other energization of the ringing relay or once per revolution of interrupter I As a result first generator R and then generator R is connected to line conductor 11 whereby the two substations are signaled alternately.

Assuming now that substation A is calling substation A in which case the upper and lower sets of wipers will have been advanced, respectively, to the third contact set in the ninth level and the third contact set in the fourth level, the operations are the same as in the last case, with the addition that the reversing relay 114 must now be operated at each energization of the ringing relay 113, for the ringers at these substations are connected from line conductor 12 to ground. An inspection of the bank wiring will now show that a conductor 151, a branch of conductor 150, extends from interrupter I to the upper contact of the set 9 up and 3 in, which in the case of contact set 9 up and 5 in was vacant. Now as the mterrupters revolve, the relays 113 and 114 are energized simultaneously twice at each revolution of interrupter I while relay 115 is energized once per revolution as before. This operation results in the alternate connection of generators R and R to the line conductor 12 whereby the substations A and A are signaled alternately.

One more casewill be considered-the case where the subscriber at substation A is callin the subscriber at substation A. The te ephone number to be called is 022, resultmg in the selection of the second sets of contacts in the second and seventh levels. From an inspection of the bank wiring it will be seen that the upper and lower contacts of the second set in the second level are connected, respectively, to generators R and R It will be seen, furthermore, that the upper and lower contacts of the second contact set of the seventh level are connected, respectively, to the interrupters. 1 and I. Also it should be noted that the live segments of the interrupters I and I are staggeredwith respect to each other. It follows therefore that in a certain part of the revolution of the interrupters the relays 113 and lltwill be energized simultaneously, followed later by the simultaneous energization of relays 113 and 115. In the first case generator R will be connected to line conductor 12 to operate the signal at substation A while in the latter case generator R will be connected to line conductor 11 to operate the signal at substation A Since all the remaining combinations shown on the chart fall within one or the other of the cases already described, it is thought that the circuits can be traced readily enough without further explanation.

While I have shown the circuits in the preferred form, they are susceptible to modifications to provide for other conditions. In addition it is to be noted that the wiring of the frequency selector bank as shown is largely an arbitrary arrangement. Care has been taken, however, to prevent the crossing together of generators by so arranging the bank wiring that whenever two adjacent contacts are in use they are both connected to the. same generator.

Having fully described and illustrated my invention, what I consider to be new and desi re to have protected by Letters Patent will be pointed out in the appended claims.

\Vhat I claim as my invention is:

1. In a telephone system, a party line provided with substation ringers connected from opposite sides of said line to ground, a calling terminal and a called terminal for said line, ring-back apparatus at the exchange. mcans for extending a connection from said line to said ring back apparatus via said calling terminal, and means for operatin said apparatus to project ringing current ack over said calling terminal to the calling line to enable one party to selectively signal the other parties on the same line.

2. In a telephone system, the combination with a party line provided with substation ringers connected from opposite sides of said line to ground, of a plurality-of grounded ringing current generators at the exchange, and automatic means controlled over said line for connecting either conductor thereof to the ungrounded pole of any generator.

3. In a telephone system, a party line,

lea

substation ringers connected from opposite sides of said line to round, and a ring-back apparatus for enabling one party on said line to *all another on the same line. said ring-back apparatus comprising means for transmitting ringing current first over one side of said line and then over the other.

4. In a telephone system, a party line, sub station ringers connected from one side of said line to ground, and a ring-back apparatus for enabling one party to call another on the same line, said apparatus comprising means for transmitting in alternation two different kinds of ringing current. over the ringer side of said line.

In a telephone system, a party line, substation ringers connccted from opposite sides of said line to ground, a plurality of grounded ringing current generators for supplying ringing currents of different character, and subscriber controlled means for selecting and connecting any one of said generators to either side of said line.

6. In a telephone system, a party line, a calling terminal for said line and a called terminal for said line, a ring-back apparatus for enabling one party to call another on the same line, means for extending a connection from said line to said ring back apparatus, said apparatus comprising means for signaling the stations on said line by projecting ringing current back over said calling terminal and over one side of said line and ground, and also comprising means operated over the two sides of said line in series for stopping the signaling operation.

7. In a telephone system, a line, an automatic switch, a plurality of generators, means for operating said switch over said line to select two of said generators, a conductor means for connecting said conductor to either selected generator sepa-' rately, and means for connecting said conductor to either side of said line separately.

8. In a telephone system, a line, an automatic switch, a plurality of generators, means for operating said switchover said line to select any one of said generators, and means for connecting the selected generator to either side of said line separately.

9. In a telephone system, a line, an automatic switch, a plurality of generators, means for operating said switch over said line to select any two of said generators, and means for connecting the said enerators in alternation toone conductor ot said line to the exclusion of the other conductor.

