US2341919A - Telephone system - Google Patents

Description

Feb. 15, 1944. F. A. HUBBARD 2,341,919

TELEPHONE SYSTEM Fil'ed July 25, 1942' 3 Sheets-Sheet 1 //vv/v TOR EAHUBBARD A T TORNE V Feb. 15, 1944. F. A. HUBBARD 2,341,919

TELEPHONE SYSTEM Filed July 25, 1942 5 Sheets-Sheet 2 FIG. 2

3m QHD MED HHU 111 i 2% HU //v l/EN Top FA Wee/m0 ATTORNEY Feb. 15, 1944. HUBBARD 2,341,919

TELEPHONE SYSTEM Filed July 25, 1942 s Sheets-Sheet 3 FIG. 3

IIHIII lNI/ENTOR EA. HUBBARD By -W W A T TORNF Y Patented Feb. 15, 1944 UNITED 1 STATES: PAT ENT; OFF-1C Esi TELEPHONE SYSTEM Francis A. Hubbard; Maplewod, N. -J., assignorw to Bell Telephone Laboratories, Incorporated,

New York, N.'Y., a corporation of New York Application July/25,1942, Serial No. 452,303 8 Claims. (Cl. 179'18) spects to efiect improvements in the functions and operation of automatic switches.

In accordance with the present invention'the foregoing objects and advantages may-be realized by means of a switching system in which a connector switch has access through its levels of terminals to individual subscribers lines and to groups of branch exchange trunks or other equivalent lines or trunks, said groups in some cases occupying two or more successive levels of terminals, and in which a test is made, following the completion of the directive primary movement of the switch to select a desired one of said levels, to determinewhether the selected level is occupied by individual lines or by a group of equivalent lines,--and in-casethe level is occupied by equivalent lines to determine thebusy or idle condition thereof. More specifically, the connector switch is provided with means enabling it to perform its secondary movement automatically to hunt for-an idle equivalent circuit in theselected level provided the level test discloses that theselected level is occupied by equivalent rather than individual subscribers lines; the switch is provided-with means forcontinuing its primary movement automatic'ally to select the next succeeding'level of terminals and to repeat thelevel test thereof provided the first selected level contains equivalent lines and all are busy it is pro-- vided with means "for continuing this level test of the equivalent lines of an exchange group until the last leveloccupied by the group is reached;-

at which time the switch'proceeds to hunt automatically without performing the preliminary level test; andthe switchis arranged to omit the level busy test in case the selected level'is 00-- cupied by individual lines and to prepare ltself' to respond directively to select and test a desired oneof the individual lines in such level. The level 1 test of the equivalentexchang lines is made by means of a seriesof discharge'tubes individual ing relays in the connector switch todetect'a level containing individual subscriberslines; to detect a level-containing: equivalent exchange lines; and to determine whether a level of equiva- .lent exchange lines contains oneor more idle lines.

A feature of the invention is a connector switch of-the character discussed above in'which the level test of the equivalentlines is performed by ';means of 'a single common'discharge'tube-con taining a plurality of control electrodes Which'- are individual-respectively to the lines in thelev'el.

Another feature of the invention is a system of this character provided with means for' temporarilyconvertmg any one of the' levelsof equiva lent lines to a level of individual lines in order that an incoming call may select any desired-one of these lines directively.

These and other features of the invention will be discussed more fully in the following detailed specification.

Figs. 1' and 2 of the'drawings accompanying; the specification disclose a portion of a telephone system incorporating features of the invention;

, Fig; 1 illustrates a subscribers'line' and a selective switch in conventional form and also: shows in detail thenoontrolling'relays, magnets and other parts :of a final selectoror-connector The invention in -its'. broadest-aspect is not limited in its application to any particular type of automatic switch nor to any particular typeof telephone or other communication-system:- For convenience of illustration,:however; it is shown its application to a fin'al-or-connector switch of the level huntingtype commonly used-" in automatic telephone systems i of the step-by step type.- -"A connectorswitch of this general-- type'is shown in detail in the patentto Hovland,

'No.1,'l4i'l,169, of February 1851930.

