US2301837A - Testing arrangement for trunks to community dial offices - Google Patents

Description

' Nov. l0, 11942. M. B. WILEY E-rAL 2,301,837

TESTING ARRANGEMENT FOR TRUNKS TO COMMUNITY DIAL OFFICES Filed Feb. 25, 1941 2 Sheets-Sheet l feder f6/mb ATTORNEY E axz Nv.1o,1942. M.B.w|| EY Em. 2,301,837

TESTING ARRANGEMENT FOR TRUNKS TO COMMUNITY DIAL OFFICES Filed Feb. 25, 1941 2 Sheets-ShedI 2 i 2X-1 l- 1 -Selecor' l E wir 'f Z'Cf /2 /LXg -JE? 32 lm, y y

u" z f PS j /cXf g-SEJ S33 I JEM. l S32 1 Commanz'tyl'al Qi'ce L INVENTORS ATTORNEY Patented Nov. 10, 1942 TESTING ARRANGEMENT FOR TRUNKS T COMMUNITY DIAL OFFICES Mason Bain Wiley and Anthony Forester, Charlotte, N. C., assignors to American Telephone and Telegraph Company, a corporation of New York Application February 25, 1941, Serial No. 380,466

19 Claims.

This invention relates to community dial telephone systems and more particularly to arrangements for testing trunks extending between a telephone exchange and a community dial office.

It sometimes happens that a community or hamlet too small to justify an ordinary manual exchange is located near a larger town or city provided with a regular telephone exchange or exchanges. Frequently in such cases the outlying hamlet or community is too far away from the city to justify direct connections from each subscriber to a central oiiice in the city. Under such circumstances it is usually the practice to provide the outlying hamlet with telephone service by means or" a so-called community dial office. This is a small cnice located in the local community and provided with relatively simple, automatic switching machinery by which the local subscribers may dial each other. A relatively few trunks extend between the community dial oflice and the exchange in the nearby city to take care of calls from the local community to the larger telephone area. An operator in the city may establish a direct connection over one of these trunks to any desired subscriber coming into the community dial office, and any local subscriber desiring a city connection can by dialing, connect his line to one of the trunks leading to the city. These community dial offices are unattended, except at such times as maintenance and inspection employees make temporary visits.

Where such a situation exists and toll circuit troubles arise in connection with the trunks leading to the community dial oiiice a somewhat elaborate procedure for clearing troubles is involved. It is frequently found necessary to send a lineman man from the testing oice at the city exchange to the outlying community dial oflice to open and cross out circuits in order to measure or locate line troubles which are often found to be only a short distance from the testing office. This, of course, results in an excessive loss of time on trunk circuits, and in addition there is the expense of the unnecessary miles traveled.

In order to overcome this difficulty, it is proposed in accordance with the present invention to provide arrangements in the dial oiice whereby the tester by dialing from the distant oice can remove the ofhce trunk equipment from the trunk conductors at the community dial office and short-circuit the trunk conductors so 4as to make measurement for faults. One of the features of the invention is to provide arrangements for preventing interference with calls in progress over the trunks.

shown applied to trunk units involving two side circuits and a phantom provided with composite circuits for signaling over the trunks, but it will be understood that the principle of the invention may be applied equally Well to simple telephone trunks.

Considering the invention in its more specic aspects, the side circuits and phantom of each phantom group are provided with connections leading to switching apparatus for establishing connections to local subscriber circuit-s, as well as multiple co-nnections appearing in the banks of selector switches whereby connection may be established from local subscriber circuits to the trunks. Inaddition to these connections, the side circuits of the phantom combination are provided with special terminals for testing purposes, and the apparatus is so arranged that when a direct connection is established from the distant office to one of these testing terminals, the composite signaling leads of the corresponding side circuit are disconnected and the side circuit is short-circuited. At the same time the side circuit and the phantom trunk (but not the other side circuit of the group) are arranged to test busy at the dial office.

An arrangement is also preferably provided to delay the opening and shorting of the trunk conductors, as above described, for a short interval. This interval is made available, so that if a local subscriber should by error dial the number assigned to one of the special testing terminals, he will be able, upon hearing a warning tone, to hang up without disturbing the trunk.

Inaccordance with the invention, provisions are also made to trip the ringing apparatus and to place a busy tone on the special testing terminal to serve as the signal for a subscriber to hang up in case he dials through error a number assigned toa testing terminal. At the end of the delay period the busy tone is changed to a dial tone. Where the connection has been established to the special terminal by the tester at the distant oice, this change to the dial tone indicates to the tester that the circuit has functioned and he may, therefore, proceed with his test.

The test circuit is also preferably so arranged as to prevent the opening and shorting of the trunk conductors, if either the desired side circuit or the phantom superposed thereon is busy, or becomes busy during the delay period. After the delay period is over, if either the desired side circuit or the associated phantom remains busy, the opening and shorting of the trunk conduc- AS illustrated, the invention is tors will be held up until both the side circuit and the phantom circuit become idle. Since the other side circuit is not interfered with by the testing operation, the busy or idle condition of such other side circuit need not afect the establishment of the testing connection to the desired side circuit.

