US2270128A - Telephone system - Google Patents

Description

T #Za I Z1 I TELEPHONE SYSTEM Filed May 27,' 1939 2 Sheets-Sheet l ATTORNE Patented Jan. 13, 1942 TELEPHONE SYSTEM Max Langer, Berlin-Hermsdorf, and ErnstHorn, Berlin-Friedenau, Germany, assignors to Fides Gesellschaft fr die Verwaltung und Verwertung von gewerblichen Schutzrechten mit beschrnkter Haftung, B poration of Germany erlin, Germany, a cor- Application May 27, 1939, Serial No. 276,140 In Germany May 30, 1938 7 Claims. (Cl. 179-9) The present invention is concerned with a circuit arrangement for determining fees in automatic remote signalling installations, in particular automatic telephone installations oi vthe type in which the subscribers meter is used for determining the amount of the fee by marking and initiating specialV switching operations. Since the meter is associated individually with a particular subscriber it is suitable, as has already be proposed, for identifying a calling subscriber or for registering his telephone number.

When, as is set forth in the present invention, the subscribers meter. is operated in known manner by current increase on the .blocking conductor and, for the purpose of initiating and carrying out special switching operations, a longer operation of meter is necessary, circumstances can occur such that during the current increase on the blocking conductor another selector can test on the arrangement to be guarded and thus the danger of double connections arises.

The present invention relates to the avoidance of this occurrence when an operation of the meter is necessary by limiting the current increase on the blocking conductor to a ti-me which is Sufficient effectively to operate the meter.

The drawings, comprising Figs. 1 and 2, to gether form a circuit diagram showing the invention applied to a line identifying arrangement. For the sake of simplicity and clarity, all arrangements and switches which are not completely necessary for elucidating the Videa vof the invention are omitted.

The two gures should be placed side by side with Fig. 1 to the left of Fig. 2. Across the top of said gures is illustrated the part of a connecting path which extends from a subscriber Tn over the preselector VW, the first group selector IGW, and a repeater UE from which a two-conductor junction line a/b extends for example to a distant exchange. As is indicated by the dotted lines outgoingfrom the first group selector IGW, the connection may pass through any number of additional selector switches before reaching repeater UE. The repeater transfers the rimpulse train sent out from the subscribers station on the initiation of the connection over the rest of the junction line and is the intermediary for the operations by which the determination of the number of the calling subscriber is initiated. Further, it transmits impulse trains corresponding to the callnumber over junction line to the station which is associated with a registering arrangement (printing or` punching. device), for 55 recording the call number. In addition to the callnumber other records can bey made by the registering arrangement (called number, duration of connection, amount of fee, period, date,

f etc.).

` Below the connecting path, and separated from it in the diagram by` a horizontalv dot-and-dash line, is a contact field and control relay arrangement KR and an impulse sender SS.; the two are separated from one another by a vertical dot-and-dash line in Fig. 2, KR. lying 'to the left of Athisline and SS to the right. The arrangement KR consists of a number .of control relays and contacts of the meters associated withlthe individual subscribers. The meter contacts are fastened together, correspondingl to the call number of the individual subscribers, in groups of 100. VIn Fig. 1 the contact eld IH .(rst hundred) is shown in its entirety, while the contact elds A.2H (second hundred) and; 3H (third hundred), are only partially shown.

The impulse sender SS after the marking of the number by meansof the control relays transmits the impulse trains corresponding to the individual digits of the call number over the junction line to the printing arrangement.

In connection with the drawings detailed description will be given only. for 'the circuits and operations for determining and transmitting the call number.

`When the pre-selector VW is set on a free line relays A andAB in the first group selector IGW are energised over the subscribers loop in known manner. Similarly in the blocking conductor the seizing relay C of the group selector and the cutoi relay T of the pre-selector are energised.r The meter Za cannot at present operate. When the first and second group selectors are set, a blocking circuit is completed in which the test relay' P of the irst group selector and the seizing relay CI invthe'repeater are energized.