In the drawings the connector switch is acces-' sible from' calling lines-,such as the subscribe'r s t lineme; over preceding switches including the serespectively'fto-the lmesinthe'level'and'a CQIII-l mon' discharge-tube whichmooperateswith test Iector S, and has access to individual-subscribers- I linesand also to'groups of equivalent lines or trunksg-such as those eXtendi-ng'to'private branch sho wniin' Fig? 2 consistsof ten rows or levels of terminals, each level including ten sets of terminals. Where an exchange group of equivalent lines includes more than ten circuits the group is assigned to as many successive and consecutive levels of terminals as may be required to serve the group. For example, if an exchange group 200 contains thirty lines, they may be allocated as shown to the first three levels of terminals in the terminal bank. Another group of exchange lines 20! including only ten lines may be allocated as shown to a single level of terminals. Other levels in the switch may be allotted to individual subscribers lines, such as the fifth level, which contains the subscribers lines 202, 203, 204, 205. Still other levels may include both individual lines and exchange lines provided the exchange line group contains less than ten lines.

The brush operating and controlling mechanism of the connector switch is designed to respond to a first directive series of impulses to select a desired level of exchange lines and then to hunt automatically in thelevel for an idle one of these lines o to step automatically from the level first selected to the next succeeding level of exchange lines provided all lines in the selected level are busy, to hunt in'the second level provided this. level contains an idle line or to step again to the next succeeding level if all lines in the second level are in fact busy, and to continue this level selecting and testing procedure, without actually entering a level in which all lines are known to be busy, until the last level of lines of the group has'been reached, at which time the switch proceeds to hunt automatically and to test the exchange lines in such last level. In such a case, that is, where the first series of impulses transmitted to the switch operates it to select an exchange group, the second and final series of impulses which are usually transmitted to a connector switch are of no utility and are therefore absorbed without performing any useful'function. The switch is also designed to respond to a first series of impulses transmitted thereto to step its brushes in the primary movement to select a level of terminals containing individual subscribers lines and then to respond directively to the final series of impulses to step the brushes of the switch -into the selected level to the terminals of the desired subscribers line.

The collective test of all of the exchange lines in a level is performed after the switch has completed its primary directive movement to select the level, and without requiring the switch to participate in its secondary movement, by special testing means associated with the switch and with the exchange lines in the level. To this end each exchange line in all levels of a group, except the last level, is provided with a two-element discharge tube for testing the busy or idle relays 222 and 223 to the first segment 224 of the vertical commutator 225, this segment being individual to the level of terminals in the switch occupied by the exchange lines 206, 201, 208, etc.

If an exchange line is idle, no ground potential is applied to the sleeve conductor, and the full negative potential of the battery associated with the cut-01f relay is applied to one electrode of the associated individual tube. When, therefore, positive potential is applied by the switch over the commutator segment 224, as will be explained more fully hereinafter, and thence through the resistor 226 to the other electrode of the individual tube, the voltage across the tube is sufficient to ionize the same. Upon the ionization of any one of the individual tubes 2i I, 2I2,

