US2123228A - Selector switch - Google Patents

Description

July 12, 1938. w. w. CARPENTER SELECTOR SWITCH 3 Sheets-Sheet 1 Filed March 51, 1937 .:it i l E35:55:z 1;

INVENTOR WWCARPE/VTER 96. M

ATTORNEY July 12, 1938.

w. w. CARPENTER 2,123,228

SELECTOR swIT'cH Filed March 31, 1957 3 Sheets-Sheet 2 INVENTOR W. W. CARPENTER ATTORNEY y 1938. w. w. CARPENTER 2,123,228

, SELECTOR SWITCH Filed March 31, 1957 s Sheets-Sheet 5 INVENTOR W. M. CARPENTER ATTORNEY Patented July 12, 1938 UNITED STATES PATENT OFFlCE SELECTOR SWITCH Application March 31,

18 Claims.

This invention relates to selector switches applicable for use in machine switching telephone systems and more particularly to switches of the terminal hunting type having access to large groups of line or trunk terminals.

In machine switching telephone systems selector switches, either of the step-by-step or power driven panel type, are used extensively as line or trunk finders and in some systems as trunk finders at selection stages under the control of controllers or markers. Heretofore such switches have been limited in their speed of operation by their inherent physical characteristics; in the case of step-by-step type switches, by the speed at which the stepping mechanism can be operated without undue wear and vibration and in the case of power driven switches of the panel type, by the speed at which the brushes may be stopped and accurately centered by the commutators on the desired set of bank terminals.

For example, the panel type line finder now widely used, employs ten sets of brushes mounted on a single elevator rod, the ten brush sets having access to ten banks of terminals in which subscribers lines terminate. With this construction it is necessary that the distances between the brush sets on the elevator rod and the distances between terminals in the banks be in accurate relationship thus increasing the cost of manufacture and assembly. Each line finder is also equipped with a stationary commutator with which brushes mounted on the elevator rod engage for making electrical connections between the brush sets and outside wiring and for controlling the stopping of the hunting movement of the switch when one of the brush sets engages the terminals of a calling line. Since the accurate centering of a brush set upon the terminals of a calling line is dependent upon the commutator, it is therefore essential that the commutator be constructed and assembled on the switch with its segments in accurate relationship with the terminals of the bank. Furthermore, since the total mass of the switch to be accelerated and decelerated comprises the elevator rod, the ten brush sets, the commutator brushes and the wiring between the brush sets and commutator brushes, the energy necessary for starting and stopping the movement of the switch is such that the hunting speed must be kept low or at approximately forty terminals per second. It is customary to mount the ten panel banks upon a single frame and to assemble thirty elevators on the frame on each side of the double-faced bank. A unit of this type is too large and heavy 1937, Serial No. 133,969

for shipment as an entirety and therefore it is necessary to partially disassemble the unit before shipment and to reassemble it at the place of installation thus further adding to the cost.

Since the central office equipment for machine switching systems is expensive it is particularly essential, therefore, that it be used with the utmost efficiency. If equipment is slow in operation, a larger amount of equipment must be installed to handle peak loads than would be the case if equipment of a faster operating type were available, thus increasing the first cost of installation and increasing the carrying charges and cost of maintenance. Furthermore, it is essential that connections shall be established between subscribers lines and central oifice equipment as speedily as possible to guard against the possibility of wrong connections should subscribers start dialing within a short interval after the removal of their receivers from the switchhooks.

It is therefore the object of the present invention to provide a switch of the hunting type which may be driven at a high terminal hunting speed, which has a small mass to be accelerated and decelerated whereby small energy is required for its operation, which makes provision for the accurate centering of a brush set on a set of bank terminals which has been placed in a calling condition without the use of a centering commutator and which is economical to manufacture, assemble and maintain.

A further object of the invention is to provide a switch which may be used in any type of machine switching system where line finders, trunk finders or marker controlled selectors of the hunting type may be employed.

In accordance with the present invention these objects are attained by providing a line-finder frame capable of accommodating the customary sixty finder switch units. Two banks of the same general type as are commonly used on the wellknown panel type switch frame are mounted vertically thereon side by side, each bank being provided with one hundred sets of vertically disposed multiple terminal strips, each strip having multiples for accessibility from thirty finder switch units on each side of the banks. By the provision of the two banks of one hundred terminal sets each, two hundred lines, trunks or links may be terminated thereon.

Mounted horizontally on each side of the frame in front of the thirty horizontal rows of two hundred terminal sets of the two banks are thirty finder switch units, For operating the thirty finder switch units on one side of the frame, two

oppositely rotatable vertical drive shafts are provided, one at each end of the frame. Two similar drive shafts are provided for operating the thirty switch units on the opposite side of the frame.

Each switch unit comprises a single brush set of three or more brushes mounted on a light carriage slidable on a tubular guide rod secured at its opposite ends to brackets attached to the outside edges of the faces of the bank, the outside connections to the sleeve brush being made by springs which slide on the guide rod and the outside connections to the other brushes being made by flexible insulated lead wires coiled around the rod on either side of the brush carriage. The brush set is traversed along the .row of bank terminals to which it is individual by a steel tape which runs over two pulleys or flanged drums mounted for free rotation on the two vertical drive shafts, respectively. The ends of the tape are secured to the brush carriage by coiled springs which function to tension the tape and to act as shock absorbers when the movement of the tape is abruptly arrested.

Each driving pulley may be clutched to the driving shaft on which it is mounted by a magnetic clutch of the pot type, the core of the clutch magnet being keyed to the drivingshaft and the armature of the magnet being connected to the associated pulley by a driving pin secured to the pulley and loosely engaging with the armature. Normally when the clutch magnet is not energized, the armature is held away from the periphery of the magnet core by a spring leaving a small air-gap between the core and the armature thereby eliminating friction. When the clutch magnet is energized the armature is attracted and the pulley is driven thereby in the rotational direction of the driving shaft.

To insure a quick stopping of the tape andbrush carriage attached thereto a magnetically releasable brake is provided. The brake includes two cooperating brake shoes, one on either side of one traverse of the tape,-one being fixed and the other secured to the armature of the brake magnet.

' .The armature is normally operated by a spring to press the shoes together to embrace the tape, the leverage of the armature being such that the movement of the shoe attached thereto is very slight but that the braking force supplied by the spring is quite large.

The brake magnet winding is arranged to be energized simultaneously with either one of the clutch magnets of the switch unit so that when either one of the clutch magnets is energized to traverse the tape in either direction the brake magnet is energized to attract its armature to release the brake.

The brush carriage is normally positioned at the midepoint between the two banks and when started in either direction operates a double throw normalling switch positioned on a mid-portion of the switch frame. This switch isinstrumental in reversing the direction of travel of the brush carriage when the connection made by the switch unit is released and for stopping the carriage in its normal position.