The arrangement shown in Figs. land 2 makes possible the determination and transmission vof the call number at any desired instant. It can, for example, be accomplshed during the setting up of a connection, after the reply of the called station or after the connection has been terminated. Itis assumed here that the reply of the called subscriber is thesignal for initiating the determination and transmitting of the call number. l

It is a common practice to connect potential to one conductor of the talking circuit when the called subscriber -replies in lorder to operate the calling ysubscribers'meterI In the present arrangement it is contemplated that this practice be followed for low valued calls, and that, for high valued calls, the same potential be connected to the speech path, but for a longer period in order to initiate the determination and transmission of the calling stations number. The switching operations in the latter case may be initiated in a simple manner by time zone metering equipment in the path reached over the repeater UE which, on the reply of the called subscriber, connects a 4potential corresponding to the metering potential to the lower conductor b of the junction line a/b. Such time zone equipment is well known, and has been omitted from the drawings since it forms no part of the present invention.

By means of this potential connection the following circuit is completed: earth in repeater UE, contact 6802, winding of relay ZE, choke Dr3, lower talking conductor b and to the battery potential connected to the time zone arrangements. The relay ZE in the repeater UE operates and completes the following circuit: earth, contact 65c2, winding I of relay U, contact 642e, 55s, 56k, resistance WiI I, battery, earth. In this circuit relay U operates, closes contact Blu, and thus completes the following circuit: earth, winding II of relay U `contacts 622e, Blu, 54s, winding of relay K, battery, earth. In this circuit moreover, apart from the winding II of relay U, the relay K of the impulse sender SS energises, opening its contact 561e and thus the circuit indicated above for winding I of relay U is broken. The completion of the energising circuit of relay U (over winding I) of other repeaters is thus prevented. Further, the relay U closes contact 13u and thus completes the following circuit: earth, contacts IIcI, 13u, winding of relay C2, battery, earth. The relay C2 which at contact 1002 extends metering current to the subscribers meter has a delayed armature release and thus operates only after a certain period. Thus the following result is obtained: In Fig. 2 at the top right hand side a repeater UEI associated with another connecting path is indicated. The contacts 58u and 59u of this repeater correspond to the contacts 6G11. and Blu of the repeater UE. When the relay U in a neighbouring repeater UEI operates owing to metering potential on its associated junction line and at this instant before operation of relay K the relay U of repeater UE is energised, then, at contact Gu, the completion of a holding circuit for relay U (winding II) of neighbouring repeater is prevented. The relay U in the neighbouring repeater therefore operates for a short period only. In order that relay U in any repeater when energised momentarily in this manner shall not give rise to faulty operation of the meter by operation of relay C2 in that repeater this latter relay is arranged to have a slow armature operation so that it will operate only after a prolonged energization of relay U. i

When the relay C2 is operated on Contact 132/. being operated for the required length of time it holds for the duration of the connection in the following circuit: earth, contact IIcI, 1202, winding of relay C2, battery, earth. Relay U remains energised together with relay K until after the determination and transmission of the call number in the following circuit: earth, winding II of relay U, contacts 63c2, Blu, 54s, winding of relay K, battery, earth. Relay K closes its Contact 95k: and thus connects earth potential to the control relay and the contact eld. The relay C2 disconnects Winding I of relay U at a further point, namely, contact 6502. Further, it opens contact 68c2 and closes contact 6'Ic2. Thus earth potential is disconnected from the lower talking conductor. This can be used as a signal bringing switch means in the time zone arrangement into effect and terminating the potential connection to the lower talking conductor. Relays C2 and U energise and the following circuit is completed for the metering relay ZR in the first group selector: earth, battery, resistance Wil 2, contacts 69u, 10c2, choke Dr2, lower talking conductor, windings of the second and first group selectors, choke Drl of the first group selector, winding of metering relay ZR, earth.

Arrangements are known which make possible the transmission of an impulse over the talking conductors during the conversation without undue disturbances. In the drawings such arrangedisturbances. In the drawings such arrangements are indicated by means of chokes, condensers and equalising networks between the conductors and which are connected to earth.

Metering relay ZR in the first group selector operates and closes the contact 2er thus bringing about a current increase on the blocking `conductor so that the meter of the calling subscriber operates. Since the contacts 69u and 10u2 in the repeater remain closed, for the time being the metering relay ZR in the rst group selector and hence the subscribers meter remain energised for some time.