condition of the line. Y These discharge tubes are main anode 2H and to the starting cathode 2I8 of the common test tube 2| 9. The starting anodej 220 of the common tube 2 I 9 is connected through resistor 221 and over the normal contacts of 213, etc., in 'this'manner the resultant voltage applied across the control gap 2l8-220 of the common tube 2 I9 is sufficient to ionize the common tube, with the result that a test relay 10! in the connector switch is operated to indicate the fact that the level contains at least one idle line. However, if an exchange line is busy, it has ground potential applied to the test conductor which prevents the'associated individual tube from operating. If all of the exchange lines in the level are busy, none of the individual tubes operates, and the result'is that the voltage applied across the control gap 2lB-220 of the tube 2I9 is insuficient to operate this tube. Therefore, the test-relay Hll in the connector switch fails to operate, indicating that all lines in the selected level are busy. In like manner-the second level of xchange lines of the group 200 is provided with a series of individual test utbesand a common tube similar to the tube 2I9 which is connected over conductor 22'! to the second segment 228 of the commutator 225, and these 7 tubes serve in the same manner to perform the collective test of the lines in the second level. Inasmuch, however, as the third level of lines is the last levelin the group and is not provided with means for making the collective test, the corresponding commutator segment 229 is connected through a resistor 230 to ground. If the switch is advanced to this last level of the group, the test circuit extending through the resistor 230 permits the test relay I01 to operate, indicating that the switch should proceed automatically to'hunt in the selected level for an idle circuit. Y

The segments of 'the commutator 225 representing levels in which individual lines appear are connected directlyto ground; For example,

segment 23! corresponding to the fifthlevel of terminals in which individual lines2il2, 203, etc.,

appear is connected to ground. -When, therefore,

selected, whereupon the switch is prepared to -re- I spond directively'to the next series of impulses and to step into the level to seize the desired in- I dividual lines therein. I r

It is sometimes desirable at night to convert'a level of private branch exchange trunks so that any one of them can be seized directively in the I central office the same as an individual subscribers line. To this end a keyor other switch 232 is provided at the private branch exchange ,1 and; 7 w e in ts o erat d c di ion caus s ;th ne gization of relay 223 in the central-office. The relay 223 disconnects the commutator segment 224 from the common test tube 2I9 and connects it directly to ground. 'In this way the segment 224 has the same appearance to the testing circuit of the connector as a segment representing a level of individual subscribers lines. During the night, therefore, the calling party can operate the connector switch in the central o'fiice by a tens digit and a units digit to select the first level of terminals and to step into the level in accordance with the units digit to seize a particular one of the private branch exchange lines for the purpose of calling a desired party in the private branch exchange.

A description will now be given of the operation of the system. Assume first that the'subscriber of line I06 wishes to extend a connection to the private branch exchange served bythe exchange group 208, occupying the first, second, and. third levels of terminals in the connector switch. The calling subscriber initiates the call and dials the preliminary digits in the usual manner, causing his line to be extended over the selector switch S to the level hunting connector switch. Thereupon a circuit is closed frombattery through the upper winding of impulse relay H33, normal contacts of relay IiM thence over the extended connection through the loop of subscribers line I06 and returning over the opposite side of the connection, normal contacts of relay IM through the lower winding of relay I03 to ground. Relay I63 operates and closes an obvious operating circuit for slow-release relay I85. Relay I05 applies holding ground potential to the sleeve conductor wt and prepares the pulsing circuit.

When the calling subscriber transmits the next or tens series of impulses, relay I03 follows these impulses and closes a pulsing circuit for the vertical or primary stepping magnet llll. On the first impulse the circuit may be traced from ground through the back contact of relay I03, front contact of relay I I35, conductor I08, closed contacts of the off-normal spring combination I69, winding of slow-release relay I I0, winding of stepping magnet It? to battery. Magnet IEIT steps the brushes 233, 23 1, 235 vertically to a position opposite the first level of the terminals and brush M8 to segment 224, the brush shaft releases the spring combination I09, permitting the springs to assume their alternate positions, and relay H6, which is slow to release, operates and shifts the pulsing circuit so that it now extends over conductor H18, closed contact springsIIlQ,

armature and front contact and winding of relay III) to the winding of magnet I01. Relay III) in operating closes a circuit from ground through,

the contact of relay I05, conductor IIl,'front contact of relay H0, springs I09, conductor -I I2, normal contacts of relay II3, winding of relay H4 to battery. Relay H4 operates in this circuit and locks in a circuit from battery through its Winding, normal contacts of relay H3, conductor H5, front contacts of relay H4 to ground at the front contact of relay I23.

