US2410866A - Telephone system - Google Patents

Description

Nov. l2, 1946. K. L. BURGENER TELEPHONE SYSTEM Filed April 17, 1944 2 Sheets-Sheet 1 INVENTR. KARL L. BURGENER 25X W4 ATToR NEY Nov. 12, 1946.

K. L. BURGENER -TELEPHONE SYSTEM Filed April 17, 1944 2 VSheets-Sheet 2 INVENTOR. KARL L. BURGENER Patented Nov. 12, 1946 UiiiilTED Tuur ori-ICE rnLEr'noNE SYSTEM Application April 17, 1944, Serial No. 531,389

`19 Claims. 1

The present invention relates to telephone systems in general, and more particularly to improved circuits for automatic individual-line ringing, automatic party-line ringing, and quick ringing cut-olf in manual and automatic telephone switchboards.

An object of the inventon is to provide new and novel circuit arrangements for applying and disconnecting automatically-interrupted ringing currents to vand from arplurality of connecting circuits in a telephone system.

Another object of the invention is to provide new and novel circuit arrangements to enable a called party, when answering a call, to out oil quickly the ringing current during either the ringing or silent periods, and to provide inY these arrangements a greater margin of operation over more severe subscriber line circuit conditions than is possible with the present practice,- cf ringing cut-off relay operation. For example, in a telephone system employing party lines, a greater number of substation ringers may be bridged across a line of higher loop resistance and lower insulation resistance with the ringing cut-off method provided in the invention than with any other system cf quick ringing cut-off known to the art.

A further object of the invention is to provide uniform quick ringing cut-off with all frequencies of ringing current, when party-line ringing is employed, in order that the ringing cut-off be practically instantaneous regardless of the frequency of ringing current which may be used for signalling the called substation. Under the prevailing circumstances of the art, ringing cut-off is relatively much slower with the higher frequencies of ringing current than with the lower frequencies. `The invention includes new and novel means for overcoming this inequality of ringing cut-off, thereby providing for uniform quick ringing cut-off over` the entire range of ringing current frequencies.

Inorder to accomplish the above described objects, the invention combines the control of the ringing application and the ringing cut-olf functions t'oone relay. This combined ringing and ringing cut-off relay operates overA a local circuit to supply ringing current to the selected line, and releases to, disconnect the ringing current from the line when the called party answers. In addition, when the connection is kcompleted by an operator, means are provided so that the operato-r starts or restarts the automatic ringing as independent operations entirely dissociated from any means for selecting the called line,v the only limiting factor being the presence of the called party on the line.

The uniformity of quick ringing cut-off on party lines is accomplished by adjusting the resistance Value of the local, or holding, circuit of the combined ringing and ringing cut-off relay in direct relationship to the frequency of ringing current used in each instance. Each frequency of ringing current is allocated a certain resistance value for `the holding circuit of the relay. For example, a greater1 resistance value is inserted in the holding circuit of therrelay when L'iO-cycle ringingl current is selected than when the ringing current is iii-cycles, in order to accomplishH an equivalent quick ringing cut-off. These adjusted resistance values enable the combinedl ringing and ringing cut-off relay to perform unil formly and emciently over the entire range of ringing current frequencies.

A feature of the invention is that the resistance value of the holding circuit of the combined ringing and `ringing cut-off relay is varied by means of compensating resistances connected in series with the holding winding of the relay, the proper resistance value being selected automatically at the time the required frequency of ringing current for signalling the desired called party is selected.

Another feature of the invention is that theV greater Vmarginv of operation for the combined ringing and ringing cut-olf relay obtained in the manner described inthe preceding paragraph, provides for quicker ringing cut-off withv any frequency of ringing current on a short line of relatively low resistance than with any other system of quick ringing cut-off relay operation. Damage to the transmitter of the answering telephone on a low resistance line, where the ringing current flow is obviously relatively large, is, therefore, minimized because the ringing cut-off is -practically instantaneous when the handsetof the answering telephone is lifted during a ringing period.