The subscribers meters are so constructed that each metering magnet, in addition to operating the armature which steps the meter wheel, operates an additional contact. The metering contacts are arranged in groups and form a coordinate system of 10 rows of 10 contacts. In the embodiment 100 meter contacts form a contact iield: IH, 2H, 3H. Each contact of a subscribers meter is arranged in the field according to the call number corresponding to the 100 digit. With the field the contact for the meter of any particular subscriber is situated at the point which corresponds to the number determined by the last two digits of the call number. If the last three digits of a call number are for example, the digits 123, the contact of that particular subscribers meter is arranged in the contact eld IH for the first 100 and at this field at theipoint which is formed by the abscissa 2 and the ordinate 3. It is therefore in the field IH at the 3rd contact in the second row.

If the last three digits of a call number are 290, the contact of the subscribers meter is in contact field 2H, second 100s, at the point formed by the abscissa 9 and the ordinate 10." It is therefore the last contact of the 9th row in contact eld 2H.

In common for all contact fields IH, 2H, two groups of relays are provided which will be named as 10's control relays ZI-ZU and units control relays EI-EIIJ. The lOs control relays are situated on the abscissae running through all contact fields. Thus the control relay ZI marking the tens digit 1 is on the abscissa 1, and the control relay Z2 marking the tens digit 2 is on the abscissa 2. The units control relays EI-EIU lie on the ordinate multipled together for all contact fields so that the control relay El marking the units digit l lies on the ordinate 1, the control relay E2 marking the unit digit lies on the ordinate 2.

Each contact field is marked by special switch means. For this purpose in each of the first two ordinates of contact field lH a winding of GI is provided, ineach of the ordinates "3 and 4" aI winding ofthe relayrGZ, in each ofthe ordinates 5 andA f6 a winding of relay G3, in each ofthe ordinates 7 and 8 a winding of relay G4 and in each of the. ordinates"9 and of the relay G5. The contacts (2691, 2792, 28g3, 29ml, 30575) of relays GI-G5 connect the relay HI which marksthe hundreds digit 1. Resistance Wi in parallel with relay fI-II delays the operation of the relays armature for a reason which will be explained later.

The same is the case in the other contact elds. In the ordinates of the contact field 2H the relays G6-GIU are connected, in the field 3H the relays GI I-GI5. .The contacts (3|g6-I) connect the relay H2 marking the hundredsdigit 2 and thev contacts (32gl I-I) connect the relay 'H3 marking the hundreds digit For connecting each of the relays H marking the hundreds digits, 5 relays .G are provided for each contact eld. Other solutions are possible which mark the contactneld in which a particular metering contact lies with a smaller number of switch means.

It is assumed that a subscriber with a number 1125 has set up a connection. The contact of the meter of this subscriber is therefore connected in the contact eld II-Iand at :the point which has abscissa 2 and ordinate 5. This therefore is the ith contact of the second row in the contact ield HI. `When, after the reply of the called party, potential is connected to the lower conductorof the subsequent arranged time zone equipment, the meter Za of this subscriber is energised, and the metering contact 25 in the contact field AIH is closed. The following circuit is then completed: earth, Contact 95k, windings I and II of tens control relay Z2, metering contact 25 in the contact field IH, Winding I of relay G3, windings I and II of relay E5, resistance Wz`3, battery, earth. The resistance ratios of the control relays are so selected that in the rst place the units relay E operates and then the tens relay Z and iinal relay G. In the above-mentioned circuit the relay E5 iirst operates and by closing its contact 20o5 shortcircuits its-high resistance winding. By means of the current increase thus produced the relay Z2 is operated, and closes its contact 1.22, shortcircuiting its high resistance 4winding I. yThe further vcurrent increase operates relay G3 over its winding I.

Thev relay E5 closes its contact -e in the units contact group EK and thus marks the units digit "5 of the call number in that the common contact 5NK of the impulse contact SS is connected over the marking line 5. The relay Z2 closes contact 8522- inthe tens contact group SK and thus marks the tens digit 2 of the call niunber in that the cam contact 2NK of the impulse sender is connected over the` marking line 2. The relay G3 closes its contact 28g/3 so that the following circuit is completed: earth, battery, winding of `relay HI, contact 2893, resistance Wz'4, earth. -A resistance Wi in parallel with relay HI is connected and causes relay Hl to operate with as a slow relay. Relay Hl closes contacts 8'Ihl in the hundreds contact group HK and thus marks the hundreds digit "1 of the call number in that the cam contact INK of the impulse sender is connected over the markingA line 1. Since it is assumed that the Contact elds 4H, 2H; -3H-have thev'same --asso-v ciated thousands group, actually the first thousands group, "thenf by means of the relays Hl-Hlll the thousands digit 1 of the call number is marked. YAll contacts of lthe thousands Contact group TK.therefore are connected to marking line 1 and `over this with cam contact INK of the impulse sender. In the case `assumed the connection of this contact is `performed by contact M.

