US1503916A - Metering arrangement for automatic telephone systems - Google Patents

Description

- W. T. POWELL METERING ARRANGEMENT FOR AUTOMATIC TELEPHONE SYSTEMS Filed Dec. 28 1920 2 Sheets-Shee l $TATI on l F'iGLJ smwwn'a INVENTOR WIHFRED T. POWELL.

BYAQWW ATII'ORNEY 1,503,916 W. T. POWELL METERING ARRANGEMENT FOR AUTOMATIC TELEPHONE SYSTEMS Filed Dec. 28. 1920 STAT l on"| BYXQCW ATTORNEY Patented Aug. '5, 1924.

U'ITE* WINFRED T. POWELL, OF ROCHESTER, NEW YORK, ASSIGNOR TO THE STROMBERG- GARLSO'N TELEPHONE MANUFACTURING COMPANY, OF ROCHESTER, NEW YORK, A

CORPORATION OF NEW YORK.

METERING ARRANGEMENT FUR AUTOMATIC TELEPHONE SYSTEMS.

Application filed December 28, 1920. Serial No. 433,678.

To all whom 2'2. may concern:

Be it known that I, VVINFRED T. Pownm,

a citizen of the United States, residing at Rochester, in the county of Monroe and 5 State of New York, have invented certain new and useful Improvements in Metering Arrangements for Automatic Telephone Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to telephone sys tems and more particularly to automatic telephone systems.

In automatic telephone systems where a plurality of subscribers stations are arranged on each telephone lme 1t 18 desirable to provide individual meters at the exchange which will distinguish between' the calls originatingat the various StittlODS.

and will charge each call'to the sub-station from which it originates. Means are known whereby calls from an individual line or calls from a party line having a plurality of sub-stations thereon are charged on meters located at the exchange, applicant, however,

base devised a novel means for accomplishing this result.

The present invention has for its purpose the arrangement of circuits whereby three ormore sub-stations on a party line of an automatic telephone system may selectively operate registers located at the exchange so that the calls from each station will be charged on its individual register.

Other features will appear from the detailed description and claims. 7

The drawings, with Fig. 1 placed at the left of Fig. 2, diagrammatically represent a portion of a telephone system employing the present invention. The circuits shown at the left of the dotted line in Fig. 1 represent the sub-stations and line conductors of a A-party telephone line, referred to as the calling line, which terminates in an individual "trunk selecting switch. Also there are shown four meters, one for each of the sub-stations on the party line. The circuits shown between the dottedlines in Figs. 1 and 2 diagrammatically represent a selector switch circuit, while at the right of the dotted lineof Fig. 2 there appears the circuits of a connector switch aswell as a second telephone line, herein referred to as the called line; This last line is also a party line similar to. the first mentioned line but only the circuits of one sub-station have been shown in detail, the remaining three sub-stations being indicated merely by their condensers and ringers. In Fig. 3 there is shown a relay, one of which is located at each sub-station for the individual .use of each subscribers sub-station.

The line switch employed in this system may be substantially similar to that disclosed in the patent to Clement 1,107,153, August 11, 1914, while the selectors and connector switches may be of the type disclosed in the patents to Keith, Erickson and Erickson, Nos. 815,321 and 815,176 both issued March 13, 1906, when modified to operate in a so-called two-wire telephone system.

The relay 5 of Fig. 3 is provided with a core 6 on which there are wound three coils7, 8 and 9. -The coil 7 and its core are separated from the coils 8 and 9 and their cores by insulating material, so that it is effective to operate'only the armature 10 whereas the windings 8 or 9 are capable of attracting the armature 11. The armature 11 is normally under tension and is provided with a hook 12 which is arranged to abut a projection 13 of the armature 10 under normal conditions. hen the armature 10 is attracted, the tension on the armature 11 will cause the hook 12 to engage projection 13 and thus mechanically lock the armature 10 in operated position. hen

it is desired to release the armature 10, the,

armature 11 is attracted to cause hook 12 to disengage projection 13.

It is believed that the invention will best be understood by describing the method of establishing and registering a telephone connection from the sub-station 1, herein designated A. to the sub-station designated B.