The invention will now be more ully understood from the following detailed description when read in connection with the accompanying drawings. In the drawings, Figure 1 shows a phantom trunk combination extending from a central office to a community dial office, together with the testing equipment at the latter oliice whereby the trunks may be tested from the central ofce; Fig. 2 shows a schematic layout of the switching equipment at the community dial oince to indicate how connections are established between subscribers at the community dial oice, how connections are made from subscribers lines to the trunks, and also how connections may be established to the special testing connections of the side circuits; and Fig. 3 shows an alternative type of timing circuit which may be substituted for the simple timing circuit illustrated in connection with Fig. l.

In Fig, 1 the central oiice of a city shown at the left is connected to an outlying community dial oilice shown at the right by means of three trunks comprising two side circuits and a superposed phantom. For this purpose a pair of conductors T1, extending from the central office to the community dial oiiice, serves as one side circuit and is connected through side circuit coils SG1 and SC1 to the side circuit terminals SSi and SS1 at the central office and the community dial ofiice, respectively. Similarly another pair of conductors T2 serving as the other side circuit is associated through side circuit coils SC2 and SC2 with side circuit terminals SSZ and SSz at the central oice and community dial oflice, respectively. From the midpoints of the primary windings of the side circuit coils above referred to phantom connections extend to the primaries of phantom coils PC and PC associated with the phantom terminals PS and PS' at the central oiiice and community dial oice, respectively.

The apparatus above referred to comprises one unit of three talking trunks extending between a central oilce and a community dial office. As many additional such units may be provided as are necessary to take care of the traflic between the central office and the community dial oiiice.

The switching apparatus for the community dial ofllce is schematically indicated in Fig. 2. Here two line circuits L1 and L2 extending to subscribers equipment (not shown) are illustrated and are intended to be representative of a larger number or" similar subscriber circuits. Each subscribers line has associated therewith line terminal equipment such as LT1 and LTS. of a well-known character, and terminates in multiple, tip, ring and sleeve contacts appearing at various line nder switches such as LF. Each of the lines also has multiple connections, consisting of a tip and ring for talking purposes and a sleeve for testing purposes, extending to the terminal banks of connector switches such as C. Throughout the drawings where similar groups of three conductors appear on the drawings, the upper wire will represent the tip conductor, the middle wire, the ring conductor and the lower wire the sleeve conductor. Ihe talking conductors are drawn in heavy lines in order that they will stand out more clearly from the associated circuits.

If the subscriber of one of the lines such as L1 should take his receiver oi the hook, the closing of the circuit would in a well-known manner condition the line terminal equipment LT1 to set the line finder equipment LFE of an idle finder LF into operation, thereby causing the brushes LFB of the line finder to hunt the calling line. As soon as the test brush of the line nnder comes in contact with the test terminal associated with the line L1, the line finder will come to rest because it iinds battery voltage appearing upon the sleeve terminal of the line. A connection is now established from the line L1 to a selector S4 associated with the line nder LF.

vThe selector is illustrated as an up-and-around switch of the step-by-step or Strowger type. While the description herein refers more particularly to this type of switch, it will be understood that the various line nder, selector and connector switches may be of other known types, such as relay switches, cross-bar switches, etc.

To complete a connection to another subscriber the calling subscriber will rst dial the hundreds digit of the wanted subscribers number. This will step the brushes SB4 of the selector Si to a particular level. In this level are contacts connected to connector switches such as C, adapted to establish connections to any subscriber of the group in which the wanted subscriber is located. Upon being stepped to this level, the brushes are then rotated automatically to the various contacts in this level until one is found whose sleeve terminal is not busy, i. e. not grounded. Assuming that the connector C is not busy, the brushes S134 will then stop on the contacts connected to the connector C. The subscriber then dials the tens digit of the wanted subscribers number to directively step the brushes CB of the connector C to the proper level. Next the dialing of the units digit causes the connector equipment CE to directively step the brushes CB around over the contacts of that bank to the particular group of three contacts multipled to the terminals of the wanted subscribers line, which it may be assumed is the line L2.

If the line L2 is not busy, it will not have ground applied to the sleeve conductor of its line terminal. In such case the connector equipment of the connector C will complete the talking connection through to the subscriber, apply ringing current to the subscribers line, and apply a busy ground to its sleeve conductor in a well-known manner. As soon as the called subscriber answers, the ringing apparatus of the connector equipment CE is tripped so that ringing ceases and the two subscribers may now converse.

In order to establish connections from the distant central oflice over one of the trunks to a subscriber at the community dial oice, the switching equipment is similar, except that ordinarily no line finders are provided because the number of trunks is too small to justify the use of line Iinders. Instead each of the trunks SS1, PS and SSz has associated with it, as shown in Fig. 2, its own individual selector such as S1, S2 and S3. These selectors are also provided with selector equipment such as SE1, SEz, etc. An operator at the distant office may dial the number of a wanted subscribers line whereupon the associated selector steps its brush in response to the hundreds digit to a particular level leading to a certain group of nal connectors such as C. The final connector is then directively operated toiestablish the connection to the wanted subscribers line. The dialing arrangements for the trunk circuits are of a somewhat different character than those employed for the local subscribers line and will be described in more detail later.