Since the moving parts of the switch unit have very little mass, the brush carriage may be accelerated or decelerated rapidly and the switch 3 is therefore capable of being operated with a very small amount of power at hunting speeds far in excess of those heretofore attained. In fact, a hunting speed of 250 terminals per second is easily attainable and a hunting speed of 400 terminals per second is possible.

To insure that the brush set when traversed at these high hunting speeds shall be stopped and accurately centered on a terminal set which has been marked in a calling condition, a particularly sensitive test circuit is provided. The test circuit comprises a test relay, the Winding of which is normally connected in a charging circuit extending from battery through a first and a second resistance and a first condenser to ground, the first resistance being shunted by a second condenser.

The relay starts to energize, but will not operate by the charging current, but the condensers both become charged. When, however, the grounded test brush engages a marked test terminal the condensers partially discharge and the relay is energized through the first resistance. If the test brush overruns the test terminal both condensers become further charged and the charging current now holds the relay operated until the charging current decays when the relay releases. The test relay upon operating stops the movement of the brush carriage and prepares circuits for driving it. in the opposite direction. If

the brush set has overrun the marked terminal set then when the test relay releases the brush carriage is driven back until the test brush again engages the marked set of terminals. second condenser is now fully charged it offers alow resistance shunt around the first resistance and the test relay reoperates opening the drive circuit to arrest further movement of the brush carriage.

Although in the foregoing brief description of the invention the two terminal banks have been described as mounted vertically on the frame with the switch units mounted horizontally, it will be obvious that the banks could be mounted horizontally one above the other, with the switch units mounted vertically. It should be particularly noted that the entire frame with sixty switch units mounted thereon is very compact and occupies relatively small floor space and that due to the relatively light weight of each switch unit the entire frame may be assembled and wired at the factory and shipped ready for installation. Furthermore, the replacement of any switch unit may be readily and speedily accomplished.

For a more complete understanding of the invention and the mode of its operation reference may be had to the following detailed description taken in connection with the accompanying drawings of which: s V

Fig. lis a side elevational view of a switch frame embodying the invention showing some of the switch units installed thereon;

Fig. 2 is a top plan view of the'switch frame;

Fig. 3 is a plan view of the normalling switch;

Fig. l is a sectional viewof the normalling switch as viewed along section line 'i l of Fig. 3;

Fig. 5 is a partial sectional View of the normalling switch as viewed along section line 5-5 of Fig. 3; V

Fig. 6 is a sectional view of a portion of a terminal bank and brush carriage as viewed along section line 6-6 of Fig. '7;

Fig. '7 is a top plan view of a portion of a terminal bank and brush carriage as viewed along section line il of Fig. 2;

Fig. 8 is a sectional View of one of the driving pulleys and associated magnetic clutch; and

Fig. 9 is a circuit diagram illustrating the manner in which the improved switch may be used as a line finder in a telephone system 'of the step-by-step type.

Referring now to the drawings, the invention Since the V will be described in more detail. Considering first Figs. 1 and 2, the switch frame comprises a base i on one end of which are secured two channel-shaped uprights 2 and 3 jointed at their upper ends by the strap 4 welded or otherwise secured thereto and joined near their lower ends by the angle bar 5 welded or otherwise secured thereto and by which the uprights are secured to the base 1. Similar uprights 6 and i joined by the strap 8 and angle bar 9 are similarly mounted in the other end of the base I. The upper ends of uprights 2 and 3 are .also joined to the upper ends of uprights 6 and l by the angle bar it! welded or otherwise secured thereto. The lower ends of the uprights 2 and 3 are similarly jointed to the lower ends of uprights 6 and l by angle bar H.

Bolted to the mid-point of the upper angle bar it! is a channel member 52 having its flanges lying parallel to the bar l6 and extending down- Wardly. A similar channel member I3 is bolted to the mid-point of the lower angle bar Ii having its flanges extending upwardly. Four vertically extending angle bars M, l5, l5 and ii, two on each side of the switch frame, are at tached by screws to the flanges of members !2 and I3 for supporting the normalling switches of the switch units as will be hereinafter described.

Bolted to the upper angle bar iii near its right end is a channel member i8 having its flanges lying parallel to the bar ii! and extending downwardly. A similar channel member is bolted to the lower angle bar 5! near its right end having its flanges extending upwardly. Two vertically positioned plates l9 and 29, one on each side of the switch frame, are attached by screws to the flanges of these channel members to .afiord support for the brake magnets of the switch units as will be later described.

Positioned side by side between the end members of the switch frame are two panel terminal banks 2i and 22. Each bank is of the general type disclosed, for example, in Patent 1,127,741 granted February 9, 1915 to A. F. Dixon, and comprises two vertical side members 23 and 24 between which one hundred sets of multiple terminal strips and insulating separators are clamped. The banks are secured to the angle bars lb and H by straps 25 and 28 which are attached to the angle bars by screws and to side members 23 and 24 of the bank by bolts 27. Each terminal strip is provided with thirty multiple terminals extending outwardly on each side of the bank and with a soldering terminal at each end whereby accessibility is aiiorded to sixty selector switch units, thirty on each side of the bank. The terminal strips are arranged in sets of four, as most clearly disclosed in Figs. 6 and '7, to which the tip, ring, sleeve and metering leads of a subscribers line may be connected as disclosed in Fig. 9, although in some instances, as for example where the switch frame is to be used for other purposes. each set might comprise three terminal strips. The corresponding sets of multiple terminals on the several sets of strips in both banks are aligned horizontally and individualized to different selector switch units. To enable the alignment of the horizontal rows of terminal sets of one bank with the corresponding horizontal rows of terminal sets of the other bank, adjusting screws 28 are provided which extend through the lower angle bar H and engage beneath the side members 23 and 24 01 the banks.

Secured to the side member 24 of each bank by lag screws 29 is a flat plate 36 to either face of which brackets 3! for supporting the tubular guide rod 33 of the selector switch unit are attached by the screws 32 as most clearly shown in Fig. 2. Slidable on each guide rod 33 is a brush carriage 36 having a rectangular frame, the ends of which slidably embrace the guide rod 33. Referring to Fig. 7 which shows the brush carriage in more detail, two spring fingers or brushes 35 are secured to the sides of the brush carriage frame and make sliding contact with guide rod 33. Attached to the front side of the frame by bolt 36 is a channel member 3'? to the out-turned flanges of which a plate 38 is secured by screws 39. Secured to the plate 38 is an angular trip rod 41 having an insulated tip 48 for a purpose to be later described.