When the subscriber at sub-station A removes his receiver from its switch hook, a circuit is closed from ground, winding of .the line relay 15, back contact and armabattery. The upper high resistance winding of relay 18 is energized and it attracts its armature, but the line relay is not energized, until the operation of this armature at which time the previously described circuit, with the exception of the upper winding of relay 18, is closed. The line relay is thus energized and attracts .its armatures. At the inner armature and front contact of the line relay, ground potential is applied to the multiple test terminals of "the. calling line at its group of connectors,

so that'this line cannot be seized as a called line.

At the lowermost armature of the line relay a circuit is closed for the motor ,magnet 22 of the line switch for advancing the line switch until an idle trunk is located.

This operating circuit is traceable from grounded battery, winding, back contact and armature of'the motor magnet 22, lowermost armature and front contact of line relay 15, lowermost back contact and armature of cut-oil relay 16, test brush 23 of the grounded battery. energized 1n thls lZlSt ClGSCllbGCl circuit but the motor magnet 22. remains inert.

line switch, conductor;26, continuity spring and contact '27 of slow releasing relay 28,

conductor 29, conductor 30, to ground at' 'the'upper armature and front contact of slow releasing relay 31 individual to an engaged trunk circuit. Under the control of circuits similar to that described the motor magnet advances its brushes 83, 89, 185,

23, 24,-an'd until an idle trunk is located. Let it b assumed that the first idle trunk tested is that shown in Figs. 1 and 2.

engages test terminal of test conductor 26,

Under this assumption, whentest brush 23 there will. be'anabsence of potential on this 'terminal so that themotor magnet 22 will not be actuated, but a circuit is closed from ground at'the inner armature and front contact of line relay 15, lowerwinding of the cut-oif'relay 16, armature, back contact and winding of the motor magnet 22, to The cut-off relay is p The cut-off relay on operation disconnects the battery bridge including the line relay l5 and extends th calling line to thewipers "2 1' and of the line switch,

As soon'as the calling line has been thus connected to its brushes 2 1 and 25, a circuit is closed through the inner back contacts and armatures of relays 32 and 28, through both windings of the impulse relay 33, to grounded battery. The relay 33 is operated in this circuit and at its armature and front contact closes an operating circuit for the slow releasing relay 31. This operation of the relays 31 and 33 occupies only a. small interval of. time during which the slow releasing relay -15 maintainsthe initial energizing circuit of the cut-off relay 16 until this relay completes a locking circuit for itself from grounded battery, through its upperwinding, lower: front-contact and sender to interrupt the circuit including both windings of the impulse relay 33 causing this relay to vibrate its armatures.

In response to the first retractlon of the armature of impulse relay 33 a circuit is closed from ground, its armature and back contact, lowermost back contact and arma ture of relay 32, lower armature and front contact of relay 31, winding of the slow releasing change over relay 35 and the primary motor magnet 34; in series to grounded battery.

In response tothis first impulse ,the

selector switch advances its brushes 37, 38, p 39 and 10 one step in its primary movement and thereby closes the oft- normal contacts 41 and 12 at this switch.

With relay 35 operated and the ofi-normal contact 42 closed, a'circuit is completed for relay 43' from grounded battery, its winding, off-normal contacts 42, front contact and armature of relay 35, upper armature and front contact of relay 31, toyground.

The relay 43 is energized inthis circuit and closes a lockmg circuit "for itself. from grounded battery, its winding, off-normal contacts 42, back contact and armature of the secondary motor magnet-4A, armature andfront contact of relay 13, to ground. In

response to theremaining impulses of this series, the: impulse relayretracts its armature intermittently to repeatedly close the a circuit for primary motor magnet 34-, as previouslydescribed, and th1s magnet ,ad-

vances the selector switch brushes 37 to 10 inclusive to select a group of trunks leading to a group of wanted connector switch-es. At thetermination of this series of impulses the relay 33 will hold its armature attracted for a relatively long period causing the slow releasing change-over relay 35 to retract its armature and thereby complete an operating circuit forthe secondary motor= magnet 44 of the selector switch. This c1rcuit extends from grounded battery, windmg of the secondary motor magnet, upper front contact and armature of relay 43, back contact and armature of relay 35, upper armature and front contact of relay 31, to ground. The secondary motor magnet is energized in this circuitto advance the selector switch brushes one step and at its armature and back contact opens the circuit which has been holding the relay 43 operateda Relay 43 now deenergizes but, if the first trunk of the selected group is busy, this condition will be indicated by the presence of ground potential on its test terminal and, as aresult of this, a circuit is closed through test brush 38, conductor 46, middle lower armature and back contact of relay 32, conductor 47, armature and back contact of secondary motor magnet 44, oif normal contacts 42, winding of relay 43, to grounded battery. The operating circuit of the secondary motor magnet 44 is thereby again closed to advance the selector switch brushes an additional step and also attracts its armature to open the energizing circuit of the relay 43. Thus therelay 43 and the secondary motor magnet 44 are alternately energized and deenergized until an idle trunk leading to a connector switch ofthe wanted group is reached. Let it be assumed that thefirst idle trunk tested is that shown in Fig. 2. This idle condition is indicated by the absence of ground potential on its test terminal 45 so that the energizing circuit for the relay 43 will not be again completed with the result that the secondary motor magnet 44 ceases to operate.