Since the exchange group 260 isdesired, the tens digit identifying this group is 1. Therefore, the switch takes a single step as described, the subscriber prepares to send the units digit, and relay III] releases after a brief interval following the reoperatio-n of the pulse relay H33. Before the next or units series of impulses arrive, however, a collective test .is made of the lines 266, 281, etc., in the first level of terminals which has been. selected by the DO-$175.

sitioning of the brushes 233, 234, and 235.. This test is performed by the relays IIlI and-I02 and, as hereinbefore explained, by the individual test tubes 2, 2I2, 2I3, etc., and the common test tube 2I9 associated with the selected level. The test circuit is closed by the release of relay Ill] and may be traced from the positive pole of battery 6, back contacts of relay H0 through the windings of relays ml and IE2 in parallel, conductor II'I, commutator brush IE8, se ment 224, on which the brush H8 is now resting, normal contacts of relay 223, conductor 235, normal contacts of relay 222, resistor 226 to conductor 2I6. If any one of the lines in thefirst level is idle, its sleeve conductor is free from ground potential, and the negative battery potential is applied through the winding of the associated cut-off relay to' the associated discharge tube. For example, if line 2M is idle, the negative potential of battery 231 is applied through the winding of cut-off relay 238 to the upper electrode of the discharge tube 255. When, therefore, the positive pole of test battery H6 is applied to the lower electrode of tube M5, the tube ionizes, and the potential drop resulting from current flow in resistor 226 is applied through the resistor 23% to the startin cathode 2i8. of the common tube 2I9. After an interval, determined by the value of resistor 22! and condenser Zdfi, following the application of the positivepotential of battery M6 to conductor 235, the full value of this positive potential is applied to the starting anode 22d, and the starting gap 2202it is ionized. As soon as the starting gap of tube 2L9 ionizes, a main discharge circuit is closed from conductor 236 through the main anode 2H, main cathode 2&4, winding of relay 222, resistor 2&2 to the negative pole of battery 243. Relays ml and 222 operate in this circuit, but relay IE2 being marginal does not receive sufiicient current to attract its armatures. Relay Illl locks in a circuit closed from battery through its winding and contact to the rounded conductor III. Relay 222 when fully operated removes the test potential from conductoriiifi and permits the tube BIS to extinguish. Relay 222 is made slow to release and retainsits armature attracted to hold the test tube 259 disconnected from conductor 236 long enough to permit the connector switch to complete its hunting operation in the selected level. The reason for holding the tube 2L9 disconnected is to prevent another connector seeking the same level or". ter minals from hunting therein while the first connector is seeking an idle line in the level.

When relay Illl operates, a circuit is closed from battery through the winding of sloW-1'e lease relay ilii, normal contacts of relay H3, conductor H9, normalcontacts of relay I02 to ground at the front contacts of relay till. Relay I It operates and locks in a circuit from battery through its winding and front contacts, conductor IZQ to ground at the front contacts of relay M l. Relay H3 opens the original holding circuit of relay Ht but before so .loing closes a new holding circuit traceable from battery through the winding of relay H4, closed contacts of relay H3, normal-contacts of the retary stepping magnet I2I, conductotr I22, normal contacts of relay I23, conductor I24 :to ground at the front contact of relay lit. The switch is now prepared to perform its secondary or rotary stepping movement automatically in line.