All hundreds relays HI-HIIJ have (at their contacts 40M,- lllh, to 112km)` control over a relay group V/W which effects the connection and operation of the `impulse sender SS. The impulse sender is connected by the closingr `of a metering contact with a considerable delayed operation since one only o1` the relays E .can operate,.then one of the relays Z, then one of the relaysprG and finally one of the relays H (slow) The delayed connection of the impulse sender is necessary so that its operation by normal (short) metering impulses which are transmitted from other connecting paths is prevented. When a metering contact is closed for a short period, and one of the units and tens relays and perhaps one of the relays G can operate, but thenormal metering impulse is much too short to operate a hundreds relay I-I over a G-relay. Hence, it will be seen that a normal (short) metering impulse can never, of itself, start the impulse sender SS.

If simultaneously or almost simultaneously with the connection of potential for a longer period, the normal metering impulse is transmitted over other connecting paths then two meter contacts in the Contact eld will be closed at the same time. Long before either can operate an I-I relay, however, the normal metering impulse will have terminated causing thel meter contact operated thereby to restore. Finally over the metering contact which is closed for a long time the above-mentioned marking circuits are completed. When this has once been done and the .units and tens relays concerned have short-circuited their high resistance windings then no other control relay can be operated notwithstanding the fact that other meter contacts may subsequently be'operated by normal metering impulses transmitted over other connecting paths. This is prevented by the locking circuit which extends according to the example as follows: earth, battery, resistance Wi3, winding II of relay E5, contact 2De5, winding I of relay G3, metering contact 25 in Contact eld IH, winding II of relay Z2, contacts 122, k, earth.

The impulse sender SS consists of a switch with forty-eight positions in which the positions I-I2, I3-24, 25-36, and 31-48, stepped over by the wiper ds are joined to contact segments. The contact segments I|2 are connected to contacts 90M, 9Ih2 to 92ml) of the thousands the contacts 81M, 88??.2 to 89MB of a hundreds contact -group are connected.

The contact segment 25-36 is connected with contacts 842|, 8522 to 862|!! to the tens contact gro-up ZK and the segment 31-48 with contacts Mel, 15e2 to 83cm of the units contact group EK.

The impulse sender has ten cam contacts INK to IUNK which are closed in certain positions of the impulse sender.

The contacts of the units tens and hundreds contact group are so connected with the cam contacts of the impulse sender that the contact marking a particular digitv in each group is connected over the corresponding marking lines 1-10 with its corresponding cam contact INK to IUNK. The contacts of the thousands group are however, as has already been mentioned, extended to the marking line 1 and over this to the cam contact NKI.

In the given example the following contacts in the individual .contact groups are closed 18e5, 8522, 81M and 90M. After the hundreds relay HI is switched in by means of contact 2893 the following circuit is completed: earth, contacts 40M, 43s, Mw, 45o, winding of relay W, resistance Wz'5, battery, earth. Relay W operates in this circuit and by opening contact Mw releases the winding of relay V from its short circuit so that this also can operate. The relay V closes its contact 46o and by short-circuiting relay W causes it to restore. The following circuit is now completed for relay X: earth, battery, resistance Wz'8, winding of relay X, contact 5010, 49o, earth. Relay X closes contact 48x and thus connects the magnet DS of the impulse sender so that its wiper ds is stepped on from the zero position to the first contact. The magnet DS has a contact 52ds which is now closed and relay Y is connected: earth, contact 5211s, winding of relay Y, not short-circuited by contact 53x, resistance Wz'S, battery, earth. The relay Y closes its contact Sly and short-circuits `winding of relay X. Contact 48a: opens and disconnects the magnet DS. The relay Y is restored since contact 52ds opens and contact 531: short-circuits the winding. The short circuit for relay X is opened at contact Iy so that this relay operates again. The interaction between relays X and Y and magnet DS continues until the wiper ds of the impulse sender has completed a rotation. The cam contacts INK to IDNK are now closed in a particular manner in dependence on the position of the impulse sender and for a certain period. It is convenient to operate the cam contacts mechanically by means of cams on the shaft. The cam contact INK for example, is closed in positions 2-I2, III- 24, 26-36 and 38-48 of the impulse sender. The cam contact 2NK is closed a step later, i. e. in positions 3-I2,

