US1437357A - Revertive test system - Google Patents

Description

W. T. POWELL.

REVERTIVEVTEST SYSTEM. APPLICATION FILED APR. 9.- I919.

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v mm mm NM m M m m Wm ATTORNEY w. T. POWELL. REVERTIVE TEST SYSTEM.

APPLICATION FILED APR. 9, 1919.

Patented Nov. 28, 1922.

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INVENTORV WIHFE 'D T. POWELL.

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ATTORNEY Patented Nov. 28, 1922.

WINFBED T. POWELL, OF ROCHESTER, NEW YORK, ASSIGBTQE T6 THE STEOllIBERG- CAELSON TELEPHONE MANUFACTURING COMPKCQJY, F RQCHESTER, NEW 3503?,

A CURBOBATIO'N OF NEW YORK.

REVERTIVE TEST SYSTEM.

Application filed April 9, 1919. Serial No. 288,781.

To all whom it may conceive:

Be it known that l, VVINFRED 'l. Pownnn,

a citizen of the United States, residing in Rochester, in the county of Monroe and State of New York, have invented certain new and useful Improvements in Revertive Test Systems, of which the following is a full, clear, concise, and exact description.

This invention relates. to telephone systems, and more particularly to such systems of the central energ i type in which the busy or idle condition of a telephone line is determined by the presence or absence of a definite potential at the test terminals of the line switching terminals in which the lines terminate.

My invention has a particular application in connection with a semiautomatic telephone system, although it is not limited to such use as there is a large and extensive demand for such a system as is herein illustrated and described in connection with manual and semi-automatic telephone systems.

In manual and semi-automatic systems it is very often desirable to supply an operator with information automatically given as to the particular line upon which the calling subscriber is located for instance, connection with the giving of toll service. The securing of such information enables charges to be made to the correct party who secures the service. Such a use of my invention is provided for in the embodiment illustrated and described herein, and means are provided for the operator to check the correctness of the information given by the subscriber as to his line number.

Also a use of my invention will be described herein where an additional object of my invention issecured, namely, of advising the operator whether'the called-for subscriber is on the same line as the calling subscriber.

In both uses of my invention as herein. illustrated, special means are provided by which an operator will obtain a distinctive signal when in testing multiple terminal of a calling line which is different from the signal secured when the operator tests a multiple terminal of a different called line. It is found in the systems of the art which. produce a musical note or tone in the re-- CeiVeI" of the testing perator Whenever the terminals of the line upon which the calling subscriber is located are tested, that this tone is apt to confuse the operator since there are many other tones used in telephone exchanges, particularly where automatic equipment is used, such as trouble tones, wrong number tones, etc,- and the result is with such systems of the prior art that the the toll service to whatever line number the subscriber wrongly may give.

i In the system of my invention, however, the apparatus thereof is so organized that a battery click will be heard it the tested terminals or" the called-for line belong to the line to which the calling subscriber is located, and a tone is hear when testing other called for line it the said called-for line is busy, nothing being heard it the said other called-for line is idle. In using my invention in connection with a toll checking system the operator encountering such atone as might be confused with the busy tone, the error would not cause her to put through the long distance call and to make the charge to the telephone line or the line number the subscriber may wrongly give.

@ther objects of my invention and the invention itself will be better understood from the description of the same which follows in which Fig. l and Fig. 2 when placed together make a complete drawing of a system of my invention as will be necessary in order to instruct those skilled in the artas to the construction and operation of the same.

In Figs. 8 and l schematic diagrams are illustrated to show the flow of currents in the several circuit branches under the different operative conditions producedin the operation of the system of my invention.

The system of my invent on is illustrated in Figs. 1 and 2 as a calling line number checking system.

Referring to Fig. l, at A I show a calling sub-station having a line switch LS, by means of which the calling substation is con .nected to an interconnecting link circuit LK any which in turn is adapted by the operation of its switch wipers a, Z2 and c to extend a connection to a trunk circuit TK, illustrated in Fig. 2.