During the period that the selector switch was testing busy trunks, the switching relay 32 was short-circuited in the following manner. At the armature and front contact of relay 31 ground is applied over conthe idle trunk is tested in themanner just which relay on operation at its upper armadescribed, the switching relay 32 is energized and extends the two sides of the talking conductors through leads 147 and 148, through both windings in series of the impulse relay 48, togrounded battery. The impulse relay is energized in this circuit and operatesthe slow. releasing relay 49 ture and front contact applies guarding po tential to the test terminal 45 of the selected trunk. At the lower armature and front contact of relay 49, a break point is closed in the operating circuit of the primary motor magnet 50. -As'soon as'the relay 32 was operated, it closed'a locking circuit for itself from grounded battery, winding of relay43, oif-normal contacts 42,'back contact and armature of secondary motor magnet 44, conductor 47, windingof relay32, its contact 51 and armature, conductor 46,

1 test brush 38, testterminal 45, upper front contact and armature of slowreleasing relay 49to ground. Also when relay 32 is operated it disconnects the impulse relay selected group' of lines.

33 of the selector switch from the calling line permitting this relay to retract its; armature and thereby subsequently cause the deenergization of relay 31. The relay 52, the purpose of which will be pointed out, is energized and locked operated in a circuit in multiple of those just described for the switching relay 32.

The connector switch is now in condition to receive the impulses corresponding to the tens digit of the wanted number. The calling subscriber thereupon operates his dial sender to transmit this series of impulses to cause the impulse relay 48 to vibrate its armature. In response to the retraction of the armature of this relay, a circuit is closed from ground, through the lower armature and front contact of slow releasing relay 49, winding of the slow releasing change-over relay 53, winding of the primary motor magnet of the connector switch, side switch wiper 54 in its first position, to grounded battery. In response to each closure of this circuit the primary motor magnet advances its brushes 55, 56 and 57 in its primary movement to select the group of lines in which the calling line terminates. On the first ener ization of the slow releasing relay 53, it closes a circuit from ground, its armature and continuity spring, winding of the escape magnet 58, to grounded battery.

The escape magnet is energized in this circuit and, since the slow releasing relay 53 does not retract itsarmature during the momentary interruptions of its operating circuit, the escape magnet will remain energized until the close of the tens series of impulses, at which time the impulse relay holds its armature attracted to open the energizing circuit of change-over relay 53 which in turn opens the energizing circuit of the escape magnet 58, This, magnet on deenergization advances the side switch wipers into their second position.

The'conn'ctor switch is now in condition to receive the series of impulses corresponding to the units digit of the wanted number. I11 response to the units series of im pulses, the impulse relay 48 again vibrates its armatures but this time it closes an operating circuit from grounc, its armature and back contact, armature and front contact of relay 49, winding of change-over relay 53, right-hand contact and armature of test relay60, winding of the secondary motor'magnet 61, side switch wiper 54 in its second position, to grounded battery.

In response to the opening and closing of this last described circuit by the operation 'of the impulse relay, the secondary motor magnet advances the brushes of the connector switch over the terminals of the It will be under stood that during this operation of the secondary motor magnet that the change-over relay is .also'energized to hold the escape magnet 58 operated.

test relay 60, its continuity spring and contact, side switch wiper 63 in its second position, test brush 57, multlple test terminal 62 and through a test brush similar to 57 and a side switch wiper similar to 63inits third position to ground at the con nector switch which has previously seized the wanted line.

current will. not be applied to the busy wanted line. Also the test relay 60 will be energized-in the circuit last described and will close a locking circuit for itselffrom grounded battery, winding of the es cape magnet 58, continuity spring and contact of relay 53, winding of test relay 60,

effective grounded battery,

continuity spring and-armature of this re lay, off-normal contacts 64:, to ground. With relay operated, a source of busy tone current is connected to the calling line from BZ, outer armature and front contact of relay 60 to the calling sub-stav:tion.