Also secured to the flanges of channel member 3'! by screws are six brushes M to 45, inclusive. Brushes M and 42, which serve as sleeve brushes, engage the opposite edges of sleeve terminals of the bank, as shown in Fig. 6, and are conductively connected together at their fixed ends and through the screws ii! to the member 3? and thereby through the carriage frame and brushes 35 to the guide rod. The brush 43, which serves as a tip brush and engages the left edges of the tip terminals of the bank, as disclosed in Fig. 6, is insulated from the springs and 42 and from the member 3?. Brush 44 which serves as a ring brush and engages the right edges of the ring terminals of the bank and brushes 45 and 46 which serve as testing and metering brushes, respectively, and engage with the opposite edges of the metering or test terminals of the bank, as shown in Fig. 6, are insulated from each other and from the member 3i. It is to be noted by reference to Fig. 6 that the contact area of test brush 45 is narrower than the contact areas of the other brushes. Brushes 43 to 4-6, inclusive, are equipped with soldering lugs as most clearly disclosed in Fig. 2.

Mounted on the bracket 3! at the left end of the guide rod 33 is a terminal block 49 in which are insulatedly secured five soldering terminals to which outside wiring may be connected. One of the terminals is ccnductively connected to the guide rod whereby an electrical connection may be made to the sleeve brushes ii and i2 and the other four terminals are connected by flexible insulated leads to the soldering lugs of brushes 43 to 46, inclusive. The two flexible leads which connect with brushes 43 and M are wound spirally around the guide rod 33 on the left side of the brush carriage 34, as indicated at 56, and the flexible leads which connect with brushes 55 and 65 extend through the tubular guide rod, are brought out through an opening in its wall near the right end thereof and are then wound spirally around the guide rod on the right side of the brush carriage and connected to the soldering lugs of brushes % 5 and 46, as indicated at 5%. By thus winding the leads spirally around the guide rod and providing a sliding connection from the sleeve brushes 4% and 42 to the guide rod, electrical connections from the terminals on block 49 to the brushes on the brush carriage are completed while permitting free sliding movement of the brush carriage in either direction along the guide rod.

For traversing the brush carriage along the guide rod a steel tape belt 52 is provided which runs over two driving pulleys or flanged drums 53 and5 i located adjacent to the end uprights of the switch frame. The two ends of the belt 52 are connected to the opposite ends of the brush carriage by spiral springs 55 which serve the dual purpose of tensioning the belt and of absorbing the the shock incident to starting and stopping the brush carriage. Two vertical drive shafts 55 and 57 are provided on the front side of the switch frame, the driving pulleys 53 of all thirty of the switch units mounted on the front of the frame being normally freely rotatable on shaft 56 and the driving pulleys 54 of the same switch units being normally freely rotatable on shaft The shaft 55 is journaled in bearings 58 and 53 secured by screws, not shown, to the vertical upright 2 and the shaft 51 is similarly journaled in bearings 65 and ti secured by screws, not shown, to the vertical upright 65. Corresponding drive shafts are similarly journaled in bearings secured to uprights 3 and l on which the driving pulleys of all thirty of the switch units mounted on the rear of the frame are normally freely rotatable.

The two vertical drive shafts 55 and 57 on the front of the frame are geared by beveled gears 52 and 53 to be rotated in opposite directions from a main horizontal power shaft 60. which is journaled in bearings 55 and 56 secured to the base i of the switch frame. A similar power shaft and gearing is also provided for rotating the vertical drive shafts on the rear of the switch frame.

For operatively coupling a driving pulley to the driving shaft upon which it is positioned a magnetic clutch is associated with each pulley. One of the pulleys 53 and associated clutch is illus trated in detail in Fig. 8. The pulley comprises a metal flanged rim 5T molded upon a core 68 of bakelite or other suitable insulating material. Mounted beneath the pulley is a magnetic clutch of the so-called pot type comprising a core 55 secured to the drive shaft 56 by the set screw l I, a magnet winding '52 enclosed within the core between the inner hub thereof and the outer peripheral pole-piece, and a disc-shaped armature l3. Interposed between the core 58 of the pulley and the shaft 55 and engaging within an annular recess in the hub of the core iii are needle bearings 59 which enable the pulley 53 to rotate freely with respect to the shaft 55. For holding the pulley 53 and needle bearings 69 in proper relationship to the clutch, a collar M is secured to the shaft 55 immediately above the pulley by the set screw 15.

The armature E3, which is interposed between the pulley 53 and the pole-face of the peripheral pole-piece of the core 75, slidably engages the hub of the core and is normally pressed away from the poleface of the core by the spider spring '16 whereby a narrow air-gap is normally maintained between the armature and the poleiace of the core thereby eliminating friction between the rotating core and the armature. The armature is coupled to the pulley 53 by pin 1'! embedded in the bakelite core 68 and slidably engaged in an aperture in the armature. Normally with the magnet winding i2 unenergized, the rotation of the shaft 55 and clutch core '55 carried thereby is without effect upon the pulley, but upon the energization of the winding l2 and the attraction of the armature 13 against the poleface of the core 1B, the armature is rotated with the core and through the pin 'il causes the rotation of the pulley 53.

One terminal of the winding #2 is conductively connected to the core 15 of the clutch and thereby to the shaft 56 and the other terminal is connected to a slip ring 18 which is mounted on the outer peripheral surface of the core 15 and insulated therefrom by the insulating ring 19. For conducting operating current to each clutch magnet winding a brush assembly individual to each clutch and a brush individual to each vertical drive shaft are provided as shown in Fig. 1. The brush which is individual to the shaft 56 comprises a flat spring secured to the upright 2 which engages with the collar 85 secured to the shaft 55. The brush assembly which is individual to each clutch comprises, as most clearly disclosed in Fig. 2, a cylindrical brush guide 82 riveted or otherwise secured to the insulating support 53 and within which a carbon brush rod 34 engaging the slip ring 78 of the clutch is slidably positioned and a contact spring 85 which engages with the outer end of the brush 5d. The spring 85 is insulatedly mounted on the support 83 and together with the support are attached to the upright 2 by screws 86.

Associated with each switch unit is a magnetically controlled brake which cooperates with the tape belt 52 thereof. The brakes of all units on the front of the switch frame are secured to the vertical plate I9 and the brakes of all units on the back of the frame are secured to the vertical plate 25. Each brake comprises an end support 5'! which is held in spaced relation from the vertical plate to which the brake is secured by sleeves 88. Screws 89 which extend through the support 87 and sleeves 88 engage in threaded openings in the vertical plate, for example the plate i5. Se-' cured to the inner side of the support 81 is an L-shaped return pole-piece through which and through the support Bl the magnet core Si is threaded. The threaded end of the core is provided with a slotted end portion by means of which the core may be turned in the threaded opening of the support 8? for adjusting the airgap between the free end of the core and'the magnet armature. For clamping the core in its adjusted position the lock nut 92 is provided. A magnet coil 93 is supported on the free end of the core 9|.

