US1592646A - Automatic telephone system - Google Patents

Automatic telephone system Download PDF

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US1592646A
US1592646A US573973A US57397322A US1592646A US 1592646 A US1592646 A US 1592646A US 573973 A US573973 A US 573973A US 57397322 A US57397322 A US 57397322A US 1592646 A US1592646 A US 1592646A
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relay
line
trunk
armature
circuit
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US573973A
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Arthur J Ray
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AUTOMATIC ELECTRIC Inc
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AUTOMATIC ELECTRIC Inc
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04QSELECTING
    • H04Q3/00Selecting arrangements

Description

July 13 1926.
1,592,646 A. J. RAY
AUTOMATIC TELEPHONE SYSTEM Filed July 10, 1922 2 Sheets-Sheet 1 Col/Y 00H EUTOR Inuan UI July 13,1926. 1,592,646
A. J. R Y
AUTOMATI C TELEPHONE SYSTEM Filed J ly 10. 1922 2 Sheets-Sheet 2 I I i335 X] 153 ffifThur JIBE Hm I Patented July 13, 1926.
UNITED s'mrss Parser caries.
ARTHUR J. RAY, OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO
AUTOMATIC ELECTRIC INC, OF CHICAGO, ILLINOIS, A CORPORATION OF DELA- WARE.
Application filed July 10, 1922.
llhe present invention relates in general to telephone systems, but is concerned more particularly with the provision of a discriminating equipment for informing a It often occurs that a manual, operating company desires to serve a particular group ol xibscribers by installing a small automatic telephone system in the district to be served. lVhen this is done, it is the usual practice to arrange trunks extending from the automatic exchange to the manual exchange, the automatic subscribers usually being given free service to subscribers in the manual exchange.
It may be, however, that in the case of certain stations it is desired to charge for calis to the manual exchange, and such sta tions are therefore provided with paystation equipment. Now. owing to the fact that most of the subscribers at the automatic exchange have free service to the subscribers in the manual exchange, some special provision must be made to inform the manual operator when a paystation line is calling. The means employed in accomplishing this result will be described t'ully hereinafter, reference being had to the accompanying drawings.
he drawings comprising Figs. 1 and 2 show by use of the usual circuit diagrams, the apparatus and circuit connections thereof which are involved in the completion of connections from the automatic substation A, Fig. 1, to the trunk line terminating in answering jack J at the manual exchange, together with cord circuit O for further extending the connections to any desired point.
Fig. 3 shows a modified trunk circuit for use where the manual exchange is of the three conductor multiple type, the trunk shown in Fig. 2 being intend d for use in exchanges of the two conductor multiple type.
The apparatus indicated in Fig. 1 1s loouted in the automatic exchange, while the AUTOMATIC TELEPHONE SYSTEM.
Serial No. 573,973.
apparatus indicated in Fig. 2 is located in the manual exchange. Inasmuch as the automatic switching equipment itself, and the manual equipment are both well known and of the usual type, no detailed description of the mechanical features of this ap paratus will be given, except in so far as it is found convenient and necessary to do so in the explanation of the operation of the circuits.
Referring to Fig. l, the substation A is one of a plurality of ordinary automatic substations terminating in the automatic exchange referred to, and is provided with the usual talking equipment and ringer, and also with a calling device of well known type which is indicated by the reference character S, through the medium of which the subscriber controls various switches to extend connections either to subscribers of the same exchange or to the operator of a manual exchange. Being a paystation, substation A is also provided with a suitable coin box indicated by reference character B, mounted so that the signals produced by the deposit of coins will be transmitted over the line to theexchange by the substation trans mitter in the customary manner. A paystation of the type illustrated and described on pages 462 to 464, in the fourth edition of American Telephone Practice, by Kempster B. Miller, may be used.
The line conductors 11 and 12 extend to the automatic exchange where they terminate in the line switch C, which may be briefly described as a rotary line switch whose movable terminals or wipers have no normal position and which have movement in a forward direction only. The construction of a line switch of this type is well known in the art, and its function also well understood, which is to extend its associated line when calling, to an idle trunk line. One of the trunk lines to which the line switch C has access is shown in the drawings as extending to the first selector E, which is a vertical and rotary selector of the well known Strowger type.
