US2506730A

US2506730A - Private branch exchange trunkhunting connector switch circuit

Info

Publication number: US2506730A
Application number: US100374A
Authority: US
Inventors: Frank A Morris
Original assignee: Stromberg Carlson Corp
Current assignee: Stromberg Carlson Corp
Priority date: 1947-04-23
Filing date: 1949-06-21
Publication date: 1950-05-09
Anticipated expiration: 1967-05-09
Also published as: GB675088A; US2567650A

Description

May 9, 1950 Original Filed April 23, 1947 F. A. MORRIS 2,506,730

PRIVATE BRANCH EXCHANGE TRUNK-HUNTING CONNECTOR SWITCH CIRCUIT l6 Sheets-Sheet l ATTORNEY May 9, 1950 F. A. MORRIS PRIVATE BRANCH EXCHANGE TRUNK-HUNTING CONNECTOR SWITCH CIRCUIT Original Filed April 23, 1947 Y l6 Sheets-Sheet 2 FIG. FIG. FIG. FIG. FIG. FIG. FIG. FIG. F/G.Z

LINE FINDER SELECTOR CONNECTOR LINE FIG. FIG. -F|G. FIG. FIG. FIG.

II. I2. I3. I4. I5. I6. T

ALLOTTER WWW REVERTING x 4I\ "W43 TO ALL LINKS 12m; BUSY TONE OUT AY-WN SEE FIG.I2 42 1 TO coIN BOX '-\.QQQQ;- TONE SOURCE gwsf cl LST l --4 l CSw. l I J FIG. 3

JNVENTOR.

FRANK A. MORRIS BY JX/ZWLV ATTORNEY May 9, 1950 F. A. MORRIS 2,505,730

PRIVATE BRANCH EXCHANGE TRUNK-HUNTING CONNECTOR SWITCH CIRCUIT Original Filed April 23, 1947 16 Sheets-Sheet 5 FXoN F YoN I I I I I I I Il U M Z T R S H w w W. m IIIIIII Z F E W I FRANK A. MORRIS I I I I I I I I I I I I ,4 Wm w l 7 ATTORNEY SEE FIG II.

x 4 I I I I I I I F I I i w m F I I I I I w l 5 I. 3 I I3 5 2 4 mi I I IIIIIIIIIllIl T I x I m T s R H X WM m: s w 3 000000000000000000000 000000 000000 000 00 00 ST FWJ o0 00000000000000000000 000000000000 0000000000 00 Y B 00 00000000000000000000 0000000000000000000000 00 A A I 00 00000000000000000000 00000000000000 00000000 00 T 4 00 0000000000000000000 000000008000000 00000 00 L I W 00 0000 000000000000000 000000800000000000000 00 N N S 000000080 0 00000000 002 03900000 00000 00 0 O A G 00000 03080000000000 000 0000 00000000 6 R I F 00 00 000000000000 00 00 00 00000000 00 CI I F 0 00: F 4000000000000 0000: 555000 00000000 00 Dr ll 00 00c 000000000000 0000 000000000000 00 0 0T T T B 5 L T R S H X May 9, 1950 F. A. MORRIS 2,506,730

PRIVATE BRANCH EXCHANGE TRUNK-HUNTING CONNECTOR SWITCH CIRCUIT Original Filed April 25, 1947 16 Sheets-Sheet 4 SMB 3M1 50F 50 8X0: 5? sf s o I I I I I I I I I I I I l I I I I I FRONT S INVENTOR. FRANK A. MORRIS BY JXM ATTORNEY BBTF FIG.5

May 9, 1950 F. A. MORRIS 2,506,730

PRIVATE BRANCH EXCHANGE TRUNK-HUNTING CONNECTOR SWITCH CIRCUIT I Original Filed April 25, 1947 16 Sheets-Sheet 5 SYo/v SH SY SPT 52 $05 SAB' l l l i I DEAD LEVEL TONE TO OFFICE DIAL TONE SOURCE A KS FRONT S BCTS ans

m D m INVENTOR.