A signal lump 8 is illustrated for the trunk circuit and adapted to operate when u call from a calling line seizes the trunk circuit TX to anounce the call to the toll operator having an interconnecting cord circuit CD, which preferably would be one of a plurality oi? cord circuits and which operator would also have an operators set which preferably would be common to the said plurality of cord circuits.

A test terminal TT of the calling line is ended from a conductor associated with the line switching; mechanism in order to enable the operator to make the checking line test. as will be hereinafter described.

and TT are pro- Other test terminals TT- vided for another line which is assumed in this description to be a busy line and on red to be an idle line respec tively. 22 tion being bad, oi? the con ditions attending the testineof each lrind of? a line; reference being bad therein to each of the terminals above referred to in such description.

The line with the substation is. is illustrated in i as having; another substation B. as well. reference being; had to the said other substation in that part of tl scriotioi'i of the system of my inv which follows, which refers to the use of my invention in connection with party lines.

in Fig. 2 a substation N, is shown lead- :ii by line conductors to terminals associtcu with the test terminals TT above referred to as belonging to another idle line. The cord circuit CD is illustrated as havingthe usual bzitterv teed supervisory relays and ',ory in order to give the opthe usual supervisory control over lit. 1 show a relay com art of the combination. cnts requires. to produce a system ct This rela is illustrated and diili'ereutial relay having two 3's. the first of which when both windi i c by current flowing: l m opposes the action of the second and tends to neutralize the magnetic effect of the second upon the urmaturcs the relay. This role might be constructed in various ways, it being: only necessary that one oi the windings opposes the effect of the first upon the relay contacts.

Referring now to the drawings I will de scribe the operation of the embodiment of my invention first, when use is made of the system oi"? my invention for interconnection with party lines to indicate to the operator when the calling line is identical with the called line and second, a description will be had or" the system of my invention when the same is used as a toll operators checking system.

Referring to Fig. l, the subscriber at substation A, upon removing his receiver to initiate a call. completes an energizing circuit for the line relay LR of the individual line switch LS over the following circuit c'round G cont ct spring 1 of cut oil relay JO, line conductor 2, primary induction coil 5, switch hook contact 8, transmitter 6, calling' device CD line conductor 4-. contact 5 or cut of? relay CO, and winding of line relsy LR to the source of current. The line relay L? energizes and closes the following circuits-ground 1 contact 6 of relay LR, terminal 7 and wiper 8 of line switch LS, contact 9 of relay CO, contact 10 of line switch stepping magnet ST and winding of line switch stepping magnet to the source of current. The stepping magnet energizes, breaks its own circuit at contact 10 and, as the armature retracts, the wipers 8. 11, 12 and 13 are advanced one step in the well lcuown manner. which brings them to rest on the second row of terminals to which are inultipled the trunk wires lending to a selector circuit like LK. Assuming this trunk to be bu at this time, there will be a contion to ground on terminal 14. placed e by the line switch which is holding this I busy he manner in which this is done 'ie seen when the point is reached in his les ription where the selector LK is seizziiz made busy. This ground now found on terminal lei will flow over wiper S, contact 10 and the winding of i o the source of current again 1c switch to step in the same .-.fore which brings the wipers l to rest on the third row of l'lre the first row, is .he circuit condition home points, the wipers need in the some manner the first step. The wipers on the fourth row of torich is assumed to be the multiple an idle tri'inlr.

The tollowinn' circuit is now closed to operate the cut oil? relay COz-grouud G resistance coil 15, normally mnde ofi normal contact 18. contact 17 0t selector secondary s1 eppinn' magnet Filvll. terminal 18 and wiper 12 of line era itch L 9 winding'of relay CO. contact 10 and winding of line switch steppine magnet EST to the source of current. It will be noted that 2. ground like G was also on terminal 19 as wiper passed it but this ground could not operate relay Ct; because it was short circuited by the ground which was or. terminal 14 for mslrinoy the trunk busy The cut oil relay G0. now energizes, disconnects the battery bridge from the line at contacts 1 and 5 and extends line conductor restin lOO 2 by way of contact 20, wiper 13, terminal 22, contact 23 of selector cut through relay CT, winding 24 of selector impulse relay IMF to ground G Line conductor 4 is also extended by way of contact 21, wiper 11, terminal 25, contact 26 of relay CT and winding 27 of relay IMP to the source of current. The line switch out off relay C also closes the following circuit for making the selected trunk test busy to other line switches: ground Gr, contact 28, wiper 8 and the multiple of terminal 29 appearing at all other line switches having access to this selector.