Since any local subscriber can use any one of the trunks which is not busy toestablish a connection to the distant central olice, ther trunks are not given special numbers like those assigned to the subscribers lines. They are not, therefore, reached through nal connectors. Instead, when a community dial subscriber wishes to make a connection to the distant central cnice, he takes his receiver off the hook whereupon a line finder such as LF seeks out his line `and connects it 'to the associated selector S4. The subscriber then dials some especially assigned digit, which causes the selector equipment SE1 of the selector to step` the brushes SE1 to the level at which the terminals of the various central oice trunks appear. l

If, for example, the digit zero is used, the'terminals of the central oice trunks will appear in the tenth level, this being the upper group of ter-` minals shown in connection with selector S4. Each of the trunks such as SS1, PS', SSz have separate connections to terminals corresponding to tip, ring and sleeve. As soon as the brush is stepped to the tenth level, the brushes automatically rotate until the sleeve brush comes in contact with the sleeve terminal of a trunkfwhich4 Returning to Fig. l, it will be noted that transe 1 formers such as SG1, SC'1 are included in' the various trunk circuits so that it is not possible 'to send dial signals or other supervisory signalsjover the trunks in the same manner as withY ordinary subscribers lines. Each of the two sidev circuits is therefore provided with composite setsto furnish composite or CX circuits for dialing' and supervisory purposes.` For example, the side circuit T1 has a composite set CS1 at the central cnice by means of which dial current or low'frequency signals may be sent to or from the com-y posite conductors CX1 and CX2. The composite sets are similar to those employed for superposing telegraph circuits upon telephone pairs.

Each set includes series condensers for passing the higher frequency telephone currents over the side circuits. Shunt coils serve to pass the dial. and other supervisory signals to the composite conductors CX1 and CX2, while substantially preventing telephone currents` from being diverted into these channels. Shunt capacities to ground are also provided to further prevent` telephone currents from being diverted into the composite circuits CX1 and 0X2.

A similar composite circuit CS 1 is associated with the side circuit T1 at the community dial office whereby composite conductors CXfi and CX2 may be extended from the side circuit. These` may be used for dialing` and other purposes as will be described later. Likewise the trunk T2 is provided with composite sets CS2 and 75v CS2 similar to those already described at the central cnice and community dial oiices respectively. These sets provide the composite circuits CXa and 0X4 at the central cnice and CX4 and CX21 at the community dial cnice.

It will thus be seen that four CX or composite circuits are provided. For example, a CX circuit extends from conductor CX1 at the central cnice through the composite set CS1, over the upper conductor of the side circuit T1, thence through the composite set CS1 to the conductor CX1 at the community dial oice. Conductor CX1 eX- tends over a contact ofA the relay B1 to the selector equip-ment SE1 of the selector S1 associated with the side circuit SS'1 at the community dial cnice. This circuit enables an operator at the central cnice to dial the switch S1 associated with the trupkSSi and thereby establish a connection to any desired subscriber at the community dial cnice. This circuitalso enables various supervisory signals identified with the side circuit SS1'-SS'1 to be transmitted between the central cnice and the community dial office during the establishment of connections. It also serves, as already described, when a subscriber by dialing zero at the community dial cnice selects an idle trunk, to establish a supervisory'signal over the trunk SS1-SS1 (if that trunk is idle and hap pens to be selected) to notify the operator at the central office that a call hasl come in over the trunk.

In a similar'manner a second composite circuit is' established over the conductors CX2y and CX2 forvariousv dialing and supervisory signal operations in connection with the phantom circuit P'S-PS. So also a third composite circuitv is established over conductor'CXa, the upper conductor of the side circuit pair T2 and the conductor CX'a, to serve for signaling and dialing in connection with the side circuit trunk SS2 and SS2. A fourth composite circuit is also provided extendingk from the conductor CX4, over the lower conductor ofthe pair T2 to the conductor CX21 at the community dial oiiice. This fourthrconductor is not needed for supervisory signal or dialing purposes, and is, therefore, used as 'an earth potential neutralizing circuit. As this circuit has nothing to do with the invention herein described, the apparatus associated therewith is not illustrated.

As has already been pointed out, when a subscriber at the community dial oflice desires a connection over one of the trunks to the distant central oiiice, such connection is not obtained by a directive action of a connector switch but by stepping the brushes of a selector switch up to a level atJ which all of the trunks appear. An idle trunk is then` picked out by a testing action, and hence each trunk is provided with a terminal at each of the selector switches used by the subscribers lines. In order that access may be had by an attendant at the distant central oice to the side circuits to measure for faults, each side circuit is` also provided with a special terminal which is reached through a connector.

For example, the connector C is provided with sets of contacts which are connected to special testing circuits TC'1 and TC`2 associated with the side circuit pairs T1 and T2, respectively. The sleeve conductors of the special connections TC1 and TC2 are led to relays A1 and A2, the former of which performs certain operations in connection with the side circuit pair T1, and the latter of which performs similar functions with respect to the side circuit pair T2. Relays B1 and B2 are respectively associated with the side circuit pairs T1 and T2 and are controlled by the relays A1 and A2, respectively, to disconnect the CX circuits from the side circuit pairs and short-circuit said pairs, as will be described in more detail later.

