US1886613A - Telephone system - Google Patents

Description

Nov. 8, 1932. J. wlcKs TELEPHONE SYSTEM Filed Dec. 14, 1931 Patented Nov. 8, 1932 UNl'iD STTES PATENT OFFICE JOHN XVCKS, Oli' OAK PARK, LLINOS, ASSIGNOR, BY MESNE ASSIGNMENTS, T0 ASSO- iTE-D ELECTRIC? LABORATORIES, ING., OF CHICAGO, ILLINOS, A CORPORATION OF DELAWARE TELEPHONE SYSTEM Application ined December 14, 1931.

The present invention relates to telephone systems in general, but is concerned moreV vertical and rotary switching mechanism;

u ot trunks connected thereto.

and the main object is the production of new and improved circuit arrangements for enabling the sets oi contacts in the bank of a selector to be variously apportioned amongst the trunk groups accessible from such selector. 'f

GENERAL Dnsoinrrion ils is well known, the ordinary Strowger switch has one hundred sets of bank contacts arranged in ten horizontal rows or levels. vWhen this switch is used as a trunk selector, each level ot contacts is ordinarily indexed by diil'erent digits and has a separate group The s-elector switches are ordinarily mounted side by side in groups or shelves, with a permanent multiple between the contact banks of all the switches in a shell?, and with arrangements for multipling the banks of a number of shelves togeher and for connecting the bank multiple with outgoing trunks; as is explained in the Mcllyea Patent No. 1,633,118, granted J une 2l, 182?. The number of shelves multipled together as regards a given level depends upon the relative amount of tratlic carried by the level in question,

In multi-oiiice telephone systems, the various groups olf trunks accessible to an otiice selector Otten vary greatly in size amongst themselves. Although, by using suitable grading, a trunk group can be Jformed which is in etre-ct a unitary group, but contains many more trunks than there are Contact sets allotted to the group in the bank oit any one selector, it is desirable, nevertheless, from the standpoint ot securing the greatest possible ciiiciency in each individual installation, to be able to ii crease and decrease the number ot Contact allotted to a contact group to an extent dictated by the relative size and cost-per-trunk ot the trunk groups concerned. To this end, the circuit arrangement has been modified in order to enable the size of a contactgroup in the bank ot the selector' to be sets Serial No. 580,779.

expanded or contracted at will by including any desired portion of the contacts in the next higher level in the same trunk group with the contacts in any given level. W'ith this novel arrangement, any level may be divided into two parts, each part being indexed by a separate digit and belonging to a different trunk group; one part is indexed by the digit normally assigned to the preceding, lower level, while the other part is indexed by the digit normally assigned to the level in question.

In operation, the improved selector responds to the digit dialled in the usual manner by raising its wipers opposite the desired level of bank contacts. It the digit dialled indexes a group lying partly in the corresponding level and partly in the next higher level, the operation ensuing at the end of the regular directed movement of the selector depends upon whether there is an idle trunk available in the selected level or not. It there is an idle trunk available, the Wipers of the selector are automatically rotated in search of this idle trunk in the usual manner. But if there is no idle trunk in the selected level, the wipers of the selector are automatically stepped to the next higher level and are there rotated over the contacts in such level to test the contacts assigned to the digit dialled. Y

It will be understood, of course, that selectors which are operated to take an additional vertical step automatically responsive to an all-trunks-busy condition are not broadly new, such selectors being known as vertical hunting selectors. lWhenever such selectors have been used in the past, however, the number of contacts in a selector bank assigned to a trunk group is always increased in multiples of ten, by assigning two levels to a trunk group instead ot one, or by assigning additional levels as may be required or desired. When such selectors are used, it is manifest that the ,total number ot' trunk groups accessible to the selector is reduced by an amount depending directly upon the number of levels of contacts taken over for over- {iow work. With the improved selector herein disclosed, however, the number of trunk cui groups accessible to a selector need not be reduced so long as no trunk group has more than nineteen contact sets allotted thereto, for the additional contacts allotted to one trunk group are in eect merely taken from some other group (which other group is thereby reduced in size), and no" group need be entirely cancelled.