Anotherv feature of the invention is that the adjusting of the resistance value of the holding circuit of the combined ringing andr ringing cutloff relay in direct relationship to the frequency of the ringing current used tosignal the called substation, enables the power inthe holding winding of the combined ringing and ringing cut-off relay to offset; or neutralize, the additive eiect of the alternating ringing current during the periods when the alternating current in the line winding of the relay is i'n Athe direction to aid the superimposed direct current in the line winding' of the relay. Hence, the power in the line winding of the relay does not overcome the power in the holding winding at any period and cause the relay to remain operated and continue to send ringing current out on the line after the called Darty has answered. Quick ringing cut-olf is thus assured with any frequency of ringing current.

There are other objects and features of the invention havingI to do for the most part with the circuit details involved in carrying out the foregoing.

The various objects and features of the invention will be understood best upon a further perusal of the description in connection with the accompanying drawings, comprising Figs. l and 2, showing by means of the usual circuit diagrams so much of the apparatus in a telephone system embodying the features of the invention as are necessary to an understanding of the same.

Referring now to the drawings, Fig. 1 illusstrates a cord circuit of a manual telephone switchboard utilizing the present invention. The invention may, f course, be applied to any wellknown type of cord circuit equipped to perform any combination of well-known functions associated with a manual telephone switchboard.

Fig. 2, when placed below Fig. 1, shows position equipment common to all of the cord circuits of the switchboard, including the various keys, relays and operator telephone set. It is understood that the common position equipment may be of any well known type, with common key functions such as are shown on Fig. 2 of Crocker Patent 1,771,842 and described in the associated specification.

The invention having been described generally, a detailed operation of the apparatus shown will now be given. For this purpose, it will be assumed that the operator receives a call over a line circuit represented by jack J on Fig. 1. This line circuit may be of any well-known conventional type either common battery or local battery, the difference with respect to the cord circuit being in the resistance value of relay I0 connected to the sleeve spring of jack J I If the subscriber line is of the common battery type, the resistance value of relay I0 will be relatively low, and if the subscriber line circuit is of the local battery type, the resistance value of relay |0 will be relatively high, The purpose of the differences in resistance values of relay I0 is to operate certain relays in the cord circuit when the line circuit is of the common battery type, and to prevent the operation of certain relays in the cord circuit when the line circuit is of the local battery type.

Assuming that the operator has received a call over a common battery line, the operator inserts the answering plug PI of an idle cord circuit into jack J i. When the plug PI enters the jack J the relay of the cord circuit is energized through the sleeve of the plug and the jack and relay I0. Relay operates, disconnects relay |2 from the repeating coil at contact I8, and connects the windings of relay I to the tip and ring conductors of the calling line through windings of the repeating coil. Relay I'I also closes the circuit of the answering, cord supervisory lamp momentarily at its upper front contact. Relay I6, however, operates through the calling party telephone loop to open the answering cord supervisory lamp circuit at a back contact. Relay I6 also supplies transmission battery to the calling party. The resistance coil which is wired in multiple with the winding of relay I 1 is for the pur- 4 pose of reducing possible shocks t0 the operator in the handling of the plug.

When a call is received at the jack JI over a local battery line instead of a common batteiy line, sleeve relay Il of the cord circuit does not operate when the plug PI is inserted into jack J I because the resistance of relay I0 is sufficiently high to prevent the operation of sleeve relay The lower winding of relay |2, therefore, remains connected to the windings of the repeating coil at contact I8, and relay I6 is not connected to the repeating coil. Consequently, no transmission battery is supplied to the calling line. Relay I2 performs no function at this time.