A timing circuit T is provided to delay the action of the relays B1 or B2 as the case may be. The interval thus provided enables a subscriber at the community dial oice, who may have dialed one of the circuits TG1 or TC2 by error, to

hang up. It will be understood, of course, that the circuits TG1 and TG2 are given numbers just as are subscribers lines so that they may be dialed from the distant central oiice through selector and connector switches in the usual manner. A relay D is provided which operates whenever the side circuit which is wanted for testing purposes is busy. This holds up the operation of relays B1 and B2 until the Wanted side circuit becomes free. Should the phantom circuit be busy, a relay C` is loperated to hold up the operation of the relay B1 or B2 as the case may be, thereby preventing the establishment of a testing connection until the phantom is free. Thus it will be seen that when a particular side circuit is wanted for testing purposes it cannot be obtained until both the Wanted side circuit and the superposed phantom are free.

The operation of testing a trunk is as follows:

Assuming that an attendant Y at the distant central oice desires to test the side circuit pair T1 for faults, he will order the operator to dial the test circuit TC1 associated with the side circuit pair T1 at the community dial oice. In order to establish sucha connection the operator may use any idle trunk other than thefwanted side circuit and the phantom circuit superimposed thereupon. In other words, the operator can use the other side circuit pair T2, if it is idle, or can use either side circuit or the phantom (if idle) of any other phantom group,

Let us assume that the side circuit pair T2 is idle and is used for establishing the connection. The operator seizes the trunk SS2-SS2 'and dials the number of the testing circuit TC1 over the composite conductor CXa, the upper conductor of the pair T2 and over the composite conductor CXs, which extends over the back contact of the third armature of the relay B2V to the selector equfprnent Sirs ci' the selector switch Ss associated with the side circuit SSz. The selector equipment operates in a well-known manner in response to the hundreds digit'to step the brushes SBa of the selector S3 up to a level in which are located the contacts of circuits leading to connectors having access to the desired test circuit TC1. The selector then hunts for an idle circuit in this level and iinally picks out, say, the circuit leading to the connector C. When the operator dials the tens digit, the connector equipment CEV connection of the testing circuit TC1 to operate f the relay A1.

As soon as the connection is established by the connector C to the testing circuit TC1, the operator at the central oice or the testboard man, if he is listening, will hear a busy tone, tor

the busy tone is normally connected by a circuit extending over the back contact of the iirst armature of relay B2, back contact of the first armature of relay B1, to the common ring conductor of test circuits TC1 and TG2. So long as the busy tone is heard the operator and the testman know that the final operation of the testing circuits has not been completed, as will appear presently.

The operation of the relay A1 completes a circuit at its fourth contact over the slow-operating relay 'IM of the timing circuitfT, said circuit extending from ground over the back contact of the fifth armature of relay B1, front contact of the fourth armature of relay A1 and through the slow-operating relay TM to battery. At its third contact relay A1 prepares a circuit for the relay B1, but this circuit cannot be completed until the slow-acting relay TM operates. Relay TM is slow enough in its operation to delay the action of the relay B1 for such an interval as will enable a subscriber who has dialed the test circuit TC1 by mistake to hang up when he hears the busy tone.

At the front contact of its second armature, relay A1 establishes a connection between the relay D and the sleeve conductor of the side circuit SS'1. Said circuit extends over the back contact of the sixth armature of the relay B1, upper back contact of the relay C, front contact of second armature of relay A1, to slow-release relay D. If the side circuit SS1 is busy, ground will be applied to its sleeve conductor and the relay D will operate to hold open the operating circuit of the relay B1, which is controlled by the timing relay TM, thus preventing any action of the relay B1 so long asthe side circuit SS1 is busy. At the front contact of its rst armature relay A1 establishes a connection between relay C and the sleeve conductor of the phantom PS. Said circuit extends from saidrsleeve conductor over the back contact of the second armature of relay B1, back contact of the second armature of relay B2, front contact of the rstarmature of relay A1 to c. the winding of relay C and thence to battery. If

the phantom circuit PS is busy, ground will appear on its sleeve conductor and the relay C will be operated. At its upper front contact relay C closes another circuit for the relay D which exl tends from ground over said contact of relay C and over the front contact of the second armature of relay A1. Consequently no operation of the relay B1 can take place until both the Wanted side circuit SS1 and its superposed phantom PS' are both idle, so that the busy'ground is removed from their sleeve conductors.

In this connection it should be noted that so far as testing on the side circuit SS1 is concerned, it does not matter whether the associated side circuit SS'z is busy or not, as the one side circuit does not affect the other. It is only the busy condition of the wanted side circuit and the superposed phantom that is important. The side circuit SS2' is at this time busy, of course, because the dialing circuit above described was established over this circuit to operate selector S3, which applied ground to the sleeve conductor of circuit SSz. This does not affect the relay D, however, as the circuit from the sleeve conductor of the side circuit SSz to the relay D is held open at the second armature of the relay A2, which is, of course, not operated at this time.

