US2013171A - Measured service telephone system - Google Patents

Description

Sept. 3, 1935- E. s. PETERSON MEASURED SERVICE TELEPHONE SYSTEM Filed Aug. l0, 1933 INVENTOR- EDWARD S. PETERSON Patented Sept. 3, 1935 UNITED STATES MEASURED SERVICE TELEPHONE SYST Edward S. Peterson, Chicago, Ill.,, assignor, by mesne assignments, to Associated Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application August 10,

18 Claims.

The present invention relates in general to measured service telephone systems, and more particularly to automatic systems of. thischaracter in which a calling subscriber establishes connections by automatic switches controlled by .a dial or calling device.

The principal object of the invention is an improved arrangement for giving measured .service to party line subscribers in an automatic telephone :system.. According to the invention an,

automatic party line may have as many as ten connected stations, with ten meters corresponding to said stations, respectively, located at the exchange. When a call is made from any station the proper meter is automatically selected and ii the call is successful it is registered on the selected meter.

The various features of the invention will be pointed out hereinafter as the constituent parts thereof are described and their operation explained, reference-being made for thispurpose to the accompanying drawing.

Referring to the drawing, Fig. 1 is a circuit diagram of the essential parts of the system.

Fig.2 is a front view of a so called eleven hole dial or calling device, one of which is installed at each-party line station.

Fig. 3 is a rear view of the dial, showing the spring assembly.

Figs. 4 to 9, inclusive, are views of thespring operating cam members and associated parts. Of these latter figures, Figs. 4, 6, and '8 are top views of the cam carrying members disassembled, while Figs. 5, '7, and 9 are, respectively, side views of the same parts.

In Fig. 1, two party line subscribers stations on a ten party line are represented by Al and A16. The line terminates at the exchange in a line switch LS of standard type. Associated with the line at the exchange are ten meters of which two, MI and Mill, are shown. There is also a meter selecting switch S.

The line switch LS and line switches associated with other party lines ofthe kind disclosed herein have access to first selectors of standard type by way of trunk circuits such as the trunk circuit T. This trunk circuit includes .a number of relays and a small stepping switch SI.

The first selector and other switches are not shown herein as they may be of any suitable type, such as the well known Strowger switches in common use. The system should, however, include means for operating the subscribers meters on successful calls. Meter operation may be by the well known.bo0ster method, as shown 193-3, Serial No. 684,477

in IS. PatentxNo. 1,186,823, in which booster battery is momentarily applied to the release trnnkiwhen. the called party answers. The circuits shown are arranged for this method of operation, but can readily be revised to take care s of meteroperation by other. methods, as, for example, by the well known reverse current method.

The eleven. hole dial used at the subscribers stations willfirst :be. described, as an understanding of this device is necessary to an understandit) ing of the operation of the system. This dial :or calling device is similar mechanically to the us-ualidial in commonuse in automatic telephone systems at the present time except that it has eleven finger holes instead of ten and transmits 15 .a .maximumof eleven impulses instead of ten impulses. The arrangement of the finger holes and the numbering thereof is shown in Fig. 2.

The calling device is conveniently manufac- .tured as .a modification of the calling device dis- 20 closed in. U. .S.. Patent No. 1,642,822, granted September 20,.192'7. 'The calling device shown in the above patent has only ten finger holes but the spacing between the first finger hole and the finger stop is double the spacing required 25 for the transmission of one impulse. In fact, when the digit one is pulled, the impulse cam is rotated .sufficient to transmit two impulses, when the digit 5 is pulled, the cam is rotated sufi'icient to transmit six impulses, and so on, 30 the digit nought corresponding to a rotation sufficient for eleven impulses. The calling device is, howevenfiprovided with a cam which rotates "with the "number wheel, which is effective to move the impulse springs out of range of the 35 "impulse cam during the last one half rotation thereof, when otherwise it would transmit the last impulse. "One impulse is always omitted, therefore, at the end of each series, so that the actual number transmitted always corresponds 40 to the --di-git pulled on the dial.