From the foregoing explanation, it will be seen that the improved `selector about to be described in detail is arranged so that great 'flexibility is a'orded in apportioning theA available total number of contact sets amongst the trunk groups which must be reached from the selector.

. A feature of the improved selector is that two separate test wipers are used, cooperating with separate bank contacts, and that one or the other of these test wipers is connected up during the automatic rotation of the selector, depending upon whether the selector is being rotated over a level to which it was' raised directly responsive to the dialled iinpulses, or being rotated over a level to which.

starting in the next lowervlevel.

.Description drawing Referring now to the drawing, comprising :a single sheet, which shows by means of the unsual circuit diagrams a suliicient amount of apparatus Vin a telephone'systein embodying the features 'of the invention to enable the invention to be understood. More in particular, the drawing shows the circuits of a selector constructed in accordance with the invention, which selector is accessible by way of the trunk line comprising conductors ll, l2, and 13 and is equipped with test wipers 3l and 32 and line wipers 33 and 34, which are ar- 'ranged to move over the contacts in bank sections 35, 36, and 37, to which trunk linesV such as T and Til are connected.

The selector is provided with line relay 20, release relay `2l, series relay 22, series auxiliary relay 23, discriminating relay 24,v

and switching relay 25. ln addition, the selecv tor is provided with the usual vertical, rotary,

and release magnets 27, 28, vand 26; and it has the oil-normal spring contacts i6, 17, and 18, as well as the overflow contacts ll and l5,

which are operated only in case the wipers mon to the selector shown and other similar '3 selectors) are connected by leads 29 and 30 5' with the overflow contacts ll'forthe usual and Well understood purposes.

31-34 are driven beyond the last set of bank contacts in a selected level. The dial-tone and busy-tone transformers 9 and l0 (com- The selector, as illustrated, is of the s0- called battery searching type in that it hunts for a trunk line having a .battery connection thereon.

The dial tone source is associated with the selector under the assumption that the selector is a rstselector, to which the connection is extended automatically upon the removal of the receiver and in the well known manner. It will be understood, of course, that, if this selector is used as a subsequent selector in the trunking system, the dial tone connection is replaced by a ground connection on the middle overflow contact spring of group 14.

The selector is also provided with a vertical test wiper 33, which is arranged to make successive contact with the contacts in the Ver- -tica-lly disposed row as the movement of the switch responsive to dialled impulses progresses.

i The Contact grouping rl`he grouping of the bank contacts will now be explained. V 35, 36, and 37 indicate three separate bank sections of the selector, sections 35 and 37 each comprising one hundred contact pairs arranged in the customary ten levels (of which only three are shown) While section 36 comprises one hundred contacts similarly arranged. Considering the bank ysections collectively, a contact set includes a pair of contacts of section 35, the corresponding contact of section 36, and the correspond- Ving pair of section 37. v y It is assumed that the truck group to which the digit 1 is assigned is a group of rather expensive interoffice trunks, while the trunk groups to which the digits 2 and 3, respectively, are .assigned are either small trunk groups or else are relatively inexpensive ,groups not requiring the eliicient trunk-use -assigned to group 2; and the last seven contact sets in the third level have been assigned I2 Number Trunk groups Cligrsset of contact sets l1 t0 l0, 21 t0 26 16 27 t0 30, 3l. t0 33 7 34 O 40 7 In explanation of the'information given in L30 Lesaele the second column of the above table, it may be pointed out that contact set number 11 refers to the first contact set in the first level, and that the succeeding contact sets inthe first row are designated 12, 13, 14, etc. to the ninth set, which is numbered 19, and the tenth set is numbered 10. The numbering of the contact sets in the higher levels follows the same lan.

It will be understood, of course, that the above indicated apportionment of contact sets amongst the three trunk groups is given by way of example only and that the relative sizes of the assigned contact sets may be varied at will. It will be understood, moreover, that the size of the third contact set may be increased, if desired, by assigning contact sets of the fourth level to the saine trunk group, following the plan used in connection with the first and second trunk groups.