' In order that the relay B1 may be operated, three conditions must obtain: (l) the relay TM o'f the timing circuit must have operated, and

this operation occurs a definite interval after the selection of the circuit TC1 with the consequent operation of the .relay A1, said interval being determined by the design of the relay TM; (2) the wanted side circuit SS1 must not be busy, for if it is busy, the action of the relay B1 cannot occur until it becomes idle; (3) the superposed phantom PS'1 must not be busy, for if it is busy, operation of the relay B1 cannot take place until the phantom likewise becomes idle.

Let us assume that the slow-operating relay TM has now operated. If the relay D is released at this time, as will be the case when both side circuit and phantom are free, the circuit for the relay B1 will be completed at once. If, however, the relay D is operated, as it will be if either the side circuit SS'1 or the phantom PS' is busy, the operation of the relay B1 cannot talee place. If we assume that the side circuit SS1 is still busy at the time the relay TM operates, the relay D will not be released until the side circuit becomes idle. Assuming the phantom circuit is idle, as soon as the side circuit SS1 becomes free the circuit previously traced over the grounded sleeve of the side circuit SSH through the winding of the relay D will no longer be completed to ground, because the busy ground has been removed from the sleeve conductor of the side circuit SS. Under these circumstances the circuit for the relay B1 will be completed from armature of the relay A1, through the winding of relay B1 to battery.

If on the other hand, after the side circuit becomes idle, the phantom PS is still busy, the relay D will not yet be released. Its circuit will be held closed by the alternative ground connected over the upper front contact of the relay C, which is operated over the grounded sleeve conductor of the phantom circuit PS. As soon as the phantom becomes idle, however, the ground is removed from the sleeve conductor of the phantom, thus releasing the relay C. This in turn releases the relay D, whereupon the relay B1 is operated over the circuit above traced.

Relay B1, by opening the back contact of its number one armature, disconnects the busy tone from the ring conductor of the test circuit TG1, and at the front contact of said armature connects the dial tone to said ring conductor. The operator (or the testman) at the distant central oflice, upon hearing the dial tone, is at once informed that the relay B1 has been operated, and `the 'test connection to be later described has been set up. At the front contact of its `second armature relay B1 connects ground to the sleeve conductor of the phantom circuit PS to render :f-

said phantom circuit busy during the testing operation of the side circuit SS'1. This is necessary because obviously the phantom cannot be used while the side circuit conductors of the pair T1 are being tested. At the front contact of its sixth armature relay B1 similarly applies ground to the sleeve conductor of the side circuit SS1 to render it busy.

At its fifth armature relay B1 opens the cir-cuit of the timing relay TM extending from ground over the back contact of said armature, and over the front contact of the fourth armature of relay A1 to the timing relay TM. The operation oi said fifth armature of the relay B1 also opens the original operating circuit of said relay B1 (which was controlled by the timing relay TM), and locks up said relay B1 over a circuit from ground, over the front contact of the fifth armature of relay B1, over the front Contact of the third armature of relay A1 and through the winding of relay B1 to battery. B1 is, therefore, held locked up so long as the relay A1 is energized. Consequently the relay B1 will not be released until the testing circuit TC1 is released with the consequent deenergization of the relay A1.

At the back contacts of its third and fourth armatures relay B1 opens the dialing and signaling circuits CX1 and CXz associated with the side circuit SS1 and the phantom circuit PS', and at the front contacts of said third and fourth armatures, relay B1 connects a short-circuit across the conductors of the pair T1, through the two coils of the composite set CS'1. side circuit is now in condition to be tested for faults by the testman, during his test the side circuit and associated phantom will be held out of service by the busy ground applied to their sleeve conductors, as already described. Also during the testing operation the dial tone is continuously applied to the ring conductor of the test circuits TG1 and TCz. If a subscriber at the community dial oiiice should dial the number of either the test circuit TG1 or TG2 through a mistake, he would hear the dial tone and would be warned thereby to hang up- It will be observed that when the operator at the distant silice established connections over the side circuit SSZ to the test circuit TG1 by dialing, the connector switch C' connected its talking brushes to the contacts to which the talking conductors of test circuit TG1 are connected. Since the connector C is ordinarily used for establishing connections to subscribers, it is, of course, provided with ringing equipment, and as soon as 'the connection above described was established, ringing current would be applied over the talking conductors oi the testing circuit TC1. A gas tube GT has its electrodes bridged across the talking conductors TG1 and TG2, and the ringing vpotential applied to the former conductors TG1 ionizes the gas in the tube GT and breaks down the resistance between its electrodes. This causes an effect similar to that produced when a subscriber takes his receiver oii the hook and completes a direct circuit connection Vbetween the talking conductors. As is well known, such a connection trips a relay in the connector equipment CE to disconnect the ringing current from the circuit. Consequently when the resistance of the tube GT breaks down, the ringing current is cut olif from the testing circuit TG1. The gas tube GT is of a known type, and is provided with a heated filament which is heated over a circuit (not shown), to produce a sensitive condition of the gas in the tube so that it is easily ionized. As the nature of these tubes is well known, no further description is necessary. It will be understood, however, that a cold cathode tube arrangement may be substituted for the hot cathode tube circuit, if so desired.