It will now be assumed that the called line was idle at the time when it was tested by the test brush 57 of'the connector switch. This idle condition is indicated by the presence of full battery potential on niultiple test contact 62 of the wanted line.

The test relay 60 will therefore not be op-- V releasingrelay 52. retracts? 1ts armatures.

erated and the escape magnet will deenergize to move the side switch wipers into their third or talking position. This is to complete a through side switch wiper 54-, winding of the cut-in relay 6'7, side switch wiper 63, to ground.

signalling circuit fromthe 33 cycle source of ringing current, lower armature and back contact of trip relay 65, lower armature and'front contact of relay 67, connector brush 56, over the lower side of front contact of relay 67, upper armature and backcontact of the slow operating trip relay 65, 1ts upper w1nd1ng,to grounded battery. i l hen the called party responds,

the trip rel ay 65 attracts its armatures and -tliereby closes a locking circuit for itself from grounded battery, its lower winding,

tery, its winding, continuity- The escape magnet is thus held operated to hold its side switch wipers in their second position so that signalling circuit from -lay 28 to the relays T2 and 73.

Relay 67' attracts rits armatures and completes a front contact and armature, conductor 66,

. off normal contact 64, to ground,-which circuit insures that the ringing current will not be reappliedto the called line until the connector switch has been released'and readjusted on a succeeding call. 'The' attraction of thearmature of trip relay 65 also serves to close break points in the talking conductor and also completes a circuit for operating the meter relay :28. appearingxat the center of Fig. 1. This circuit is traceable froin g-roundedbattery, winding of meter relay .28, lower front contact and armature of relay 52, uppermost frontcontact and armature of relay 32,. conductor 68, selector brush 39, conductor 69, uppermost front contact and armature :of trip, re-

lay 65, conductor66,off-normal contact 64,

to ground, 7

It should here be pointed out that. if the called party does not respond,under:which condition the calling partyfshould' not. be

charged with a call, thenthe trip relay '65 will not be operated and: in. consequence :no

circuit will be completed'for the metering relay 28. The response ofthefcalledparty energizes the battery feed relay. 7 0. inbridge of the called line- This relay attracts its armatures to provide reverse battery supervision on :toll calls to this connector.

At the termination of" he conversation,

when the calling party replaces'his receiver on its switch hook, the impulserelay .48 of Fig: 2 deenergizes and shortly afterward the slow releasing: relay 49. retracts fits ar- -1nature and at 158 11131361 armature and front contact breaks the circuit that. has

ubeenpholding the selector-switcl1 operated.

1t willalso be remembered that the relays 32 :and 52. have been held. operated in this cir-' wit, and, when'it is opened, the relay 32 deenergizes and shortly afterward the slow The deenergization of relay132 connects the calling .line conductors through its back conspring and uppermost armatnre of relay 28 "continuit s rin and u) oer armatureof relay 52,-to ground. When shortlyafter- 'ward relay 52 retractsitsxarmatures, the

locking circuit of 'relay'28 is opened and the conductor :26 extending to the line switch now leads to the continuity spring and up- .permost armature of relay 28, continuity spring and contact of relay 52, conductor 74E, through'the contacts of relays 72.:and 73',

which relaysrare at that time operated. as

will be described. The relay 28 'now deenergizes and disconnects the lead 26 from relays 72 and 7 3 and opens the holding circuit of the line switch. Also when'relay 32 deenergizedya circuitwas closed for the reposition, the registration of the call is then effected in the following manner.

Since it has been assumed that station #1 was calling, when the receiver of this substation is placed on its switch hook,

a circuit is closed from ground, through the uppermost armature and front contact (mechanically locked closed) and middle winding of relay 18, normal contacts of the switch hook, conductor 20 of the calling line, inner upper armature and front contact of relay 16, line switch brush 25,,inner' upper armature and back contact of relay 32, inner armature and front contact of relay 28, right-hand winding of relay 72, right-hand winding and middle winding of relay 73, to grounded battery. The current in this circuit has no effect on relays 72 and 73 since the middle winding of the relay 18 is of such high resistance. Since neither the relay 72 nor relay 73 has been operated, the meter magnet 78 of the meter assigned to substation #1 is operated in a circuit extending from grounded battery, winding of this magnet, lowermost fronticontact and armature of the cut-off relay 16, line switch brush 23, conductor 26, continuity spring and uppermost armature of relay 28, continuity spring and armature of relay 52,

back contacts and armatures of relays 72 and 73, through resistance 79 and booster battery, to ground. The meter magnet 78 is operated and, when the slow releasing relay 28 shortly afterwards deenergizes, the

operating circuit of the meter magnet is opened and it deenergizes.