'The stepping circuit for the rotary magnet I2I may be traced from battery through the winding of said magnet, closed contacts of relay H3, normal contacts of relay I25, closed contacts of relay I14, conductor I26 to ground at the front contact of relay I05. Magnet I2I steps the brushes I33, I34 and I35 on to the first set of terminals in which the line 206 appears. Near the end of its stroke the magnet I2| opens its contacts, and relay H4 releases. Relay H4 in turn opens the circuit of the magnet, and it restores and prepares for the next step. If the line 206 is busy, a ground potential exists on the sleeve conductor 244, and relay I I4 immediately reoperates in a circuit from battery through the winding of said relay, front contacts of relay II3, normal contacts of magnet I2l, conductor I22, normal contacts of relay I23, conductors I24 and I21, brush 235 to ground on the test conductor 244. Relay I I I reoperates the magnet I2I, and the brushes are stepped to the next set of terminals, whereupon relay IM releases and in turn releases the magnet. This process continues as long as the test brush 235 encounters busy terminals. During the hunting movement relay II3 retains its armatures operated by reason of its slow-release characteristic. When the switch reaches the first idle exchange line, such as the line 2I0, the absence of ground potential on the sleeve conductor prevents the reoperation of the test relay I I4. After an interval, therefore, the slow-release relay II3 releases its armatures and opens the circuit of the stepping magnet I2I.

When relay I I3 releases as above described following the seizure of the idle exchange line 2I0, a circuit is closed from ground through the contacts of relay I05, conductor I28, normal contacts of relay II4, lower Winding of cut-through relay I25, normal contacts of relay I I3, conductor I22, normal contacts of relay I23, conductors I24 and I21, brush 235 thence through the winding of cut-ofi relay 230 to battery. Relay I25 operates and locks in a circuit from battery through its upper winding and front contact to ground at the front contact of holding relay I05. Relay I25 extends the talking conductors through to the brushes 233 and 234 of the connector switch and prepares for the application of ringing current to the selected exchange line 2 I 0.

The ringing circuit for applying ringing current may be traced from the ringing generator I29, interrupter I30, contacts of relay I25 to the lower winding of ringing trip relay I3I, normal contacts of said relay, front contacts of relay 525, brush 23d thence over the line 2 I and returning over the other side of the line to brush 233, operated contacts of relay I25, normal contacts of relay I3I to ground. Relay I3I operates, serves to trip the ringing operation in the usual manner and when operated locks over its upper winding and contact to ground through the contact of hold relay I05. Relay I3I also completes the tip and ring conductors of the talking circuit. When the called party answers, the back bridge relay I04 operates in the well-known manner and reverses the direction of current flow over the connection back toward the calling line.

At the end of the conversation the calling and called parties disconnect, and relays I03 and 04 release. A circuit is now closed from battery through the winding of release magnet 532, vertical off-normal springs I09, normal contacts of relay I04, normal contacts of relays I05 and I03 to ground. Magnet I 32 operates and restores the connector switch to its normal position, and the other switches in the connection are released. The restoration of the connector switch causes the release of magnet I32 by opening the offnormal contacts I09, and the release of hold relay I05 opens the holding circuits of relays IOI, I25 and I3I. 7

Assume now that all lines 206, 201, 208, etc., in the first level of the group 200 are busy at the time the connector switch positions its brushes opposite this level in response to the tens digit. All lines being busy, a ground potential exists on each of the sleeve conductors, and no one of the individual tubes 2| I, 2I2, 2I3, etc., operates when battery H6 is connected over the test conductors I I1 and 236 to these tubes. Since no one of the individual tubes operates, the potential on electrodes 2I8 and 220 is the same, and the starting gap 2IB--220 fails to ionize. The tube 2I9, therefore, does not discharge its main gap, and neither of the test relays IN and I02 nor the relay 222 is able to operate, the values of resistors 225, 239 and 245 being too high to permit operating current to flow.

Since relay IIO released following the completion of the primary movement of the switch and relay IOI fails to operate in the test circuit closed by relay II 0, a circuit is prepared for the vertical magnet I 01 in order that it may advance the brushes to the next level of terminals. The circuit for magnet I01 may be traced from battery through its winding and normal contacts, offnormal contacts I09, conductor I33, normal contacts of relays H0 and IOI to ground. Magnet I0! steps the brushes 233, 234, 235 to the next or second level of the terminals, interrupts its own circuit and deenergizes. As soon as the commutator brush I I8 engages the segments 228 representing the second level of terminals, the test circuit is completed over conductor 221 to a common tube, similar to tube 2I9, for the second level and to associated individual tubes similar to tubes 2| I, 2I2, etc. If this second level contains an idle line, relay IOI operates immediately and opens the circuit of magnet I01 to prevent it from stepping the switch to the next level. The switch then proceeds as above described to hunt automatically in the second level for an idle line therein.