Secured to the free end of the pole-piece 95 by suitable screws is an L-shaped bracket 55 provided at the end adjacent to the free end of the polepiece with ears between which the magnet armature 95 is pivoted. One end of the armature overlies the end of the pole-piece 9i and the magnet core 5! and is provided near its pivot with a brake shoe 96 which cooperates with a brake shoe 9'! attached to the plate 19. The coiled spring 98, one end of which is secured to the outer end of the armature 95 and the other end of which is secured to the free end of bracket 94%, is provided for normally retracting the armature 95 and forcing the brake shoe 95 carried thereby toward the stationary brake shoe 97 to clamp the tape 52 therebetween. The position of the brake shoe 96 with respect to the pivot'point of the armature, to the point of attachment of the spring 58 to the armature and to the end of the armature which overlies the end of the core Si is so chosen that the motion of the brake shoe is very slight, in the order of a few thousandths of an inch, but that the braking effort applied thereto by the spring 98 is quite large. Since, however, the end of the armature which overlies the magnet core has considerable leverage, the magnet coil 53 when energized is quickly able to overcome the spring 98 and to disengage the brake shoe 95 from the tape 52.

Each switch unit is provided with a normalling switch Itll, the normalling switches of the switch units on the front of the switch frame being attached to the vertical angle bars I4 and I5 and the switches of the switch units on the back of the frame being attached to the angle bars Iii and II. The normalling switch which is disclosed in Figs. 3 to 5, inclusive, comprises a horizontal mounting plate having downwardly and outwardly extending ears I02 and H33 by means of which it may be secured by screws to the angle bars, two contact pile-ups secured thereto and insulated therefrom by the hard rubber insulating strip I6 and a switch bar pivoted on the central portion of the mounting plate between the two contact pile-ups.

The left-hand contact pile-up comprises two separate bottom contact members E and Iilfi positioned adjacent to the insulating strip I04 and out of contact with each other, the member N25 having a soldering terminal I97 and the member i538 having a soldering terminal Hi8. Superimposed on the members I85 and Ifit is a hard rubber insulating strip I89 on the upper portion of which is superimposed the contact member l i having the soldering terminal I I I. The contact members 3% and H6 are arcuate in formation and extend parallelly toward the pivoted switch bar. For securing the members of the contact pile-up to the support IIlI, bolts H2 are provided which extend through the contact members and insulating strips lli l and I99 and are insulated from the contact members by insulating sleeves surrounding their shanks and by insulating washers I I3 inserted beneath their heads.

The right-hand contact pile-up comprises a bottom contact member II I positioned adjacent to the insulating strip I84 having a soldering terminal H5, an insulating strip H6 superimposed thereon and two contact members Ill and II8 superimposed on the strip IIE, the member II'I having a soldering terminal I I9 and the member IIS having a soldering terminal I28. The contact members H4 and Ill are arcuate in formation and extend parallelly toward the pivoted switch bar. For securing the members of the contact pile-up to the support IQI, bolts H2 are provided which extend through the contact members and insulating strips Ifl l and H6 and are insulated from the contact members by insulating sleeves surrounding their shanks and by the insulating washers H3 inserted beneath their heads.

The pivoted switch bar is a composite member comprising two blades I2! and I22 separated from each other by an interposed strip of insulating material. The composite switch bar is pivoted on a bolt I 23 which extends through the metal sleeve IZ I, the mounting plate IEI, insulating strip I M, contact member I65, the composite switch bar, the contact member IIS and the insulating washer I25 and is held in place by the lock nuts I25. For insulating the bolt from the contact members I 35 and I I8 and from the blades IZI and I22, the bolt is surrounded by an insulating sleeve as most clearly shown in Fig. 4. As thus assembled the switch blade I2I is in electrical contact with the contact member H8 and the blade I22 is in electrical contact with the contact member I535, good contact therebetween being insured by the spiral spring I27 which is interposed between the head of the bolt I23 and the mounting plate IBI surrounding the sleeve I24.

Pivoted to the outer end of the switch blade I22 are two fingers I28 and I29, the inner ends of which are normally positioned against the stop pins I36 by the coiled spring I3I, the ends of which are secured to the inner ends of the fingers. In the upper portion of Fig. 2 the switch unit brush carriage is shown in its normal position at the mid-point between the terminal banks in which position the insulated tip 48 of the trip rod 4? attached to the brush carriage is engaged between the fingers I28 and of the switch bar of the associated normalling switch and the switch bar is thus held in its neutral position, or the position disclosed in Fig. 3.

Should the brush carriage move to the left, as viewed in Fig. 3, and engage the insulating tip 38 of its trip rod ll against the finger I28, due to the engagement of the finger against the stop pin I31! the movement of the brush carriage will rotate the switch bar about the pivot bolt I23 thereby engaging its blades I2I and I22, respectively, with the contact members H6 and I93 whereby two circuits are established, one from soldering terminal III? of contact member We through switch blade I22 and contact member Illl": to the soldering terminal I68 thereof and the other from soldering terminal IZii of contact member I i8 through switch blade IEI and contact member Hi? to soldering terminal III. Should the brush carriage move to the right, as viewed in Fig. 3, and engage the insulating tip d8 of its trip rod 4? against the finger I29, the switch bar then will be rotated to the right thereby engaging its blades iii and I22, respectively, with the contact members I II and I It whereby two circuits are established, one from soldering terminal Ii]? of contact member I05 through switch blade I22 and contact member I It to the soldering terminal I I5 thereof, and the other from soldering terminal I20 of contact member H8 through switch blade Ill and contact member II! to the soldering terminal IIE thereof. The purpose of these circuits will be apparent from the following description of the application of the invention to a typical telephone system.

For the purpose of illustrating one of the many possible uses of the selector switch hereinbefore described, the switch has been shown in Fig. 9 as a line finder in a machine switching telephone system of the well-known step-by-step type. It is to be understood, however, that it could be equally well used in any type of telephone system where line, trunk or link hunting functions are to be performed.

Referring now to Fig. 9, two of the subscribers lines I32 and I33 of a group of two hundred lines are shown terminating, respectively, in the banks 2i and 22 of a line-finder frame. The brushes II to 46, inclusive, clutch magnets l2 and I36, brake magnet 93 and normalling switch I 69 of one of the switch units on the line-finder frame, the control relays individual thereto, the control relays common to all switch units on the frame and the brushes and some of the relays of the first selector switch IQI] individual to the linefinder switch unit are also shown.

