USRE23056E - Relay automatic telephone system - Google Patents

Description

Dec. 7, 1948. J. H. voss RELAY AUTOMATIC TELEPHONE SYSTEM 0 C) 8 l 61+ 5 O. 2 3 O 2 g a r 0 10 Sheets-Sheet 1 Original Filed Dec. 12, 1945 ITO m E M m 1 I 1 1] ..Fl I I MM B W T w m n w w M m r U Q B. o m E Tm mm mm INVENTOR. JOHN H. MOSS ATTOR N EY 1948- J. H. voss Re. 23,056

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PouJum @5010 INVENTOR. JGIN H. VOS BY ATTORNEY Reiuued Dec. 7, 1948 Examiner UNITED STATES PATENT OFFICE RELAY AUTOMATIC TELEPHONE SYSTEM John H. Voss, Rochester, N. Y., assig'nor to Automatic Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware 19 Claims.

The present invention relates in general to telephone systems, but more particularly to small community automatic exchanges or C. A. X's of the all relay typ generally similar to that described in Patent No. 2,333,039, issued October 26, 1943, to Edward S. Peterson.

An automatic telephone system of this type must be low in cost, and yet must provide most of the services provided with a larger system, plus some additional. It usually has a capacity of less than 200 lines, and should be sumciently flexible to permit adding or changing lines or services with a minimum of disturbance. For reasons of economy, many of the lines in such a system will be multi-party lines, and as likely as not, code ringing will be employed for signalling, particularly with the smaller'switchboards.

Such an exchange will usually not have any toll operator, but must provide means whereby any subscriber can get access to an idle trunk leading to a toll operator at some nearby exchange, easily and quickly. Means must also be provided whereby a special subscriber, or a local or distant operator, may have easy access to groups of direct trunks to certain other ex changes. Provision must also often be made for additional trunk groups leading to one or more private branch exchanges or P. B. X's, in the community.

It is the main object of the present invention to provide improved means for automatically selecting idle toll, inter-ofllce or P. B. X trunks in an all relay system of the character described, without any sacrifice of speed, convenience or flexibility. Speed is obtained by the pre-selection of idle trunks, in all cases. Convenience is achieved through the use of single-digit call numbers for all toll and inter-omce trunks, with four-digit call numbers used in all other cases. Finally, flexibility is obtained through provisions permitting the assignment of trunks and subscribers lines to any tens group, under normal circumstances.

Another object of the invention is to provide separate points of access for light traliic and heavy traffic trunk groups, thereby to permit calls to both classes of trunk to proceed simultaneously, and independently of each other.

A further object of the invention is to provide a separate point of access for P. B. X trunks, so as to permit calls to such trunks to proceed simultaneously with calls to other classes of trunks, without delay or interference between them.

Still another object of the invention is to provide means whereby two trunk groups may be assigned in the same tens group, thus avoiding in certain cases, the use of more tens relays than are actually required, in the links.

Other objects and features of the inventio will be apparent from the specification and claims following, considered in conjunction with the accompanying drawings comprising Figs. 1 to 11, which show one embodiment of the invention as applied to a line all relay system of the type described. It should be understood that the arrangement illustrated is merely one embodiment of the invention and not necessarily the preferred embodiment, and that numerous modifications and rearrangements thereof are possible, without departing from the spirit or scope of the invention as disclosed.

Referring to the drawings, Figs. 1 to 5 inclusive, when arranged as indicated in Fig. 11, with adjoining lines abutting, represent the essential parts of one of the connectors employed in the all relay links of this system. For purposes of simplicity, various special features of this connector, such as restricted service, reverting call facilities, timing of permanents or shorted lines, and incompleted calls, and the timing of conversations, have been omitted. For similar reasons, the finder end of the link has also been omitted, together with the associated allotter or link selector, common control relays, and line circuit. These parts are not considered necessary to an understanding of the invention, and furthermore, are very similar to those disclosed in the Patent No. 2,333,039 issued to Edward S. Peterson, previously mentioned. The same 3- relay line circuit is employed, with the same cut-of! and lockout relays in series, and provisions for disconnecting the line control or C lead through the finder from the associated control normal or CN lead to the connector terminals, whenever the line relay of the line circuit is operated, and for reconnecting them when the line relay is restored to normal. The finder is also identical, with the same arrangement of tens and units relays, and the units divided into the same two sub-groups 1 to 5 and 6 to 0, controlled by five units relays and one sub-group relay.

Figs. 6 to 8 inclusive, when likewise arranged as indicated in Figure 11, with respect to one another and the connector, represent the various types of additional equipment required to provide the automatic trunk selecting features already mentioned. In Fig. 6, for example, the relays on the left of the sheet are the Group access relays, whose function is to pass trunk calls from the connectors to the proper trunk groups, in regular order, by way of the Group select relays on the right of the same sheet. The operation of one of the group select relays, in conjunction with an operated one of the group access relays. extends the units conductors and the busy conductor of the connector, through to the proper group of Trunk select relays such as indicated by the rectangles 655 and 656, or such as shown in the upper part of Fig. 9.

Fig, 7 shows a group of P. B. X trunk select relays" whose function it is to pre-select the next idle trunk in the associated P. B. X trunk group, by preparing, in advance, a circuit to the connector units relay or relays corresponding to said next idle trunk. This circuit becomes effective immediately whenever these relays are seized by a connector. The P. B. X select relays are reached directly from the connector, no intervening group access or group select relays being provided. For this reason, the select relays of this group require separate sets of units-controlling contact springs for each connector.

Fig. 8 shows a separate group of Trunk access relays associated with a second group of trunks in the same tens group, in this case, group 30. The function of these relays is to pass trunk calls from the connectors to the associated trunk group by way of a separate set of trunk select relays, such as indicated in the lower part of Fig. 9, no intervening group select relays being employed. The operation of one of the trunk access relays therefore, extends the units conductors and the busy conductor of the connector direct to the trunk select relays involved.

Fig. 9 shows the arrangement of the trunk select relays, two separate groups being indicated, both associated with the tens group 30. The function or these relays is to pre-select the next idle trunk in the associated trunk group. This they do by preparing, in advance, a circuit to the connector units-relay or relays corresponding to said next idle trunk. This circuit then becomes effective whenever the trunk select relays are seized by the group access and group select relays or by the trunk access relays.