Now, the only modification which is required in the above described calling device to make it transmit a maximum of eleven impulses is the omission of the cam which moves the impulse 5 spri11g-sr:out.of.range of the impulse cam. When this cam is left off no impulses are omitted or cancelled. .The. mechanism of the eleven hole calling device, therefore. may be the same as shown in the patent except that the cam re- 5 zferred to is not provided.

In order to make the finger holes correspond .to the modified mechanism a difierent number wheel is providedsuch as is shown in Fig. 2. It willbe seen that this number wheel has eleven finger holes, the additional hole being provided, referring to the dial of the patent, in the space between the finger stop and the No. 1 finger hole. The digit number card behind the dial is so arranged that this new finger hole bears the digit 1. The digits assigned to the other ten finger holes are all rotated one space in a clockwise direction, so that the old No. 1 finger hole becomes No. 2, No. 2 becomes No. 3, and so on. This leaves one finger hole after No. to which the digit 11 is assigned, all as shown in the drawing, Fig. 2. Of course, an arbitrary designation can be used in the eleventh finger hole if desired.

The eleven hole dial described in the foregoing is further provided with certain sets of contact springs and cams for operating them which are required in the party line metering system and these additional parts will now be described, reference being made to Fig. 3 and Figs. 4 to 9, inclusive. Fig. 3 shows a rear view of the complete calling device including not only the additional parts referred to but also the 01d parts. This is necessary in order that the complete arrangement may be understood.

The contact springs normally provided consist of impulse springs 16 and I1, and a set of shunt springs I5, as may be seen by reference to the hereinbefore mentioned patent. These springs are clamped between bushings as shown and lie in a plane above the back of the calling device where they can be operated by the cams provided for that purpose. The additional springs provided are a pair consisting of springs 18 and l I and another pair consisting of springs i3 and Hi. There is also a member [2 formed somewhat like a contact spring. All these springs and member [2 are assembled along with the impulse springs and shunt springs above referred to. Springs 10, H, and I8 and member 12 are insulated in the usual way, but spring 19 is assembled alongside of impulse spring I! without any intervening insulation. The four extra springs and the member 52 are offset so that the ends thereof lie in a plane above the plane of the impulse and shunt springs. The member 12 supports a pivoted cam 13 for operating contact spring I l.

Referring now also to Figs. 8 and 9, the reference character 3| indicates the usual tapered hub which is used to attach the upper end of the helical main spring to the finger wheel shaft. The detailed construction of the hub and the associated parts is shown and described in U. S. Patent No. 1,615,311, granted January 25, 1927. It is sufficient to state here that the hub 3| fits over the end of the main finger wheel shaft and rotates with it. To the hub 3| is attached a member 21 having a portion thereof formed as a cam 30 for operating the shunt springs l5. A similar cam is shown in Patent No. 1,642,822. The cam 53 shown in this patent is, however, not provided, for reasons previously explained. and in place thereof the member 21 is formed with two projections 28 and 29.

Referring now to Figs. 6 and '7, the reference character 22 indicates a disc having two cars 23 and 2d. The disc 22, as shown in Fig. 3, rests on the projections 28 and 29 and the openings in ears 23 and 24 correspond to the openings in the projections 28 and 29. Rivets in these openings hold the parts together. Ths disc 22 carries two cams 25 and 26 for operating the cam I3, Fig. 3. There is also a pin 33 projecting from the upper surface of disc 22. This pin lies on the circle described by the holes 34 in member 20 next to be described.

The member 20 is shown in Figs. 4 and 5 and can also be seen clearly in Fig. 3. It comprises a disc-like portion corresponding in size to disc 22, and a cam 2!, the latter being provided for operating spring 18. Member 28 is secured to disc 22 by means of a small machine screw which passes through member 23 into a threaded hole in disc 22. The cam 2i has an enlarged portion with an opening therein so that the screw can be reached with a screw driver. When the member 20 is secured in place the pin 33 lies in one of the openings 34.