FRANK A.MORRI$ FIG. 6 SEE FIG.I3

ATTORNEY May 9, 1950 F. A. MORRIS 2,506,730

' PRIVATE BRANCH EXCHANGE TRUNK-HUNTING CONNECTOR SWITCH CIRCUIT Original Filed April 25, 1947 '16 Sheetsfi-Sheet 6 CSL CRD CIIYC CA CTT C?!- l l I i I I l I I I l I l l i I I l L L l l l l I I BCTS BRS

0H INVENTOR. 5 FRANK A. MORRIS 7 BY 5 FIG. 14 \7 ATTORNEY May 9, 1950 F. A. MORRIS PRIVATE BRANCH EXCHANGE TRUNK-HUNTING CONNECTOR SWITCH CIRCUIT Original Filed April 25, 1947 16 Sheets-Sheet 7 FRONT S .5 Mm R O M A K N A R F FIG.8

ATTORNEY May 9, v1950 F. A. MORRIS PRIVATE: BRANCH EXCHANGE TRUNK-HUNTING CONNECTOR SWITCH CIRCUIT Original Filed April 23, 1947 I6 Sheets-Sheet 8 70 C O/VMC TS OFRfLAYS arpz ,q/vo mp2 (H6. /4.)

, INVENTOR. FRANK A. MORRIS May 9, 1950 F. A. MORRIS PRIVATE BRANCH EXCHANGE TRUNK-HUNTING CONNECTOR SWITCH CIRCUIT Original Filed April 23, 1947 16 Sheets-Sheet 9 R. 2 mm B L A H m w M Km Ms MR H R a 5 a E 0 0 N X N (H/ F 0F m r w w P H x INVENTOR. FRA/VK AMORR/S ATTORNEY F. A. MORRIS PRIVATE BRANCH EXCHANGE TRUNK-HUNTING May 9, 1950 CONNECTOR SWITCH CIRCUIT Original Filed April 23, 1947 l6 Sheets-Sheet l0 JEEP/G. 4.

INVENTOR. FRANK A. MORE/S ATTORNEY May 9, 1950 F. A. MORRIS 2,506,730

PRIVATE BRANCH EXCHANGE TRUNK-HUNTING CONNECTOR SWITCH CIRCUIT Original Filed April 23, 1947 16 Sheets-Sheet 11 JNVENTOR. FRANKA. MORRIS A TTOR/VEY May 9,, 1950 F. A. MORRIS PRIVATE BRANCH EXCHANGE TRUNK-HUNTING CONNECTOR SWITCH CIRCUIT Original Filed April 23, 1947 16 Sheets-Sheet 12 APT A 1 A 2 A A'PA ALs seer/as. r'*\ I I I 1 I l 1 i INVENTOR. 17615- FRANK A. Mom/s A TTOR/VEY May 9, 1950 F. A. MORRIS 2,506,730

PRIVATE BRANCH EXCHANGE TRUNK-HUNTING CONNECTOR SWITCH CIRCUIT Original Filed April 23, 1947 16 Sheets-Sheet 13 70 xx bAA/AS 0/" F/IVDE/P 5 W/ 7' C H Fsw. (F16. 411mm com/5c 70/? sw/rcH csw. (F/G. 9)

BCAS MAP 573 apr BALM 5 mm O VA fie 14.

ATTORNEY F. A. MORRIS PRIVATE BRANCH EXCHANGE TRUNK-HUNTING May 9, 1950 CONNECTOR SWITCH CIRCUIT Original Filed April 25, 194'? 16 Sheets-Sheet l4 INVENTOR. FRA/VKA. MORRIS ATTORNEY May 9, 1950 F. A. MORRIS 2,506,730

PRIVATE BRANCH EXCHANGE TRUNK-HUNTING CONNECTOR SWITCH CIRCUIT Original Filed April 25, 1947 16 Sheets-Sheet 15 B250 916 R150 PIS PPT 915W PZSW l I I J 7'0 Fp N I esA/b' faQ Fa FRANK A. Mom/s ATTORNEY May 9, 1950 F. A. MORRIS 2,506,730

PRIVATE BRANCH EXCHANGE TRUNK-HUNTING CONNECTOR SWITCH CIRCUIT Original Filed April 23, 1947 16 Sheets-Sheet 16 I /TLTO T7EW I I l I I l I I I I I I I all IIIMMI 6 A MW mm TO M IIIII I M A VA T .R A X R A 2 6 F T w 4 m m A I 5 2 II I I I T d l E w T I I .l A 6 A 3 M& 5 w 0 M U -5 3 Z a P (Q13; 1. 7 a m 3 w m m 1 -u F m M 5 .H E R MD Mm I I I I l IIII TN 5 w MR 6 7 6 mI|.||..|| n W a iillwl o m U 10 0 7 H L 8/ 2 E w 7 F 11 ||I||1|I||||I| Em ATTORNEY Patented May 9, 1955}.

