US2291224A

US2291224A - Selecting system

Info

Publication number: US2291224A
Application number: US377996A
Authority: US
Inventors: Nathan I Hall
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1941-02-08
Filing date: 1941-02-08
Publication date: 1942-07-28
Anticipated expiration: 1959-07-28
Also published as: NL69254C; GB549325A

Description

' Y SELECTING SYSTEM Filed Feb. 8,'1941 2 sheletsheet 1 LWP' www las 1 .9

ATTORNF July 28, 1942. N. l. HALL 2,291,224

' SELECTING SYSTEM Filed Feb. v8, 1941 `2 Sheets-Sheet 2 /NVENTOR N. l, HALL A T TORNE V Patented July 28, A1942 UNITED sELEcTmG SYSTEM Nathan I. Hall, Long Island City, N. Y., assigner to Bell Telephone-Laboratories, Incorporated, A

New York, N. Y., a corporation of New York y Application February s, 1941, serial No. 377,996

7 claims. (o1. 179-18) This invention relates to selecting and switching systems and particularly to systems in which selections are made automatically in a group of lines, trunks, or other circuits.

An object of the invention is to obtain a more uniform and more eihcient use of the lines, circuits, or other elements comprising a group in which selections are made.

Another object is to obtain a preferential selection of circuits which varies in accordance with the-extent of their us'e.

Another object of the invention is to improve the eiiiciency of switching systems by obviating the selection of circuits which have no available outlets.

These and other objects of lthe invention are realized by means of a switching system in which a plurality of equivalent groups of lines or trunks are accessible to automatic switches for extending calls or other connections, in which the several groups are selectable under the control of associated devices having varying degrees of sensitivity, and in which the selectability or preference for any particular' group of lines is varied by varying the sensitivity of the associated device in proportion to the number of calls extended to the lines of said group. More specifically the selecting system above mentioned may serve to extend subscribers lines over automatic switches to the trunks of a, plurality of groups. Any line, when calling, causes the application of operating voltage to a plurality of ldischarge tubes which are related respectively to the several groups of trunks, the rst tube to discharge in response to the applied voltage serving to cause the extension of the calling line to an idle trunk in the corresponding group. Since the order in which the tubes of the group operate depends upon the relative speed with which the ionizing current increases in their control gaps, it is possible to obtain a preferential distribution of the calls among the diierent trunk groups by controlling the sensitivity of said control gaps. 'I'his desirable end is accomplished by providing an impedance element for each trunk group and connectgroup becomes loaded its associated control tubes `become less sensitive, and other tubes will discharge first' to extend subsequent calls lto other groups of trunks.

A feature of the invention is a selecting system inwhich calling lines have access through links to groups of trunks, in which discharge tubes respond to calls on said lines to extend these calls over associated links to the associated trunk groups, and in which the busy condition of all telephone system to groups of links, trunks, or

other circuits. More particularly it is assumed that the subscribers lines appear on primary line switches of the well-known cross-bar type and that these primary switches have access through links and secondary line switches to groups of trunk circuits.

In Fig. 1 two frames of primary and secondary 'line switches are illustrated. One of these frames comprises ten primary cross-bar switches of which two, switches |00 and |0|, areill'ustrated.` This frame also includes ten secondary line switches of which two, switches |02 and |03, are illustrated. Ten groups of subscribers lines lol-|05 appear in the vertical contacts of the ing this element in common to the electrodes of all tubes which cause the extension of calls into said group. Each call extended into a particular group causes an increased current to flow v`through the common impedance element, which in turn lowers the voltage on the control electrodes of all tubes serving this group. This lowered voltage renders these tubes less .sensitivel than the tubes pertaining to other groups of trunks containing lighter loads. Hence as a ten corresponding primary switches,A and the vhorizontal rows of contacts of these switches are connected by link circuits to the vertical contacts of the secondary switches on the frame. For example, the No. 0 rows of horizontal contacts of the ten lprimary switches |00-I0l are connected to the ten corresponding vertical rows in the No.` 0' secondary switch |02. Similar1ythe N o. 9 rows of horizontal contacts of switches |00-I 0| are connected to the corresponding vertical rows of contacts of the No. 9 secondary switch |03, and the same is true of the intervening contact rows in the switches |00 and |0|.

. The ten secondary switches |02, |03 have access respectively to ten groups of trunks 06-| 01. These groups of trunks are connected to the horizontal rows of contacts in the respective secondary switches.