The functions of the parts just described may now be considered more in detail. It is intended that the springs H) and H shall be closed only if the digit 1]. is pulled on the dial and that when closed these springs will remain closed until the dial returns to normal. When the digit 11 is pulled the entire assembly including disc 22 is rotated in a counterclockwise direction, Fig. 3, and the parts are so designed that as the finger of the operator approaches the finger stop cam 26 engages cam 13. Further movement of the finger dial causes cam 26 to rotate cam i3 on its pivot with the result that when the dial has been rotated to the limit the cam 13 will be standing substantially perpendicular to the end portion ii of spring H. For safety, the parts should be adjusted so that cam i3 is moved slightly past dead center, as it is required to stay in this position while the dial is returning. The operation of cam 13 obviously closes spring H against spring I2. As the dial returns the cam 25 will engage cam i3 just before the dial reaches normal and the further movement of the dial to normal moves cam l3 to its original position as shown in Fig. 3.

If any digit of a lower value than the digit 11 is pulled on the dial the cam i3 will not be operated, for cam 26 will never reach it.

The springs l6 and ii) are adapted to be closed by cam 2 I. To this end the spring is may be provided with a bushing which can be engaged by the cam. This cam presses spring 58 against spring 19 when the dial is pulled down and also when it returns. As will presently appear, 110v.- ever, it is only when the dial is returning that the springs i3 and 59 have any effect. The member 28 is adjustable so that cam 2i can be made to engage springs i8 during any desired impulse interval while the dial is returning to normal. As shown in Fig. 3 member 28 is set so that cam 25 closes the springs during the last or eleventh impulse interval. By loosening the screw, member 2E3 can be raised and rotated to position pin 33 in a different hole 32. This circular row of holes and the cooperating pin are provided as an accurate and easy way of adjusting the cam to any desired position.

Referring now to Fig. 1, it will be assumed that the subscriber at station All! desires to make a call, and the ensuing operations will be described.

Station All) is one of ten stations on the party line having conductors H and 42 extending to the automatic exchange. As mentioned hereinbefore there are ten meters at the exchange which correspond respectively to the ten stations. When any station makes a call a necessary operation to be performed before the call can be completed is the selection of the proper meter in order to prepare to record the call. The selection is preferably accomplished preliminary to setting up the desired connection and is taken care of by the subscribers themselves through the medium of dialling an additional digit. This extra digit is the digit 9 i It maybe stated that all the subscribers on the line have instructions to the effeet that the digit 11 must be prefixed to all regular exchange numbers.

When the receiver is removed at station Alli, the transmitter is bridged across the line in the usual way, resulting in the closure of a. circuit over line conductors ii and 432 for the line relay 56 of the rotary line switch L8. The operation of the line switch is well known and hence need not be explained. It will suffice to say that the op-er ation of the line relay causes the line switch to select an idle trunk leading by way of a trunk circuit such at T to a first selector. If the trunk on which the wipers Sit-56 are standing is idle it is at once seized by the operation of switching relay i. If this trunk is busy the wipers are rotated by stepping magnet 52 until an idle trunk is found, the idle condition being determined by the test wiper 55, which picks up ground potential from busy test contacts to keep magnet 52 operating and to shunt relay 5i.

Assuming that the trunk comprising conductor l5t* i53 is the first trunk found idle, when the wipers arrive at the contacts associated with this trunk the rotation will cease and the switching relay 5! will operate, disconnecting the line conductors it and 52 from the line relay 5t and from ground, respectively, and extending them by way of wipers 53 and 5t to trunk conductors i553 and 553, respectively. As a result of the fore going line relays Hi3 and m2 of the trunk circuit T operate over the line from the calling station. Relay Hi3 closes a circuit at armature ME for release relay we. The latter relay, on energizing, prepares various circuits which will be described later, and also, at armature E 2i, places ground on the release trunk conductor W2. This completes the usual holding circuit for switching relay 5! of the line switch.

The line relay m2 is connected to ground through the secondary winding of the dial tone transformer shown and hence as soon as the connection is extended to the trunk circuit by the line switch the calling subscriber will receive a tone indicating that he can commence dialling the desired number. As before stated, the digit 11 must be prefixed to all numbers and therefore the dial is first operated in accordance with this digit.