DETAILED DESCRIPTION The invention having been describec generally, a detailed description of the operation of the apparatus shown will now be given.

Seizure of the selector lt will now be assumed that the selector shown in the drawing is seized over the conductors 11 to 13, in which case a ground potential is applied to conductor 11, and the loop from a calling line is extended to talking conductors 12 and 1.3. The application of a ground potential to conductor 11 results merely in a momentary flow of current through the resistance element 19, and in tho guarding of the selector against seizure from other sources.

The closing of the loop from the calling line to conductors 12 and 13 results in the operation of line relay 2O through the contacts of switching relay 25. Then line relay 2O operates, it opens a point in the circuit of vertical magnet 27 at its lower armature, and at its upper armature it closes a circuit for the upper winding of release relay 21 in series with the lower windings of relays 22 and 21. More in detail, the circuitclosed at the upper armature of relay 2O is as follows: from ground by way of the upper and lower offnormal springs 18, normally closed contacts controlled by the iniier-upper armature of release relay 21, upper winding of relay 21, up per armature of relay 20, and the lower windings of relays 22 and 21 to battery. The current-flow through this circuit is suiiicient to operate release relay 21, whose upper winding has a relatively large number of turns, but series relay 22 is not operated in this circuit because the lower winding of relay 22 has only a relatively small number of turns.

The same is true as regards the lower winding of relay 21.

Then relay 21 operates, it opens a point in the circuit of release magnet 26 at its lower armature; places a ground potential on release trunk conductor 11 at armature 51 so as to maintain conductor 11 grounded after the ground potential has been removed at the point of seizure; supplies ground potential direct-ly to the lower terminal of its upper winding at its inner-upper armature in substitution for the ground potential initially applied through olf-normal contacts 18; and at armature 52 it applies ground potential by way of off-normal contacts 18 to the upper winding of series relay 22, thereby closing a circuit through the upper winding of relay 22 and the lower winding of relay 21, in which circuit the upper winding of relay 22 is shunted around'the upper winding of relay 21 and the lower winding of relay 22. The closing of this new circuit does not disturb the already-operated relay 21, but it results in the strong magnetization of and the immediate operation of series relay 22, as the upper winding of relay 22 comprises a relatively large number of turns.

lllhen relay 22 operates, it prepares a new circuit for its own Lipper winding at its upper armature; opens a point in the connection extending to vertical test wiper 33 at its lower armature; and at its inner-lower armature it closes a circuit for the resistancesliunted, series-auxiliary relay 23. Relay 23A Athereupon operates and prepares an operating circuit for vertical magnet 27 at its innerlower armature; prepares a test cicuit by way of vertical test wiper 38 at its lower armature; and at its upper armature it opens a;

point in the circuit of rotary magnet 28.

From the foregoing explanation, it is seen that, responsive to the operation of line relay 2O when the selector is seized, relays 21, 22, and 23 operate successively, and that the selecto-r is thereby prepared for operation in response to the usual manipulation of the calling device on the calling line.

Dial tone to the calling substation, thereby giving a characteristic signal to the calling subscriber to inform him that he may now start to dial the desired number.

Dzreetz'oely setting the selector When the first digit of the desired number is dialed, line relay 2O is deenergized momentarily a number of times depending upon the value of the dialled digit. Each time it is momentarily deenergized, line relay 2O closes a circuit for vertical magnet 27 at its lower armature, whereupon vertical magnet 27 is operated to raise the shaft of the switch, together with the wipers affixed thereto, one

step. By the operation of vert-ical magnet,-

the wipers are, therefore, raised step by step until they come torest opposite the desired level of bank contacts. As a further result oi each momentary deenergiZat-ion of line relay 20, the upper winding of relay 21 is placed in a local closed circuit at the normally closed contacts controlled by the upper armature of relay 20,.and the initial circuit for the upper winding of relay v21 through the lower windings of relays22 and 21vis opened. Since the lower winding of relay 21 has only a relatively small number of turns therein and cannot remain operated in series with the upper winding of relay 22, the relay is held operated between successive impulses by virture of the circulatingcurrent owing in the closed circuit including the upper winding of relay 21.