Fig. 10 shows a schematic layout of the Figs. 1 to 9 on a single sheet with circuit details omitted, and only the basic interconnections indicated in order to more clearly portray the relationships between the various figures. Thus the two rectangles I000 to I M at the left represent two identical connectors such as shown in the Figs. 1 to 5 inclusive, while the two rectangles I020 and I030 immediately adjacent represent the Group access relays of Fig. 6 and the Trunk access relays of Fig. 8 respectively. The rectangle I040 represents the Group select relays of Fig. 6; the rectangles I050 and I060 on the extreme right of the sheet represent the Trunk select relays indicated at 655 and 656 in Fig. 6; and the rectangle I010 represents the group of trunk select relays shown in the upper half of Fig. 9, Rectangle I080 on the other hand represents the Trunk select relays in the lower part of Fig. 9, and rectangle I090 the P. B. X trunk select relays of Figure 7. With respect to the interconnections, the upper three leads at the connectors, marked GSIO, G820, G830 are outgoing group select" leads, and directly under these is an incoming group select ground lead marked GSG. Below this are two outgoing "group access leads designated GA and GA2. and underneath this-is an incoming units" lead, which actually represents the five possible numerical units leads plus the units sub-group lead. Still below all of these are three additional leads to the P, B. X trunk select relays, including an outgoing sub-group select lead and a P. B. X trunk select lead designated US and TS respectively. and a second incoming units lead representing again a possible five units leads and a units sub-group lead. Both sets of units leads are multipled together inside of the connector, as shown in Fig. 4.

To continue the description of the equipment shown in the individual circuit drawings in somewhat greater detail, Fig. 1 shows the incoming end of a connector in one of the finder-connector links of this system. Conductors and 8| at the upper left of this figure are the talking conductors from the finder, where of course, they may be connected as required to any calling line, and are so connected, almost instantly, upon the initiation of a call. Conductor 82 is a supervisory conductor from the finder, where it is grounded or not grounded on a call depending on the nature of the calling line, and whether or not reverse battery supervision is desired. Conductor 83 is the line control or C conductor to the finder where it is switched through to the line circuit of a calling line at the same time that the talking conductors are connected to the calling line. This conductor is grounded in the connector, immediately upon the seizure of this equipment by a call. Conductor 84 is the hold conductor which is also grounded in the connector immediately upon its seizure by a call, and serves to lock up the operated tens and units relays of the finder preparatory to the release of the allotter and the associated common equipment. Conductors 05 and 86 are looking conductors, which are opened in the connector upon its seizure to prepare the release of the associated link select relay in the allotter, thereby to permit pre-selection of the next idle link. The other, open ended conductors in this figure go to the tone and timer equipment, the ringing interrupter and the ringing generator as indicated. The ringing interrupter places negative battery on conductor 88 during each ringing cycle, and momentarily on conductor 89 just before the start of each ringing cycle.

Fig. 1 also comprises ten relays as shown numbered I00 to I90 inclusive. Relay I00 is a switch through relay which operates on a call to a trunk, to by-pass the talking condensers and connect the talking conductors straight through to the trunk repeater, which then takes over the normal function of the connector such as timing, pulse repeating, and the like. Relay H0 is the connector line relay, which operates over the talking conductors 80 and 8| upon seizure of the connector, and causes the operation of the release relay I30 and the hold relay I40. Relay I20 is the battery reversing relay, normally controlled from the back bridge relay I60. Relay I50 is the counting chain release relay which controls the resetting of the pulse counting relays after each digit of the call number dialled by the calling party. Relay I10 is the ringing digit switching relay which operates upon the dialling of the ringing digit to prepare the ringing circuits; relay I80 is the pickup relay which operates from the ringing interrupter to assure that the ringing current will be connected to the called line only at the start of a ringing cycle; and relay I90 is the ring-cut-off relay which operates to stop the ringing, when the called party answers.

Fig. 2, which is a continuation of the connector circuit, consists also of ten relays, numbered 200 to as indicated. Relay 200 is a drain relay,

which operates in conjunction with the ring coding relay 220, to prevent ringing voltages from being stored up in the line. Relay 2 I I) is the ring switching relay, which is controlled from the sixth counting relay, and determines which side of the called line is to be rung. Relays 230 and 240 are the busy test and idle test relays, which determine the busy or idle condition of the called line, relay 250 is the preliminary digit switching relay, and relays 260 to 280 are digit transfer relays which operate in succession after the first, second and third digits of a local call number, to prepare various switching and control circuits which will be discussed in more detail in the description of the operation. Relay 290 on the other hand is a dialling transfer relay, which operates on each digit of a call number, to hold the switching circuits open during the actual pulsing, and releases to close them after each digit.

Fig. 3 contains ten counting chain relays designated 3"! to 300 inclusive and three counting chain control relays Sill, 320', and 330. These counting relays control the outgoing switching circuits of the connector, and operate in response to the dial pulses, as repeated over the pulsing circuit of the connector. The counting relays operate in succession during the first half of each pulse, and a counting control relay operates in series with them during the second half of each pulse, each pair of relays being released when the succeeding pair operates. The counting control relays are used reflexively, so that relay 3H) will operate with counting relay 3 l 0, and also with relays 340, 310 and 3M. Likewise, relay 320' will operate with counting relays 320, 350 and 380, and relay 330 with counting relays 330, 360 and 390. The last operated relays complete the switching operations required, between digits, and then also release, in preparation for the succeeding digit.

Fig. 4 shows a portion of the connector tens and units relays, together with the units switching or sub-group relay 400. Only one tens or group relay is shown, that being the relay 410 in the upper right corner of the sheet, representing the first tens group, also designated as group Till. These tens group relays are operated selectively by the counting relays in response to the dialling, and when operated connect the outgoing talking and control conductors of all ten lines or trunks in that group to the switching springs of the r various units relays. To save space, only 4 lines are shown outgoing from relay "0, these being the first, fiIth, sixth and tenth, or more properly, lines ll, I5, I5 and I'll, represented by the four sets of three conductors each, extending to the right from relay "ll. In a fully equipped H10 line switchboard, ten of these relays would be required in each connector. A total of five units relays is also provided in each connector, although only two are shown in Fig. 4. These are the relays llll and 450 representing the units 1 and 6, and 5 and respectively. The units relays are also operated selectively by the counting relays, or indirectly by the trunk selecting relays, and when operated, each relay serves to connect two sets of talking and control conductors from the tens relays to the break-make springs of the units switching relay. As to which of these sets is actually connected through to the talking and control conductors I58, I65 and M in the connector, depends on the position of the units switching relay 400 which is also controlled from the counting relays or from the trunk selecting relays in the same manner as the units relays, to determine the units sub-group. With relay "0 normal, the 1 to 6 sub-group is involved, and with relay 400 operated, the 5 to 0 sub-group is indicated. Thus with relays I10 and H0 operated, if relay 400 is normal, the connector will be cut through to line H, by way of back contacts I, 402 and 4, make contacts ll I, 2 and H3, and make contacts 415, 415 and 411; while if relay "0 is operated, the connector is cut through instead to line l6, by way of make contacts 401, 402 and 404, make contacts 4, H5 and H5, and make contacts 48!, 482 and 483. And so on, for the entire ten lines of the group controlled by the group relay 410.

In Fig. 5 are shown additional tens or group relays designated 520, 530 and 550 representing groups 20, and 50 respectively. Each of these relays is identical with the group relay I'll of Fig. 4, and operates similarly, except that group relay 550 is associated with the P. B. X trunks. As in the case of relay "ll, only four sets of line conductors are shown outgoing from each of these relays, all having corresponding values. Thus with reference to group relay 520, the four lines indicated represent the lines II, 25, 25 and 20, in that order, while the four lines shown outgoin from the springs of relay 53!! represent the lines 3|, 35, 36 and 30. And for relay 550, the outgoing lines shown are the lines 51, 55, 5E, and 50.