If onthe other hand all lines in the second level are busy, this fact is determined by the collective test, and the magnet I0! operates again to step the brushes to the third and last level of the group 200. When the commutator brush II8 reaches the segment 229 representing the third level, it encounters ground potential through the resistor 230. This closed test circuit permits the fiow of sufiicient current to operate the test relay IOI but insufficient to cause the operation of the marginal relay I02. Relay IOI looks through its right winding and opens the stepping circuit of magnet I01 and prepares the circuits of the switch in the manner above described for the secondary or hunting movement in the level of terminals to determine whether any one of the lines in the level is idle.

Next it will be assumed that the subscriber of line I00 wishes to converse with the subscriber of the individual line 205. Since the line 205 occurs in the fifth level of terminals, the calling subs scriber dials a number having the tens digit 5'? and a units digit corresponding to the position of line 205 in the level. At the completion of the tens digit the brushes 233, 234 and 235 assume their position opposite the fifth level of terminals,

. sponding segment. 23 I.

segment 23I is connected directly to ground;

andthe commutator brush I I8 engages the corre- It will be seen that the therefore both relays IN and I02 operate in-the test circuit when slow-release relay I I releases relay I02 before it has time to attract its armature to close its locking circuit.

Upon each release of theimpulse relay I03 in response to theimpulses of the units digit the stepping circuit is closed from ground through the back contact of relay I03, front contact of relay I05, conductor I03, off-normal springs I 00, innerleft back contact of relay H0, front contact of relay I 02, normal contacts of test relay I35 -thence-'inparallel through the winding of slowrelease relay I23 and through the back contact of relay H3 andthe winding of the rotary stepping magnet I2Ito battery. Relay I23 operates on the first impulse, closes the stepping circuit "through its left front contact independently of the test relay I35, opens the locking circuit of relay H4, permitting'the latter to release, and maintains its armature attracted during the impulse series. At theend of the series the brushes 233, 230, 235 'come to rest on the terminals of the desired line 205, and a test circuit is closed. to determin the condition of said line. test circuit may be traced from battery through the winding of test relay-I35, normal contacts of The relay I25, front contacts of relay I23, conductors I24 and I2I, brush 235 to the sleeve conductor 240 of line 205.

If the line 205 is busy, ground potential exists on the sleeve conductor 200, and relay 135 operates in thecircuit above traced. ,A brief interval following the completion of the rotary movement ofthe switch-and. the operation of relay I35,slow-release relay I23 releases and in so doing opens the originaloperating. circuit for test relay I35. RelayI35, howevenlocks in a circuit from battery. through its winding, normal contacts of relayv I25,v normal continuitycontacts of relay I23, front contactof relay I35 to the grounded conductor I28. Rela I35 completes a circuit from the tone source I36 through the front .contact of said relay to the talking conductor I31.

. sleeve conductor 245, and test relay I35 fails to operate. When thereafter relay I23 releases its armatures, a circuit is closed .from battery through th winding of the. cut-off rela 2 I'I thence over the. sleeve conductor 245, brush 235, conductors I21 and I24, back contacts of relay I23, conductor I22, normal contactsof relay II3,

lower winding'of relay I25, normal contacts of relay II 4 to the grounded conductor I28. Relay I25 energizes and before'opening the circuit just traced closes a locking circuit for itself traceable from battery through the upper winding and front contact of the relay, conductor 30 to ground at the contacts of'the hold relay #I05. Ringing current is now'applied to the'calle'dline .manner already described.