It will first be assumed that the subscriber whose line is indicated at I32 as terminating in bank 2 I, or the left bank of the line-finder frame, initiates a call by removing the substation receiver from the switchhook thereby establishing a circuit for the line relay I35. This circuit may be traced from battery through the winding of relay I35, the right back contact of cut-oif relay I38, ring conductor I31 of the line, through the sub station, returning! over tip conductor I38 to ground at the left back contact of relay I35. Line relay I55 thereupon operates disconnecting at its back contact the winding of the subscribers message register magnet 139 from-the metering and test terminal I48 of the bank 2i, at its right front contact connecting the terminal I44 to the winding of test relay I4I which is common to all two hundred subscribers lines which terminate in banks 2! and 22 and at its left contact establishing a circuit from ground thereover, over the back contact of group relay I42 which is common to the one hundred lines including line I33 terminating in bank 22, to battery through the winding of group relay I43 which is common to the one hundred lines including line I32 terminating in bank 2I.

Group relay I43 upon operating opens at its back contact the operating circuit of group relay I42 to, prevent any line in its one-hundred line group, from starting a line finder at this time and at its outer right contact establishes a circuit for start relay I44 which is individual to the line-finder unit disclosed. This circuit may be traced from battery through the left winding of relay I44, the outer left back contact of start circuit relay I45 also individual to the line-finder unit disclosed, outer right contact of relay I43 torground at the right back contact of common relay I 50.

Relay I44 upon, operating prepares an operating circuit over its left front contact through the right winding of relay I45, at its left back contacts disconnects ground from the switch blades I2I and I22 of the normalling switch Iiill, at its inner right front contact prepares a locking circuit for itself, at its neXt-to-inner right front contat prepares an operating circuit for the right drive clutch magnet I34 of the line-finder unit disclosed, at its middle right front contact establishes an operating circuit for the left drive clutch magnet I2, at its neXtto-outer right front contact establishes an operating circuit for the brake magnet 93 and at its outer right front contact establishes a loop circuit for operating the line relay I45 of the first selector switch I90. This latter circuit may be traced from battery through the right winding of relay I46, left back contact of cut-through relay I41, outer right front contact of relay I44, inner right back contact of relay I41 to ground through the left winding ofrelay I45. Relay I45 operates 'over this circuit and establishes an obvious operating circuit for slow-to-release relay I48 thereby preparing the selector switch for subsequent operation and connecting ground to holding conductor I59.

The left drive clutch magnet 72' and the brake magnet 93. now operate simultaneously, the circuit for magnet I2 extending from battery through the magnet winding, the middle right front contact of relay I44, the inner right front contact of relay I43 to ground at the back contact ofcommon relay I49, and the circuit for magnet 93 extending from battery through the magnet winding, the neXt-to-outer right front contact of relay I44 to ground at the back contact of common test relay I4I. With magnet operated, the brake shoe 96 carried by its armature is withdrawn from the driving tape 52 of the linefinder switch unit and with clutch magnet 12 energizedthe driving pulley 53 is coupled to the vertical driving shaft 56 whereby the tape 52 is driven in such a direction as to move the brush carriage 34 of the switch unit toward the left in a hunting movement over a horizontal row of sets of terminals of the bank 2I to which the switch unit has access.

Upon the initial movement of the brush carriage from its normal position between the two banks of terminals, the trip rod 4? carried thereby moves the switch blades I2I and I22 of the normalling switch I65 to the left in which position the blade I2I engages terminal HE] and blade I22 engages terminal I55 for a purpose to be later described. As the brush carriage advances, the brushes M to 46 carried thereby successively engage the sets of bank terminals of the one hundred lines including line I32 which appear in the left bank 2!.

For arresting the movement of the brush carriage when the test brush 45 thereof encounters the test terminal of a calling line the fast operating test relay MI is provided whose winding is normally connected in a series circuit from battery through the 1000-ohrn resistance I55, the -ohm resistance I5! and a first condenser I52 to ground, the resistance I55 being shunted by a second condenser I53. Condensers I52 and I53 are thus normally fully charged over this circuit. When now in the advance of the brush carriage the narrow test brush 45 engages the test terminal I45 of the calling line to which the winding of the test relay I4I has been connected, as previously described, a circuit is established from ground through resistance I58, the right back contact of relay I45, test brush 45, terminal 445, right front contact of relay I35, resistance I55 and winding of relay I4! to battery. Relay I 4| will tend to operate over this circuit, but may not have time to fully operate if the brush carriage is then traveling at high speed since the test brush 45 may overrun the test terminal I40 and make a passing contact therewith for only a small fraction of a second. For example, if the brush carriage is moving at a testing speed of three hundred terminals per second, the engagement of test brush 45 with terminal I44 may be for only approximately .0013 second. This time is not sufficient to operate relay I4I for releasing the brake magnet 93 and for stopping the brush set on the calling line terminal set. Condensers E52 and E53 and resistances I55 and I5! are therefore provided to insure a positive and uniform circuit for operating the test relay while without them the relay would not have time to operate either due to the testing speed of the test brush 4-5, or due to the vibration of the test brush on the test terminal.

When therefore the test brush 45 momentarily engages the test terminal I40 a discharge path for condenser I52 is established from ground through resistance I58 applied over the test brush, through resistance I5I and condenser I52 to ground, over which path condenser I52 discharges sufficiently so that when the test brush overruns and leaves the test terminal I40 sufficient current will flow from battery through the winding of relay I4I, condenser I53 which is now charged and offers a low resistance, resistance I 5i and condenser I 52 to ground to cause the operation of test relay I4I. Relay I4I will now remain operated until condenser I52 becomes fully charged at which time due to the decay of the charging current, relay I4! will release.

As soon as relay I 4i operates it opens at its back contact the operating circuit of brake magnet 93 which immediately releases clamping the moving tape 52 of the finder switch unit between the brake shoes 96 and 91 to immediately arrest the movement of the tape. Magnet 93 is made slightly slow to release at this time by the removal of the shunt from the circuit extending through resistance IBI, condenser 62, back contact of relay I83 and the back contact of relay 559 to ground. t substantially the same instan' the energization of test relay MI establishes an operating circuit for relay M extending from ground over its front contact, through resistance 55d and the winding of relay I49 to battery. Relay 9 59 upon operating opens at its back contact the operating circuit of the left drive clutch magnet '32 and locks itself in a circuit extending from battery through its winding, resistance ie' l an its own left contact, winding of relay 859 to ground at the left back contact of relay ltd. Relay E59 does not, however, operate in this locking circuit since its winding is shunted by ground applied over the front contact of relay I4! so long as relay I4! remains operated.