PRIVATE BRANCH EXCHANGE TRUNK- HUNTING CONNECTOR SWITCH CIRCUIT Frank A. Morris, Rochester, N. Y., assignor to Stromberg-Carlson Company, a corporation of New York Original application April 23, 1947, Serial No. 743,415. Divided and this application June 21, 1949, Serial No. 100,374

3 Claims.

The present invention relates to telephone systems and more particularly to P. B. X trunk hunting in automatic telephone systems.

ihis is a division of my co-pending application Serial No. 743,415, filed April 23, 1947 and assigned to the same assignee as the inventions described herein.

It is an object of my invention to provide a new and improved connector circuit which provides improved P. B. X trunk hunting.

GENERAL DESCRIPTION dual allotter in which each half is normally 1 brought into action by half of the lines, there being, for example, 50 lines assigned to each allotter. Provision is made for transferring all the lines to one-half of the allotter under certain conditions.

After the line finder-selector link has selected the calling line, the selector is caused to hunt, upon the dialing of the first digit of the called number, to select an idle connector in that group of connectors designated by the first digit. After selection of the connector, second and third digits are transmitted to cause the connector step-bystep switch to move to a position corresponding to the called subscriber.

Line circuit.In connection with a system such as that described herein, there is provided a line circuit at the terminating, as well as at the originating, end of each call. The line circuits are arranged to supply ground over a start lead to initiate operation of the allotter; to mark the position of the calling line in the banks of the finder step-by-step switch; to transmit all links busy tone to a subscriber when all of the finder-selector links are in use; to transmit coin box tone to a manual operator when the system is so arranged; to prevent the indefinite holding of a line finder and selector combination when a permanent fault appears by disassociating or looking out the faulty line from the switching equipment after a period of time determined by common timing equipment; and also to eliminate the line, start and marking grounds on terminating calls in order to prevent the unnecessary use of the line finder-selector links.

Line finder.-The line finder, as indlcated above, is employed to find the calling line. In addition to this primary function, the line finder is used to attach the ti and ring conductors or leads to the calling line; to conduct a busy test to prevent cutting through metallic connections if a connector has seized the calling line during the process of line finding; to cut tip and ring conductors through to the connector on a metallic basis if the busy test is successful; to recycle the allotter if the line finder fails to stop in either direction of motion of the step-by-step switch; to provide trunk call identification to succeeding circuits; and to provide direct control of all links busy and link test marking paths to the allotter. The line finder may be provided with means for discriminating restricted calling levels and timed calling levels. 1

All0tteT.The dual allotter, as stated above, serves primarily to control the operation of a pre-selected line finder and to pre-select another idle link upon completion of a line finding operation. The allotter is also used to pre-impulse the selector associated with the idle line finder when the allotter is energized; to drive the line finder in whatever direction is necessary to attach the finder-selector link to the calling line; to drive the line finder in one direction only to attach the link to a calling trunk as distinguished from a calling subscribers line; to recycle it the line or trunk is not found within a prescribed time; to transfer functions so that one side of the allotter can carry the entire load of the line group in case of trouble or in case all links normally served by the other side become busy; to operate peg count meters; and to return the all links busy tone when required.

SeZector.-The purpose of the selector circuit, as indicated previously, is to select a group of connectors under the direction of the dial and hunt automatically for an idle trunk in that group. In order to accomplish its purpose, the selector is caused to repeat the dial pulses received from the calling party in order to select the desired group of connectors, to hunt in the selected group for an idle trunk in the level selected by the dial, and then to establish a connection to the succeeding switching equipment. There may also be provided provisions for digit canceling, digit adding, permanent-time release and the transmission of link idle and link busy indications to the allotter. I

Connector.-The primary functions of the connector are to select a subscriber line and to establish ringing of the desired called station under the control of the calling party. The connector may be of various types' depending upon the kind of service which it may-be called upon to perform, such as party line ringing of either the harmonic or code type, P. B. X trunk hunting, conversation timing from one or both ends of the system, and revertive calling.