If station #2 is calling instead of station #1, at the time when its switch hook is replaced, an energizing circuit is closed through the middle winding of relay 81,

causing it to attract its lower armature and effect the release of its upper armature in the manner previously described. The operation of the lower armature closes a circuit traceable from ground, armature,

front contact and lower winding of relay 81, conductor 17 of the calling line, inner lower armature and front contact of cut-off relay 16, line switch brush 24, inner lower armature and back contact of relay 32,

lower armature and front contact of relay 28, left-hand winding of relay 72, left-hand winding and middle winding of relay 73, to grounded battery.

These two windings of relay 73 are differentially arranged so that it is not operated but since an operating circuit extends through only the left-hand winding of differentially wound relay 72, this relay attracts its armatures. When relay 52 deenergizes, the meter magnet individual to sub-station #2 is operated in a circuit extending from grounded battery, resistance 21, uppermost front contact and armature of cut-off relay 16, winding of meter magnet 82, line switch brush 83, outermost front contact and armature of relay 72, back contact and armature of relay 73, resistance 79 and booster battery, to ground. Similarly when the relay 72 deenergizes due to the opening of its operating'circuit, the

-meter magnet 82 deenergizes.

In the event that sub-station #3 had initiated a call, the replacing of the receiver of this sub-station on its switch hook causes the operation of the lower armature and the release of the upper armature of relay 85 of the sub-station. In this case the operation of the lower armature closes a circuit through the low resistance 86, conductor 87, normal contacts of the switch hook, inner upper armature and front contact of cutoff relay 16, line switch brush 25, inner upper armature and back contact of relay 32, inner upper armature and front contact of relay 28, right-hand winding of relay 72, right-hand winding and middle winding of relay 73, to grounded battery. Also a circuit is closed from ground at the lowermost armature and front contact of relay 86, through the lower winding of this relay, line conductor 17, inner lower armature and front contact of cut-off relay 16, line switch relay 73 are energized, the difierential effect of this relay is overbalanced and attracts its armatures to operate the #3 meter. This circuit extends from grounded booster battery, resistance 79, armature and front contact of relay 73, inner armature and back contact of relay 72, line switch brush 185, meter magnet 186, uppermost armature and front contact of cut-01f relay l6, resistance 21, to grounded battery.

If station #4 had originated the call, circuits similar to those closed from substation #3 will be completed, except in this instance the lower winding is of high resistance. This permits the lower armature of relay 187 to be operated but prevents the difierential effect in relay 72 so that it attracts its armatures. This is effectiye to actuate the meter magnet 88 in a circuit traceable from grounded booster battery,

resistance 79, armature and front contact of relay 73, inner armature andfront contact of relay 72, line switch brush S9, winding of the meter magnet 88, uppermost armature and'front contact of cut-off relay 16, resistance 21, to grounded battery.

It should be noted thatthe low resistance circuit through the receiver and transmitter of a station using the line will prevent the operation of a sub-station relay at another station, thus acting as a lock-out system.

Itavill be understood that the three rectangles generally designated 90', 91 and 92 each represent a group of connector switches which is provided with signalling current of proper frequency to signal one of the stations on a party line accessible to this group of connectors.

What is claimed is:

1. Ina telephone system, a telephone exchange, a plurality of telephone lines terminating thereat, a plurality of substations on each telephone line, a meter at the exchange for the individual use of each substation, a plurality of relays for operating the meter of a calling substation, means operated on the completion of a call to a wanted sub-- station, and other means co-operating with said last mentioned means and responsive to the concluding of a call for variably operating said relays.