When the digit 11 is pulled the dial is rotated in a clockwise direction, see Fig. 2, and the cam assembly as shown in Fig. 3 will be rotated in a counter clockwise direction. At the beginning of the rotation cam 2i forces spring iii momentarily against spring it but this is of no effect. As the rotation is completed, cam 2t engages cam l3 and operates it as described hereinbefore, with the result that spring 5 i is forced into engagement with spring iii and held there. As can. be seen from the circuit drawing this prepares a circuit for grounding the upper line conductor 4! by spring it on the return movement of the dial. It may be mentioned also that at this point that the rotation of the dial also results in the rotation of cam til which permits the shunt springs maining in operated position because it is slow.

to release. The first time relay iii? falls back it closes a circuit for stepping magnet i3t of switch Si which extends by Way of grounded armature ii i, armature lit, armature E32, and winding of magnet i3 4 to battery. Switch Si therefore advances one step. Line relay M32 falls back with relay its and closes a circuit for slow acting relay it'l the circuit extending from ground by way of armature itll, armature Hi3, armature ill, and winding of relay lii'i. Relay Edi operates and remains energized throughout the time relay N32 is responding to the interruptions of the line circuit. Relay Nil closes a circuit for relay lot which operates and locks itself to the release trunk conductor 52 at armature iii. Relay its also opens the original circuit of the stepping magnet le t at armature E32 and the circuit of relay id? at armature tilt. However, the contacts at these two armatures have already been shunted by the operation of armatures, 529 and iii; of relay ml. Line relay Hi3 therefore continues to send impulses to magnet E34. It will be noticed that off normal springs 536 are closed at the first step of switch Si, but relay holds open the circuit of release magnet IE3 at armature lZl.

At the same time that it sends impulses to switch Si, the line relay E53 sends impulses to the meter selecting switch S over the following path: Ground at use or lit, armature M5, armature ii armature E22, conductor 55E, wiper 5-4, conductor M, and winding of stepping magnet 5 to battery. The switch S is therefore advanced along with switch Si. On the first step of switch S the oif normal contacts 3 are closed. The circuit of release magnet (i is however held open by slow acting relay 5, which operates in parallel with magnet 5 and holds up during impulses.

The relays operate as described with the result that after ten interruptions of the line circuit have been produced ten impulses will have been transmitted to magnets iii.- and 5 and switches Si and S will have advanced to their tenth positions. The impulse cam next produces the eleventh interruption. At this time cam 25 closes springs is and iii, these springs remaining closed during the time impulse springs iii and ii are opened by the impulse cam. The conditions during the eleventh interruption are therefore modified by the grounding of the upper line conductor ti. As a result relay 8512 alone responds, relay E53 being held up over the temporarily grounded line conductor 4!.

When relay H22 falls back alone it closes a circuit for relays Hi5 and M6 in parallel, said circuit extending from ground by Way of armature H6, armature H4, and windings of relays Hi5 and tilt to battery. Relay tilt is slow to pull up and cannot operate responsive to a standard length impulse such as is delivered by relay ill? under control of the dial. Relay till: operates, opens the impulsing circuit for magnet 5 of the meter selecting switch S at armature i'22, and locks itself over a circuit including ground, armature i2'l, armature 82d, and armature 523. A branch of the locking circuit extends from the upper end of the upper winding of relay 585 by way of armature 025, wiper 135 of switch Si, tenth contact in bank, and winding of relay illi to battery. Relay Hit energizes and locks itself to the grounded release trunk conductor I152 .at

armature III. At armature IIU relay IGI supplies ground to the locking circuit of relay I85, as the original ground is to be shortly removed by the falling back of relay I07.