The selector E in common with a plurality of: similar selectors has access to a plurality of groups of trunk lines, the majority of which groups in this particular instance extend to connector switches for connecting with called lines of the automatic exchange,
while the trunk lines of a certain group extend to the manual exchange. A trunk line of the latter group is shown in the drawings and is a two-wire two-way trunk, provided with a group of appropriate controlling relays D, and extending by way of conductors 98 and 99 to conductors such as 100 and 101 associated with various supervisory and discriminating equipment at the manual operators osition at which calls may he answered by use of cord circuits such as 0.
On the drawing marked Fig. 1, the relays which have slow acting characteristics are denoted by the shading on the lower ends of their cores or else by the solid black portion onthe upper ends of their cores. The relays which have cores shaded on the lower end are the usual so called slow acting relays and are slow to fall back but not noticeably slow to pull up. On the other hand, the relays which have their upper ends their cores shown solid black are slightly slow to pull up in addition to being slow to fall back.
A general description of the apparatus having been given, a more detailed description will now be gone into. For this purpose it will first be assumed that the subscriber at the substation A desires to extend a connection to a subscriber in the manual exchange.
lVhen the re:;eiver is removed at substation A, a circuit is completed over the line conductors 11 and 12 for the line relay 1% of the individual line switch C. Upon energizing, the line relay completes at its arn'iature 20 a circuit which extends through the switching relay 13 and resistance in multiple and the stepping magnet 15 in series to battery, and at its armature 19 connects the test wiper 26 to the above circuit at a point midway between the switching relay and the said stepping magnet. The resistance 10 placed in multiple with the winding of relay 13 is for a purpose which will hereinafter be clearly pointed out and need not be considered at this time. The operation now depends upon-whether the first selector trunk with which the wipers of the line switch C are in connection is busy or is not busy. If this trunk line is busy the test contact 31 associated therewith will have a ground potential upon it, the switching relay 13 will be short circuited, and the stepping magnet 15, which interrupts its own circuit, will operate as a buzzer to advance the switch wipers 27, inclusive, step by step in search of an idle trunk line. This operation will continue as long as the testwiper 26 continues to engage grounded or busy test contacts. However, we may assume that in the present case when the call is initiated the selector E is idle, and the test contact 31 therefore is not grounded. Under these circumstances, when the line relay 14 is energized the switching relay 13 is energized immediately afterwards, with the result that the line conductors 11 and 12 are disconnected from the winding of the line relay 14 and from ground, respectively, and are extended by wt y of armatures 16 and 1S and their working contacts, wipers 25 and 27, bank contacts 30 and 32, and armatures (SO and 62 and their resting contacts, to the upper and lower windings of the line relay of the selector E.
As .soon as the line is extended to the selector E as above described, the line relay 50 will be energized and will close the circuit of the slow acting release relay 51. Upon energizing, the la 'ter relay prepares the circuits of the selector for operation in its vertical movement in the usual manner, and also completes a holding circuit extending back to the line switch C as follows: Ground, working contact of armature 63 and the said armature, conductor 64, bank contact 31, test wiper 26, armature 17 and its working contact, winding of the switching relay 13, and the winding of the stepping magnet 15 to battery. It is understood that the above holding circuit is completed before the slow acting relay 14 has had time to deenergize. In addition to maintaining the switching relay energize-d, the holding circuit also serves to provide ground to the multiples of test contact 31 and also to the multiple test contacts in which the private normal conductor 28 terminates in the banks of the connectors which have access to the line of substation A, thereby guarding the connection against intrusion inthe customary manner.
The calling subscriber may now operate his calling device S in accordance with the proper digit to obtain connection with a desired trunk. Interruptions are thereby produced in the circuit of the line relay 50, and the said line relay is accordingly dcenergized and energized a plurality of times momentarily, transmitting at each deenergi zation an impulse of current tl'irough the slow acting series relay 52 and the vertical magnet 56 to battery. By the operation of the vertical magnet the selector shaft is raised the required number of steps, whereupon the wipers 72, inclusive, will be standing opposite the level of bank contacts in which are terminated the trunk lines extending to the desired manual exchange. The slow acting relay 52 is energized in series with the vertical magnet, retaining the armature attracted throughout the vertical movement of the switch, and upon the closure of the vertical oil normal springs 59 completes a circuit for the stepping relay 53. Upon energizing, relay 53 prepares a circuit for the rotary magnet 54 at its lower armature, and at its upper armature establishes a locking circuit for itself. At the end of the vertical movement of the switch the slow acting relay 52 is deenergized and closes the circuit of the rotary magnet, which is thereupon energized to advance the wipers 72, inclusive, into engagement with the first set of bank contacts in the level opposite which they were raised. The rotary magnet 54 also breaks the locking circuit of the stepping relay 53 which accordingly deenergizes and breaks the circuit of the rotary magnet, which thereupon deenergizes also and again closes its interrupter contact.