Relay IMP of selector LK upon energizing, closes a circuit from ground G contact 30, and winding of the holding relay H to the source of current. Relay H energizes and closes contact 31 which holds the ground G on the holding trunk 32 as long as this selector is held by relay INIP. The original circuit to the holding trunk was traced through off normal contacts 16 but as this contact opens upon the first step of the selector, the above traced substitute path is provided.

The foregoing operations have all been brought about by the removal of the receiver 7" at the substation. Assume now that the selector LK has access to several levels, each of which contains trunks leading to an operator handling different classes of service.

First will be described the operation of what is known as arevertive call, i. e., when the subscriber at substation A asks the operator to connect him with number 1234:,

. for instance, which number belongs to the subscriber at substation 13 who is on the same line with A.

The subscriber at substation A new operates the dial CD in accordance with the digit which corresponds to the position of the required set f contacts in the bank of the selector, there y breaking the continuity of the loop a number of times by the opening and closing of the dial impulse springs in the well known manner. As a result of these interruptions the impulse relay IMP is deenergized a corresponding number of times, sending an impulse at each deenergization from ground G to the slow acting relay CH and the primary stepping magnet PM in series by way of contacts 33, 34 and 35. While these impulses are being sent by relay IMP, relay H being slow acting, remains in its operated position. The primary stepping magnet PM is operated at each deenergization of relay IMP and steps the shaft carrying wipers a, b and c to the required level or row of contacts. Relay CH, being slow acting, retains its armature in the operated position during the series of impulses and closes a circuit for the test relay T, as follows: ground G", contact 36 of relay CH, and winding of relay T to the source of current. Relay T looks over the following circuit: ground G resistance coil 15, contact 31 of relay H, contact 17 of magnet SM, off normal contact 40, contact 38 of relay T and winding of relay T to the source of current. At the end of the series of impulses the relay CH deenergizes, there- .by completing the circuit for the secondary stepping magnet SM from ground G low resistance coil 15, contact 31 of relay H, con tact 17 of magnet SM, olf normal contact 40, contact 38 of relay T, contact 37 of relay CH, contact 4-1 of magnet SM, and winding of SM to the source of current. The magnet SM operates, advances the wipers a, Z) and 0 one step on to the first set of contacts and breaks its own circuit at contact L1 allowing the arinature to retract. All trunks in this level which are busy will have grounds on the terminals like 42, which grounds will cause relay T to remain ener gized from ground on these terminals 42,

wiper 6, contact 38 of relay T and the winding of relay T to the source of current. The switch shaft and wipers will be advanced past all these busy trunks by means of the following circuits :ground on the terminal 42, wiper 6, contact 38 of relay T, contact 37 of relay CH, contact 41 and winding of magnet SM to the source of current. As soon as the wipers reach a trunk which has no ground on the test terminal like 42, magnet SM will not again energize and relay T will deenergize. The test relay T, upon deenergizing, completes acircuit for the cut through relay CT, from ground G resistance coil 15, contact 31 of relay H, contact 1'7 of magnet SM, off normal contact 4.0, contact 39 of relay T, and the winding of relay CT to the source of current. Relay CT energizes, disconnects the line conductors 4:9 and 44: from the battery bridge relay IMP at contacts 23 and. 26 and extends the line conductors 49 and at by way of contacts 45 and 46 and wipers a and c to the trunk line conductors 7 and 48 leading to the trunk circuit TK. A circuit is now closed from ground G contact 50 of trunk circuit cut off relay TC, trunk wire 4'7, closed circuit of substation A; trunk wire 48, contact 51 of relay TC and the winding of the trunk line relay TL to the source of current.