Relay IGI also disconnects the line relays I92 and 03 at armatures IE9 and IE2 and connects the incoming trunk conductors I59 and IE3 to automatic trunk conductors M5 and IE5, respectively, extending to the first selector. The line and release relays of the selector accordingly energize and the latter supplies a holding ground to the release trunk conductor I52. At the trunk circuit the deenergization of line relay W3 is followed by the deenergization of relay I84 which breaks the circuit of relay IN. The latter relay, on falling back, closes a circuit for the release magnet I33 of the switch SI. SI is therefore restored to normal, whereupon the circuit of release magnet I33 is broken at off normal springs Relays IIll, I88, and IE5 remain energized throughout the connection, the first two being locked to release trunk conductor I52, and the last named relay being locked to ground at armature Illl of relay IGI. It will be recalled that the energization of relay Iii-5 opens the impulsin circuit to magnet 5 of the meter selecting switch S at armature I22. Atthe same time a circuit is closed at armature I2! which extends ground to conductor l5I by way of resistance The resistance is high enough to prevent the operation of magnet 5, but the relay 6 is held up. The meter selecting switch therefore remains with its wiper 2 standing on the tenth contact, with the result that meter MID is connected to conductor 43 and to release trunk conductor I52.

The calling subscriber at station All) may now dial the digits in the desired number, and the first selector which has been taken for use together with other switches will be operated in the usual way to complete the desired connection and signal the called subscriber. When the called subscriber answers, a booster battery is momentarily inserted in the circuit of the release trunk conductor I52. The increased voltage operates the connected meter MIB to register the call. When the subscriber at station AID replaces his receiver the bridge across the line is broken and the connection is released in the usual manner. The removal of ground from release trunk conductor I52 permits the switching relay of the line switch LS to restore and permits the energized relays in the trunk circuit T to fall back. Relay lII disconnects ground from conductor I5I, whereupon relay 6 falls back. This closes a circuit for release magnet 4 of switch S, which restores the switch to normal, springs 3 opening in normal position to open the circuit of magnet ll.

It will be understood that although in the calling device at station Alli the cam 2| is set in the position shown in the drawing, Fig. 3, with the pin 33 in the tenth hole, at the other stations the cams corresponding to cam 2i are set difierently, in fact, each cam has a different setting corresponding to the number of the associated station. At the No. I station, for instance, the cam is set with pin 33 in the first hole. The operations which take place when the subscriber at station AI makes a call will now be briefly explained. The station apparatus at Al is not shown in detail but is the same as at station All) except for the different setting of cam ill.

The results which follow the removal of the receiver are the same as previously described.

When the preliminary digit 11 is pulled on the dial the cam such as I3 is set in the described manner in order to prepare for grounding the negative line II on the return movement. When the dial returns relays I92 and IE3 fall back responsive to the first line interruption and. the latter relay delivers an impulse to switch SI and also an impulse to switch S, advancing these switches one step each. During the second interruption cam 2i closes springs I8 and I9, grounding line conductor ll and thus preventing line relay I03 from falling back. Relay I05 is therefore energized and locked up, opening the impulsing circuit to magnet 5 of switch S. Ground is supplied to relay 6 through resistance I60. During the third interruption springs I8 and I9 are not in engagement as cam ZI has passed on, so that the third and succeeding interruptions operate the line relays I92 and H13 in the normal way. The latter relay resumes the transmission of impulses to switch SI but sends no more impulses to switch S because of the fact that relay I05 has operated. Switch S therefore is left standing with its wiper 2 in engagement with the first contact, thus connecting up the No. I meter. Since eleven interruptions are produced, and since the efiect of one is lost by holding up relay I63, just ten impulses will be delivered to switch SI, which is thus advanced to the tenth contact in its bank. Wiper I35 at this point closes the circuit of relay Illl and the ensuing operations are the same as described.

From the foregoing the manner in which the corresponding meters are selected responsive to calls from the other stations on the line will be readily understood. Each subscriber always prefixes the digit 11. Eleven interruptions are always produced therefore, effective to control the trunk circuit T, and during one interruption, which one depends on the station calling, the negative line is grounded to operate relay I05 and stop the meter selecting switch S. Switch SI continues to operate responsive to the remaining interruptions and delays the operation of relay IGI until the preliminary series of interruptions is finished.