It will be noted that the short-circuit across the conductors of the pair T1 is established by means of contacts in the composite leads CX1 and CX2 instead of by means of contacts directly connected in the conductors of the pair T1 themselves. This is a desirable arrangement, as it avoids any unbalance as between the conductors ci the pair T1 due to variations in contact resistance.

When the testing operation is completed, the

operator will cause the release of the connector switch C in the usual manner. This releases the relay A1, which in turn releases the relay B1 and restores the circuits, including the composite legs, to normal.

Should it be desired to test the pair T2, the number of the test circuit TCz will be dialed over another trunk, thereby causing the operation of the relay A2. The relay A2 at its fourth armature completes a circuit for the timing relay TM, and if the side circuit SS2 and the phantom PS are idle, so that their sleeve conductors are ungrounded, the relays C and D will not be operated. In such case relay A2 in conjunction with the timing relay TM will complete a circuit for the relay B2 from ground, over the front contact of the timing relay TM, back contact of the relay D, auxiliary back contact of the fifth armature of the relay B2, front contact of the third armature of the relay A2, and through the winding of the relay B2 to battery.

Relay B2 at its upper armature disconnects the busy tone from the ring conductor of the circuit TC2, and applies dial tone over the front Contact of said armature, and over the back contact of the number one armature of relay B1, to said ring conductor. At its second and sixth front Contact respectively, relay B1 applies busy ground to the sleeve conductors on the phantom circuit PS and the side circuit SSz. At its third and fourth armatures relay B2 opens the composite circuit CX3 and CX'4 and establishes a short-circuit between them, thus in eplect short-circuiting conductors of the pair T2. It will be noted that this disconnects the ground potential neutralizing circuit CX21 from the lower conductor of the pair T2. In order to prevent improper action of the neutralizing circuit, the fourth armature of the relay B2 is provided with an auxiliary front contact which, when the auxiliary circuit CX21 is opened, connects the network N to said auxiliary circuit.

The timing circuit T, which depends upon the action of a simple slow-acting relay TM, is so designed that the relay TM operates in an interval oi about fifteen to thirty seconds. If a more precise interval of time is desired to enable hanging up of his receiver by a subscriber who has dialed the testing circuit in error, a timing circuit T', such as shown in Fig. 3, may be substituted for the testing circuit T at the points a and b. This employs a gas tube GT' of a cold cathode type.

The operation of this circuit is as follows:

`When ground is applied to the point a in Fig. 3

in response to the operation of one of the relays A1 or A2 of Fig. 1, the relay 2li is operated. This connects 90 Volt battery through a resistance 2l to charge a condenser 22. This condenser is of such capacitance that after a predetermined interval the potential across it becomes sufficiently high to cause the gas in the tube GT to be ionized and break down the resistance through the tube. This causes current to iiow from the ground connected to one of the electrodes of the tube through the relay 23 to battery, thereby operating said relay 23. Relay 23 at its upper front contact connects ground to the point b to operate the relay B1 or B2, as the case may be. At its lower armature relay 23 opens the circuit of relay 28 and completes locking circuit for its own winding from point a, through the resistance 24, and through the winding of relay 23 to battery. Relay 2li upon releasing connects ground through the resistance 2l to the condenser 22 causing the latter to discharge and restore tube GT to normal.

It will be obvious tha the general principles herein dislcsed may be embodied in many other organizations widely different from those illustrated Without departing from the spirit oithel invention as defined in the following claims.

What is claimed is:

1. In a communication system, a central ofce, an unattended community dial cnice, a trunk extending between said offices, subscribers lines entering said community dial office, dial operated switching apparatus at said community dial oiiice to establish connections between subscribers lines at said oiiice and to establish connections between such lines and said trunk, a testing terminal for said trunk at said community dial oiiice, and means whereby said terminal may be dialed from said central clce, said means including means whereby said trunk is shortcircuited to establish a testing condition cn said trunk at said community dial omce.

2. In a communication system, a central ofce, an unattended community dial oiiice, a trunk extending between said oiiices, subscribers lines entering said community dial office, dial operated switching apparatus at said community dial ofce to establish connections between subscribers lines at said cfce and to establish connections between such lines and said trunk, a testing terminal for said trunk at said community dial oiiice, and means whereby said termina] may be dialed from said central oice and said trunk short-circuited for testing purposes at said community dial office.

3. In a communication system, a central ofiice, an unattended community dial oflice, a trunk extending between said offices, subscribers lines entering said community dial cnice, dial operated switching apparatus at said community dial ofiice to establish connections between subscribers lines at said ofiice and to establish connections between such lines and said trunk, a testing terminal for said trunk at said community dial oiiice, means whereby said terminal may be Vdialed from said central oice to short-circuit said trunk to establish a testing condition on said trunk at said community'dial oce, and means to delay the establishment of such condition a predetermined time to permit a subscriber to hang up without interfering with the trunk in case the subscriber should erroneously dial the number of said test terminal.