Relay TL now energizes and closes a circuit from ground G contact 53 of relay TL, resistance coil 55, trunk wire 43, wiper b of selector LK, contact 39 of relay T and winding of relay CT to the source of current.

This circuit is closed before relay H of the selector releases, therefore this substitute ground for holding relay CT is applied before the original one is opened at contact 31 of relay H. Relay TL also closes a circuit from ground G contact 52 of relay TL and the signal lamp S to the source of current. (The wire from lamp S may lead to he source of current through a pilot relay or be connected direct as desired).

The operator, in response to this signal. inserts the answering plug A'P in the jack rial whereupon the following circuit is closed to energize relay TC:ground G winding of sleeve relay S. sleeve 56 of plug sleeve 57 of jack A5 and winding of relay TC, to the source of current. Relay TC opens the trunk circuit battery bridge at contacts 50 and 51 and the calling substation will be fed talking battery through the windings of answering supervisory relay AS by way of the tip and ring contacts of the plus; and jack.

Relay TL now releases and breaks the holding ground circuit for the selector at contact 53 but not until another substitute ground has been established from ground G winding of relay S, sleeve 56 of plug AP, sleeve 57 of jack AJ, contact 54. of lay TC to the holding trunk l3. Relay TL releasing also extinguishes the signal lamp S by opening contact 52.

The operator now operates the listening irey LT associated with the cord circuit used and receives the request of the calling party in the well known manner, after which she tests the called line multiple by touching the tip 64fv of the calling plug GP to the sleeve TT. TT or TT which represents the sleeve jack of the calling line, of another busy line o iris 7 and an idle line respectively. If the called for line is idle there will be no difference of potential established when this test is made. the circuit on the sleeve of the tested jack going to main battery as shown at TL. he operator will then insert the plug CP into the jack TL and ring the hell of the called party by operating the ringing key ill: wlrca applies ground G to the tip conductor and generator G G G or G (depending on the frequency required which is selected by the operator depressing one of the keys 65, 66, 67 or 68) to the ring conductor fO of the called line. Upon response of the called party at substation N a direct current path is closed through the transmitter 71 and the primary induction coil 72. This closed circuit operates the calling supervisory relay CS, through which relay is led the talking battery for station N. Talking tery for the calling station A is fed through relay AS and the two paths are connected together by condensers 73 and 74;. When the conversation is completed, the called party at substation N hanging up the receiver deenergizes relay US which causes the calling supervisory lamp ST to burn and the calling party at substation A hanging up the receiver deenergizes relay AS which causes the answering supervisory lamp SG to burn. The operator now withreams? draws both plugs All and Cl from the jacks which causes the selector LK and the line switch LS to release in a manner to be later described.

Assume now that the called line is busy when the operator touches "the tip G lof the cord to the sleeve of the jack. The circuit condition of the sleeve of a busy line is shown BL where CG represents the resistance of cut oil relay CO and the line switch stepping magnet ST in series and till represents the resistance of sleeve relay or 5L of the cord circuit to which this line is connected. It a calling line has not yet been answered resistance CO represents either resistance coil 15 or 55 depending on the distance which the call has progressed. l Vhen the operator makes this test the followii circuit is closed: ground coil winding- ST]. sleeve TT oi jacl: Lil, tip 6 of plug Cl contact 81 of relay t ill, common test wire 82 and winding '75 of relay 'lll to the source of current. Relay Tlt energizes and closes contact 77 which places the tip of the plug 64 in series with winding 76 of relay TR into connection with the sleeve of the calling line by way of common wire 84 and contact 85 of listening lrey LT. This circuit condition is shown schematically in Fig. 4: where the same reterence numbers are used in connection with corresponding parts of the circuit in F l and Fig. 2. Thus it will be seen tl at relay TR gets current through winding 45 v. ien it is energized and that, when contact 7? is closed current also traverses winch :ing 76 wnich winding is wound on the core of relay TR in a direction opposite to winding 75. This immediately deenergizes relay TR, opens contact 77 when relay TR will again energize. This action continues which produces a buzzing tone in the op erators receiver by opening and closing the circuit across inpedauce coil MP and connecting condenser thereto. This buzzing tone indicates to the operator that the called for line is busy, she so informs the calling subscriber who hangs up the receiver and she then withdraws the answering plug AP. This disconnects ground G from the sleeve 57 or the jack All allows relay TC to dcenergize and as there is now no ground on the holding trunk 43. relay CT of selector LE and relay C0 f line switch LS both deenergize.