Having inserted the plug PI into jack J I, the operator throws the talk key of the cord circuit in order to converse with the calling party. The operation of the talk key closes the circuit of splitting relay 29, the operation of which divides the cord circuit into two sections in the well-known manner, and extends both sections to the operator common position circuit shown in Fig. 2. The tip and ring of the answering plug PI are connected to the common position circuit inductively through the windings of the repeating coil and then via the upper and lower front contacts of relay 29 and conductors 00 and 6I. The operator telephone set shown at the left on Fig, 2 is, therefore, connected to the answering plug P| via contact |01 of relay |04, upper winding of operator induction coil, contact |05 of relay |04, contact I| 2 of cut-off answer key and conductor 60 for the tip side; and viacontact |0| of relay |04, lowerwinding of operator induction coil, contact |02 of relay'I04, contact |08 of cut-off answer key and conductor 8| for the ring side. The operator may now obtain the number of the desired station from the calling party.

The operation of splitting relay 29 also switches the calling section of the cord circuit, including the sleeve conductor of calling plug P2 and the associated sleeve relay 40, to the common position circuit shown in Fig. 2, but these switchings perform no functions at this time. The resistance coil wired in multiple with the winding of relay 29 provides spark protection for the Contact of the talk key.

Having ascertained the number of the desired line, the operator restores the talk key to normal and then inserts calling plug P2 into jack J2 which is assumed represents the desired line. As in the case of the line circuit connected to jack J the line circuit connected to jack J2 may also be of either the common battery or local battery type, and the resistance value of relay 48 connected to the sleeve spring of jack J2 will be correspondingly low or high.

The restoration of the talk key to normal position releases the splitting relay 29, and the restoring of relay 29 disconnects the common position circuit from the answering and calling sections of the cord circuit, and re-establishes the transmission circuit between the answering and calling-sections of the cord circuit. Relay 29 also re-connects the sleeve of the calling plug P2 to the sleeve relay 40.

The cord circuit is equipped with a tipbusy test and, consequently, in case the line circuit is of the multiple jack type, the operator may make the conventional tip busy test before inserting the calling plug P2 into jack J2. The tip busy test circuit may be traced from the n sleeve of jack J2, tip of calling plug P2, contact 46 of ringing call key, contact 42 of relay 40, conductor 53 to the common position circuit shown in Fig. 2, upper right-hand winding of theA monitor and busy test coil toposi-ti-ve battery, and inductively to the corresponding upper left-hand winding of tn'e monitor and busy test coil to the operators receiver. The lower right-hand winding oi the monitor and busy test coil is extended along by means of conductor 53, said conductor 59 being twisted into a pair with conductor 58 to obtain the busy test clicks will not be introduced induetively into other cord circuits. Conductor 59 is not connected to the cord circuit.

Assuming that the selected line isv of the. common battery type, sleeve relay 43' is, energized, when the calling plug P2 is inserted'. into jack J2, through the sleeves of the jack and the plug and the center back contact of relay 29. The opera-q tion of sleeve relay 4i] causes sleeve relay I9 to operate through contact 3B, as sleeve relay i9 is of such resistance that it will operate from the rela tively low resistance of relay 48 in multiple with the winding of sleeve relay 4D. Sleeve relay 40 opens the tip busy test circuit at contact 42, and extends the tip conductor through contact 4l to the combined ringing and ringing cut-off relay 33.

Sleeve relay la disconnects relay 23 at contact 23, connects the transmission battery feed relay 23 to the inside terminals of the calling half of the repeating coil, extends ground potential from the front contact of relay l5, contact 2l of relay i3 to contact 24 of relay 23, and completes the circuit of the calling'cord supervisory lamp from contact 22 through contact 31 of relay 33 and the upper back contact of relay 23.

Assuming that the desired telephone connected to jackJZ is-to be signalled with the, ringing frequency 2, the operator depresses momentarily the ringing key 55 all the way down, and the ringing key 55 will return tok and remain in the ringing position, in the well-known manner, with its back contacts openand the front contacts closed. The iirst action of the downward stroke of key 55 automatically restores any of the keys 53, 54, or E which maybe in the ringing position, and then contact 51 is operated at the bottom of the downward stroke. it is understood that the four keys 53, 54, 55 and 5G and the common contact 51 are mounted on one escutchecn and interlocked by means of a ladder releasing mechanism in the well-known manner so that only one key-may be in the ringing position at one time.