As a result of the mechanism of the selector being moved from its normal position, olinormal contacts 17 prepare a circuit for rclease magnet 26; oil-normal contacts 1G disconnect resistance element 19 4from conductor 11 and prepare a circuit ior rotary magnet 2S; and od normal contacts 18 open the initial circuit of the upper winding of series relay 22 in series with the lower winding of release relay 2l, and close a new circuit for these two windings as follows: from ground by wa i of the inner-upper armature of relay 21, normally closed contacts controlled by the upper armature et relay 20, upper armature of relay 22, the normally open olf-normal contacts in group 18, armature 52, upper winding of relay 22, and the lower winding of release relay 21 to battery. By this explanation, it will be seen that the circuit initially establis Led through the upper winding of relay 22 and the low winding of relay 21 has been shifted so that it is dependent upon normally open contacts controlled by relay 20, and is closed, therefore, only while relay 20 is in a deenergized condition.

Each time relay 2O :ce-operates following the delivery of an impulse to vertical magnet 27, it removes the shunt i trom around the winding ot relay 21, whereupon this winding is again included in circuit series with the lower windings ot relays 22 and 21. At the same time, with the altered circuit for the upper winding of relay 22 in series with the lower winding of relay 21, current from the upper winding of relay 21 divides and a part of it flows through the upper winding of relay 22 on its way to the lower winding ot relay 21. lV ith relay 2O in an operated condition, it will be observed that the lower winding of relay 22 is connected in shunt ont the upper winding ot the relay, and both windings are in series with the two windings of relay 21. Under this condition, the current-flow through the windings of relay 22 in series with the windings of relay 21 is insufiicient to maintain relay 22 operated, but relay 22- remains operated during the receipt of the remaining' impulses by virtue of the circulating current flowing through its two windings in series, the upper Winding acting as the driving coil, shunted by the low-resistance, low-turn lower winding.

l/Vhen line relay 2O comes to rest in an energized condition at the ends of the series oi impulses, the circulating current through the two windings of relay 22 in series shortly subsides, permitting relay 22 to restore. Upon,

restoring, relay 22 disconnects itsown upper winding at its upper armature, so as to prevent the relay from subsequently operating until the selector has been released and-again seized it connects up the vertical test wiper 38 atits lower armature; and at its innerlower armature it opens the initial'circuit of the shunted lseries auxiliary relay 23. Relay 28 remains operated for a slight interval because of the circulating induced current which flows through its winding in series with the shunting resistance element.

The vertical test'cz'rcm't 88 is now resting on a test contact associatedv with the virst level of bank contacts. As will be pointed out subsequently, this Contact is grounded in case all the trunk lines connected to the contact sets in the irst level are in use, in which casethe wipers of the selector `are automatically given an additional vertical step to bring them opposite the second level.

Tmmc hunting For the purpose of the present description, it will assumed first that at least one ofV the trunk lines accessible from the first level of contacts is idle, in which case no ground potential is Vencountered by the vertical test wiper 38, and the automatic vertical step is not taken. Under this condition, thefalling back of the series auxiliary relay 23, which follows closely upon the restoration of relay 22, results in the closure of a circuit for rotary magnet 28 to rotate the wipers over the first level of bank contacts.- The circuit for rotary magnet 28 includes armature 51 of relay 21, oli-normal contacts 16, overflow contact-s 15, upperv armature of relay 21, upper armature oir' relay`28, inner-lower armature of relay 25, and the self-interrupting contacts of magnet 2S.

Trim-,7c seizure The-automatic rotation of the wipers'responsive to the buzzer-like action of magnet 28 continues until switching relay 25 operates, upon an idle trunk being encountered.