In any measured service system some consideration must be given to the possibility that some subscriber will attempt to put through a call without going through the required operations, with the object of defrauding the company. The mechanical construction of the calling device herein shown positively requires that the digit ll be prefixed to each number called. Unless this digit is prefixed the cam I3 is not operated, and unless cam I3 is operated no grounding of the line 4! can occur during the impulse transmission. Without such grounding of the line relay 15 cannot be operated and relay IEJI cannot be operated to connect the line through to the first selector. In order to prevent tampering with the calling device the instrument may be sealed, or preferably, a drop of sealing wax may be placed over the screw which retains cam 2| in position. Thus any attempt by a subscriber to change the setting of cam Zl so as to charge his calls to a different subscriber can be defeated, or at any rate, will be detected on the next inspection.

However, a subscriber may attach wires to the line terminals of his instrument and to the ground terminal and attempt to simulate the operation of the calling device, applying the ground during some random interruption or during some interruption which will not result in selection of his meter, if the setting of the meter cam 2| is known. The fact that switch SI must receive ten impulses makes it rather difiicult to obtain any results this way, as any momentary cessation of the impulses for a longer period than the normal spacing will let relay i ii! fall back, releasing switch Si. As an added precaution relay M5 is provided. Ihis relay it will be recalled is slow to pull up and will not energize in the normal operation of the system. However, in attempting to get through the trunk circuit T by manipulating wires, the operator is liable to ground the line for too long a period and any substantial increase in the length of the impulse delivered to relay its results in the energization of relay list in parallel with it. Relay N95 is thus prevented from looking up because relay W6 is slightly slow LO- release and will hold the locking circuit open at armature use until after it is opened at armature, I23. Unless relay we is locked up, relay lti cannot be operated, even if the switch 8! is successfully stepped around, and the line cannot be extended through to the first selector.

The invention having been described, the particulars as to which the protection of Letters Patent is desired will be pointed out in the appended claims.

What is claimed is:

1. In an automatic telephone system, a party line, meters at the exchange, one for each station on the line, means at the exchange responsive to the same fixed preliminary digit dialled at any calling party line station for giving the party line access to automatic switches for completing the required connection, and means at the exchange variably responsive to said digit depending on the station calling for selecting the meter which corresponds to the calling station.

2. In an automatic telephone system, a party line, meters at the exchange, one for each station on the line, a meter selecting switch, means for controlling said switch responsive to the dialling of a preliminary digit of the same value from any calling station on said line, and means at the exchange for rendering the dialling of the regular digits ineifective unless the said preliminary digit is dialled first.

3. In an automatic telephone system, a party line, meters at the exchange, one for each station on the line, a meter selecting switch, means for operating said switch responsive to the dialling of a preliminary digit at a calling station, means at each station for changing the character of one impulse of the series transmitted by the dialling of said preliminary digit, and means for stopping the operation of said meter selecting switch upon the receipt of the changed impulse.

4. In an automatic telephone system, a party line, meters at the exchange, one for each station on said line, a meter selecting switch, means for starting the advance of said switch responsive to the first of a preliminary series of impulses transmitted from a calling station on said line, means for stopping said switch upon the receipt of a variable number of impulses of the series, the number depending on the station calling, and means for extending the line to the first numerical switch responsive to the receipt of the last impulse of the series.

5. In an automatic telephone system, a party line, meters at the exchange corresponding to the stations on said line, means at each station for changing the character of one impulse of a series, said means being set for a different impulse at each station and being ineffective unless a series of impulses corresponding to a particular digit is transmitted, a meter selecting switch at the exchange which is set in motion at the beginning of the series of impulses corresponding to said particular digit, and means for stopping said switch responsive to the changed impulse of the series.

6. In an automatic telephone system, a party line, a station on said line, a meter at the exchange corresponding to said station, a calling device at the station, a meter selecting switch at exchange responsive to a portion of a series of impulses transmitted by said calling device, sufficient to cause the switch to select said meter, means in the calling device for altering the next impulse of the series so that said switch cannot respond thereto, and means responsive to said altered impulse for rendering the switch unresponsive to the remaining impulses of the series.