I in. the manner above described, the tripping relay I3l isoperated to disconnect the ringing current when the called party answers, and relay I 04 operates as a supervisory relay to reverse the current back over the calling loop.

When the subscribers replace their receivers at the end of conversation, relays I00, I00 and I05 .release, and-a release circuit for the switch is a closed from battery through release magnet I32,

springs I09, normal contact of relays I04, I05 and I03 to ground. Magnet I32 restores the switch to its normal position, and all operated relays are released.

Assume now that it is desired to convert the first level of the group of private branch exchange lines 200 to individual lines in order that a calling party may select a particular one of these lines which has been previously designated for calling the private branch exchange during the night. To eifect this conversation, the operator in the private branch exchange closes the key 232 thereby operating the relay 223 in the central office. Relay 223 disconnects the testing tube MS from the commutator segment 220 and connects said segment directly to ground. If, therefore, a call is made causing the selection of the first level of lines, test relay NH and I02 operate as above described, and'the switch prepares to receive the next or units series of impulses and to step in response thereto into the level to seize the correspondin line leading to the private branch exchange. Thereupon ringing current is applied to the seized line to signal the telephone which has been connected tothe line by the private branch exchange operator. Following conversation release takes place in the In the modification 0f the collective testing arrangement shown in Fig. 3 the individual tubes 2, 2I2 and 2I3 and the common tube 2I9-for a single level of lines are replaced by a single discharge tube.- 300. Tube 300 is provided with a series of starting cathodes 30!, 302, ,303', 304

" which are connected individually to the sleeve conductors of the exchange lines in the 1eve1 of theconnector switch. If any one .of the lines in the level is idle at the time, the connector positions itsbrushes opposite the level, negative hattery potential through the winding of the correcircuit to operate rela 301.

- main anode is sufficient to start theionization of the tube,-whereupon the main discharge gap, in-

cluding anode 3H and main cathode 3E2, discharges, and sufficient current flows in the test Relay 308 is marginal and does not operate. With relay 30! operated and relay 300 released, the connector switch automatically hunts in the level for the charge when the test is made.

idle line.

If, all lines in the level are busy, however, ground potential is applied to the corresponding starting cathode, and the tube 300 does not dis- Under this conditionboth relays t0? and 308 remain unoperated, and the connector switch is caused to take I another step to position its brushes opposite the next level of lines of the group.

Ii all levels of the group preceding the last level are busy; the, brush 309 is finally stepped to the segment- 3l3 corresponding tothe last level of the group, and the test circuit is closed through the resistor 3M. Relay 301 operates in this circuit and relay 3'08 remains unoperated, and the connector automatically hunts in the level for an idle line.

c When the connector is driven to a level of terminals containing individual lines, such as the level corresponding to commutator segment 3l5, a direct ground potential is encountered, and both relays 301 and 308' operate. Under this condition the connector is prepared to respond directively to the units series of impulses to seize a desired line in the level,

What is claimed is:

1. The combination in a telephone system having an automatic selecting switch arranged to participate in a primary selecting movement and in a secondary selecting movement of a plurality of rows of terminals for said switch, a group of equivalent lines occupying one of said rows, individual lines occupying another of said rows, means for operating said switch directively in its primary movement to select any desired row of said terminals, means effective upon completion of said directive primary movement for making atst of the selected row to determine whether it contains equivalent lines or individual lines and if equivalent lines to determine their busy or idle condition, means effective if the selected row contains equivalent lines and is found to have an idle one therein for causing said switch to operate automatically in its secondary movementto test said equivalent lines individually, and means effective if the selected row contains individual lines for causing said switch to operate directly in its secondary movement to select a desired one of said individual lines.