The operation now depends upon whether the trunk line with which the wipers have connected is busy or is not busy. If this trunk line is busy the test contact associated therewith will be grounded and the stepping relay 53 will be energized over a circuit which extends by way of the test wiper 71, armature 61 and its resting contact, off normal springs 59, interrupter contact of the rotary magnet, and the winding of the stepping relay 53 to battery. The
stepping relay will therefore again close the circuit of the rotary magnet 5&1 which will operate to rotate the switch wipers into engagement with the next set of bank contacts. This operation in which the step ping relay and the rotary magnet are alternately energized and deenergized will continue as long as the test wiper 71 continues to engage grounded or busy test contacts. In the present case it will be assumed that the trunk line shown in the drawings is the first idle trunk line, and when therefore the test wiper 71 arrives at test contact 74; and the rotary magnet is deen'ergized, the stepping relay 53 will not again be operated, but instead the switching relay 55, which heretofore has been short-circuit-ed, will be energized by current flowing over the following path: Grounded conductor 64, winding of the switching relay 55, off normal springs 59, interrupter contact of the rotary magnet 5 1, and the winding of stepping relay to battery. Relay 55 is of such high resistance that the stepping relay 53 is not operated. Upon energizing, .relay 55 disconnects the incoming line conductors from the windings of the line relay 50 and extends them by way of armatures 60 and 62 and their working contacts, wipers 70 and 72, bank contacts 73 and 7 5, upper and lower windings of relay to battery and ground, respectively. Relay 80 operates and closes at its armature 86 a circuit for the relay ea. The relay 84 in operating, closes at its armature 89, a circuit from ground, working contact of armature 89 and said armature, release trunk conductor 90, winding of relay 81, bank contact 7 1, and wiper 71 to armature 61, and its working contact, where the circuit divides, one branch exstation line.
tending through the switching relay 55, over the previously traced circuit to battery; the other branch extending over conductor 61, and over they previously traced circuit to the switching relay 13 and resistance 10 to battery.
It may be stated at this time, that the relay 81, included in the release trunk cir cuit, is a marginal relay, its operation being dependent upon an additional current flow which occurs when the substation calling is a- .paystation line over that which occurs when the substation calling is a non-payhis additional flow of cur rent is brought about by inserting a resistance in multiple with the switching relay of the individual line switches of pay station lines, such as resistance 10 in multiple with switching relay 13 of the line switch G.
Since the substation calling is a paystation line, whenthe release relay 8% energizes to ground the release trunk, the relay 81 is also operated, resulting in the connec tion of the generator Gen. 2 to conductor 93, instead of generator Gen. 1. The relay 84, in operating, at its armatures 87 and 88 also disconnects the trunk conductors 98 and 99 from the outgoing line switch C and at these same armatures transfers the trunk conductors 98 and 99 to a signalling circuit which may be traced as followst Ground, generator Gen. 2, working contact of armature and said armature, conductor 93, resting contact of armature 91 and said armature, Working contact of armature 88 and said armature, trunk conductor 99, con'duc-' tor 101, spring 114: and its resting contact,
conductor 115, armature 109 and its resting contact, junction point 113, upper winding of relay 106 and tuned alternating current relay in parallel, conductor 126, conductor 11,0, resting contact of spring 111 and said spring, conductor 100, trunk conduc-.
tor 98, armature 87 and its working contact,
armature 92 and its resting contact, and up per winding of ring out off relay 83 to bat tery. Ring cut off relay 83 will not operate on alternating current, but relays 105 and 106 operate, relay 105 being tuned to operate only when the generator Gen. 2 is used, while the relay 106 is adjusted to operate on current from either generator. Relay'105 closes a circuit for relay 108. The relay 108 closes a locking circuit for itself at arinature116 and its working contact, and at its armature 117 disconnects the call signal lamp L, and connects at the same armature the call signal lamp L Relay 106 at its armature 138 closes a locking circuit for itself, and at armature 118 completes a circuit for the call signal lamp L which may be traced from ground, armature 112 and its resting contact, working contact of armature 118 and said armature, armature 117 and its working contact, and lamp L to battery.