I5-24, 21-36 and 39-48 of the impulse sender, and the cam contact 3NK in a further position i. e. in positions 4--I2, I6-24, 28-35 and 11S- 43. In Fig. 2 a table is given which shows the positions in which the different cam contacts are closed.

When the impulse sender has executed its first step the wiper ds is operated from zero position to the first contact segment I-I2 and the shaft contact 56ds0 is opened together with the shortcircuit for the winding of the impulse relay J. As mentioned above the relay Y energises after each connection of magnet DS at contact 52ds. When wiper ds reaches the first contact the following circuit is completed: earth, battery, resistance Wz'1, contact 41g, winding of relay J, resistance WiB, earth. In this circuit relay J operates which by closing its contact 517 transmits the first impulse for marking the first digit of the call number of the subscriber on the lower talking conductor on the following path: earth, battery resistance Wz'IU, contacts 51j, 66u, 6102, Winding of relay ZE, choke DTS, lower talking conductor b. This impulse travels over the junction line to the station where a registering arrangement is provided (printing or punching device) and typewheels are set corresponding to the impulses transmitted. If the impulse sender has stepped its wiper ds into the position 2 the cam contact INK is closed. When relay Y is connected again by contact 52ds the impulse relay J receives no impulse since the following short-circuit is completed for its winding: earth, battery, resistance Wi1, contact 411/, wiper ds of contact segment I--I2, contact M marking line 1, cam contact INK, resistance Wi6, earth. In the given example therefore a single impulse only is transmitted for marking the thousands digit of the call number. In the registering arrangement the type wheel for the thousands digit is therefore positioned on contact 1. The short-circuit of relay J completed by the closing of contact 41g continues as long as the wiper ds is on contact segment I--I2 since the cam contact INK is closed in positions 2-I2 of the impulse sender.

The impulses for marking the hundreds digit of the call number are transmitted while the wiper ds is on the second segment I3--24. In the hundreds contact group HK, the contact 81h| which is connected with the cam contact INK is closed. In the position I3 of the impulse sender the cam contact INK is opened. It closes in positions III- 24. After contact I3 has y been reached and relay Y is connected at contact 52ds, relay J energises since it is not short circuited and, by closing contact 517, transmits an impulse over the lower talking conductor to the registering arrangement. If the wiper ds is switched from contact I3 to contact I4 impulse relay J can no longer be energised after relay Y operates and contact 41g closes since the following short-circuit exists: earth, battery, resistance Wi1, contact 41g, wiper ds of contact segment I3 to 24, contact 81hl, marking line 1, cam contact INK, resistance WiS, earth. Thus for marking the hundreds digit of the call number a single impulse only is transmitted. In the registering arrangement the type-wheel for the hundreds digit is thus set on digit 1." The relay J cannot be energised on further stepping on of the impulse sender since contact INK remains closed until wiper ds has left segment I3--24. The transmission of the marking signal for the tens digit of the calling subscribers number follows. In the tens contact group ZK contact 8522 which is connected over marking line 2 with the cam contact 2NK has been operated. This contact is opened in positions 25 and 26 of the impulse sender and closed in positions 21 to 36. When the wiper ds has reached contact 25 and relay Y is connected, relay J is energised in the previously mentioned circuit so that an impulse is transmitted to the registering arrangement by the closing of contact 517'. When the wiper ds reaches contact 26 and relay Y is operated, relay J is again energised and a second impulse is transmitted to the registering arrangement. When the wiper ds is stepped further and reaches contact 21, after relay Y is connected and Contact 41g closed, the relay J can no longer be energised since the following short-circuit is completed for its winding: earth, battery, resistance W11, contact 41y, wiper ds of the contact segment 25 to 36, contact 8522, marking line 2, cam contact 2NK, resistance Wifi, earth. When the impulse sender is stepped on over segments 25--36 the relay J is no longer operated. For marking the tens digit of the call number two impulses are thus transmitted to the registering arrangement and the type-wheel for the tens digit is set on digit 2.