These group relays operate from the counting relays, in conjunction with the units and sub-group relays to select the dialled line, exactly as explained for the group relay 410 of Fig. 4.

In Fig. 6, a group access relay such as 5 I II, 520 or 630 is provided, for each connector in the system, although only three are indicated in this case. These relays operate when seized by the associated connector on a trunk call and connect the units switching leads ,from the connector through to the group select relays to the right of this figure. The group access relays are operated only momentarily, and are provided with a special lockout chain which prevents a second relay operating while any other relay is operated, in order to prevent, or reduce the likelihood of double connections. Lockout relay 5 and kick-oft relay 650 are common relays which are also a part of the group access relays. Relay 540 operates momentarily when any access relay is operated, to open the operate circuit of the other access relays, and if the call is not cut through promptly, relay 550 restores to give the busy signal and at the same time preselect the next idle trunk. A group select relay, such as 650, 510 or 680 in Fig. 6, is provided for each tens group to which toll or interomce trunk groups have been assigned. These relays operate from the tens relays in the connector, from a special ground provided by the group access relays, and extend the units switching leads from the operated access relay, through to the proper trunk select relays.

In Fig. 7 is shown a complete set of trunk select relays for a P. B. X trunk group having a total of ten trunks. In practice, in a small town, such a large group of P. B. X trunks would seldom if ever be required, and the number of relays would be reduced accordingly. However, the complete set is shown here, to better indicate the arrangement. The relays shown in the lower row, such as H0, I20, etc., are the trunk busy relays, one of which is required for each trunk in the group except the last. This applies regardless of the number of trunks involved. One of these relays is connected to the test conductor of each trunk in the group but the last, and operates from ground on this lead whenever the associated P. B. X trunk is engaged. The relays shown in the upper row. such as H5, 125, etc., are the trunk select relays, and one of these is required for each P. B. X trunk in the group. They are controlled entirely from the trunk busy relays, and no more than two of these relays including the first, can be operated at any given time. The function of each of these relays is to prepare a circuit to the corresponding units relay or relays in the connector, which circuit is completed in response to the dialling of the third digit in the P. B. X call number. Since no locking circuit is provided, the first idle trunk is selected in all cases. Separate sets of units and sub-group contacts must be provided on these relays for each connector in the system.

In Fig. 8, a trunk access relay such as Bill, 820, or 830 is required, for each connector in the system, although here also, as for the group access relays, only three are shown. These relays perate momentarily when seized by the associated connector over the separate access leads provided, and serve to connect the units switching conductors from the connector, direct to the special group of trunk select relays in the lower part of Fig. 9. The arrangement of the trunk access relays is identical with that of the group access relays of Fig. 6, except for the omission of the group-seiect-ground springs such as 6| I. These springs are not required in this case, since no group select relays are used. Relays 840 and 850 are the lockout and kick-oil relays corresponding to the relays 640 and 550 of Fig. 6. The arrangemen-t of these relays is again identical, except that the lockout relay 840 provides the trunk select relays with the units operate ground normally obtained from the group select relays of Fig. 6.

In Fig. 9 is shown the basic circuit for the regular trunk select relays, two separate relay groups being shown. each equipped to handle three trunks. In these circuits, a trunk busy relay such as Bill or 950, and a trunk select relay such as MS or 955 is required for each trunk in the group. Each trunk busy relay is normally operated, through a series of break contacts in the associated trunk repeater, and releases whenever the trunk is seized by a call, whether incoming or outgoing. The trunk select relays operate one at a time in rotation. under the control of the trunk busy relays, to preselect the next idle trunk. As each select relay operates, it releases the previously operated select relay. and prepares the circuit of the proper units relay in the connector. Ground for the operation of the connector units relays is received from the group select relays of Fig. 6 or the trunk access relays of Fig. 8 as required. Relays 940 and 980 are reset relays whose function it is to re-set the select chain after the last trunk has been seized, and relays 945 and 985 are all-trunks-busy relays, which control the various counting meters indicated, such as, if desired. a peg count meter, an all trunks busy meter, and an overflow meter.

Both sets of trunk select relays in Fig. 9 are identical and are, as stated. associated with the same tens group. Their select springs are also associated with the same units relays, namely 1-6, represented by connector relay H0, and 2-7 and 3-8, not shown. In the lower set of trunk select relays in Fig. 9, however, the upper select springs are wired to the units switching or sub-group conductor, such as 996. By this means, the upper set of relays is made to serve the #1, 2 and 3 terminals of the 30 group tens relay in the connector to which the first three trunks are assigned, while the lower set is made to serve the #6, 7 and 8 terminals of the same tens relay to which the second three trunks are assigned.

These trunk groups of course, can be readily expanded, contracted or re-arranged in almost any manner desired within the tens group, assuming that corresponding changes are made in the trunk select relays, and any line terminals not used for trunks may be assigned to subscribers lines. The same thing applies to the more usual case where but one trunk group is assigned to any one tens relay, as with the select relay sets indicated by the rectangles S55 and 655 in Fig. 6. Such groups may include as many as ten trunks if desired. This of course would require a full set of ten select relays, with the units switching lead connected up in five of them, and not connected in the other five.

Numbering scheme The switchboard is normally arranged so that toll trunks and inter-oifice trunks are assigned to tens groups, Ill, 20, 30 and 40, while P. B. X trunks are assigned to tens groups 50 and 60. The trunk groups usually start on the first terminal and use successive terminals of the tens group, in order to facilitate expansion. This is not essential however. Subscriber lines may be assigned to any tens group where terminals are available.

Toll and inter-ofiice trunks are seized, in all cases, by dialling a single-digit number. These single-digit numbers are 0, 9, 8 and '7." Normally, the digit 0 operates group relay #10 (tens relay 410), the digit 9," group relay #20 (tens relay 520), the digit 8, group relay #30 (tens relay 530), and the digit 7, group relay #40, not shown. In the arrangement employed in the present disclosure however, both of the digits 8" and 7 will operate group relay #30, thus eliminating the need for group relay #40, or freeing it for other uses, such as calls to subscribers lines entirely. On all trunk calls, the proper units relay is operated automatically, from the trunk selecting equipment, as previously indicated.

Subscriber call numbers consist invariably of four digits, always beginning with a preliminary digit 2," followed by a variable tens digit, a variable units digit, and a variable ringing or code selecting digit. The last three digits may be any digit from 1 to 0 inclusive, or as permitted by the assignment of trunks.

P. B. X. call numbers also consist of four digits, the first or preliminary digit being always 2, the second or tens digit either a 5 or a 6," the third or units digit a 1, and the fourth or ringing digit also a 1. The complete call numbers would thus be either 2511 or 2611." The units digit 1 in this case, may or may not operate the first units relay, as this depends entirely on the idle or busy condition of the first P. B. X. trunk. The final digit 1" selects the first ringing code in all cases. This consists of a single long ring of about two seconds duration, repeated intermittently.