4. In a communication system, a central cffice, an unattended community dial oii'lce, a trunk exending between said oiiices, subscribers lines entering said community dial oiice, dial operated switching apparatus at said community dial oiiice to establish connections between subscribers lines at said oice and to establish connections between such lines and said trunk, a testing terminal for said trunk at said community dial oflice, means whereby said terminal may be dialed from said central oice to short-circuit said trunk to establish a testing condition on said trunk at said community dial oi`ce, means to delay the establishment of such condition a predetermined time to permit a subscriber to hang up without interfering withthe trunk in case the subscriber should erroneously dial the number of said test terminal, and means to indicate to such subscriber that he has established a connection to a test terminal as distinguished from a line.

5. In a communication system, a central oiiice,

an unattended community -dial oice, ia trunk `extending between said oflices, subscribers lines entering said community dial oice, dial operated switching apparatus at said community dial office to establish connections between subscribers lines at said office and to establish connections between such lines and said trunk, a testing terminal for said trunk at said community dial olice, means whereby said `terminal may be dialed from said central oice to short-circuit said trunk to establish a. testing condition on said trunk at said community ldial oice, and means to prevent the establishment of such test conditions when the trunkwhose test terminal is dialed happens to 'be busy.

6. In a communication system, a central ofce, an unattended community dial oce, a trunk extending between said oices, subscribers lines entering said community dial cnice, dial operated switching apparatus at said community dial oilice to establish connections between subscribers .lines at said oflice and to establish connections between such lines and said trunk, a testing terminal for said trunk at said community dial oliice, means whereby said terminal may be dialed from said Acentral oflice to short-circuit said .trunk to establish a testing condition on said trunk at said community dial oflice, means to prevent the establishment of such test conditions when the trunk whose test terminal is dialedhappens to be busy, and means to automatically establish said test condition when the trunk ceases to be busy.

'7. In a communication system, a central office, an unattended community dial oili'ce, a trunk extending between said offices, subscribers lines entering said community dial cnice, dial operated switching apparatus atsaid community dial oiiice to establish connections between subscribers lines at said oiiice and to establish 'connections between such lines and Vsaid trunk,A a testing terminal for said trunk at said community dial oiiice, means whereby `said .terminal may be dialed fromsaid central office to short-circuit said trunk to establish a testing condition on said i trunk at said community dial oflice,.and means to render said trunk busy when said testing condition has been established.

8. In a communication system, a central ofiice, an unattended community dial oillce, a group of trunks including two side circuits and-a phantom extending between said oflices, subscribers lines entering said community dial oice, .dial operated switching apparatus at said community dial oiiice to establish connections between 'subscribers lines at said oflice and to establish connections between such lines `and any of said trunks, a. testing terminal for each of said side circuits at said communityfdialfolice, and means whereby the testing terminal of any side circuit trunk may be dialed from the central oilice, said latter means including means "to short-circuit any side circuit trunk dialed to establish a testing condition on said trunk at the community dial oiiice.

9. In a communication system, a central ofce, an unattended community dial oflice, a group of trunks including two side circuits and a phantom extending between said offices, subscribers lines entering said community dial office, dial operated switching apparatus at said community dial ofce to establish connections between subscribers lines at said oiice and to establish connections between such lines and any of said trunks, a testing terminal for each of said side circuits at said community dial office, and means whereby the testing "terminal of any side circuit trunk may be dialed from the `central office and :said trunk short-circuited for testing purposes at said community dial office.

10. 'In a communication system, a central ofiice, Aan `unattended community dial ofce,a group of .trunks including two side circuits and a phan- -tom extending between said oices, subscribers lines entering said community `dial ofce, dial `operatedfswitching'apparatus at said community 4dial oilicezto establish connections between subscribers lines at said office `and to establish connections between such lines and any of said trunks, a testing `terminal for each of said side circuits atsaid community dial oflice, composite circuits ior said trunks established over the conductors of said side circuits, one of said cornposite circuits 'being assigned `to each trunk for dialing and `signaling purposes, and means wherebythe testing terminal of any side circuit trunk may be dialed from the central oice to short-'circuit the latter side circuit trunk to establish ra testing condition on said trunk at the community'dial office.

l1. In a communication system, a central ofce, 1a :community dial oiiice, a group of trunks :including two side circuits and a phantom eX- tending Ybetween said offices, subscribers lines entering said community dial office, dial operated switching 4apparatus at said community dial ofce to establish connections between subscribers lines at said office and to establish connections between such lines and'any of said trunks, a testing terminal for each of said side circuits at said `community dial oice, composite circuits for said trunks established over the conductors of said side circuits, one of said composite circuits being assigned to each trunk for dialing and signaling purposes, and means whereby the testing terminal o-f lany side circuit trnuk may be dialed from vthe central oflice to disconnect said i composite circuits from the trunk at the community dial oflice and short the conductors oi the side circuit at the terminals of said composite circuits to put the trunk in condition for testing.