Relay cuit for tact CT, contact 58 of relay H off normal contact 59 and winding 60 of release magnet REL. Magnet REL in addition to releasing the selector Lli in the well known manner, closes a circuit from ground G contact 62 of magnet REL, low winding 61 of magnet lt-EL, trunk wire 63, line switch. ter- CT closes the following release cirthe selector LK: ground G con 33 of relay IMP, contact 34 of relay' minal 29, wiper 8, contact 9 of relay CO, contact 10 of line switch stepping magnet ST and winding thereof to the source of current. This causes the line switch Wipers to be advanced one step which brings them to a normal or home point. l/Vhen wiper 8 leaves terminal 29 the winding 61 of selector release magnet REL is opened and it deenergizes.

Returning to the point where the operator makes the test of the called line, if the number wanted is on the same line with substation A, (B for instance) a different condition is found and it is shown schematically in Fig. 3. In Fig. 2 the circuit condition of the multiple jack in this case is shown at CL where the sleeve TT is shown extending back to the cut off relay C0 of the calling line switch. When the operator makes the test the following circuit is closed: ground G winding of relay S, plug sleeve 56, jack sleeve 57, contact 54: of relay TC, trunk wire 43, selector terminal 42, wiper 5, off normal contact 10, contact 17 of magnet SM, trunk wire 32, line switch terminal 18, wiper 12, trunk wire 83, sleeve TT of jack CL, tip 64: of plug GP, contact 81 of relay SL, common test wire 82, and winding 75 of test relay TR to the source of current. This energizes relay TR which closes contact 7 7 establishing the circuit condition shown in Fig. 3. Thus it is seen that relay TR gets current through winding 7 5 as before but in this case the closure of contact 7 7 does nothing but short circuit winding 7 6 and the relay will not be deenergized. Therefore it will not buzz to produce a buzzing tone in the operators receiver as before but will operate once and produce a click in her receiver. She knows by this signal that the called party is located on the same line with the calling party and instructs the calling party to hang up while the called partys bell is rung. She may then ring the wanted hell by either plugging into the jack CL and operatlng the ringing key BK or by operating a ringing key in connection with the answering plug, not shown but well understood. Disconnection is brounght about in the manner previously described.

The wires 86, 87 and 88 shown at the top of Fig. 1 may be connected to the banks of a connector switch so that this line may be called from an automatic system.

When this system is used in connection with toll or other service where a charge is to be made against the calling party, the operation is as follows :--the calling subscriber at substation A. removes the receiver, dials the number necessar to cause selector LK to select a trunk T and the operator answers, all of which is done in exactly the same manner as before described. The subscriber now informs the operator that connection is desired with a distant point and she proceeds to make out a ticket containing the necessary information, part of which is the number of the calling partys line. The operator now touches the tip 64 of the plug LP to the sleeve of the multiple corresponding to the number given by the calling party. If the correct number was given, the circuit condition would be the same as that previously described for the case where the operator tested the jack TT shown in Fig. 3, in which case she would hear the single click. She therefore knows that the proper line number was given. If, when she makes the test, no sound is heard she will know that the party has given her a wrong line number because she knows that she is testing an idle line. If a wrong numher is given, which number happens to be busy at the time the test is made, the same condition will be established as previously described when the operator tested jack BL, a buzz will be produced in her receiver and she will again know that the party did not give the proper line number.

When this system is used as a checking test, the jacks 89 and 90 and the associated wires are not needed, therefore less space is required in the multiple especially if the test terminal TT is made of-a small metal point.