P. B. X trunk hunting allows the assignment of successive numbers to a business establishment, or the like, whose telephone needs are siifiiciently great to justify the assignment of two or more consecutive telephone lines,.in which case, the

connector tests the lines in successionuntil a free line is found. Normally, when the first line is called, testing begins over the entire group. vProvision may be made, as for night service, for example, such that if any line other than the first in 'thegroup is called, that line only is tested. This feature allows the listing in the telephone directory of all telephone lines, except the first, as night lines for particular individuals whereby at such times they receive the benefit of individual line service.

Further objects and advantages as well as a detailed understanding 'of my invention will be apparent from a study of the following description when read in connection with the drawings in which Fig. 1 illustrates the basic features of a 'step-by-step switch which maybe used tocarry out the principles of my invention, Fig. 2 is a chart showing the relationship of the various figures of thedrawin'gs and which enables acomfp'lete'wiring diagram to beassembled if the various'figures of the drawings are placed in the'indica'ted locations, Fig. 3 illustrates the line circuit of my system, Fig. 4 depicts the finder switch 'and'associated circuitaFigs. 5 and'6 illustrate'the various componentsparts of a selector embodying "the'principles of myinvention, Figs. 7 and 8 and 9 show "a connector circuit illustrating the principles "of my invention, Fig. 10 shows a terminating line circuit, Figs. 11, 12 and 13 illustrate a 'dual "allotter for use in the system described herein, Fig. 14 illustrates equipment which is common to the system, Figs. 15 and 16 illustrate an "alternative reverting call circuit and Figs. 17 .and l8 illustrate modifications of features of the'circuits 'shown'in Figs.4, 11 and 12 and Figs. 7,3and19respectively.

With respect to Figs. 5 and 6 relating to the selector, it is desired to point out that if perinanent timing lock-out is to be employed, the equipment within the dashed rectangle marked 'W'iththe numeral B is used, but if the lock-out feature is not desired, the ground connection indicatedwithin the dotted rectangle C is substituted. Attention is also called to the dashed rectangle D which is used if digit adding functions are required, in which case wiring M is used. If digit adding is not employed, rectangle D is omitted and wiring N is substituted.

Referring to the connector, illustrated in Figs. 7, 8, and 9, a number of alternative provisions are made. If directory number revertivecallin'g is employed, the apparatus shown within the dashed rectangle E and D, W, and X wiring is used, but if the special revertive call circuitillustrated in Figs. 15 and 16 is furnished, the parts shown within rectangle E are omitted and"D, W and Y Wiringis used. If the trunk hunting feature is utilized, the parts shown in rectangle F are included and wiring C is used instead of D. If dual timing is made part of the system, wiring D is used, but if this service is not provided, wiring W is used.

Step-by-step switch It is believed that a complete understanding of the principles of my invention requires not only an explanation of a complete telephone system, but also a description of a suitable step-byste'p switch. There is illustrated in Fig. 1, a switch specially adapted for use in the system embodying my invention and known by the trade name XY's'witch. This switch derives its name from the fact that the wipers or contact brushes, during movement to a desired position, traverse first intaprimary-direction and then in the same plane but in-a secondary direction at right angles to the first direction, which, in the right-hand rectangularco-ordinate system are X and Y directions, respectively.

There is provided a carriage l, which makes the primary and secondary stepping movements and has a set of contact brushes comprising two pairs 50f

wipers

2 and 3 mounted on it for tip, ring, sleeve and hunt connections, respectively.

hese wipers are bifurcated, employing twin contacts that make connection directly onto bare wires which run in banks behind the switches. The bare wires may be arranged in molded frames which may be rigidly mounted to the-cells which in turn hold the switches.