The units digit of the call number is now marked. In the units contact group EK the contact 18e5 has rbeen. operated and is connected withimarkingfline :5.:and cam contactv NK.Y The camzcontactrNKas can. be seen `frompthe table inrFig; 2Iis-openintpositions 31--41 of the impulse'sender .fand .closed in positions l2-48.

When.;..the.1wiperids reaches vcontact t?,Y the impulse relay vJ receives i an impulse .after lrelay Y is'r connected whichis; transmitted to contact 51g' Aforvregistering. When the vwiper reaches positions-38,139, 40A` and4l the relay J is energised each' time andeach time an impulse is transmitted` tol the. registering; arrangement. Afterzfiv'e impulses `have .been` transmittedto the registering arrangement wiper dsreaches position 42 and immediately cam Contact SNK. closes.

vImpulse relay J isznotienergised whilethe impulsesenrlery isstepped further sincethe following short-circuitI exists for its4 winding: earth,

battery,` resistanceV Wil, contactl'ly, wiper ds of the segment 31-48, contact 1865, marking line 5; cam; contact SNK, resistance Wi, earth. By means ofthe ve impulses transmitted the typewheel for the units4 digit in the' registering arrangement isset ion 'position 5.

From this last contact-,wiper ds reaches the initial positionin: which contact ,9.611501 is closed andthe direct short-circuit 'for the. winding of thezrelay 'Jfis again in force. After relay Y is connected andreleases` and` relay X by shortcircuiting its winding at contact Ely, the following lcircuitzis. completed: earth, battery, resistance Wil, contact 411g, wiperds. in the zero position, contact 9311,. winding .II andl I of relay S, earth. Relay S operates in this circuit, opens contact 113s and thus the circuit for relay V. Relay V opens contact 4911 and prevents further operation of the impulse sender SS. After relay Y releases and contact 411/ opens'the circuit for relay Siis broken. Its vrelease is somewhat delayed in View of the short-circuit of its winding II at contact 94s. When relay S is energised contact 54s is .opened and the circuit for relay U (winding ID of the repeater and relay K of the impulse sender is broken. Contact 69u opens and disconnects metering potential from the lower talking conductor b, restoring the relay ZR in the first group selector. Contact 221' opens and the potential necessary for energising the meter Za of the subscriber is again disconnected so that it restores.

Relay K releases and opens contact 95k in the impulse sender and the contact for the control relays, so that these restore. When contact 60u closes, other repeaters can be connected with the common impulse sender SS for the purpose of determining and registering a call number.

As is clear from the description as long as battery potential is connected over contacts 'E002 and 69u in the repeater to the lower conductor b` and therefore as long as relay ZR in the first group selector and the subscribers meter Za. are both energised and determination and transmission of the number of the calling subscriber is continued. Normally the current increase is produced on the blocking conductor by metering relay ZR in the group selector for the purpose of operating the meter. When this stronger current is continued for some time, as in the present case, the danger arises that the cut-off relay of another preselector testing on the seized group selector will operate, so that in view of the long application of a stronger current to the c-conductor double connections can occur.

To avoid such mistakes entirely the following disconnectingthe low resistance Wz'2; on, the.` one Vhand maintainsthepmeter Za operated for` the wholetune relayZR is energised,l andon `the other` hand.v another 'testing preselector is ,no longer able to. seize'. the group. selector.