The selection of frequency 2 by the operator depressing ringing, button 55, causes the combined ringing and ringing cut-off relayA 33 to operate from ground potential, front contact of relayV l5, contact 2l of relay I9, contact 24 of relay 23, contact 51 oi the ringing key, upper winding of relay 33 to negative battery, andl to lock up from ground potential, front contact of relay l5, contact 2l of relay I9, contact 24 of relay 23, upper back contact of ringing key 53, upper front contact of ringing keyy 55, compensating resistances 5l and 52 in series, contact 33 of relay 33, upper winding of relay 33 to negative battery;

The operation of the combined ringing and ringing cutnoii relay 33 connects the tip conductor of the calling plug P2 to ground potential through Contact 43 of ringing call key, contact 4l of relay 43 and contact 35 of relay 33, and also connects negative-battery superimposed ringing current from the lower front contact of ringing key 55, lower back contact of ringing key'5, lower, or line,A winding of relay 33, contact 32 of relay 33, contact 44A of theringingcall key tothe ring cone` a balance so thatv 10.l

called party lifts the hand-setfrom the telephoneA cradle.

The operation of the combinedi ringing andk ringing cut-off relay 33 also opens the calling."

cord supervisory lamp at Contact 31 thus giving the operator ringing supervision, well-known as dark keyshelf, to indicate that the operators work on this connection has been completedluntil disconnect supervision is received. Disconnect supervision will be received when the calling and called parties have completed their conversation and reutrneol. their handsets to the respective cradles.

When the called party answers, the circuito'f the direct current through the lower, or line, winding of the combined ringing and ringing cutoi relay 33 is closed through the telephone loop. This direct current in the line lay 33 and relay 33 restores to normal, removing ringing current from the line and extending the tip and `ring conductors oftlie calling plug P25 to the repeating coil. Relay 231 operates onv the called party loop to supply transmission battery,- and' also opens the calling cordI supervisory lamp.

If the called party should disconnect prematurely and the calling party requests thevoperator to reestablish the connection, the operator may restart the ringing on the called line by depressing ringing keyv 55 all the way Adown momentarily, and relay 33 will again operate and lock up and reconnect ringing current to the tip and ring. conductors of calling plug P2.` AIt is unnecessary for vthe operator to request therequired. frequency Ifor the rering,.as the ringing key used` for the original ringing will remain in the ringing position (partly depressed) until later released by the depression of ringingk key button 53, 54, or |56 ona new call.

When a connection requires the use of fre.- quency 5, the operators ringing routine. is changed somewhat since there are only four ringing key buttons on the ringing key assemblycornprising keysY 53, 54, 55 and 56. The lever type ringing call key associated with the calling plug P2 is used for ringing the called linewith frequency 5, and is mechanically associated with the button type ringing keys 53, 54, 55 and 56 inA suchl a well-known manner that when theV lever type ringing call key is operated, any of the ringing keys 153, 54, 55 or 53 that may be in the ringing position will be automatically released and restored to normal. The automatic ringing start for frequency 5`is established through contact 45 of the lever ringing call key since contact 45 of the lever ringing call key is in multiple with con-v tact 41 of the button ringing key assembly, thus operating and locking up relay 33 in a similar The desired telephone winding neutralizesthe direct current in the holding winding: of' re-` manner to that described for frequency 2. The ringing circuit for frequency may be traced from the lower back contacts of ringing keys 53, 54, 55 and 56, through the lower winding of relay 33, contact 32 of relay 33, ring conductor of calling plug P2, out on the line and returning over the tip conductor through contact of relay 33 to ground potential.

When the called line is of the local battery type, the operator signals the desired telephone manually by means of the lever'ringing call key associated with the calling plug P2. Uninterrupted generator of frequency 5 is supplied to the ring side of calling plug P2 through contact 43 of ringing call key and then out on the line and returning over the tip conductor to ground at Contact 4l of ringing call key.