While I have illustrated and described a specific embodiment of my invention, it will be understood by those skilled in the art that the same is capable of use in other types of systems which may vary widely in structural details, but what I claim as my invention is defined in the following claims v y 1. In a telephone system, the combination with a plurality of telephone lines, a line interconnecting link circuit, an automatic switch for connecting said link circuit to a telephone line, an operators set adapted to be associated with the said link circuit, test terminals for each of the lines, answering ack terminals for each of the lines and co-operating answering terminals for the said link circuit, an operators receiver for the said operators set, a test circuit associated with the said operators receiver and the said link circuit, and means to produce a battery click audible busy tone in the operators receiver when a test is made of a test terminal of the same line to which the answering terminals of the link circuit are already connected, and means to give a different signal when another busy line is tested.

2. In a telephone system, the combination with a plurality of telephone lines, a line interconnecting link circuit, an operators set adapted to be associated with the said link circuit, test terminals for each of the lines, answering jack terminals for each of the lines and co-operating answering terminals for the said link circuit, an operators receiver for the said operators set, a test circuit associated with the said operators receiver and the said link circuit, means to produce a battery click audiblebusy tone in the operators receiver when a test is made of a test terminal of the same line to which the answering terminals of the link circuit are already connected, and means to associate a tone producing source of current with the said operators receiver instead ol the said battery click source of current if the tested terminal of the called-for line is a different line than that already connected to the link circuit by said answering terminals and said answering line jack terminals.

in a telephone system, the combination with a plurality of telephone lines, a line interconnecting link circuit, an operators set adapted to be associated with the said link circuit, test terminals for each of the lines, answering jack terminals for each of the lines and co-operating answering terminals for the said link circuit, an operators receiver for the said operators set, a test circuit associated with the said operators receiver and the said link circuit, means to produce a battery click audible busy tone in the operators receiver when test is made of a test terminal of the same line to which the answering terminals of the link circuit are already connected, means to associate a tone producing source of current with the said operators receiver instead of the said battery click source of current if the tested terminal oi? the called-for line is a different line than that already cormected to the link circuit by said answering terminals an, said answering line jack terminals, and disabling means for said hi 'erv click and said tone test means should the tested terminal of the called-for line be associated with a line ditiierent from that to which the link circuit is already connected, and which different line is in an idle or unused condition.

4. In a telephone system, the combination with a plurality of subscribers lines, answering terminals and a plurality of multiple terminals for each line, means including a. link circuit for establishing connection for two 0t said lines. means in said link circuit for testing a busy line, a testing mechanism, and means for operating said testing mechanism when a terminal of the calling line to which the link circuit is already con nected is tested to give the operator an audible busy signal of one character, and to give the operator an. audible signal of another character when a terminal of a line other than the calling line is tested, when the said other line is in a busy condition, said test-- ing mechanism comprising a differentially wound relay, one of the windings of which contains in its circuit normally open contacts or" the said relay.

5-. In a telephone system, an operators cord circuit provided with a. calling plug, a testing conductor normally associated with. said plug, a relay winding in said testing conduct-or, a second relay winding, said windings being so connected in their respective circuits that the combined efl'ect of current flowing simultaneously through the two windings is to disable the said rela energizing circuits for both of the said windings under the control of said calling plug and testing conductor, and normally open contacts of said relay interposed in one or" the said relay windings.

6. In a telephone system, an operators cord circuit provided with a calling plug, a testing conductor normally associated with said plug, a relay winding in said testing conductor, a second relay winding, said windings being so connected in their respect-ive circuits that the combined effect of current flowing simultaneously through the two windings is to disable the said relay, energizing circuits for both of the said windings under the control of said calling plug and testing conductor, and normally open contacts of said relay interposed in the second one of the said relay windings.

7. In a telephone system the combination with a central station, a plurality of tele phone lines terminating thereat, a busy testing circuit, means for completing said circuit, a modifying circuit for the said busy testing circuit, and means to produce currents of differentcharacteristics when said first circuit is closed, the operation of said means being controlled by the character of the said energizing circuit.