To insure that relay E49 will operate and lock. even though its operating circuit is momentarily opened due to the vibration of the front contact of test relay Ml, resistances I56 and I55 and condensers lfit and 55? are provided, the condensers being normally charged over a path extending from battery through the winding of relay M9, condenser Itl'l, resistance I55, condenser I55 to ground. Should the front contact of relay MI chatter upon closing, a momentary closure thereof while of insufiicient duration to cause relay t ltto operate and lock, will cause condenser to discharge sufiiciently over the discharge path traced from ground over the front contact of relay Mi through resistance I55 and condenser 555 to ground so that if the front contact of relay Mi should then momentarily open due to chatter, sufficient current will flow from battery through the winding of relay M9, condenser I5? is now charged and offers a low resistance, resistance and condenser I56 to ground to cause the operation of relay Hi9 which will then look as previously described.

As soon as relay I49 operates it completes the operating circuit for the right drive clutch magnet I34 which be traced from battery, winding of magnet I34, next-to-inner right front contact of relay I4 3, middle right front contact of relay I43 to ground at the right front contact of relay Hi9. Upon the release of test relay M! as previously described, ground is removed from the operating circuit of relay I49 and from one terminal of the winding of relay I59 and relay I59 now operates in the locking circuit of relay H39 in turn establishing an obvious operating circuit for slow-to-release relay I63. At its back contact relay MI again establishes the previously traced operating circuit for brake magnet 93. With brake magnet 93 and the right drive clutch magnet ISG both operated, the brush carriage is now driven toward the right thus moving the test brush 55 back upon the test terminal I49 of the calling line at which time, since the brush carriage has not had time to attain a high speed, an operating circuit for test relay I 45 is established from ground applied to the test brush through resistance I58, thence over test terminal I lIl, condenser I53 which being fully charged offers a low resistance to the flow of current in parallel with resistance I58, winding of relay MI to battery. Relay MI now operates to open the circuit of the brake magnet 93 and since with relay I653 operated the circuit through resistance It! and condenser I 52 is ineffective, magnet 93 releases quickly to arrest the movement of the brush carriage with the brushes thereof in engagement with the terminal set of the calling line I32.

Relay MI upon operating now shunts down relay I59 which immediately releases and opens the circuit of relay I63. Before slow-to-release relay I53 has time to release, with relay I59 released, an operating circuit is established for relay I60 which may be traced from ground at the back contact of relay I59, front contact of relay I63, winding of relay I68, inner right front contact and right winding of relay I44 to battery. Relay I66 now operates opening at its right back contact the initial operating circuit of relay M l, opening at its left back contact the locking circuit of relay M9 which, however, is now maintained operated under the control of relay MI, and at its right front contact establishes the operating circuit of start circuit relay M5. The circuit of relay I45 may be traced from battery through its right winding, the outer left front contact of relay M4 to ground at the right front contact of relay I Bil. Relay I45 upon operating looks over its inner right front contacts to ground at the left contact of relay I48. When relay I63 finally releases, after a predetermined interval following the release of relay i539, the circuit through the winding of relay I68 and locking winding of relay lid is opened and relays i653 and Hi l now both release since the initial operating circuit of relay #34 has now been opened through the operation of relay I 55. With relay M4 now released the circuit of clutch magnet S34 is now opened.

With start circuit relay I 35 operated the tip and ring conductors E38 and I3? of the calling line are extended over terminals 564 and !65, brushes 43 and M, outer right front contacts of relay I 15, back contacts of cut-through relay M? to the windings of relay I45 for holding relays ME and i 38 operated, and a circuit is established for operating the cut-off relay E36 of the calling line which may be traced from ground at the left contact of relay I 48, conductor IE9, inner right front contact of relay M5, brushes ll and 42 in multiple, sleeve terminal I66 to battery through the winding of cut-oil relay I36. This same ground is also applied to the test multiples I ill of the calling line appearing in the banks of all connector switches having access to the line to mark the line busy to such connector switches. Relay M5 at its outer leftfront contact also extends the start wire extending from the contacts of group relays I 32 and IE3 so that if any other line in the two-hundred line group of subscribers lines is calling, the start relay of another available line-finder unit, corresponding to relay I44, may be operated to start such other line-finder unit. At its right back contact relay I45 also opens the circuit of test relay I'll which releases and in turn releases relay Hi9 and at its next-to-inner right front contact relay I 25 connects the test brush 55 and metering brush 45 together preparatory to the control of metering.

The cut-off relay I36 upon operating disconnects the winding of line relay I35 from the calling line whereupon relay I35 releases reconnecting the message register magnet I39 to the terminal I59, opening at its right front contact a 7 second point in the operating circuit of test relay MI and at its left contact opening the operating circuit of group relay I43 which will now release if no other line in the same onehundred line group of lines in which the calling line I32 is located is at the timein a calling condition. The common control relays I4I, I49, I59, I62 and I63 are now released and in condition to control another line-finder switch unit for establishing a connection with another calling line.

The calling line being now operatively connected with the first selector switch I90, the calling subscriber may proceed to operate his substation dial to directively set up a connection to a desired subscribers line, cut-through relay I47! operating in the usual manner after the operation of the selector switch I98 to cut thetalking circuit through to the succeeding selector switch and to disconnect the windings of relay I46, which relay thereupon releases in turn releasing relay I48. Locking ground for relay I45 and for maintaining cut-off relay I36 operated is thereafter supplied in the usual manner from the succeeding selector switch over a front contact of cut-through relay I4? and conductor I69. If the call is successfully made, metering ground is connected as indicated at I68 in the usual manner thereby establishing a. circuit from such ground to brush 45 and in parallel over the next-to-inner right front contact of relay I45 to brush 45, thence over terminal I40 and the back contact of line relay I35 to battery through the message register magnet I39.

When the established connection is no longer required and the subscribers restore their receivers to their switchhooks, the selector switches employed in establishing the connection are restored in the usual manner and holding ground is removed from conductor I69 thereby releasing cut-off relay I 36 of the calling line and re-- leasing relay I45. With both relays I45 and I44 released, ground is connected over the back contacts thereof to switch blades I2! and I22 of the normalling switch IEIII. It will be recalled that the blades of this switch were moved to the left by the movement of the brush carriage to the left. Therefore, a circuit is now established from ground over the middle left back contact of relay I45, the outer left back contact of relay I44, switch blade I2I, contact terminal III) and winding of right drive clutch magnet I34 to battery and a second circuit is established from ground over the inner left back contact of relay I45, the inner left back contact of relay I44, switch blade I22, contact terminal H36 and winding of brake magnet 93 to battery. Magnets I 34 and 93 now operate, magnet 93 releasing the brake shoe 96 from the tape 52 and magnet I34 causing the tape 52 to be driven in such a direction as to move the brush carriage toward the right. When the trip rod 47 engages the finger I28 carried by the switch bar I22 of the normalling switch,

, it rotates it away from the associated stop pin I32 against the tension of spring ISI and snaps over it into engagement with the finger I29 and since the finger I29 is prevented from pivoting by its associated stop pin I36, the switch blades I2I and I22 are moved by the continued move- 'ment of the brush carriage intotheir neutral position. As soon as the switch blades become disengaged from the contact terminals. I III and IE5, the circuits of magnets I34 and 93 are opened thereby arresting the further movement of the brush carriage. The brush carriage is now in its normal position midway between the two terminal banks as disclosed in Fig. 2.