Assuming that the first idle trunk line encountered is the trunk T10, extending from the tenth set of bank contacts in the iirst level, the advance of the wipers continues until this trunk line is reached, whereupon the normally connected test wiper 32 encounters a battery potential by way of test conductor 34, completing an operating circuit for the upper winding of switching relay 25 to ground at armature 51. Upon operating, relay 25 opens the circuit of rotary magnet 28 at its inner-lower armature (thereby terminating the rotary movement), at the same time completing a locking circuit for its lower winding in series with rotary magnet 28. Rotary magnet 28 does not operate in series with the lower winding of relay 25 on account of the high resistance of this winding. Switching relay 25 also opens a point in the circuit of release magnet 26 at armature 53; connects the now-grounded incoming release-trunk conductor 11 directly with the test wiper 32 at its upper armature, thereby shunting its upper Winding; and at its two lowermost armatures it disconnects the incoming conductors 12 and 13 from the windings of the line relay 20 and extends them by way of wipers 33 and 34 to concluetors 35 and 36.

Responsive to the above-mentioned operation of switching relay 25, the usual line and release relays (not shown) associated with the trunk T10 are operated, and ground potential is placed on conductor 34, thereby providing a holding circuit for the selector and for the preceding switching apparatus after the slow-acting release relay 21 of the selector illustrated has fallen back, as will now be explained:

When line relay 20 is disconnected at the contacts of relay 25, it falls bacl and closes a point in the circuit of vertical magnet 27 at its lower armature. Vertical magnet 27 is not operated at this -time because the series auxiliary relay 23 is in a. restored condition. Line relay 20, at its upper armature and associated contacts open-circuits and shortcircuits the upper winding of the release relay 20, at the same time opening the circuit through the lower windings of relays 22 and 21 (relay 22 is in a restored condition at this time). It is to be noted that series relay 22 does not operate at this time because its upper winding has been disconnected at the upper armature of the relay. Relay 21 falls baclr as soon as the circulating current in the upper winding subsides somewhat.

Releasing lVhen the ground potential is removed from release trunk conductor 34 of trunk T10 when the connection is to be released, switching relay 25 restores and closes a circuit for release magnet 26 at armature 53. By the operation ot release magnet 26 the selector is restored to normal position, whereupon the release-magnet circuit is opened at ott'- normal contacts 17, while at oft-normal contacts 16 battery potential is re-applied to conductor 11 by way of resistance 19 so as to marlr the selector as available for further use.

Selecting L trunk a the next higher level It will now be assumed that all the trunk lines accessible from the first level of bank contacts are in use when the wipers of the select r are brought to rest 'opposite the first level of bank contacts as hereinbefore described. Under this condition, there is a selector in engagement witheach ot the trunk lines accessible from the rstlevel of bank contacts. Keeping in mind that the contact sets and vertical test contacts are multipled together throughout all ofthe selectors having access tothe trunk lines under discussion, it will be seen that ground potential is eX- tended by bridging wipers, such as wiper 31 of the selector illustrated, through the contact multiple to all of the number one contacts in the bank of the vertical test wipers, such as test wiper 33. Under this condition, theretore,- test wiper 33 encounters a ground potential, resulting in a circuit being closed for vertical magnet 27 through contacts of the restored series relay 22 and contacts of the still-operated slow-restoring relay 23. This circuit includes the lower winding of discriminating relay 24 andthe self-interrupting contacts of magnet 27. RelayV 24 and vertical'magnet 27 energize in series, relay 24 operating slightly ahead of the magnet, which has a larger, heavier armature, and must elevate the shaft. Vhen relay 24 operates, it prepares a locking circuit for its upper winding at its inner armature, and at its upper armature it disconnectstest wiper 32 and connects up test wiper 31.