To summarize briefly:

l. A first digit 0 indicates a call to a toll trunk;

2. A first digit 9, 8 or '7 indicates a call to an inter-ofllce trunk;

3. A first digit 2 indicates a call to a subscribers line or to a P. B. X. trunk;

4. First digits 1, 3, 4, 5 or 6 are not used, and if dialled, inadvertently or otherwise, they are absorbed, and are thus for all practical purposes without effect.

The general description of the apparatus and its general method of functioning having been completed, a detailed description of the operation of the circuits will now be given, by actually following a few typical calls through the system.

Seizure of the connector When a finder, upon the initiation of a call, connects the calling line through to the associated connector, the connector line relay IIO operates over the calling line loop as follows: ground through the upper winding of relay IIO, break contacts I2I, break contacts Il, line conductor 80, through the calling subscribers line and telephone instrument, back over line conductor 8|, through break contacts I02, break contacts I22, and the lower winding of relay IIO to negative battery.

The connector line relay I I0 operating, at make contacts II I closes a circuit from ground through break springs I00 to release relay I30 which operates. The release relay I30 in turn, at make contacts I3I closes an obvious circuit to the hold relay I40, which also operates.

The hold relay I40 upon operating, at make contacts I44 connects ground from make springs I3l to the control conductor 03 and thence back through the finder of the link to the cut-oil and lockout relays in the line circuit of the calling line, which relays operate in series and disconnect the line relay of the line circuit from the line. The subscribers line relay thereupon restores to start the release of the allotter and at the same time re-connects the control and control normal leads together as previously mentioned.

The hold relay I40 also, at make contacts I49 connects ground to the tone and timer start conductor 81 in order to start the timing and tone generating equipment, and at make contacts I4I connects dial tone to the calling line. This latter circuit extends from ground battery and the secondary of the dial tone induction coil to the dial tone conductor 24! shown in the upper part of Fig. 2, through break contacts 2'" and 2 0I, conductor I56, makes contacts I, conductor I35, line condenser I 09, break contacts I22 and I02, negative line conductor 8|, through the calling subscriber's telephone and back over the positive line conductor 80, and through back contacts IM and I2I and the upper winding of connector line relay 0 to ground. Dial tone is made audible at the calling telephone over this circuit as an indication that dialling may proceed.

The hold relay also, at make contacts I42 prepares locking circuits for relays I20, I10, 2I0, 230, and the counting relays of Fig. 3; at make contacts I43 prepares the pulsing circuit; at make contacts I45 prepares a circuit for the test relay 240; and at make contacts I48 prepares locking circuit for test relay 240, and for the transfer relays 260, 210, and 280. Finally at make con tacts I41, relay I40 grounds the hold conductor 84 back to the finder to hold the finder tens and units relays operated, and at break contacts I48 opens a locking circuit to the associated link select relay in the allotter, by way of the locking conductors 85 and 00, thereby to permit the release of this relay and the preselection of the next idle link.

Call to a subscribers station The connector is now ready for dialling, with the line, release, and hold relays IIO, I30 and I40 operated. The operation on a call to a regular subscribers station will be described first, it being understood that a 4 digit number starting with the digit "2 is used on all such calls. Subscribers lines may appear of course in any tens group, but for purposes of illustration it will be assumed that the call is to a station having the call number 2151. The calling subscriber on hearing the dial tone, proceeds therefore to dial the first digit 2.

The connector line relay IIO follows the dial pulses and at each pulse, its make contacts I II momentarily open the circuit of release relay I30. Because of the slow release nature of relay I30 however, due to the use of a copper sleeve over the coil, this relay is not outwardly affected and remains operated. At each release of the line relay also, its break contacts II I momentarily close the pulsing circuit to the counting relays, and to the transfer relay 230 which is in parallel with this circuit. Relay 290 operates on the first pulse, and because of its slow release nature, due again to the use of a copper sleeve over the coil, remains operated during the succeeding pulses of each digit, releasing shortly after the end of each series of pulses.

On the first release of line relay IIO therefore, the back contacts III close a circuit to the pulsing relay 3I0 as follows: ground at break contacts I06, break contacts III, make contacts I43, break contacts I1 I, conductor I19, break contacts 234, conductor 205 left, break contacts 333', break contacts 323', break contacts 3I3', and the winding of the counting relay 3I0 to negative battery. A branch of this circuit also extends from break contacts 234 over conductor 200 right, to the windin of transfer relay 200 and negative battery.

Relays 230 and 3I0 operate over this circuit, the principal function of relay 200 being at this time to open the grounding circuits to the springs of the counting relays. The counting relay 3I0, at its make contacts 3, extends its operating ground to the winding of the counting control This latter relay is not affected at the moment however, due to having ground also on the other side of its winding, from make contacts I42, by way of break contacts I5I and I03, conductor I61, break contacts 233, conductor 205, and break contacts 324', Relay 3I0 also, at make contacts 3I6, prepares the operate circuit of the next counting relay 320.

Upon the re-energization of line relay H0, at the end of the first impulse, make contacts III re-close the circuit of release relay I30, while break contacts III open the pulsing circuit momentarily to the transfer relay 290 and counting relay 3I0. Relay 200 maintains its armature in the operated position during this interval, due to its slow to release nature, as previously mentioned. The opening of the operate circuit to the pulsing relay 3I0 however, removes the short circuit from the winding of the counting control relay 3I0. Relay 3I0 thereupon operates in series with relay 3I0, locking the latter relay in its operated position over the following circuit: ground through make contacts I42, break contacts I5I, break contacts I03, conductor IGI, break contacts 233, conductor 205 left, break contacts 324', winding of relay 3I0, make contacts 3, and the winding of relay 3I0 to negative battery.

Relay 3 I 0' upon operating, at its break contacts 3I3' disconnects the pulsing circuit from the operating circuit of counting relay 3I0 and at make at make contacts I42,

contacts 3I3' connects it to the operating circuit of counting relay 320 by way of make contacts 3I6. The operation of the remaining contacts on relays 3I0' and 3I0 is without eifect at this time.

Upon the next release of line relay H0, at the start of the second impulse of the first digit make contacts III again open the circuit of release relay I30 momentarily, while the make contacts III again connect ground to the impulsing circuit momentarily. Counting relay 320 operates over this circuit which as before is from ground at break contacts I06, through break contacts III, make contacts I43, break contacts I1I, conductor I19, break contacts 234, conductor 206 right to the winding of relay 290, conductor 206 left, break contacts 333' and 323' and thence through make contacts 3I3' and 3I6, and the winding of relay 320 to negative battery.

Counting relay 320 upon operating, at make contacts 323 prepares a circuit to the preliminary digit switching relay 250, at make contacts 326 prepares the operating circuit of counting relay 330, and at make contacts 32I extends its own operating ground to the winding of the counting control relay 320. Relay 320' does nothing however, at the moment, because of also having ground on the other side of its winding, from make contacts I42, by way of conductor 205. Relay 290 remains operated.