.After the operator has completed a connection between the calling and called party, she may operate the talk key of the cord circuit to split the cord circuit into two sections and switch automatically both sections of the cord circuit to the common position circuit shown in Fig. 2, for the purpose of monitoring the established connection, talking to either party without overhearing by the other party, refunding and collecting paystation deposits, or performing any other functions that may be associated with the common position circuit. As previously explained, the operation of splitting relay 29 switches the tip and ring conductors of the answering` plug PI to the common Iposition circuit via conductors 60 and 6|. The tip and ring conductors of the calling plug P2 are switched to the common position circuit via contact 46 of the ringing call key, contact 4| of relay 40, contact 36 of relay 33, the upper make-before-break contact of relay 29 and conductor 64 for the tip side; and contact 44 of the ringing call key, contact 3| of relay 33, the lower make-before-break Contact of relay 29 and conductor 65 for the ring side.

'Ihe operation of relay 29 by the talk key also connects .the sleeve of the calling plug P2 to the common position circuit via the center make-before-break contact of relay 29 and conductor 63; and the sleeve relays I9 and 40 in multiple via the center front contact of relay 29 and conductor 62. The purpose of disconnecting the sleeve of the calling plug P2 from the associated sleeve relays I9 and 40 and extending both units to the common position circuit is to enable the operator to insert automatically a dial in the sleeve conductor of the calling plug P2 when the call is to be extended to an automatic switchboard. The circuit details of the dial connections have been omitted from Fig. 2 as it is understood that such details are not essential to an understanding of the invention.

Fig. 2 is equipped with cut-oil keys for cutting off either the answering or calling plugs and connecting them to the operators telephone equipment shown to the left on Fig. 2. A commonV monitoring key is also shown in Fig. 2 which, when operated, causes the associated switching relay |04 to connect the operator's receiver to a monitoring coil for the purpose of monitoring an established connection without materially reduc ing the transmission eiciency orin any wayinterfering with theconnection. The monitoring' circuit may be traced from operator receiver, upper winding of monitor coil, contact |06 of relay |04, contact |2 of cut-oi answer key and conductor 60 for the tip side, and from operator receiver, contact |03 of relay |04, contact |08 of cut-off answer key and conductor 6| for the ring side. Operating the cut-off answer key dis-V connects the operator telephone set at contacts |08 and 2, and places a bridge I0 across the repeating coil via conductors 60 and 6|, thus enabling the operator to converse with the called party via conductors 64 and 65 without overhearing by the calling party. In a similar manner, the operator may converse privately with the calling party by operating the cut-off call key. Fig. 2 may incorporate any of the Well-known common position key operations such as dial keys, refund and collect paystation keys shown in Crocker Patent 1,771,842 and any other key functions known to the telephone art.

Disconnect supervision is obtained on a completed connection where both the calling and called lines are common battery, when the calling and called parties restore their handsets to the respective cradles, and the transmission battery feed relays I6 and 23 correspondingly restore to normal. Responsive to the releasing of relay I6, the circuit of the answering cord supervisory lamp is closed from ground potential at the upper make contact of relay back contact of relay I6, answering supervisory lamp to negative battery; and responsive to the releasing of relay 23, the circuit of the calling cord supervisory lamp is closed from ground potential at contact 22 of relay I9, contact 3'! of relay 33, upper back contact of relay 23, calling supervisory lamp to negative battery.

Disconnect supervision when the calling line is of the local battery type is obtained by the calling party turning the hand generator of his telephone. As previously explained, sleeve relay does not operate when the answering plug Pl is 4inserted into jack J because of the high resistance value of relay |0. The lower Winding of relay |2, therefore, remains connected to the repeating coil at contact |8. Ringing current from the hand generator causes relay |2 to operate and close Contact |5 and thereby complete the holding circuit of relay I2 from ground potential at contact 30 of relay 29, contact |5 of relay |2, upper winding of relay I?. to negative battery. Responsive to the locking of relay |2, the circuit of the answering cord supervisory lamp is closed from ground potential at contact I4 relay |2, answering supervisory lamp to negative battery. The resistance coil wired in multiple with the upper winding of relay 2 provides spark protection for contact |5. The resistance coil |3 connected in multiple with the lower winding of relay |2 when relay |2 is locked up, provides a lay-pass for subsequent ringing current to protect relay I2 from accidental ring down should suincient ringing current pass through its lower winding to neutralize momentarily the holding current in the upper winding.