It will now be assumed that the subscriber whose line I33 is disclosed as terminating in the right terminal bank 22 initiates a call thereby operating line relay III] to mark the test tei minal III with calling potential and tooperate the group relay I42. The circuit of relay I42 may be traced from ground at the left contact of relay Ilii, back contact of group relay I43, winding of group relay I42 to battery. In response to the operation of group relay I42, relay I44 is operated in the manner previously described and operating circuits are established thereby for the brake magnet 93 and the right drive clutch magnet I34. The operating circuit of magnet 93 is the same as previously traced. The operating circuit for magnet I34 may be traced from battery through the winding of magnet !34, next-to-inner right front contact of relay I44, middle right front contact of relay I42 toground at the back contact of relay I49.

Upon the energization of magnets 98 and I34 the brush carriage is driven to the right for hunting in the right terminal bank 22, the initial movement of the brush carriage moving the switch blades I ZI and I22 of the normalling switch I82 to the right into engagement respectively with contact terminals I If and H4. The circuits now function in the manner previously described except that the test relay I4! is now controlled tostop and center the brushes M to 46, inclusive, on the terminal set of the calling line I33 due to the engagement of the test brush 45 with the test terminal III. In this case, however, in the event that the brushes overrun the terminal set, the operation of relay I49 causes the operation of the left drive clutch magnet I2 to drive the brush carriage back to the terminal set over a circuit extending from battery, winding of magnet I2, middle right front contact of relay I44, inner right front contact of group relay I42 to ground at the right front contact of relay I49. I

When ground is removed from holding conductor I 69 upon the termination of the connection and relay hi5 releases, with relay I44 at that time released and the switch blades I2I and I22 in their right operated positions, circuits are established for the brake magnet 93 and the left drive clutch magnet 22 to drive the brush carriage toward the right intoits normal position. The circuit of brake magnet 93, may be traced from battery, winding of magnet 93, contact terminal H4, switch blade I22, inner left back contacts of relays I44 and I45 to ground and the circuit of clutch magnet I2 may be traced from battery through the winding of magnet I2, contact terminal II'I, switch blade I2I, outer left back contact of relay I44 and middle left back contact of relay 45 to ground. When the brush carriage reaches its normal position the switch blades I2I and I22 of the normalling switch are moved into their neutral position arresting the further movement of the brush carriage.

What is claimed is:

1. In a telephone system, a selector switch having a bank of terminals and a brush set cooperating therewith, means for advancing said brush set in a hunting movement over said bank of terminals, testing means for arresting the hunting movement of said brush set when it engages a marked terminal of said bank, and means controlled by said testing means for reversing the direction of movement of said set to return it to said marked terminal in the event said brush set overruns said terminal in its hunting movement.

2. In a telephone system, a selector switch having two banks of terminals and a brush set cooperating therewith normally positioned midway between said banks, means for advancing said brush set in a hunting movement over either one of said banks, testing means for arresting the hunting movement of said brush set when it engages a marked terminal of a bank, and means for reversing the direction of movement of said brush set in the event said brush set overruns said terminal in its hunting movement.

3. In a telephone system, a selector switch having a bank of terminals and a brush set cooperating therewith, means for advancing said brush set in a hunting movement over said bank of terminals, testing means for arresting the hunting movement of said brush set when it engages a marked terminal of said bank, means controlled by said testing means for reversing the direction of movement of said brush set to return it to said marked terminal in the event said brush set overruns said terminal in its hunt,- ing movement, and means controlled by said testing means for arresting the return movement of said brush set when it again engages the marked terminal of said bank.

4. In a telephone system, a selector switch having a panel bank of terminals and a brush set cooperating therewith, a belt for traversing said brush set across said bank, means for driving said belt one direction to traverse said brush set in hunting movement over said bank of terminals or in the reverse direction to return said brush set towards its normal position, testing means for arresting the hunting movement of said brush set when i engages a marked terminal of said bank and means operated by said testing means for controlling said driving means to reverse the direction of movement of said belt to return said brush set to said marked terminal in the event said brush set overruns said terminal in its hunting movement.

5. In a telephone system, a selector switch having a panel bank of terminals and a brush set cooperating therewith, a belt for traversing said brush set across said bank, a pair of driving pulleys over which said belt runs, means for driving one of said pulleys to traverse said belt in one direction to move the brush set in a hunting movement, means for driving the other of said pulleys to traverse said belt in the opposite direction to move said brush set in a return movement toward its normal position, testing means for arresting the hunting movement of said brush set when it engages a marked terminal of said bank, and means operated by said testing means for disabling said first driving means and for rendering said second driving means effective to return said brush set to said marked terminal in the event said brush set overruns said terminal in its hunting movement.

6. In a telephone system, a selector switch having a panel bank of terminals and a brush set cooperating therewith, a belt for traversing said brush set across said bank, a pair of driv ing pulleys over which said belt runs, said pulleys being normally loosely journaled respectively on two oppositely rotating driving shafts, a first magnetic clutch operative to connect one of said pulleys to-its driving shaft to traverse said belt in one direction to move said brush set in a hunting movement, a second magnetic clutch operative to connect the other of said pulleys to its driving shaft to traverse said belt in the opposite direction to move said brush set in a return movement towards its normal position, testing means for arresting the hunting movement of said brush set when it engages a marked terminal of said bank, and means operated by said testing means for disabling said first magnetic clutch and for rendering said second magnetic clutch effective to return said brush set to said marked terminal in the event said brush set overruns said terminal in its hunting movement.

'7. In a telephone system, a selector switch having two panel banks of terminals and a brush set cooperating therewith normally positioned midway between said banks, a belt for traversing said brush set across said banks, means for driving said belt, control means for causing said belt to be driven in one direction to move said brush set in a hunting movement over one of said banks, control means for causing said belt to be driven in the opposite direction to move said brush set in a hunting movement over the other of said banks, means operative in accordance with the bank in which a marked terminal is located for determining which one of said control means shall be eifective, testing means for arresting the hunting movement of said brush set when it engages a marked terminal in either bank, and means operated by said testing means for disabling the control means then effective and for rendering the other control means effective to return said brush set to said marked terminal in the event said brush set overruns said terminal in its hunting movement.