A further embodiment is shown which pre.-

vventsi a double; seizing of the group selector during; the potential"connections-actually by setting up. the blocking conductor in such a man- .ner' asV that .shown in thesketch (under the talkingl conductor b in the group selector IGW, Fig: 1) enclosed :ina dotted outline.y

When. ,they relay ZRin the group selectorisv energised iby the potentialconnection, contacts der; and .5er are closed. The resistanceWil3 is connectedsby :contact 4er and 'an electrolytic condenser EC. bycontact 5er.y The resistance Wil3 fis, so. arranged k,that testing on the seized groupselector'by v'another preselector is not possible. At the: moment whenthe condenser EC is. connected a` high charging impulse occurs, the Ameter is operated and is maintained'inits joperated.; position overV resistance Wz'li?,v as the relayrZR is energised..l

The determinationand transmission of.v the call 'number need not 'bef undertaken for each connection.. It .can b'e arranged thatthese operations only occur in the case, of connections of a particular kind, e. lg. for;high1valued'connections lonly...v

Naturally; the digit wheelsy of. the meter are also 4stepped on: bythe potentialconnection for the purpose of determining and transmitting the call number. Hence the meter shows an amount which is higher than the Afee to be charged. This lack of agreement however can easily ybe removed since the number of times the registering arrangement is seized is known.

We claim:

1. In a telephone system, a switch, means for seizing said switch, a guard circuit thereupon eiective including an electro-magnetic device and a source of potential, said device having a certain potential impressed upon it over said ircuit by said source but being normally not operated by said potential, a resistor, a relay, means operated to connect said resistor and the winding of said relay in said circuit to change the potential impressed upon said device by said source thereby to operate the device, said relay operated responsive to the connection of its winding in said circuit and effective thereupon to disconnect said resistor from said circuit, thereby to again change the potential impressed upon said device by said source.

2. In a telephone system, a switch, means for seizing said switch, a guard circuit thereupon effective including a source of current, an electromagnetic device and a resistor in series, said device being normally traversed by current from said source but not operated by said current, a relay, a second resistor, means operated to connect the winding of said relay in shunt with said first resistor and also to connect said second resistor in shunt with said first resistor thereby to increase the current ow through said device to a value sufcient to operate the device, said relay operated responsive to the connection of its winding in shunt with said rst resistor and effective thereupon to disconnect said second resistor to reduce the current flow through said device.

3. In a telephone system, a switch, means for seizing said switch, a guard circuit thereupon effective including an electromagnetic device and a source of current, said device being normally traversed by suflicient current from said source to guard said switch, but said current being insufficient to operate said device, a condenser, means operated to connect said condenser in said circuit in such a way as to supplement the normal current rlow through said device by condenser charging current, said device operated by the transitory increase in current flow over said circuit during the charging of the condenser.

4. In a telephone system, a switch, means for seizing said switch, a guard circuit thereupon effective including an electromagnetic device and a source of current, said device being normally traversed by suflicient current from said source to guard said switch, but said current being insufcient to operate said device, a condenser, means operated to connect said condenser in said cirl."

cuit in such a way as to supplement the normal `current flow through said device by condenser charging current, said device operated by the transitory increase in current flow over said circuit during the charging of the condenser and thereafter maintained operated over said circuit independently cf said condenser.

5. In a telephone system, a switch, means for seizing said switch, a guard circuit thereupon eifective including a source of current, an electromagnetic device and a resistor in series, said device being normally traversed by insuicient current from said source to cause the device to operate, a condenser, a second resistor, means operated to connect said condenser in shunt with said nrst resistor and also to connect said second resistor in shunt with said first resistor, thereby to increase the current traversing said device to a value sufficient to operate the device, the charging current for said condenser traversing said device to assist in said operation thereof and said device maintained operated, after the charging current has ceased to iiow, by current flowing through said two resistors in parallel.

6. In a telephone system, 'a switch having a blocking conductor normally maintained at one value of potential when the switch is idle and at another value of potential when the switch is engaged, a marginal electromagnetic device connected to said conductor while the switch is engaged but adapted not to be operated by potential of said other value, means operated while the switch is engaged to momentarily vary the potential of said conductor to a value different from said other value and then to restore it substantially to said other value, said device operated by the potential of said different value and thereafter maintained operated by the potential to which said conductor is restored.

7. In a telephone system, a switch having a blocking conductor normally maintained at one value of potential when the switch is idle and at another value of potential when the switch is engaged, a marginal electromagnetic device connected to said conductor while the switch is engaged but adapted not to be operated by potential of said other value, means operated while the switch is engaged to change the potential to a value diiierent from said other value and then substantially at once to change it again to a value intermediate said different value and said other value, said device operated by the potential of said diierent value and thereafter maintained operated by the potential of said intermediate value.

MAX LANGER. ERNST HORN.

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