8. In a telephone system, the combination with a plurality of telephone lines, a main exchange switchboard, one of the telephone lines being a poly-station telephone line, a switchboard having answering terminals for the said poly-station telephone line, and a. plurality of multiple terminals for said telephone line, a link circuit for the answering switchboard section, an operators receiver adapted to be operatively associated with the said link circuit, tone producing means for energizing the operators receii tr to cause it to give distinctive audible sine nals, means to interconnect said link circuit with said answering line terminals, means to test a terminal of a desired called-for line, by causing a terminal of the said link circuit to contact therewith, and controlling means including differential relay for said audible signal ynoducing means to differently operate the said controlling means to causea tone signal to be produced by the operators receiver when the tested. called line terminal is associated with abusy called line different from the line to which the link circuit has already been connected, and to cause a different kind of an audible signal to be produced by the said receiver when the tested terminal 01 the called-for line is associated with the line to which the link circuit has already been connected, said audible signal producing means being inoperative to produce an audible signal in the operators receiver when the tested terminal of tie called-for line is associated with an idle or unused line.

9. In a telephone system, the combination with a central station, a plurality of telephone lines terminating thereat, a testing circuit, an operators telephonereceiver associated therewith, and means including a differentially wound relay to produce a current of distinctive characteristics when said testing circuit is closed, the operation of said means being controlled by said circuit.

10. In a telephone system, the combination of a plurality of telephone lines, linl circuits for interconnecting said lines, an operators telephone set arranged to be associated with the said link circuit, test terminals for each of said lines, a test circuit and a difierential relay associated with said link circuit, a locking circuit for said difierential relay including one of its windings arranged to be maintained closed during the testing by said test circuit of the terminals of a telephone line of one character and arranged to be intermittently closed during the testing of the terminals of a line or another character, and means controlled by said differential r lay to distinctively signal said operators telephone set.

11. In a telephone system, the combination of a plurality of telephone lines, certain of said lines being poly-station lines, link circuits for interconnecting said telephone lines, an operators position at which said link circuits are located, a testing circuit, and a testing relay having two windings, one of said windings being energized during the testing of abusy line by said test circuit, and the second of said windings being intermittently short circuited during the testing of one line and permanently short circuited during the testing of a polystation line that has originated the call.

12. In a telephone system, a plurality of telephone lines, certain of said lines being provided with a lurality of sub-stations, an operators position and a plurality of link circuits through which a calling telephone line is serially extended to said operators position, said extended connection terminating in a manual switch, a test circuit including a double wound relay arranged to test a wanted line under the control oisaid manual switch, one of said windings being energized over a circuit including said test circuit during the testing of any busy line, the second of said windings being intermittently or permanently short circuited during the testing of a busy line dependent on the character of said line.

18. In a telephone system, a plurality of telephone lines of different character, means for characterizing telephone lines by a busy or idle condition, linlr circuits and numerical and non-numerical switches for extending a calling line to an operato-rs position, manual means for testing the condition of a wanted line, and means operative thereupon for indicating the character of the busy line being tested.

i l. In a telephone system, a plurality of telephone lines of diflerent character, means for characterizing telephone lines by a busy or idle condition, link circuits and numerical and non-numerical switches for extending a calling line to an operators position, means including a diflerential relay for testing a wanted line, and means operative upon the actuation of said differential relay for indicating the character oi": a busy line tested.

15. In a telephone system, a plurality of telephone lines including main lines and poly-station lines, means for characterizing said telephone lines by a busy or idle condition, a link circuit and numerical and nonnumerical switches for extending a calling line to an operators position, a test circuit including relay mechanism, and a manual switch at said operators position for can tending said test circuit, said test circuit while testing a main called line being completed at said line, and in the case of a revertive call said test circuit extending serially through said link circuits and switches, and a signal controlled by said test circuit and relay mechanism.

In testimony whereof, I hereunto subscribe my name this 7th day of April, A. D.

WINFRED T. POWELL.

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