Disconnect supervision when the called line is of the local battery type is obtained by the called party turning the hand generator of his telephone. Sleeve relay I9 does not operate when the calling plug P2 is inserted into jack J2 because ofthe high resistance value of relay 48. The lower winding of relay 26, therefore, remains connected to the repeating coil at contact 20. Ringing current from the hand generator causes relay 26 to operate and close contact 28 and thereby complete the holding circuit of relay 26 from ground potential at contact 30 of relay 29, contact 28 of relay 26, upper winding of relay 26 to negative battery. Responsive to the locking of relay 26, the circuit of the calling cord supervisory lamp is closed from ground potential at the upper front contact of relay 26, upper back contact of relay 9 23, calling supervisory lam-p to negative battery. The resistance coil I2"! wired in multiple with the upper winding of 'relay 26 provides spark protection for contact 2li. The resistance coil 25 connected in multiple with the lower winding ci relay 26 when -relay 26 is locked up, provides a by-pass for subsequent ringing current to protect relay 26 from accidental vring down should Sunicientringing current pass through its lower wind- .ing to neutralize momentarily the holding current in the upper winding. The vcondenser in series with the lower winding of relay 2li is provided for the purpose of preventing supervisory signal interference between a common battery line on one cord circuit and a local battery line on another cord vcircuit should the operator use the talk keys of both cord circuits for over-lap service.

A common group of iive push button ringing keys shown at the lower left on Fig. l is multipled to the lever ringing keys associated with the answering plugs of the cord circuits to enable the operator. to rering parties on the answering plug PI. The rering is done on a manual basis only, with the operator applying the ringing current by means of the lever ringing key associated with the answering plug Pl. No wiring is required on the 4frequency 5 ringing key, as frequency 5 is wired through the back contacts of the ringing keys associated with frequencies I, 2, 3 and 4 to the ringing common contact on the R side of the lever ringing key. Frequency 5 ringing button is depressed when frequency 5 `ringing current is required, in Order to release and restore any of the ringing keys associated with frequencies l, 2, 3 or 4 that may be in the ringing position.

The lever ringing keys associated with both the answering and calling plugs, and also splitting relay 33, are tted with an extra iront contact for starting the .ringing machine whenever Ysuch well-known ringing varrangements are provided.

It should be understood that while `the foregoing description and .associated drawings disclose the invention as specifically used on connecting circuits ofthe manual vswitchboard cord type, the invention is not limited to such connecting circuits but may be applied to any type of connecting circuit in which automatic ringing is employed.

Having described the invention and what is considered new and desired to 'be protected by Letters Patent is set forth in the following claims:

What is claimed ist l. In a telephone system, a calling and a called line, operator-controlled means for establishing a connection between said lines, a source vof sicnalling current, a relay, operator-controlled means for operating said relay to close `a signalling circuit including said source and the called line, and means eiiective upon the response of the called party for operating said relay in series with said line to disconnect said signalling circuit from said line. y

2. In a telephone system, a calling and a called line, operator-controlled means a connection between said lines, a source of vsignalling current, a relay having a pair of windings, operator-controlled means Tor completing the circuit of one winding ci said relay for causing said relay to operate and close a signalling circuit `including said source, the other winding of said relay and the called line, and means effective upon the response of the called party for releasing said relay to disconnect said signalling circuit from said line.

3. In a telephone system, a called. party line,

i or :est a'blisloingV crater-controlled .means for to signal the called operator-controlled means for establishing a connection to said party line, a` plurality of signalling current sources, means for vselect-nig the proper source to signal a party on said line, a relay having two windings, operator-controlled means for operating said relay through one winding thereof to close a signalling circuit including said selected source, the other winding of said relay and the called line, and. means controlled by the called partys response .for .releasing said relay to disconnect said sourcefrom the called line.