Upon the next re-energization of line relay IIO, at the end of the second and final impulse of the first digit, make contacts III again close and re-establish the circuit of release relay I30, while break contacts III open and again remove pulsing ground from the pulsing circuit, thereby opening the operate circuits to relays 290 and 320. This removes the short circuit from the counting control relay 320 and this relay therefore operates in series with counting relay 320 over the following circuit: ground through make contacts I42, break contacts I5I and I03, conductor I61, break contacts 233, conductor 205, break contacts 334', winding of relay 320', make contacts 32I and the winding of relay 320 to negative battery.

Relay 320' upon operating, at break contacts Relay 320' upon operating, at break contacts 324' opens the locking circuit of relays 3I0' and 3 I0, whereupon both of these relays release. Relay 320' also, at break contacts 323' disconnects the pulsing conductor 206 from the operate circuit of counting relay 320, and at make contacts 323' connects it to the operate circuit of counting relay 330, by way of make contacts 326. Finally, relay 320 at make contacts 325', grounds conductor 204 leading to break springs 294 on the transfer relay 290. The other contacts of relay 320 are without effect at this time.

Transfer relay 290 now releases. after a short delay, and at break contacts 294, 293 and 292 connects ground to conductors 253, 254 and 259 and thence through the cable 221 to the springs of the counting relays. This circuit is from ground conductor I66, conductor 203, make contacts 325', conductor 204, conductor I99 right, and break contacts 294, at which point the circuit divides and goes on to the counting relays over three separate paths. One of these paths is through break contacts 292, 264 and 215 and the conductor 253 to the counting relays, where only open contacts are encountered. This branch is therefore without effect at this time. A second path is through break contacts 265, 216, 211 and 293, and the conductor 259 to the .0k

ing relays, where again only open contacts are encountered. This branch is therefore likewise without effect when a 2 is dialled. The third path is through break contacts 265, break contacts 215, conductor 254, through cable 221, conductor 254 in the counting relays, make contacts 323, conductor 226, and the winding of relay 250 to negative battery.

The preliminary digit switching relay 250 now operates, and at make contacts 25I extends its operating ground to the winding of the preliminary digit transfer relay 210. This latter relay however, has ground also on the other side of its winding, from conductor I84 left and make contacts I46 on the hold relay, and does nothing at the moment. Relay 250 also, at make contacts 252 completes a circuit to the counting chain release relay I50 as follows: ground from make contacts I46, through conduc or I84, make contacts 252, break contacts 214 and 263, conductor I86, and the winding of relay I50 to negative battery.

The counting chain release relay I50 operates momentarily over this circuit, and at break contacts I5I disconnects ground from the conductors I61 and 205, and hence from the counting and counting control relays 320 and 320', which as previously explained, are held locked in series over these conductors from the ground at make springs I42. Relays 320 and 320 thereupon release and restore their springs to normal. The opening of make contacts 325' and 323 opens the operate circuit of the preliminary digit switching relay 250. This removes the ground shunt from the preliminary digit transfer relay 210, permitting the latter relay to operate in series with relay 250 and locking both relays operated. The locking circuit for these relays is from the ground. at make contacts I46, over conductor I84, through the winding of relay 210, make contacts 25I, and the winding of relay 250 to negative battery.

The preliminary digit transfer relay 210 upon operating, at break contacts 21! obviously opens the dial tone circuit to the calling line, and at make contacts 212 prepares an alternative circuit for the transfer relay 290 from the pulsing circuit, shunting the break contacts 234 on the busy relay 230. At break contacts 213 relay 210 opens the circuit of the switch-through relay I00, and at make contacts 213 prepares a circuit for operating the counting chain release relay I50 from the units relays. Relay 210 also, at break contacts 214, opens the original circuit to relay I50, thereby causing the release of this relay, and at; make contacts 214 prepares a circuit for operating relay I50 from the tens group relays. Finally, relay 210 at contacts 215, 216 and 211 opens the circuits leading to the counting relay conductors 253, 254 and 259, and prepares circuits to the conductors 255 and 256 leading to the group selectin springs of the counting relays. Connector relays I I0, I30, I40, 250 and 210 are now operated.

The second digit of the call number 2151 causes line relay II 0 to release and re-operate once only, in response to the second operation of the dial. On the break of the pulse, when relay IIO releases, transfer relay 290 and counting relay 3I0 again operate in parallel over the pulsing conductors I19 and 206, from the ground at break springs I06, as previously explained. Release relay I30 remains operated as usual, since its circuit is only broken momentarily at make contacts III. On the make of the pulse, when line relay IIO re-operates, the circuit of release relay I30 is reestablished and the operate circuit of relays 290 and 3I0 is broken. The opening of the op- Examine erate circuit of the counting relay 3 I permits the operation of counting control relay 3I0 as before, in series with counting relay 3I0, from ground at make springs I42, by way of conductors I61 and 205, and break springs 324'. Relay 3I0 therefore remains operated.

Transfer relay 290 releases however, after a short delay, and at break contacts 234 and 292 connects ground to conductors 255 and 256 and the associated group springs of the counting relays. This circuit is from ground at make contacts I42, over conductors I66 and 203, through make contacts 3I5, conductor 204, conductor I53 right, and break contacts 234, at which point the circuit divides and goes on to the spring of the counting relays over two separate paths. One of these paths is through break contacts 265, make contacts 216, and conductor 256 to the counting relays, where only open contacts are encountered. The other circuit is through break contacts 292, break contacts 264, make contacts 215, conductor 255, over the cable 221, conductor 255 at the counting relays, make contacts 3I4, conductor 42I, and the winding of the first tens-group relay 410 to negative battery.

Tens relay 410 operates over this latter circuit and closes its contacts, thereby preparing circuits to all of the lines in the called line tens group. At make contacts 414. group relay 410 extends its own operating ground to the winding of the tens digit transfer relay 260, by way of conductor 2". Relay 260 does nothing at this time however, due to having ground also on the other side of its winding from make contacts I46, through conductor I64. Group relay 410 also, at make contacts 413 completes a circuit for the operation of the counting chain relase relay I50 as follows: ground at make contacts I 46, conductor I64, make contacts 413, conductor 225 down, make contacts 214, break contacts 263, conductor I86 and the winding of relay I 50 to negative battery.

The counting chain release relay I50 operates over this circuit and at break contacts II disconnects ground from conductors I61 and 205 and hence from the counting and counting control relays 3I0 and 3I0 which are held locked in series over these conductors from ground at make contacts I42. Relays 3I0 and 3I0 thereupon release and restore their contacts to normal. The

opening of make contacts 3I5' and 3I4 opens the operate circuit to the group relay 410. This removes the shunt from the winding of the tens digit transfer relay 260, whereupon relay 260 operates in series with relay 410 and locks the latter relay in its operated position over the following circuit: ground at make contacts I46, conductor I84, winding of relay 260, conductor 2I1, make springs 4 I4, and the winding of relay 410 to negative battery.