2. Ina telephone system, a telephone ex change, a plurality of telephone lines term'n nating thereat, a plurality of substations on each telephone line, a relay located at each substation, a meter at the exchange individual to each substation, means including antomatic progressively movable switches for interconnecting said substations and means including the relay of the calling telephone line for operating the individual meter of said line, l

3. In a telephone system, a telephone (EX-,7

change, a plurality of telephone lines terminating thereat, a plurality of substations on each telephone line, each substation being provided with a relay having interlocking armatures, a meter at the exchange for each substation, means including automatic switches for completing telephone connections between said-substationsand means including circuits controlled at the arma tures of the relay of the calling substationforoperating the individual meter of said substation.

4. In a telephone system, a telephone exchange, a plurality of telephone lines ter minating thereat, a plurality of substations on each telephone line, a relay having aplurality of windings at each substation, a meter at the exchange for each substation, means including automatic switches for completing telephone connections between said substations, means for initially energizing the substation relay of thecalling substation in a circuit including two sides of the calling line in series andmeans responsive t the operation of said substation relay for operating the individual meter of said substation.

5. In a telephone system, a telephone exchange, a plurality of telephone lines terminating thereat, a plurality of substations thereby for. subsequently short-circuiting said winding, and means co-operating with. the substation relay of the callingsubstation for operating. the individual meter of this station on the completion ofa call.

6. In a telephone system, a telephone exchange, aplurality of telephone linesterminating thereat, a plurality of substations on each xof said telephonelines, means 'ineludingautomatic-switches for completing telephone connections between said substations, an individual meter at the exchange 'for each substation and means including a plurality of .diiierentially wound controlling relays operated on the ,release'ofa telephone connection for operating the individual meter of the callingsubstation.

7. In a telephone system, a telephone exchange, a plurality of telephone lines terminating thereat, a plurality of: substations on each of said telephone lines, an individual meter at the exchange foreachsubstation, means including automatic switches for completing a telephone connection between substations and a plurality of differentially wound controlling, relays arranged to be variably operated on the release of a telephone connection for operating the indi= .vidu'al meter of the, calling substation;

8. In. a telephone system, a. telephone ex change, a plurality of telephone linesterminating thereat, a plurality of substations on each telephone line, an individual meter at the exchange for each substation, each meter being provided with a magnet having but one operating winding, meansincluding automatic switches for completing telephone connections between said. substations, a plurality of differentially wound controlling relays arranged tobe operated on'the release of a telephone connection for operating the: magnet'individual to the meter of the calling. substation.

9.- In a telephone systenna telephone exchange, a plurality of telephone lines terminating thereat, a plurality of substations on said telephone lines, an mdividual meter at the exchange for each substation, eachv meter being provided with an operating magnethaving but a single winding, means including automatic switches for interconnecting said substations and means including differentially wound controlling relays arranged to be variably operated on the release of a telephone connection for operating the magnet of the meter individual to the calling substation.

10. In a telephone system, a telephone exchange, a plurality of telephone lines terminating thereat, a plurality of substations on each telephone line, a relay located at each substation having a winding of relatively low resistance and a winding of high resistance, a meter at the exchange for each substation, means including automatic switches for completing telephone connections between said substations, and means including circuits extending through the windings of the relay of the calling substation for operating the individual meter of said substation.

11. In a telephone system, a telephone exchange, a plurality of telephone lines terminating thereat, a plurality of substations on each telephone line, a relay located at each substation having a winding of relatively low resistance and a winding of high resistance connected to the sides of its telephone line, a meter at the exchange for each substation, means including automatic switches for completing telephone connections between said substations, and means includin circuits extending through the windings of the relay of the calling substation for operating the individual meter of said substation.

12. In a telephone system, a telephone exchange, a plurality of. telephone lines terminating thereat, a plurality of substations on each telephone line, a relay located at each substation having a winding of relatively low resistance and a winding ofhigh resistance, one Winding being connected to one side of said telephone line and the other winding being connected to the other side of said telephone line, a meter at the exchange for each substation, means including automatic switches for completing telephone connections between said substations, and means including circuits extending through the windings of the relay of the calling substation for operating the individual meter of said substation.

13. In a telephone system, change, a plurality of telephone lines terminating thereat, a plurality of substations on each telephone line, a meter at the exchange individual for each substation, a plurality of relays for operating the meter of a calling substation, at least one of said relays being ditl erentially wound, means for interconnecting said telephone lines, and means including certain of said relays actuated responsive to the completion of a call for operating the meter individual to the substation that initiated the call.

In witness whereof, I hereunto subscribe my name this 22nd day of December A. D. 1920.

a telephone eX- VVINFRED T. POXVELL.

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