i When magnet 27 near the end of its stroke, and just before vertical test wiper 38 leaves the first-level test contact and comeskinto engagement with the associated second-level contact, it interrupts its own circuit and the circuit of relay 24, whereupon vertical magnet 27 deenergizes, and again closes its interrupter contacts. The vertical magnet can not again operate, however, because the series auxiliary relay 23 has a sufficiently stiff adjustmentfthat it Jfalls back and disconnects vertical test wiper 38 before magnet 27 can operate the second time, even though the second-level test contact may be grounded. lt may be pointed out that discriminating relay 24 is rendered sufficiently slow-acting by the usual vcopper collar around its core that it does not ,tall baclr while the self-interrupting contacts of the vertical magnet are open. As soon as relay 23 falls back and vertial magnet 27'has restored its interrupter contacts, a locking circuit exists for relay 24 rae in series with vertical magnet 27, and by way of both windings ofrelay 24 in series. Magnet 27 does not operate in this circuit because of the relatively high resistance of the upper Winding of the relay.

vBy the above-described automatic vertical stepping operation the wipers of the selector have beenraised one step from their set position opposite the iirst level to a position opposite the second level of bank contacts. The regular rotary movement is now brought about by the rotarymagnet 28 and responsive to the closure of the circuit of rotary magnet `28 at the upper armature of the seriesauxiliary relayA 23. Since the discriminating relay 24 is now operated, and the test winding of relay 25 has been disconnected from wiper 32 andtransferred to wiper 31, the

ktesting is performed in the second level of 120 bank' section 35 in place of in the second level of bank section 36, as is done when the Wipers are brought opposite the second level of the bank contacts responsive to the dialling of the digit 2. Assuming that the first set of contacts in the second levelfis idle (the eleventh contact set in trunk Agroup one), wiper 31 encounters a battery potential on conductor 37 of the trunk T11, whereupon switching relay 25 operates with the hereinbefore described results.

It may be particularly pointed out at this time that therelease trunk conductors of trunk lines reached from the level above the one corresponding to the digit assigned to the concerned trunk group are connected to the bank section' 35 instead of bank section 36, thereby enabling a discriminating test to be made so that there is no danger of the selector seizing a trunk line in other than the dialled group.

AZZ-tf/Ywncs-busg/ condition Assuming now that all trunks are busy in the first group when the digit 1 is dialled as hereinbefore described, the wipers are given an automatic vertical step following their alignment opposite the iirst level of bank contacts responsive tothe digit 1. Following this additional and automatic vertical step, the Wipers are rotated over the bank contacts in the second level in search of an idle trunk. Sin-ce the remaining six trunks in group one are all in use, the hunting action of the selector continues until the wipers pass over all of the contacts in the second level, as no battery potential is encountered by wiper 31 on any of its contacts.

When the wipers 31 to 34 pass off the last set of bank contacts in the second level, the overflow spring-combination, including centact sets 14 and 15, are actuated. At oinormal contacts 15 the circuit of rotary magnet 28 is interrupted, thereby terminating the rotary movement, while at the overflow contacts 14 busy-tone current is substituted for dial-tone current, givingl the calling subscriber a characteristic busy signal to prompt him to release the partially established connection and make the attempt later.

Completing a connection a the eccomi group Assuming now that the selector shown in the drawing is seized and prepared for operation in the usual manner and that the calling subscriber dials the digit 2, the Wipers of the selector are stepped vertically into association with the second level of bank contacts, following which the series relay 22 falls back and connects up the vertical test wiper 38 in order to determine whether or not there is an idle trunk line available in the second level and assigned to group 2. Assumingthat there is such a trunk line, vertical magnet 27 is not operated further, as no ground potential is encountered by wiper l38; and the hunting operation takes place on the second level. Since discriminating relay 24 is not operated in this case', the testing operation is performed with wiper 32. Since the first six contacts in the second level of the bank of wiper 32 are not connected to any trunk lines, the effective testing does not begin until the seventh contact set 'is reached. Either the seventh contact set or one of the succeeding contact sets is Jtound to the idle, and the connection is completed in the usual manner.

From the explanation hereinbefore given, it will be understood that the wipers of the selector are automatically raised to the third level, and wiper 32 is replaced by Wiper 31 in case all of the second-group trunk lines terminating in the second level are busy.

It will be understood, of course, that the manner disclosed herein for controlling the application of ground potential to the contacts in the vertical test bank is merely eX- emplary, and that suitable arrangements, including so-called chain relays connected to the release trunk conductors of the trunk lines involvedmay be used whenever found lto be desirable.