The tens digit transfer relay 260 upon operating at break contacts 26I opens a second point in the dial tone circuit, and at make contacts 262 prepares a circuit for the units switching or subgroup relay 400, over conductors 2I3 and 2I4. Relay 260 also, at break contacts 263 opens the circuit to the counting chain release relay I50 causing this relay to release, and at make contacts 266 grounds the ringing machine start lead I98 by way of conductor I91 and break contacts I15. Finally, relay 260 at break-make contacts 264 and 265 opens the circuits leading to the counting relay conductors 255 and 256 associated with the tens selecting springs, and prepares circuits to the conductors 251 and 258 leading to the 14 units selecting springs of the counting relays.

Connector relays IIO, I30, I40, 250, 260, 210 and 410 are now operated.

The third digit of the call number 2 51" causes the connector line relay IIO to release and reoperative five times, the transfer relay 290 operating as before on the first pulse, in parallel with the pulsing circuit, and remaining operated until shortly after the last pulse of the digit, since it is re-energized momentarily at each release of relay IIO.

At the first release of relay IIO therefore, relay 290 and the counting relay 3I0 operate from break contacts III, over the plusing conductors I10 and 206, relay 3I0 preparing its own locking circuit as before at make contacts 3, and at make contacts 3I6 preparing the circuit of counting relay 320. On the re-operation of relay H0, the pulsing circuit is opened as before at break springs III, and counting control relay 3I0 operates in series with the first counting relay 3I0, from ground on the locking conductors I61 and 205, by way of break springs 324 and make springs 3I I.

At the second release of relay II 0, counting relay 320 operates from ground on the pulsing conductors I13 and 206, by way of make contacts 3I3' and 3I6. Relay 320 at make contacts 32I prepares its own locking circuit, and at make contacts 326 prepares the circuit of counting relay 330. On the re-operation of relay I I0, break contacts III again remove ground from the pulsing conductors I19 and 206 whereupon the counting control relay 320' operates in series with the second counting relay 320, from ground on the locking conductors I 61 and 205, by way of break springs 334 and make springs 32I. Relay 320 at break-make contacts 323 disconnects the pulsing conductor 206 from the counting relays 3I0 and 320 and connects it to the counting relay 33 0. Relay 320' also at break contacts 324 opens the locking circuit of relays 3I0 and 3I0, causing the release of these relays.

At the third release of relay IIO counting relay 330 operates over the pulsing conductors I19 and 206, by way of make contacts 323' and 326. Relay 330 at make contacts 33I prepares a locking circuit for itself and at make contacts 336 prepares the operate circuit of counting relay 340. On the re-operation of relay IIO, break contacts III again open the pulsing circuit to conductors I10 and 206, and on the removal of its ground shunt, counting control relay 330' operates in series with counting relay 330 from ground on the locking conductors I61 and 205, by way of break springs 3I4 and make springs 33I. Relay 330 at break make contacts 333' disconnects the pulsing conductor 206 from the counting relays 3I0, 320, and 330 and connects it to the fourth counting relay 340. Relay 330' also at break contacts 334 opens the locking circuit of relays 320 and 320, and causes the release of these relays.

At the fourth release of relay II 0, the fourth counting relay i340 operates from the pulsing conductors I13 and 206, by way of make contacts 333' and make contacts 336. Relay 340 at make contacts 34I prepares a locking circuit for itself through the winding of counting control relay 3| 0, and at make contacts 346 prepares the operate circuit of counting relay 350. On the reoperation of the relay IIO ground is again removed from the pulsing conductors I19 and 206 and hence from the operate circuit of counting relay 340, whereupon the counting control relay 3I0 operates in series with relay 340, from Examiner crate circuit of the counting relay 3| permits the operation of counting control relay 3 I0 as before. in series with counting relay 3I0, from ground at make springs I42, by way of conductors I61 and 205, and break springs 324. Relay 3I0 therefore remains operated.

Transfer relay 290 releases however, after a short delay, and at break contacts 294 and 292 connects ground to conductors 255 and 256 and the associated group springs of the counting relays. This circuit is from ground at make contacts I42, over conductors I66 and 203, through make contacts 3I5', conductor 204, conductor I99 right, and break contacts 294, at which point the circuit divides and goes on to the spring of the counting relays over two separate paths. One of these paths is through break contacts 265, make contacts 216, and conductor 256 to the counting relays, where only open contacts are encountered. The other circuit is through break contacts 292, break contacts 264, make contacts 215, conductor 255, over the cable 221, conductor 255 at the counting relays, make contacts 3I4, conductor 42I, and the winding of the first tens-group relay 410 to negative battery.

Tens relay 4'10 operates over this latter circuit and closes its contacts, thereby preparing circuits to all of the lines in the called line tens group. At make contacts 414, group relay 410 extends its own operating ground to the winding of the tens digit transfer relay 260. by way of conductor 2". Relay 260 does nothing at this time however, due to having ground also on the other side of its winding from make contacts I46, through conductor I84. Group relay 410 also, at make contacts 413 completes a circuit for the operation of the counting chain relase relay I50 as follows: ground at make contacts I45. conductor I84, make contacts 413, conductor 225 down, make contacts 214, break contacts 253, conductor I86 and the winding of relay I50 to negative battery.

The counting chain release relay I50 operates over this circuit and at break contacts I5I disconnects ground from conductors I61 and 205 and hence from the counting and counting control relays 3I0 and 3I0' which are held locked in series over these conductors from ground at make contacts I 42. Relays 3I0 and 3I0' thereupon release and restore their contacts to normal. The opening of make contacts 3I5' and 3I4 opens the operate circuit to the group relay 410. This removes the shunt from the winding of the tens digit transfer relay 260, whereupon relay 260 operates in series with relay 410 and locks the latter relay in its operated position over the following circuit: ground at make contacts I46, conductor I84, winding of relay 260, conductor 2, make springs 4, and the winding of relay 410 to negative battery.

The tens digit transfer relay 260 upon operating at break contacts 26I opens a second point in the dial tone circuit, and at make contacts 262 prepares a circuit for the units switching or subgroup relay-400, over conductors 2I3 and 2I4. Relay 260 also, at break contacts 263 opens the circuit to the counting chain release relay I50 causing this relay to release, and at make contacts 266 grounds the ringing machine start lead I96 by way of conductor I91 and break contacts I15. Finally, relay 260 at break-make contacts 264 and 255 opens the circuits leading to the counting relay conductors 255 and 256 associated with the tens selecting springs, and prepares circuits to the conductors 251 and 258 leading to the 14 units selecting springs of the counting relays.

Connector relays IIO, I30, I40, 250, 260, 210 and 410 are now operated.

The third digit of the call number 2151 causes the connector line relay IIO to release and reoperative five times, the transfer relay 290 operating as before on the first pulse, in parallel with the pulsing circuit, and remaining operated until shortly after the last pulse of the digit, since it is re-energized momentarily at each release of relay I I0.