The carriage is driven by the cog roller or tubular shaft assembly l which slides along the shaft 5 during the X motion. The cog roller 4 is shown in the form of a double-cut tubular gear with ratchetteeth cut parallelto its length and rack teeth out as rings. The annular rack teeth mesh with and .are driven in the Xinotion by 'a suitable sprocket or gear 6. Forstepping in the X direction, the X magnet [located in the upper left corner of the plate 6, operates, through a pawl 9, the ratchet wheel it! which is suitably mounted on the sprocket assembly. In response to repeated pulses the magnet 7 steps the cog roller "assembly "4 along the shaft 5, :pOsitiOning the wipers on the carriage l succesively before each wire bank. Since four wipers are involved and each wiper has its own set-of ll wires, 44 rovvsof wires each 11 deep are lined up-along the front edge of the mechanism plate, immediately before the wipers (see Fig. 4). The eleven pairs 'of wires that are lined up before a pair of wipers constitute'a wire bank.

The XY switch is nominally a point switch, i. e., is'normally given ten steps in the X direction and ten steps in the Y direction, thereby making possible the selection by the wipers, of any one of 100 lines.

To mark the level of X travel, for finder operation, timing or discriminatory purposes, an

auxiliary set of contact brushes adapted to be positioned according to the :position of the primary movement or set of brushes, another pair of wipers indicated by the numerals i5 and la enters a separate bank comprising X and X levels. Wipers H and H a are operated by apinion [2 assembled with the sprocket 5 through a rack 13 to which it is attached. Thus, as the X magnet steps the sprocket 6, both the cog roller 4 and wiper rack 13 move, roller '4 to the right and rack 13 upwardly, as viewed in the drawing. When the X wiper H has found the proper level, thereby positioning the wipers on the carriage before the proper wire banks, the X magnet l is ale-energized and the Y magnet l5 takes over.

The Y magnet I5 is located in the lower central portion of the mechanism plate. In stepping, its

5 pawl I 6 operates directly on the ratchet teeth of the cog roller d, turning it, and thus driving the

wipers

2 and 3 into the wire banks through the interaction between rack and pinion 2|.

The X position of the wipers is shown by reference to a scale i'l attached to the mechanism plate and the Y position by reference to a numbered drum l8 located on the tubular shaft as sembly. Thus, the position of the wipers is determined directly and quickly.

It should be recognized that the momentum of the switch, if not arrested, would carry each step beyond its limits. This is more easily realized when one considers that the stepping is of the order of fifty per second. In order to stop the X motion at each step, the end of the armature 35 of the X magnet engages a tooth of the sprocket at the bottom point of the armature travel. The sprocket motion is, therefore, locked each time the X magnet completes a pulse.

In the Y motion, a cam (not shown) on the underside of the Y armature operates against a member 22 called the stop bar. This stop bar is rocked forward at each downward stroke of the Y armature. A knife edge on the stop bar 22 engages a ratchet wheel 23 on the end of the cog roller l locking the rotation of the cog roller, and thus the advancement of the wipers, at the completion of each Y armature stroke.

There are provided X off-normal contacts or switches 25, Y off-normal contacts 01' switches 25, over-flow contacts or switches 2'? and a release switch 28.

The off-normal and overflow switches are mounted as a common assembly located in the The X and Y off-normal springs 25 and 26, re-

spectively, perform similar functions, that of informing the relay equipment associated with each switch as to the position of the brushes or wipers. Operation of the X off-normals, for instance, indicates that the switch has taken at least a single step in the X direction. Operation of the Y 01fnormals similarly indicates that at least a single step has been taken in the Y direction.

The circuit function of the off-normals differs in each use of the switch but, in general, indicates that it has either moved in one direction and should now move in another or all necessary motion has taken place. There is, however, one circuit function common to all switches and that is to remove current from the release I when the brushes have returned to the normal position. When the release signal is given, current is kept on the release magnet 38 until the switch is fully home and is then removed to avoid unnecessary current flow and heating. Both the X and Y off normals are used in this function since the switch can be moved independently in either direction.

In the event of certain incorrect manipulations or an all-trunks-busy condition, hunting switches may progress the entire length of the bank without encountering a stopping signal. Unless some means of correction were provided, they would continue to hunt vainly until the circuit was deenergized. Overflow springs 21, arranged to operate in the extreme position of the brushes in either the X or Y directions (namely the eleventh X or Y step), interrupt the magnet current in order instantly and permanently to stop useless stepping until the switch is released.