What is claimed is:

1. In a two-motion selector switch having its bank contacts divided into parallel rows and having a motion in one directionto 'select a contact row and a motion in another to respond to the designation of a trunk line group by hunting 'for and extending connection to anyV idle contact set assigned group. N v

2. In combinatlon, a selector havingV its to such contact bank arranged in parallel rows,there Lil) being a separate digit assigned to each row, groups of trunk lines corresponding to said rows, respectively, one ot said trunk line groups occupying contacts in the row assigned thereto and additional contacts in the next adjacent Contact row, means in said selector responsive to a digit control for bringing the selector into association with the corresponding contact row, means for then causing the selector to search over the contact row for an idle trunk line, means effective in case all trunk lines reached from such contact row are in use and in case there are additional trunk lines in the same group reached from the nent adjacent contact row for automaticallyT advancing the selector to the next contact row before the trunk searching operation takes place, and means for restricting' the trunk searching action ot the selector to the trunk lines in the group corresponding to the digit in accordance with which the selector was initially positioned.

3. In combination, a. selector having bank Contact sets arrangeo in groups, each group normally corresponding to a separate digit designation, the contacts in one ot said groups being divided between two trunk groups bearing diiiierent digit designations, means for bringing said selector into association with said contact group as a result of control being exercised over the selector in accordance with either of said two digit designations, means thereupon eiiiective for starting said selector searching over the contact sets in said groups successively, and means automatically eiiiective and dependent upon the digit in accordance with which the selector received its contro-l for preventing the selector from making connection with any trunk line ot one group and for permitting the selector to make connection with any idle trunk line in the other group.

4. In combination, a selector having its contact bank arranged in groups, means eliective for setting the selector' into association with a contact group by a directed movement or by a non-directed automatic movement, the contacts of said group being divided between two separate groups ot trunk lines, and means eiiective depending' upon in which of the two ways the selector was brought into association with the contact group for predetermining with which trunk group connection will be made.

5. In combination, an automatic trunk selector having its bank contacts arranged in groups, trunk lines connected in the bank of said selector and having different digit designations, means tor operating said selector in accordance with the digit designation of any trunk line group to bring the selector into association with a group ot contacts to which trunk lines of said group are connected, said selector having' two test wipers, one being normally effective and the other being normally ineective, means effective when said selector is brought into association with a group ot contacts and responsive to all trunk lines terminating in the said contact group corresponding into the digit setting of the selector being in use tor automatically operatsaid selector' into association with a different one ot the contact groups, and means thereupon effective for substituting the normally ineffective test wiper for the normally effective one.

6. In combination, an automatic trunk hunting selector switch having its contact bank arranged in groups, means tor directively associating the wipers ot' said selector with said group in accordance with digit designations, means in said selector for causing the wipers to be brought into association with a contact group by means oi a non-directed movement, said selector having two test wipers, and means for selecting either of said test wipers tor use to the exclusion of the other, depending upon whether the selector is brought into association with a contact group by means of a directed movement or a nondirected movement.

7. ln combination, an automatic trunking selector having its contact bank divided into groups, directing means for setting the wipers of said selector into association with any group by advancing the wipers successively from group to group, there being one trunk group occupying contacts in one contact group and certain ot the contacts in the next succeeding Contact group, with a second trunk group occupying the remaining contacts in the last-mentioned contact group, means ettcctive when the selector is directively set on the iirst ot said two contact groups for automatically giving the selector an additional non-directed movement to the next succeeding contact group in case all of the trunk lines connected to the contacts ot the first contact group are in use, means thereupon etliective for causing the selector to search for and seize any idle trunk line of the iirst group connected with the contacts ot the second contact group, and means for preventing the selector from connecting with any one ot the trunk lines ot the second contact group unless the selector was initiallv and directively positioned on the second contact group. In witness whereof, I hereunto subscribe my name this 11th day of December, 1931.

JOHN l/VICKS.

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