8. In a telephone system, a selector switch having two panel banks of terminals and a brush set cooperating therewith normally positioned midway between said banks, a belt for traversing said brush set across said banks, a pair of driving pulleys over which said belt runs, means for driving one of said pulleys to traverse said belt in one direction to move said brush set in a hunting movement over one of said banks, means for driving the other of said pulleys to traverse said belt in the opposite direction to move said brush set in a hunting movement over the other of said banks, means operative in accordance with the bank in which a marked terminal is located for determining which one of said driving means. shall be efiective, testing means for arresting the hunting movement of said brush set when it engages a marked terminal in either bank, and means operated by said testing means for disabling the driving means then effective and for rendering the other driving means effective to return said brush set to said marked terminal in the event said brush set overruns said terminal in its hunting movement.

9. In a telephone system, a selector switch having two panel banks of terminals and a brush set cooperating therewith normally positioned midway between said banks, means for advancing said brush set in a hunting movement over either one of said banks, means operative in accordance with the bank in which a marked terminal is located for determining the direction in which said brush set is advanced, testing means for arresting the hunting movement of said brush set when it engages a marked terminal in either bank, means for reversing the movement of said brush set in the event it overruns said terminal in its hunting movement, a normalling switch controlled by the movement of said brush set in either direction from its normal position, and means including said normalling switch to cause the return of said brush set to its normal position.

10. In a telephone system, a selector switch having two panel banks of terminals and a brush set cooperating therewith normally positioned midway between said banks, means for advancing said brush set in a hunting movement over either of said banks, means operative in accordance with the bank in which a marked terminal is located for determining the direction in which said brush set is advanced, testing means for arresting the hunting movement of said brush set when it engages a marked terminal in either bank, means for reversing the movement of said brush set in the event it overruns said terminal in its hunting movement, a double-throw normalling switch engageable by said brush set when said brush set is in its normal position and movable into either of its operated positions by the movement of said brush set in either direction from its normal position, and circuits controlled by said normalling switch to cause the return of said brush set to its normal position.

11. In a telephone system, a selector switch having a panel bank of terminals and a brush set cooperating therewith, a belt for traversing said brush set across said bank, means for driving said belt in one direction to traverse said brush set in a hunting movement over said bank of terminals or in the reverse direction to return said brush set toward its normal position, a test relay operable when said brush set engages a marked terminal during its hunting movement, an electromagnetically controlled brake engage- ;"able with said belt and operable upon the operation of said test relay to stop the movement of said belt and said brush set, and a relay operable upon the operation of said test relay for reversing the direction of movement of said belt to return said brush set to said marked terminal in the event said brush set overruns said terminal in its hunting movement.

12. In a telephone system, a selector switch having two panel banks of terminals and a brush set cooperating therewith normally positioned midway between said banks, a belt for traversing said brush set across said banks, means for driving said belt, control means for causing said belt to be driven in one direction to move said brush set in a hunting movement over one of said banks, control means for causing said belt to be driven in the opposite direction to move said brush set in a hunting movement over the other of said banks, means operative in accordance with the bank in which a marked terminal is located for determining which one of said control means shall be efiective, a test relay operable when said brush set engages a marked terminal in either bank during its hunting movement, an electromagnetically controlled brake engageable with said belt and operable upon the operation of said test relay to stop the movement of said belt and said brush set, and a relay operable upon the operation of said test relay for disabling the control means then eiiective and for rendering the 'other means efiective to return said brush set to said marked terminal in the event said brush set overruns said terminal in its hunting movement.

13. In a telephone system, a selector switch having two panel banks of terminals and a brush set cooperating therewith normally positioned midway between said banks, a belt for traversing said brush set across said banks, means for driving said belt, control means for causing said belt to be driven in one direction to move said brush set in a hunting movement over one of said banks, control means for causing said belt to be driven in the opposite direction to move said brush set in a hunting movement over the other of said banks, two groups of lines terminating respectively in said two banks, a line relay for each of said lines operable when said line is in a calling condition, a group relay common to each group of lines and operable when the line relay of any line of its group is operated, circuits controlled by said group relays for determining which one of said control means shall be effective, and a test relay associable with the test terminal of any line of said group by the operation of the line relay of said line for arresting the hunting movement of said brush set when it engages the test terminal of said calling line.

14. In a telephone system, a selector switch having a bank of terminals and a brush set 00- operating therewith, means for advancing said brush set in a hunting movement over said bank of terminals, an electrostatically controlled test relay for arresting the hunting movement of said brush set when it engages a marked terminal of said bank, and means controlled by said relay for reversing the direction of movement of said brush set to return it to said marked terminal in the event said brush set overruns said terminal in its hunting movement.

15. In a telephone system, a selector switch having a bank of terminals and a brush set cooperating therewith, means for advancing said brush set in a hunting movement over said bank of terminals, a test relay for arresting the hunting movement of said brush set when it engages a marked terminal of said bank, a condenser for sensitizing said relay, and means controlled by said relay for reversing the direction of movement of said brush set to return it to said marked terminal in the event said brush set overruns said terminal in its hunting movement.

16. In a telephone system, a selector switch having a bank of terminal sets each including a test terminal and a brush set including a test brush cooperating therewith, means for advancing said brush set in a hunting movement over said bank of terminals, 2. test relay, means for associating said test relay with any test terminal to mark said terminal as calling, a condenser, a resistance, a charging path for said condenser extending through said resistance and the winding of said test relay over which said condenser is normally fully charged, a discharge path for said condenser and an operating path for said relay effective when said test brush engages the test terminal to which said relay is connected over which path said condenser partially discharges and said relay tends to operate if said test brush makes only a momentary contact With said test terminal, said condenser recharging over said charging path in the event said test brush overruns said test terminal whereby said relay operates over said charging path, and means controlled by said relay for arresting the hunting movement of said brush set and for returning it to said test terminal.

1'7. In a telephone system, a selector switch having a terminal bank and a brush set cooperating therewith, means for advancing said brush set in a hunting movement over said bank of terminals, an electrostatically controlled test relay for arresting the hunting movement of said brush set when it engages a marked terminal of said bank, a relay controlled by said test relay for reversing the direction of movement of said brush set to return it to said marked terminal in the event said brush set overruns said terminal in its hunting movement, and electrostatic means for insuring the operation of said reversing relay.

18. In a telephone system, a selector switch having a terminal bank and a brush set cooperating therewith, means for advancing said brush set in a hunting movement over said bank of terminals, a test relay for arresting the hunting movement of said brush set when it engages a marked terminal of said bank, a relay for reversing the direction of movement of said brush set to return it to said marked terminal in the event said brush set overruns said terminal in its hunting movement, a condenser, a resistance, a charging path for said condenser extending through said resistance and said reversing relay over which said condenser is normally fully charged, and a discharge path for said condenser and an operating path for said reversing relay closed over the contacts of said test relay upon the operation thereof over which said condenser partly discharges and said reversing relay operates if the contacts of said test relay momentarily open.

WARREN W. CARPENTER.

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