The operator, upon observing the lighted condition of the lamp L is thus informed that a connection is desired by a paystation line.
The operator will now proceed to answer the call by inserting the plug P into the jack J, which completes an operating circuit for relays 107, 120, and 121, which circuit may be traced as follows: Ground, winding of relay 120, tip of plug P, tip of side of jack J, conductor 126, resting contact of spring 127 and the said spring, winding of relay 107, ring side of jack J, ring of.
plug P, winding of relay 121 to battery. The relay 107, in operating, at its armature 112 breaks the holding circuit for relays 106 and 108, and these relays now restore. Relay 107 at its spring 127 controlled by armature 112 breaks the original circuit of the relay 120, and completes a holding circuit for itself from direct ground at its armature 112. The opening of the operating circuit of relay 120 by relay 107 is of no effect, inasmuch as a new circuit is completed at once by'the operation of the polarized relay 104-. The operation of relay 104 is brought about by the closure of armature 130 and its working contact, whichcompletes an operating circuit for the polarized relay 104 by bridging the same across the calling trunk. This bridging of the polarized relay across the calling trunk closes a direct current circuit for ring out off relay 83; which relay operates to close a locking cir cuit for itself over the release trunk conductor 90, and to open the ringing circuit and close the talking circuit at armatures 91 and 92. The new holding circuit for relay 120 completed by the operation of relay 104 may be traced as follows: Ground, winding of relay 120, tip of plug P, tip side of jack J, conductor 110, winding of the impedance coil 125, working contact of armature 131 and said armature, conductor 129, ring side of jack J, ring of plug P, and the winding of relay 121. to battery. The operator at the cord circuit 0 may now operate her listening key'K and converse withthe calling subscriber, after which she may proceed to extend the connection and require the calling subscriber to deposit the proper coin or coins to pay for it.
After the conversation is completed, the calling subscriber will restore his receiver, which will cause the release of the various automatic switches. The relay Set of the relay group D upon deenergizing transfers the conductors 98 and 99 from connection with ground and battery respectively at the battery feed coil 82, to battery and ground at the line switch C The line relay 1% opcrates, causing the line switch to hunt for an idle first selector trunk, and placing ground on the private normal conductor to guard the called end of the connection until the operator pulls the plug; while the reversal of current flow in the conductors 98 and 99 causes the polarized relay 104 to deenergize. It will be recalled that the energization of relay 120 was dependent upon the operation of relay 104, and this relay being now deenergized, the relay 120 deenergizes and completes a circuit for the disconnect signal lamp L The operator. upon seeing the lamp L lighted, will withdraw the plug P from the jack J, causing the deenergization of relays 107 and 121. The deenergization of relay 107 removes the bridge includ ing polarized relay 10 1 from across the calling trunk and causes the release of line switch C causes the disconnect lamp L to be extinguished. All apparatus used in the connection just described has now been restored to normal, and is in readiness to be used for any subsequent calls.
The operations which take place when a noupaying subscriber extends a connection to a manual exchange will now be briefly described. As previously pointed out, when any line which is entitled to free service to the manual exchange sets up a connection, the marginal relay in the trunk is not operated because the cut-off relay such as relay 13 is not shunted by a resistance. For in stance, assuming that the trunk line comprising conductors 98 and 99 connected to conductors 100 and 101, respectively, is selected by a preceding selector, the current flow over the release trunk is reduced to such a value that the marginally adjusted relay 81 of the relay group D does not receive suliicient current to operate, and as a result the generator Gen. 1 will be used. As previously stated the tuned relay 105 will not respond to current from Gen. 1, the relay 108 will not be operated, and the call signal lamp L will therefore be used.
A brief description of the operation of the modification shown in Fig. 3 will now be given, and for this purpose it will be as"- sumed that the trunk conductors 98 and 99 extend to conductors 102 and 103 instead of 100 and 101. In the present instance the signalling current extends over conductor 99, conductor 1.03, conductor 1 13, armature 138 and its resting contact, winding of relays 105 and 106 in multiple, conductor 110, resting contact of spring 11.1 and said spring, conductor 102, conductor 98, armature 87 and its working contact, armature 92 and its resting contact, upper winding of ring out off relay 83 to battery. The operation of relay 105 closes a circuit for relay 108. The operation of relay 108 prepares a locking circuit for itself at armature 13st, and at armature 135 disconnects lamp and prepares a circuit for lamp L Relay 106 at its armature 130 completes a locking circuit for itself, at its armature 137 The deenergization of relay 121' completes a holding circuit for relay 108, and at the same armature completes a circuit for lamp L.