At the first release of relay IIO therefore, relay 200 and the counting relay 3I0 operate from break contacts III, over the plusing conductors I10 and 206, relay 3I0 preparing its own locking circuit as before at make contacts 3, and at make contacts 3 I6 preparing the circuit of counting relay 320. On the re-operation of relay IIO, the pulsing circuit is opened as before at break springs II I, and counting control relay 3I0' op erates in series with the first counting relay 3I0, from ground on the locking conductors I61 and 205, by way of break springs 324 and make springs 3| I.

At the second release of relay II 0, counting relay 320 operates from ground on the pulsing conductors I19 and 206, by way of make contacts H3 and 3I5. Relay 320 at make contacts 32I prepares its own locking circuit, and at make contacts 326 prepares the circuit of counting relay 330. On the re-operation of relay I I0, break contacts III again remove ground from the pulsing conductors I19 and 205 whereupon the counting control relay 320' operates in series with the second counting relay 320, from ground on the locking conductors I51 and 205, by way of break springs 334' and make springs 32I. Relay 320' at break-make contacts 323' disconnects the pulsing conductor 206 from the counting relays 3l0 and 320 and connects it to the counting relay 330. Relay 320 also at break contacts 324' opens the locking circuit of relays 3I0' and 3I0, causing the release of these relays.

At the third release of relay IIO counting relay 330 operates over the pulsing conductors I19 and 206, by way of make contacts 323' and 326. Relay 330 at make contacts 33I prepares a locking circuit for itself and at make contacts 336 prepares the operate circuit of counting relay 340. On the re-operation of relay IIO, break contacts III again open the pulsing circuit to conductors I19 and 206, and on the removal of its ground shunt, counting control relay 330' operates in series with counting relay 330 from ground on the locking conductors I61 and 205, by way of break springs 3I4' and make springs 33L Relay 330' at break make contacts 333' disconnects .the pulsing conductor 206 from the counting relays 3I0, 320, and 330 and connects it to the fourth counting relay 340. Relay 330 also at break contacts 334' opens the locking circuit of relays 320' and 320, and causes the release of these relays.

At the fourth release of relay IIO, the fourth counting relay i340 operates from the pulsing conductors I 10 and 205, by way of make contacts 333' and make contacts 336. Relay 340 at make contacts 34I prepares a locking circuit for itself through the winding of counting control relay 3l0, and at make contacts 346 prepares the operate circuit of counting relay 350. On the reoperation of the relay IIO ground is again removed from the pulsing conductors I19 and 206 and hence from the operate circuit of counting relay 340, whereupon the counting control relay 3I0' operates in series with relay 340, from ground on the locking conductors I61 and 205, by way of break springs 324' and make springs 34I. Relay 3I0' upon operating, at make contacts 3| 3' further prepares the operate circuit for counting relay 350, and at break contacts 3I4 opens the locking circuit of relay 330' and 330, whereupon these relays release.

At the fifth release of relay I I0, the fifth counting relay 350 operates from pulsing conductors I18 and 206, by way of break contacts 333 and 323', and make contacts 3I3' and 346. Counting relay 350 at make contacts 35I prepares a locking circuit for itself through the winding of relay 320 and at make contacts 356 prepares the operate circuit of counting relay 360. On the reoperation of relay I I0, removal of pulsing ground from the pulsing conductors I19 and 206 and hence from the operate circuit of the counting relay 350 permits the operation of counting control relay 320' in series with relay 350, from ground on the locking conductors I61 and 205, by way of break springs 334 and make springs 35I. Relay 325' upon operating, at make contacts 323' further prepares the operate circuit of counting relay 380, and at break contacts 324' opens the locking circuit of relays 3I0' and 340, causing the release of these relays. The other contacts of relay 320 have no particular functions at this time, although make contacts 32I close an alternative circuit to the ringing machine start conductor I38 from ground through make contacts 266 and conductor 201. The original circuit, through make contacts 268, conductor I01 and break contacts I15 remains intact however, for the time being.

Transfer relay 290 now releases, shortly after the fifth and last digit, and at break contacts 284 and 262 connects ground to conductors 251 and 258 and thus to the associated units springs of the counting relays. The circuit starts as before from ground at make contacts I42, and passes through conductors I66 and 203, make contacts 325', conductor 204, conductor I98 right, and break contacts 284, at which point the circuit divides and proceeds over two separate paths. One of these paths is through make contacts 265, break contacts 288, conductor 258, cable 221, and conductor 258 again in the counting relays, where only open contacts are encountered. The second path is through break contacts 292, make contacts 264, break contacts 285, conductor 251, cable 221, conductor 251 in the counting relays, make contacts 355, conductor 435, and the winding of the -0 units relay 450 to negative battery.

The units relay 450 operates over this circuit, and at make contacts 45I and 452 extends the talking conductors of the connector to the called line I5. Thus, the talking conductor I58 in the upper part of Fig. 4, is connected through break contact I, make contacts "I and make contacts 418 to the line conductor I5, while talking conductor I65 is connected through break contacts 402, make contacts 452 and make contacts 413 to the line conductor I5. Similarly, test conductor 2I5 is connected through break contacts 404 and make contacts 453 and 480 to the test conductor I5" of the called line, which will be assumed to have negative battery on it, indicative of an idle line.

The units relay 450 also, at make contacts 458, extends its own operating ground to the winding of the units digit transfer relay 260, by way of conductor 2I8. Relay 280 is not affected at the moment, however, due to having ground also on the other side of its winding, from conductor I84 and make contacts I46. Finally, relay 450 at make contacts 451, completes a circuit to the counting chain release relay I50 as follows: ground at make contacts I46, conductor I84, make contacts 451, conductor 2I8, make contacts 213, break contacts 284, conductor I86, and the winding of relay I50 to negative battery.

The counting chain release relay I50 operates over this circuit, and at break contacts I5I disconnects ground from conductors I61 and 205, to which the counting and counting control relays 350 and 320' are held locked in series, as previously explained. Relays 350 and 320' therefore release and restore their contacts to their normal position. When the make contacts 325' and 355 open, they open the operate circuit to the units relay 450. This removes the ground shunt from the winding of the units digit transfer relay 280. Relay 280 thereupon operrtes in series with the units relay 450, and locks the latter relay operated, from ground at make contacts I46, by way of conductor I34, the winding of relay 280, conductor 2I8, make contacts 458, and the winding of relay 450 to negative battery.

The units digit transfer relay 280 upon operating, at break contacts 284 opens the circuit to the counting chain release relay I50, causing the release of this relay. At break contacts 285 and 286, relay 280 opens the circuits to conductors 251 and 258 leading to the units springs of the counting relays, and at make contacts 285 prepares a circuit to the ringing digit switching relay I10. At break-make contacts 28I, relay 280 disconnects the units switching or subgroup relay 400 from conductor 2| 3 leading to springs no the sixth counting relay, and connects the ring switching or side-of-line-select relay 2I0 to the same conductor 2I3. At make contacts 282, relay 280 prepares an alternative looking circuit for the counting relays, shunting break contacts 233 on the busy relay. This action is without significance at this time, however. Finally, at break-make contacts 283, relay 280 disconnects the busy test relay 230 from the test conductor 2l5 and connects the idle test or switching relay 240 thereto in its stead.