10. In a telephone system, a subscribers line, a plurality of ringing generators for supplying ringing currents of difi'erent character, and means including a switching device controlled over said line whereby a subscriber thereon may select at his option any one of said generators separately or any two of said generators simultaneously.

lluIn a telephone system, a subscribers metallic line circuit, substation ringers connected from each side of said circuit to ground, a plurality of grounded ringing current generators for supplying ringing currents of diiferent character, an automatic switching device for selecting any one of said generators. and means for connecting the ungrounded pole of the selected generator to the two sides of said line circuit alternately. I

12. In a telephone system, a party line, substation ringers connected from each limb of said line to ground, a plurality of grounded ringing current generators for supplying ringing currents of ditterent character, an automatic switching device for selecting any two of said generators, and means for connecting the ungrounded poles of said generators alternately to one limb of said line.

13. In a telephone system, a party line, substation ringers connected from each limb of said line to ground, a plurality of grounded ringing current generators for supplying ringing currents of different character, an automatic switching device for selecting any two of said generators, and meansfor connecting in alternation the ungrounded pole of one selected generator to one limb of said line and the ungrounded pole of the other selected generator to the other limb of said line. a

14-. In a telephone system, a party line, a plurality of ringing current generators for selective signaling on said line. a plurality of interrupters for controlling the signaling operation. and an automatic switching device controlled over said line for simultaneously selecting one of said generators and one of said interrupters.

15. In a telephone system, a party line. a plurality of ringing current generators for selective signaling on said line, a plurality of interrupters for controlling the signaling operation, and an automatic switching device contiolled over said line for simultaneously selecting any two of said generators and one of said interrupters.

16. In a telephone system, a party line, a plurality of ringing current generators for selective signaling on said line. a plurality of interrupters for controlling the signaling operation, and an automatic switching device controlled over said line for simultaneously selecting two of said generators and two of said interrupters.

17. In a telephone system, party lines, a plurality of ringing current generators for selective signaling on said lines, controlling circuits of difi'ercnt character for cont rolling the signaling operations, and subscriber controlled means for simultaneously selecting one of said generators and one of said controlling circuits.

18. In a telephone system, a party line,-

substation signals connected in different relation to said line, ringing current generators and mechanism for connecting the same to said line, controlling circuits of difi'erent character corresponding to the different arrangements of said signals for controlling said mechanism, and subscriber controlled means for selecting the proper controlling circuit.

19. In a telephone system, a line, a plurality of ringing current generators, an automatic switching device controlled over said linefor selecting one of said generators and for connecting one conductor of said line thereto, a relay for controlling said connection connected to the other conductor of said line, and a second relay for reversing the said line conductors as regards their connection, respectively, to the selected generator and the said first relay.

20. In a telephone system, a party line, substation ringers connected from opposite sides of said line to ground, anda ring-back apparatus for enabling one party on said line to call another on the same line, said ring-back apparatus comprising two or more relays for causing ringing current to be transmitted first over one side of said line and then over the other.

21. In a telephone system, a party line, substation ringers connected from one side of said line to ground, and a ring-back apparatus for enabling one party to call another on thesame line, said apparatus comprising a plurality of relays for controlling the application of two difierent kinds of ringing current to the ringer side of said line alternately.

22. In a telephone system, a line, an automatic switch, a plurality of generators, means for operating said switch over said line to select two of said generators, a con ductor, a relay for connecting said conductor to either selected enerator separately, and another relay for connecting said conductor to either side of said line separately.

23. In a telephone system, a line, an automatic switch, a plurality of generators, means for operating said switch over said line to select any one of said generators, and means for connecting the selected generator to either side of said line separately while said switch remains in an operated condition.

- 24. In a telephone system, a line, an automatic switch, a plurality of generators, means for operating said switch over said line to select any one of said generators, and for connecting the selected generator to either side of said line separately.

25. In a telephone system, a line, an automatic switch, a plurality of generators, means for operating said switch over said line to select any two of said generators, and means comprising two or more relays for connecting the said generators in alternation to one conductor of said line to the exclusion.

' of the other conductor.

26. In a telephone system, a subscribers metallic line circuit, substation ringers con nected from each side of said circuit to ground, a plurality of grounded ringing current generators for supplying ringing currents of different character, an automatic switching device for selecting any one of said generators, and electromagnetic means for connecting the ungrounded pole of the selected generator to the two sides of said line circuit alternately.

27 In a telephone system, a party line, substation ringers connected from each limb of said line to ground, a plurality of grounded ringing current generators for supplying ringing currents of diiferent character, an automatic switching device for selecting any two of said generators. and electromagnetic means for connecting the ungrounded poles of said generators alternately to one limb of said line.

28. In a telephone system, a party line, substation ringers connected from each limb ofsaid line to ground, a plurality of ground ed ringing current generators for supplying ringing currents of different character, an automatic switching device for selecting any two of said generators, and automatic means for connecting in alternation the 'unground ed pole of one selected generator to one limb of said line and the ungrounded pole of the other selected generator to the other limb of said line. I

Signed by me at Chicago, Cook county, State of Illinois, this 31st day of July, 1916.

WINFRED T. POWELL.

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