, The release springs 28 have two important functions in connection with the release of the switch. First, it is necessary to continue the release signal until the switch is fully home despite any re-energization of the circuit which might occur. Second, there must be positive protection against premature seizure of a switch before it is fully home. In the XY switch, the first is accomplished by a release spring contact establishing a self-locking electrical circuit which keeps the driving pawls 9 and I6 removed from the ratchet wheel (X motion) and the cog roller (Y motion). The lock is interrupted when the switch returns home. The second function is performed by a second release spring which maintains a busy indication until the switch is home, thus preventing its seizure until everything is normal. When the release magnet 30 is energized, stop members 3! and 32 are removed from engagement with cog roller 4 and sprocket l0, respectively, through operation of armature 33. The Y return movement of the carriage is then performed by a spring 35 coiled in the tubular shaft of the cog roller and the X movement by a spring (not shown) coiled around the shaft of the sprocket 6.

Detailed circuit description In the following detailed description, a call is traced from the calling partys station to the called partys station. Revertive calling is then discussed and finally circuit refinements to provide special features and to take account of special conditions are described.

The telephone system herein described in detail comprises a single selector and, therefore, serves a 1000-line system and requires the transmission of four digits, one to select the desired group of connectors, the second to determine the tens digit of the called number, the third to select the units digit of the called number, and the fourth to ring the called line. The principles of my invention, of course, are not limited to the particular choice of circuits described herein as a, system and my invention is equally applicable to any desired combination of the various circuit components.

In describing the circuits involved, the various relays are designated by letter combinations. The first letter indicates the part of the system in which the relay is located, i. e., L indicates line circuit, F indicates finder, A indicates allotter, S indicates selector, C indicates connector, R indicates a special reverting call circuit and B refers to common equipment. Following the initial letter are one or more letters which are usually the initials of the name of the relay with which they are associated and which serve to identify that relay. For example, C refers to a calling relay, PT to a permanent timing relay, D to delay, and X and Y to switch motion. Thus, SXD refers to a slow release (delay) relay associated with the X motion of the selector switch. The relay contacts and armatures are identified by the same letters referred to above followed by a hyphen and then a numeral. Thus, SXD-2 designates an armature of the SXD relay.

It may be noted that in the described system, when the battery is connected into the system but no calls are being made, the ALB and ALI relays are energized but all other relays are deenergized. The ALB and ALI relays remain energized as long as there is an idle link (a link comprising a finder and a selector). The other relays are energized at various times during the progress of a call. Hence, in the drawings, the

armatures of the ALB andALI relays are shown in the operated positions while the armatures of the rest of the relays areshown unoperated. The term battery when used in the. following circuit description refers to the negative side of bat-- tery. The positive side of battery'is' grounded and hence the term ground refers to positive battery.

Line circuit Referring to Figure 3 of the drawings, a call is initiated by removing the receiver from the hookswitch or cradle, thereby closing the hookswitch contacts ll as shown in Fig. 3 and completing a circuit through a suitable dialing mechanism 42 to the tip and ring leads, I and R, respectively. Closure of the hookswitch completes a circuit for the energization of the line relay LL. Relay LL is a two-winding relay. One terminal of the lower winding is connected to battery and the other terminal is connected to the ring lead R through contact LCO-t and armature LOO-3. The circuit to ground from the tip lead T comprises armature LCO-i, contact LCD-2, the other coil of relay LL, contact LLO-l and armature LLO-2 to ground. If all-links-busy tone is to be provided, the foregoing circuit is grounded through a transformer as indicated in dashed lines in Fig. 3instead of directly as shown by the solid line.

Operation of line relay LL grounds a start lead LS'I to the dual allotter in order to cause a preselected finder to hunt for the calling line, grounds the X-mark lead to mark the tens position of the calling-line in the banks of the line finder switch FSw (Fig. l) andalso grounds the H lead to mark the units position of the calling ine in the banks of the line finder FSw.

The X-mark circuit is as follows: ground-at armature LL-I, contact LL'-'2'of line relay LL,

armature LLO-G, and contact LLO-5 of lockout relay LLO to the contact in the-X bank-of the line finder switch FSw'corresponding-to the calling line. The hunt lead H is grounded as follows: ground at armature LL-3, contact LL-4, armature LLO-i I, and contact LLO-l2, tothe contact in the hunt bank of the'line finder corresponding to the calling line.