The called line being idle, as stated, a circuit for the operation of the idle test relay 240 is now established as follows: ground at break contacts I 01, through make contacts I45, conductor I83, upper winding of test relay 240, break contacts 235, make contacts 283, test conductor 2I5, break contacts 404, make contacts 453, make contacts 480, line test conductor I5" and the windings of the cut-off and lockout relays in the line circuit of the called lineto negative battery. The line cut-off and lockout relays operate over this circuit to clear the called line of attachments in the usual manner.

The idle test relay 240 also operates and at its preliminary make contacts 244 locks itself through its lower winding to the locking ground on conductor I84, from make contacts I46. At make contacts 2 and 242, relay 240 prepares circuits for connecting ringing signals to the called line. At make contacts 243, relay 240 connects direct ground from conductor I83 to the line test conductor, by way of break contacts 235, make contacts 283 and the connector test conductor 2I'5. At make contacts 245, relay 240 also prepares a circuit to the ring pickup relay I80. Finally, at make contacts 246, relay 240 prepares a start circuit to the ringing interrupter. Connector relays IIO, I30, I40, 240, 250,260, 210, 280, 450 and 410 are now operated.

The fourth and last digit of the call number "2151 now causes the connector line relay I I to release and re-operate once only. Upon the release of relay IIO, the closure of the break contacts I I I sends a pulse of current over conductors I19 and 206 as before, to again cause the operation of transfer relay 290 and counting relay 3I0. Upon the reoperation of relay I I0, the opening of the break contacts II I opens this circuit and permits the counting control relay 3I0 to operate in series with the counting relay 3 I0 as previously explained, from ground on conductor 205.

Counting control relay 3I0 upon operating, at make contacts 3I I completes the previously mentioned alternative start circuit to the ringing machine, from ground at make contacts 288, through conductor 201, make contacts 3| I, and conductor I98 to the ringing generator. This circuit shunts the break contacts I15 on the ringing digit switching relay I10, thus assuring continued operation of the ringing machine when relay I operates. At make contacts 3 I 2', relay 3I0' further prepares the start circuit for the ringing interrupter. Relay 3I0 also, at break-make contacts 3I3' prepares the usual operate circuit to the second counting relay, and at make contacts 3I5' prepares the operate circuit of relay I10.

Transfer relay 290 now restores, after a slight interval, and at break contacts 294 and 292 completes the operating circuit to the ringing digit relay I10, which is as follows: ground from make contacts I42, conductors I66 and 203, make contacts 3I5', conductor 204, conductor I99 right, break contacts 294 and 292, make contacts 204 and 285, conductor I91, break contacts of the make-before-break springs I12, and the winding of relay I10 to negative battery.

The ringing digit switching relay I10 now operates, and at make contacts I12 locks itself to the grounded conductors I88 and 203. At break contacts "I, relay I10 opens the pulsing circuit to the counting relays, and at make contacts I13 connects the code conductors I94 and I95 together, preparatory to their connection to the coding relay 220. At make contacts I14, relay I10 completes the start circuit to the ringing interrupter as follows: ground at make springs 3I2', conductor 209, make contacts 248, conductor I99, make contacts I14, and start conductor 90 to the ringing interrupter. Relay I10 alsO, at break contacts I15 opens one of the start circuits to the ringing machine, and at make contacts I19 connects ground from conductor I99 to one side of the ring pickup relay I80.

When therefore, the interrupter places negative battery momentarily on the pickup lead, Just before the start of the next ringing cycle, a circuit is completed for the operation of the ring pickup relay I80 as follows: ground at make contacts I42, conductors I69 and 203, make contacts 3I5', conductor 204, conductor I99 left, make contacts I16, break contacts I62, upper winding of pickup relay I80, conductor I99, make contacts 245, conductor I92, and the break contacts of the make-before-break springs I8I to negative battery on the pickup conductor 89. Relay I80 thereupon operates, and at make-before-break contacts I0l locks itself to steady negative battery from the interrupter on the hold battery conductor 89, and at the same time disconnects itself from the pickup conductor 89. Relay I80 also, at make contacts I82, connects conductor I93 and the coding relay 220 to the code conductors I94 and I95, and thence to the code springs of the counting relays. Since the interrupter removes negative battery from conductor 88 at the end of the code cycle, this action is repeated at each ringing cycle with the pickup relay I pulling up at the start of the cycle and restoring at the end of the cycle.

Ground pulses representative of the first ringing code now pass from the ringing interrupter, shown as the rectangle 92 at the lower right in Fig. 3, to the coding relay 220 through make springs 3I2 on the operated counting relay 3I0. This circuit is from ground at the coding springs of the interrupter, cable 93 and conductor 3I9, make contacts 3I2, conductor I94, make contacts I82, conductor I93 and the winding of relay 220 to negative battery. For the first code, each code cycle consists merely of one long ring of about two seconds duration followed by a silent period of about three seconds, repeated intermittently until the called party arswers. This is the code employed for ringing on single party lines. The interrupter of course, also connects various combinations of long and short coding pulses to the other ringing conductors at the same time, through the cables 93 and 94, but as these circuits are all open at the springs of the other counting relays, this action is without eifect in the present instance.

The coding relay 220 follows the code pulses, and on each energization connects ringing current to the called line over the following circuit: the negative out" terminal of the ringing machine or ringing generator, the ringing conductor 9| in the upper right of Fig. 1, winding of the slow-to-operate ring-cut-off relay I which is shown with a copper sleeve over the core and a copper slug at the armature end, conductor I83, break contacts 2 I2, make contacts 223, make contacts 242, talking conductor I85, break contacts 402, make contacts 452, make contacts 419, the called line negative line conductor I5, through the ringer at the called station and back over the called line positive line conductor I5, make contacts 418, make contacts 45I, break contacts 40I, talking conductor I58, make contacts 24I, make contacts 222, and break contacts 2II to ground. The bell at the called station now rings intermittently, in the usual manner. In the case of a call to a party line, with divided ringing, this circuit of course would go directly to ground at the subscriber's ringer instead of returning over the positive line conductor. In this case also, the last digit of the call number, and consequently the ringing code, would be varied as necessary.

Relay 220 also, at each energization, at make contacts 22I completes a circuit for providing ring-back tone to the calling line. A portion of the ringing current passes back over this circuit which may be traced as follows: ringing generator, conductor 9I, winding of ring-cut-off relay I90, conductor I63, the low capacity condenser 2 I6, make contacts 22I, conductor I51, conductor I35, talking condenser I09, break contacts I22, break contacts I02, negative line conductor 8|, through the calling telephone, back over the positive line conductor 80, break contacts IOI, break contacts I 2|. and the upper winding of relay I I0 to ground. The ringing current is thereby made audible to the calling subscriber as a low tone, to indicate that the called line is being signalled. The ringing current itself is of course prevented from getting into the calling line by the open break contacts 222 and 223 on the one hand. and by the open make contacts IOI and I02 on the other hand.

Relay 220 also, at make contacts 224 completes

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