2, The combination in a telephone system having an automatic selecting switch arranged to participate in primary and secondary selecting movements of a plurality of rows of terminals for said switch, a plurality of equivalent lines appearing in subgroups in successive rows of terminals, individual lines occupying another of said rows, means for operating said switch directively in its primary movement to select any desired row of said terminals, means for testing each row of terminals to determine whether it contains 'a subgroup of equivalent lines in which one is idle r all are busy or whether it contains individual lines, means efiective if the selected row contains equivalent lines and has an idle one therein for causing the switch to operate automatically in its secondary movement to test the equivalent lines in the selected subgroup, means effective if the selected subgroup is busy for causing the switch to continue its primary movement automatically to select and test the subgroup of equivalent lines in the next row, and

' means effective if the row selected by said directive primary movement contains individual lines for causing said. switch to operate directively in its secondary movement to select a desired one of said individual lines.

3. The combination in a selecting system of a selective switch having levels of terminals and primary movement 'for making a testof 'the:selected level to determineif it contains trunks or individual lines, means effective if the selected level contains trunks for making a collective test of all trunks in the level and for causing the switch to hunt automatically over said trunks in its secondary movement if the level contains an idle trunk, means effective if the trunks of the selected level are all busy for moving the switch automatically to succeeding levels of said-group where the collective test is repeated until the switch reaches the last level of the trunk group, means effective when said last level is reached for causing the switch to omit said collective test and to hunt automatically in the level for an idle trunk, and means effective if the level selected by the primary movement of the switch contains individual lines for causing said switch to operate directly in its secondary movement to select a desired one of said individual lines.

4. The combination in a selecting system of an automatic switch having levels of terminals and arranged to operate in a primary movement to select a level and in a secondary movement to select terminals in the level, of groups of trunks occupying certain levels of said terminals, discharge tubes individual respectively to said trunks for testing the condition thereof, means for operating said switch directively in its primary movement to select a desired level of terminals in which one of said groups of trunks appears, and means controlled by said discharge tubes for making a collective test of all of the trunks in the selected level to determine whether said level contains an idle trunk.

5. The combination in a selecting system of an automatic switch havin levels of terminals and arranged to operate in a primary movement to select a level and in a secondary movement to select terminals in the level, of a group of trunks occupying two or more successive levels of said terminals, discharge tubes, one for each of the trunks in said group, for testing the condition thereof, means for operatingsaid switch directively in its primary movement to select the first level of terminals in which said group of trunks means to repeat the collective test, and means effective if the collective test indicates an idle trunk in a selected level for causing the switch to operate automatically in its secondary movement to hunt for an idle trunk in such level.

6. The combination in a selecting system of an automatic switch having levels of terminals and arranged to operate in a primary movement to select a level and in a secondary movement to select terminals in the level, groups of trunks occupying certain levels of said terminals, discharge tubes individual respectively to said trunks for testing the condition thereof, common discharge tubes, one for each level of said trunks, each of said common tubes cooperating with the individual tubes of the corresponding level, means for operating said switch directively in its primary movement to select a desired level of terminals in which one of said groups of trunks appears, and a test circuit including the common occupied by one of said trunk groups, each of said 7 common tubes having a plurality of control electrodes individual respectively to the trunks in the associated level, means for operating said switch in its primary movement to select any desired level of terminals having one of said groups of trunks appearing therein, and means including said common discharge tube and effective at the completion of the primary selecting movement for performing a collective. test of the trunks in the selected level to determine the busy or idle condition thereof.

8. The combination in a selecting system of an automatic switch having levels of terminals and arranged to operate in a primary movement to select a level'of terminals and in a secondary movement to select terminals in a level, groups of equivalent lines appearing in certain of said levels, individual lines appearing in other of said levels, means for operating said switch directively in its primary movement to select either a level of equivalent lines or a level of individual lines, test means for causeing said switch to operate automatically in its secondary movement to hunt over said terminals when the selected level contains equivalent lines, means effective when said switch is operated to select a level of individual lines in its primary movement for causing it to operate directively in its secondary movement to select one of the desired individual lines in said level, andmeans for altering the condition of said test means to convert any desired level of equivalent lines to individual lines.

FRANCIS A. HUBBARD.

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