12. In a communication system, a central office, an unattended community dial oflice,

ya group of trunks including two side circuits and a phantom extending between said oices,

subscribers lines entering said community dial oiiice, dial operated switching apparatus at said community dial ofhce to establish connections between subscribers lines at said oilice and to establish connections between such lines and any of said trunks, a testing terminal for each of said side circuits at said community dial of-oe, means whereby the testing terminal of any side circuit trunk may be dialed from the central oice to short-circuit said trunk to establish a testing condition on said trunk at the community7 dial office, and means to delay the establishment of such lcondition a predetermined time to permit `a subscriber to hang `up without interfering with the trunk in case the subscriber should erroneously dial the number of the test terminal of the trunk.

13. In a communication system, a central office, an unattended community dial oice, a group of trunks including two side circuits and a phantom extending between said oilices, subscribers lines entering said community dial office, dial operated switching apparatus at said community dial office to establish connections between subscribers lines at said office and to establish connections between such lines and any of said trunks, a testing terminal for each of said side circuits at said community dial oice, means whereby the testing terminal of any side circuit trunk may be dialed from the central oice to short-circuit said trunk to establish a testing condition on said trunk at the community dial oce, means to delay the establishment of such condition a predetermined time to permit a subscriber to hang up without interfering with the trunk in case the subscriber should erroneously dial the number of the test terminal of the trunk, and means to indicate to such subscriber that he has established a connection to a test terminal as distinguished from a line.

14. In a communication system, a central ofiice, an unattended community dial oiiice, a group of trunks including two side circuits and a phantom extending between said oiiices, subscribers lines entering said'community dial office, dial operated switching apparatus at said community dial office to establish connections between subscribers lines at said oflice and to establish connections between such lines and any of said trunks, a testing terminal for each of said side circuits at said community dial oilice, means whereby the testing terminal of any side circuit trunk may be dialed from the central office to short-circuit said trunk to establish a testing condition on said trunk at the community dial oflice, and means to prevent the establishment of such test conditions when the trunk whose test terminal is dialed happens to be busy.

15. In a communication system, a central ofce, an unattended community dial oii'ice, a group of trunks including two side circuits and a phan tom extending between said olices, subscribers lines entering said community dial oiiice, dial operated switching apparatus at said community dial oiiice to establish connections between subscribers lines at said oihce and to establish co-nnections between such lines and any of said trunks, a testing terminal for each of said side circuits at said community dial cnice, means whereby the testing terminal of any side circuit trunk may be dialed from the central oftlce to short-circuit said trunk to establish a testing condition on said trunk at the community dial odice, means to prevent the establishment of such test conditions when the trunk whose test terminal is dialed happens to be busy, and means to automatically establish said test condition when the trunk ceases to be busy.

l5. In a communication system, a central ofrice, a community dial cnice, a group of trunks including two side circuits and a phantom eX- tending between said offices, subscribers lines entering said community dial oiiice, dial operated switching apparatus at said community dial ofce to establish connections between subscribers lines at said oiiice and to establish connections between such lines and any of said trunks, a testing terminal for each of said side circuits at said community dial omce, means whereby the testing terminal of any side circuit trunk may be dialed from thev central oiice to establish a testing condition on said trunk at the community dial oiiice, and means to prevent the establishment of such test conditions when either the trunk whose test terminal is dialed or a phantom trunk composited thereon happens to be busy.

17. In a communication system, a central ofce, a community dial olice, a group of trunks including two side circuits and a p-hantom extending between said oi'ices, subscribers lines entering said community dial oliice, dial operated switching apparatus at said community dial oiiice to establish connections between subscribers lines at said oice and to establish connections between such lines and any of said trunks, a testing terminal for each of said side circuits at said community dial oiice, means whereby the testing terminal of any side circuit trunk may be dialed from the central office to estab lish a testing condition on said trunk at the community dial olce, means to prevent the establishment'of such test conditions when either the trunk whose test terminal is dialed or a phantom trunk composited thereon happens to be busy, and means automatically to establish said test condition when both of said trunks cease to be busy.

18. In a communication system, a central oflice, an unattended community dial ofce, a group of trunks including two side circuits and a phantom extending between said offices, subscribers lines entering said community dial office, dial operated switching apparatus at said community .dial oiiice to establish connections between subscribers lines at said oiiice and to establish connections between such lines and any of said trunks, a testing terminal for each of said side circuits at said community dial oice, means whereby the testing terminal of any side circuit trunk may be dialed from the central oice to short-circuit said trunk to establish a testing condition on said trunk at the community dial office, and means to render said side circuit trunk busy when said testing condition has been established.

19. In a communication system, a central office, a community dial oce, a group of trunks including two side circuits and a phantom extending between said ofces, subscribers lines entering said community dial cnice, dial operated switching apparatus at said community dial ofi'lce to establish connections between subscribers lines at said office and to establish connections between such lines and any of said trunks, a testing terminal for each of said side circuits at said community dial oilce, means whereby the testing terminal of any side circuit trunk may be .dialed from the central ofiice to establish a testing condition on said trunk at the community dial oice, and means to render said side circuit trunk and the phantom trunk composited thereon busy when said testing condition has been established,

MASON BAIN WILEY.

ANTHONY FORESTER.

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