.4. In a telephone system, subscribers lines, op-

extending `a connection to one of said lines, a signalling current source including a direct current qsuperimposed on an alternating current, a relay having two windings, operator-controlled means for energizing said relay through one winding thereo'f- .to close a signalling circuit yincluding said Isourcaft'he other winding of said relay 'and the called line, the alternating current component of said source supplying the power .ior'signalling the .called'line and means including the direct current component of said source and responsive lto the called subscriber answering for releasing said .relay "to disconnect said source.

5. In a telephone system, subscribers" lines, means for extending a connection to one o'f said lines, a source of signalling current, a relay including a winding, a key for causing said relay to operate and complete a signalling circuit including said source, said winding and Ythe called line, and means for releasing saidrelay responsive to the called subscriber answering, said signalling circuit being instantly disconnected when said relay releases.

6. In a telephone system, a called line, means for establishing a connection to said line, a signalling current source, a double-wound relay, a key vfor completing a circuit through one winding of said relay for causing said relay to operate and lock through said Winding yto close a signalling circuit for said line, said signalling Acircuit including said source, the second winding oisaid relay and the called line, and means ycontrolled lby the called partys response vfor causing .the release of said relay `to disconnect said .source from said line.

'7. In a telephone system, `a 'called party 1ine, means for establishing a connection to said party line, a plurality of signalling current sources, a plurality of keys for selecting the proper source substation on said line, :a relay having a pair of windings, a circuit controlled by any one of said `plurality of keys for energizing .and locking said relay through one winding thereof to close a signalling circuit including said selected source, the other winding of said relayand the called line, said relay releasing responsive -to answeringr to disconnect the called substation said source from said line.

8. In a telephone system, a called party `line, mean-s for establishing a connection to said line, a plurality of signalling current sources, a plurality of resistances, a relay, means for selecting the proper source to signal the called substation, for selecting a portion of said plurality of resistances dependent vupon the particular source selected, and 'for operating said relay in series with said selected portion of said resistancesto close a signalling circuit including said selected source and the called line, and means controlled by the called substations response for operating said relay to disconnect said signalling circuit.

V9. rIn a Ytelephone system, a called party line,

means for establishing a connection to said line, a plurality of signalling current sources, a plurality of resistances, a relay, means for selecting one of said sources to signal a party on said line, for selecting a portion of said plurality of resistances dependent upon the particular source selected, and for closing a circuit for said relay in series with said selected portion of said resistances, a signalling circuit closed by the operation of said relay, said signalling circuit including said selected source, said relay and the called line, and means eiective upon the response of the called substation for releasing said relay to disconnect said source.

10. In a telephone system, a party line, means for extending a connection to said line, a plurality of signalling current sources, .a plurality of resistances, a differentially-wound relay, means i'or selecting the proper source to signal the called substation, for selecting a portion of said plurality of resistances dependent upon the particular source selected, and for energizing said relay through one winding ithereof in series with the said selected portion of said resistances, a signalling circuit closed by the operation of said relay, said signalling circuit including said selected source, the other Winding of said relay and the called line, said relay releasing in response to the called station answering to disconnect said signalling circuit.

11. In a telephone system, a party line, means for extending a connection to said line, a plurality of alternating `current signalling sources including a direct current superimposed on each of said plurality of sources, a plurality of resistors, a relay, means for selecting one of said sources to signal a party on said line, for selecting one or more of said resistors to form a resistance of, certain value dependent upon the particular sour-ce selected, and for connecting said relay in series with said selected resistor or resistors, a signalling circuit including said selected source and the called line and closed by the operation of said relay, the alternating current component of said source supplying the power for signalling the called substation, and means including the direct current component of said source and controlled by the called stations response for operating said relay to open said signalling source.