The operator upon observing the lighted condition of lamp L, is thus informed that the call has originated at a paystation, and will therefore handle the call accordingly. Upon inserting the plug P into the jack J an operating circuit is completed for relay 107 thru the lamp L, but this lamp does. not operate at this time due to the high re sistance of the lower winding of relay 107. The operation of relay 107, causes the common ground to be removed from relays 106 and 108 at armature 139, and these relays therefore deenergize, and ground is also removed from the call signal lamp L causing the same to be extinguished. At armas ture 138 the original energizing circuits for relays 106 and 105 is broken, and at the same armature and its working contact the polarized relay 104 is bridged across the calling line, which causes the operation of relay 83 as previously described. Relay 104 does not operate however at this time as the current flow is in the wrong direction, its operation being just opposite to that of polarized relay 104. The operator now throws her listening key and after conversing with the calling subscriber may extend the connection in any well known manner. When the conversation is completed the calling and called subscribers replace their receivers, when the receiver at the calling substation is replaced line relay 80 is deenergized, which results in the deenergization of release relay 84. Relay 84 in falling back, removes ground and battery respectively from conductors 98 and 99, and con meets these conductors to battery and ground respectively at the line switch C The reversal of current flow through the polarized relay 104 causes that relay to operate. The operation of relay 104 shunts out the high winding of relay 107 causing the lamp L to light to inform the operator that the sul scriber at the automatic exchange has re placed his receiver. The called subscriber upon replacing his receiver causes the lamp L to be lighted over the usual supervisory circuits, to indicate to the operator that disconnection is desired.
The manner of extending calls from the automatic exchange to the two types of manual exchanges having been described, a brief description will now be given of the operations which take place when calls originate at the manual exchanges.
First assuming that the manual operator is provided with cord circuits such as the cord 0. The operator will insert the plug P into an idle jack such as J causing the relays 140, 141 and 107 to be energized in the same manner as were relays 120, 121 and 107 when a call was answered. soon nection in a well known manner.
using cord circuits such. as O.
relay 107 operates, the circuit for relay 140 is opened at spring 127 whereupon this relay falls back and lights the lamp L Relay 104 is also bridged across the conductors 98 and 99. The direction of current flow through relay 104 at this time, however, is such as not to cause its actuation. Relay 140 therefore remains deenergized. The operator throws the key K, substituting the calling device S for the polarized relay 104. The closure of the bridge across the trunk line conductors 98 and 99 causes the switch C to operate to select an idle trunk, and to make busy the trunk conductors 98 and 99 to calls originating in the automatic exchr-inge. The operator proceeds to oper ate the calling device S to extend the con- After completing the dialing operation the opera tor restores the key K to normal, again throwing the polarized relay 104 in bridge of the trunk line. lVhen the called subscriber responds the current flow in the calling trunk is reversed, and the relay 104 opcrates. The relay 140 is therefore again energized to extinguish the lamp L When the conversation is completed the called subscriber replaces his receiver causing the current flow in the polarized relay 104 to be again reversed resulting in the deenergization of relay 140 thus causing the lamp L to be again illuminated to inform the operator that a disconnection is desired.
It will now be assumed that a connection is to be extended from a manual exchange In this case the operator inserts the plug P into an idle jack, such as J, throws the key K, and pro ceeds to set up the connection in the same manner as has been described. lVhen the key K is restored the polarized relay 104' is energized, in this case causingthe lamp L to light. hen the called subscriber removes his receiver the current flow is reversed and the relay 104 is restored thus causing the lamp L to be extinguished. When the called subscriber replaces his receiver the. current flow is again reversed and lamp L is again illuminated to inform the operator that a disconnection is desired.
Having described my invention what I consider to be new anddesire to have protected by Letters Patent will be pointed out in the appended claims.
hat is claimed is:
1. In a telephone system, a two-way twoconductor trunk line extending from an automatic exchange to a jack in a manual exchange, calling stations of two characters in said automatic exchange, automatic switching mechanisms operable under con trol of any calling station to extend the associated line to said trunk line, a plurality of call signals associated with said trunk line at the manual exchange, and a relay in said trunk line controlled by certain of said switches for determining which of said signals is to be operated.