Ground on the start lead is utilized to oper ate a start relay in the allotter (Figs. 11, 12 and 13) which initiates the energization of the line finder switch (Fig. 4) chosen by the allotter to serve the call. The start lead is traced over the following circuiti ground at armature LL-l', contact LL Z, armature LLO t, contact LLO-5, resistor 43; and start lead LST, to the allotter.

When the calling line is found, as will be: more fully described hereinafter, ground is placed on the sleeve lead S in the sleeve bank of the finder timipg play ACT armature Asbqncontact A824 switch F'Sw (Fig. 4) and conducted to the lirie circuit by lead S. Presence ofground on the sleeve lead S operates the cut-ofi relay LC O over a circuit extending from grounded sleeve lead S, armature LLO-B, contact LLO-Q, winding of cutoff relay LCO to battery. If provision is made for the transmission of coin box tone to an operator, the cut-off relay LCO is connected to battery through a transformer winding as indicated in dotted lines in Fig. 3 instead of directly as shown by the solid line. Cut-01f relay LCO locks up through a circuit extending from grounded sleeve lead S, through contact LCD-9, armature LCD-8, and winding of relay LCD to battery. Operation of the cut-ofi'relay 8 is-now independent of subsequent operation of lock-out relay LLO.

When the cut-off relay LCO is'energized, the tip and ring leads, T and R, respectively, are disconnected from the line relayLL by the opening of the line circuit at contacts LOO-2 and LCD-'4. De-energization of relay LL removes ground fromthe marking leads at contacts LL-! and LL4 respectively.

The energization of cut-off relay LOO also causes ground to be placed on the winding of lockout relay LLC), the circuit extending from the grounded sleeve lead S through contact LCD-5 and armatureLGQ-G to one terminal of the winding of relay LLO. The other terminal of the LLO coil is connected to battery. Operation of the look-out relay LLO'breaks the original energization path to the cut-off relay LCO at contact LLO-'9 but the cut-off relay LCO remains lockedup as explained above. Lock-out relay LLO' locks up to thegrounded sleeve lead S through its own armature LLO-B and contact LLO-l and hence is independent of any subsequent action of cut-off relay LCO.

Allotter and line finder In the "at rest condition of the allotter, i. e.. circuits connected but no calls being made, the allotter is cut through to an idle link' comprising an interconnected finder and selector by means of contacts and brushes of the rotary link selector switch ALS. The link busy relays ALB andA LB associated with left and right hand portions, respecti'vely, of the allotter and the link idle relays ALI and A'LI are normally picked up by grounds derived through chains of contacts in the" line finder and the selector. Thus, referring to relay ALB (see Fig. 12), one side of its winding or coil is connected to battery. The other side of the coil ALB is connected to ground over a circuit extending through contactDK-l and armDK -Zof the disable key DK, armature AS2-I8 and contact ASE-lli of start relay AS2, ALB lead tothe finder (Fig. 4), armature FYon-3 and contact F'Yom l of the finder Y off-normal switch FYon, contacts of themake busy'switch FMB, ALB lead from the finder to the selector (see Figs. 5 and 6), armature SYOn! and contact SY n-Z of the selector Y off-normal switch SYOn, conductor 36, contact SD-B and armature SD-4 0f selector delay relay SD, and contacts of the selector make busy switch SMB to ground. Inasmuch as all finder selector links are multipled, if any link is not operated or employed, relayALB is energized through at least one closed off-normal contact in the finder and the selector.

The operating circuit for link idle relay ALI is as follows: battery, upper winding of ALI, armature APT-l and contact APT-2 of the permanent arm and contact of rotary switch element 55 of link selector switch ALS, link idle lead FLI to the line finder (Fig. a), spring or armature'FYon-i and contact FYon-S of the finder Y off-normal switch FYOn, armature FZ-I and contact FZ-Z of release magnet FZ, armature and contact of make busy switch FMB, link idle lead LI to the selector, contacts of the selector make busy switch SM B, contact SYon-S, spring or armature SYon-4 of the selector Y off-normal switch SYon, contact SZ-l and armature 52-2 of release magnet SZ to ground. In order to make link idle relay ALI pick up as rapidly as possible and insure halting of allotter cycling upon reaching an idle link, a second or lower winding is provided for relay ALI