7. In an automatic telephone system, a party line, meters at the exchange corresponding to the stations on said line, calling devices at said stations, means in each calling device for inserting in aseries of impulses a special impulse to control meter selection, the position of said special impulse in the series depending on the calling device being operated, means in each calling device requiring the same particular digit to be pulled in order that the special impulse can be sent, and means at the exchange preventing access to the numerical switches unless the special impulse is received.

8. In an automatic telephone system, a party line, meters at the exchange one for each station on the line, a trunk line, means for extending said party line to said trunk line responsive to a call, a line relay bridged across said trunk line and responsive to a series of impulses sent from the calling station, means at the calling station for introducing a pause in the operation of said line relay responsive to said series of impulses, and meter selecting means controlled by said line relay prior to the occurrence of said pause but not afterward.

9. In an automatic telephone system, a trunk circuit accessible to party lines, two line relays controlled, respectively, over the two talking conductors of said trunk circuit, a switch control circuit over which one of said relays transmits impulses, and a relay controlled jointly by both line relays for opening said circuit.

10. In an automatic telephone system, party lines, a meter selecting switch individual to each line, a trunk circuit, two line relays bridged across said trunk circuit, means for extending a calling party line to said trunk circuit, means for controlling said line relays over the calling party line, a circuit over which one of said relays transmits impulses to the said switch which is individual to the calling line, a relay for opening said circuit, and a circuit for said last mentioned relay controlled jointly by said line relays.

11. In an automatic telephone system, a normally open trunk accessible to calling lines, two line relays bridged across said trunk, a counting device controlled by one of said line relays, a third relay which is controlled jointly by said line relays, a fourth relay for closing through the normally open connections in the trunk, and a circuit for said fourth relay controlled jointly by said third relay and by said counting device.

12. In combination, a central station, a line extending from said station to a plurality of remote stations, a plurality of devices at the central station, one for each of said remote stations, an impulse sender at each remote station, selecting means for said devices at the central station controlled by a series of impulses sent over the line from any remote station, differently adjusted means in each sender effective to change the character of one impulse of the series, and means for stopping the operation of the said selecting means when the changed impulse is received, whereby the device corresponding to the sending station is selected.

13. In combination, a line connecting transmitting and receiving stations, two impulse responsive switching devices at its receiving station, a sender at the transmitting station operable to send a continuous series of impulses over said line, automatic means for changing the character of one impulse of the series, and controlling means at its receiving station for causing both switching devices to respond to said impulses until the changed impulse is received and only one of said switching devices to respond to the remaining impulses.

14. In combination, a line, means for transmitting a series of impulses over said line, means for automatically changing the character of one impulse of the series, and a selecting device controlled over said line by the impulses received prior to the receipt of the changed impulse and not by those received subsequently.

15. In combination, a line, two circuits including said line, means for transmitting a series of impulses over one circuit, automatic means for transmitting an impulse over the second circuit coincidental with an impulse of said series, a switching device responsive to said series of impulses, and means responsive to the impulse transmitted over said second circuit for rendering said device non-responsive.

16. In an automatic telephone system, a party line, meters at the exchange, one for each station on the line, a meter selecting switch, means for operating said switch responsive to the dialling of a preliminary digit at a calling station, means at each station for changing the character of one impulse of the series transmitted by the dialling of the said preliminary digit, each said means changing the character of a different impulse, and means for controlling the extent of operation of said switch dependent upon which of the impulses is changed.

17. In an automatic telephone system, a party line, meters at the exchange corresponding to the stations on said line, means at each station for changing the character of one impulse of a series, said means being set for a different impulse at each station and being ineiTective unless a series of a particular value is transmitted, a meter selecting device at the exchange, means for operating said device while the series of impulses is being received, and controlling means for determining the meter selected by said device in accordance with the position of the changed impulse in the series.

18. In combination, a line, a selecting device, means for operating said selecting device responsive to a portion of a series of impulses transmitted over said line, means for automatically changing the character of one impulse of the series, and means for making the number of impulses effective to operate said device dependent on the position of the changed impulse in the series.

EDWARD S. PETERSON.

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