12. In a telephone system, a party line, operator-controlled means for extending a connection to said line, a plurality of signalling current sources, a plurality -of resistances, means for selecting the proper source to signal a party on said line, and for selecting a portion of said plurality of resistances dependent upon the particular source selected, a relay, operator-controlled means for closing a circuit for said' relay in series with said selected portion of said resistances, a signalling circuit closed by the operation of said relay, said signalling circuit including said selected source and said line, and Vmeans effective upon the response of the called party for releasing said relay to disconnect said source from said line.

13. In a telephone system, a called party line, operator-controlled means for establishing a connection to vsaid party line, a plurality of signalling current sources, a plurality of resistances, a relay, operator-controlled means for selecting the proper source to signal the called substation, for selecting a portion of said plurality of resistances dependent'upon the particular source selected, and for closing a circuit for said relay in series with said selected portion of said resistances, and a signalling circuit closed by the operation of said relay and including said selected source, said relay and the called line.

14. In a telephone system, a called party line, operator-controlled means for establishing a connection to said line, a plurality of signalling current sources, a plurality of resistors, a plurality of keys for selecting one of said sources to signal a party on said line, and for selecting one or more of said resistors to form a resistance of certain value a relay, a circuit controlled by any one of said plurality of keys for operating said relay in series with said selected resistor or resistors, a signalling circuit closed by the operation of said relay and including said selected source and said line, and means controlled by the called substations response for operating said relay to disconnect said source.

l5. In a telephone system, a party line, means for extending a connection to said line, a plurality of signalling current sources, a plurality of resistors, a plurality of keys for selecting different sources to signal different stations on said line, and for selecting one or more of said resistors dependent upon the particular source selected, a relay, a circuit controlled by any one of said keys, a signalling circuit closed when said relay is energized in series with said selected resistor or resistors over said operating circuit responsive to the operation of one of said keys, said signalling circuit including said selected source, said relay and the called line, and means effective upon the called stations response for releasing said relay to open said signalling circuit.

16. In a telephone system, a party line, means for extending a connection to said line, a plurality of signalling current sources, a plurality of resistors, a plurality of keys for selecting dilTerent sources to signal diierent stations on said line, and for selecting portions of said resistors dependent upon the particular source selected,

a double-Wound relay, a circuit controlled by any one of said keys for energizing and locking said relay through one winding thereof in series with said selected portion of said resistors, a signalling circuit closed by the operation of said relay and including said selected source, the other Winding of said relay and the called line, and means controlled by the called station answering for releasing said relay to disconnect said source from said line.

17. In a telephone system, a called party line, means for establishing a connection to said line, a plurality of alternating current signalling sources including a direct current superimposed on each of said plurality of sources, a plurality of resistors, a plurality of keys for selectingr different sources to signal diierent stations on said line, and for selecting portions of said resistors to form resistances of certain values dependent upon the different sources selected, a relay, a circuit controlled by any one of said plurality of keys for causing said relay to be energized in series With a particular selected resistance value, and a signalling circuit closed by the operation of said relay and including said selected source and the called line, said signalling circuit being disconnected when said relay releases responsive to the called station answering.

18. In a telephone system, a called party line, means for establishing a connection to said line.

a plurality of signalling current sources, a plurality of resistances, a differentially-wound relay, a balancing circuit including one winding of said relay, means for connecting diierent ones of said sources to said line through the other winding of said relay to signal diierent stations on said line, and for connecting diierent values of resistance in series with said balancing circuit to compensate for different sources connected to the other winding of said relay.

19. In a telephone system, a party line, means for extending a connection to said party line, a plurality of signalling current sources, a plurality of resistances, a differentially-Wound relay, a balancing circuit including one winding of said 14 relay, means for connecting any of said sources to said line through the other Winding of said relay to signal a party on said line, and for connecting the proper value of resistance in series with said balancing circuit for providing the proper power in the balancing circuit winding of said relay to neutralize the power developed in the other winding of said relay when the called `party answers, said neutralization causing the 10 release of said relay to disconnect said source.

KARL L. BURGENER.

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