2. In a telephone system, a two-way twoconductor trunk line extending from an automatic exchange to a jack in a manual exchange, calling stations of two characters in said automatic exchange, automatic switching mechanisms operable under control of any calling station to extend the associated line to said trunk line, a plurality of call signals associated with said trunk line at the manual exchange, and a relay in said trunk line responsive only if the calling station is of a particular character for operating a particular one of said signals.
3. In a telephone system. a two-way twoconductor trunk line extending from an automatic exchange to a jack in a manual exchange, calling stations of two characters in said automatic exchange, automatic switching mechanisms operable under control of any calling station to extend the associated line to said trunk line, a plurality of call signals associated with said trunk line at the manual exchange, and a device in said trunk line capable of discriminating between the two kinds of lines in the automatic exchange, and means controlled by said device for operating one or the other of said signals depending on the character of the calling line.
4. In a telephone system, a two-way twoconductor trunk line extending from an automatic to a manual exchange, a plurality of call signals at said manual exchange, calling lines of two characters in the automatic exchange having means including series of automatic switches for extending connections to said trunk line, and means in said trunk line controlled by said switches for determining which one of said call signals is to be operated when a connection is extended thereto.
5. I11 a telephone system, a trunk line extending from an automatic exchange to an operators position at a manual exchange, a plurality of call signals associated with said trunk line, calling lines of two characters having means including series of automatic switches for extending connections over said trunk line, a plurality of alternating current relays in bridge of said trunk line for controlling the operation of said signals, means in said trunk for automatically extending alternating current of one frequency over said trunk line when a line of one character is calling to cause one of said relays to be operated, and means included in certain of said switches for causing alternating current of another character to be extended over said trunk line to cause the operation of both of said relays.
6. In a telephone system, a trunk line extending from an automatic exchange to an operators position at amanual exchange, a plurality of call signals associated with said trunk line, calling lines of two characters having means including series of automatic switches for extending connections over said trunk line, two alternating current generators of different frequency, means in said trunk responsive when the calling line is of one character for transmitting alternating current of one frequency over the trunk line to operate one of said signals, and responsive when the calling line is of the other character for transmitting alternating current of the other frequency over said trunk line to operate the other of said signals.
7. In a telephone system, a twoway twoconductor trunk line extending between an automatic and a manual exchange, a plurality of call signals associated with said trunk at the manual exchange, calling lines of two characters, means including automatic switchingapparatus for extending said calling lines to the manual exchange, a holding trunk included in said switching apparatus over which the connection is maintained established, and a relay included in said holding trunk non-responsive when one character of line is calling to permit one of said signals to be operated, and responsive when another character of line is calling to cause another of said signals to be operated.
S. In a telephone system, a trunk line, means for transmitting alternating currents of different frequencies over said trunk line, a relay bridged across said trunk line and responsive to any frequency of current, a signal normally responsive to the operation of'said relay, a second relay bridged across said trunk line and responsive only to a particular frequency of current, and a second signal responsive to the joint operation of both said relays.
9. In a telephone system, lines of different classes, an operators switchboard, means for extending said lines to said switchboard responsive to calls, class signalling means at the operators switchboard, and means including alternating current generators of different frequencies and alternating current relays controlled thereby for controlling said signalling means.
10. In a telephone system, lines of different classes, an operators switchboard, means including a trunk line for extending said lines to said switchboard responsive to calls, class signals at said switchboard, and means for transmitting alternating currents of different frequencies over said trunk line to control said signals.
In witness whereof, I hereunto subscribe my name this 8th day of July, A. D. 1922.
ARTHUR J. RAY.
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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2594505A (en) * 1949-12-09 1952-04-29 Bell Telephone Labor Inc Calling line identification and registering system
US2633500A (en) * 1947-04-03 1953-03-31 Int Standard Electric Corp Cordless switchboard telecommunication exchange

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2633500A (en) * 1947-04-03 1953-03-31 Int Standard Electric Corp Cordless switchboard telecommunication exchange
US2594505A (en) * 1949-12-09 1952-04-29 Bell Telephone Labor Inc Calling line identification and registering system

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