Each of the ten horizontal rows of each primary switch is provided with a select magnet and a space-discharge tube. For instance, the No. horizontal row of switch |00 is provided with select magnet |08 and tube |09, and the No. 9 horizontal row of the switch is provided with select magnet 0 and tube |||.v As will be described more fully hereinafter, the presence of a call on one of the subscriberslines causes the application of operating voltage to the control gaps of all tubes associated with the corresponding primary switch. When the first tube discharges in response tol the operating voltage', thev associated select magnet operates to select'the horizontal circuit or link for extending the call to the corresponding secondary switch. 4'I hereafter the voltage on all remaining tubes is reduced to prevent another one from discharging and causing a double connection.

magnets and discharge tubes for each or the non; y

zontal rows. The secondary switches may have access to ten separate trunk groups, or they may, as illustrated herein, have access to the trunk groups |06| 01 appearing in the switches on the rst frame. The purpose of giving two or more frames access to the same trunk groups is to provide these vgroups with an adequate load.`

The tubes disclosed herein may be of any suitable type, such asthose having .envelopes filled with'argon, neon or other gases. i.

A description will now be given ofthe detailed operation of the circuits, and for thislgpurpose reference may be had st to Fig. 2. `Assume that the subscriber of line 20|, appearing in the primary line switch 200, initiates a call. The re-v moval of thesubscribers receiver closes a circuit from battery through the left winding of line relay 202, contacts of hold magnet 203, thence over conductor 204, through the loop 0.! the subscriber's station and returning over conductor 200 through the contacts of magnet 203 and the right winding of relay 202 to ground.. Relay 202 operates and closes a circuit from ground through its contacts, conductor 200 through the winding of magnet 203, armature and back contact of'said magnet, conductor 201,resista.nce 203 to the start'v sistor 2|4, armature and contact of relay 2|! to the negative pole of battery 2|3. The voltage thus supplied across the control gap 20S- 2H is ing of magnet 203 tolground'at the contacts of relay 202. Relay 2|3 operates in this circuit, but the resistance of this relay and the resistance of element 2 |4 is suilici'ent to preventl the hold magnet 203 from operating at this time.

When relay 2|3 operates, it closes a circuit from the positive pole of battery 222, common resistor 223, contacts of relay 2 I3 to the common conductor 224, which is connected to the start anodes 22S-226 of the ten discharge tubes 221-220 associated respectively with the ten horizontal links 22S- 230. Each idle link in the group of ten links 229-230 is characterized by the presence of negative battery potential on the test conductor thereof, and busy links are characterized bythe presence of ground potential on the test conductor. For example, if link 229 is busy, ground potential is connected through the contacts Aof a suitable relay 23| over the sleeve conductor 232 to the start cathode 233 of the associated tube 221. With ground potential connected to the start cathode 233 the voltage applied to the starting gap by the battery 222 is insufficient to ionize the same'.

If, however, the link circuit 230 is idle at this time, an ionizing circuit for the tube 223` may be traced from the positive pole of battery 222, resistor 223, contacts of relay 2|3, conductor 224, starting anode 226, starting cathode 234, test conductor 235, resistor 23S, contacts of control relay 246, common resistor 241, to the negative pole of battery 231. The control gap.228234 ionizes, and insimilar fashion the control gaps of all other tubes representing idle links ionize. As soon asthe ionizing current in the control gap of some one ofthe tubes corresponding to idle links reaches sufficient value, ionization-transsufficient to ionize this gap, but the current ilowin'g is not suiilcientito operate either the magnet I 203 or the relay 2|3. Assuming that ino other line is calling at' the moment, the screen grid 2| 1 of tube 2|0, which is connected in-common with the screen grids of the other tubes, such` 2|3, cathode 2| l, anode 220, conductor 22|, wind-f fers from the control anode to the main cathode. Assuming that the tube 223 the first one to reach this transfer stage, a circuit may be traced from the'positive pole of battery 222, resistance 223, contacts of relay 2|3. conductor 224, anode 220, cathode 230, common conductor 233, wind- .cathode 240 of tube 221 is instantly made more positive to prevent the transfer of ionization of this tube in the event the link 223 hadbeen idle.

Thus the ionization of a single one of the tubes prevents the transfer of ionization in all other tubes to prevent the possibility of any double connections.

Shortly after ionization transfers to the main cathodem of the tube m the main anode zap discharges, and current now flows in a circuit traceable from the negative pole of battery 2 l3,

contacts axd winding of relay 2|5, cathode 233, main anode 245, winding of select magnet 24| to ground. The magnet 24| prepares the switch for the selection of the idle link 230 and also closes a short circuit around the resistor 2I4.

The removal of re'sistor'2l. permits sumcient current to4 flow in the circui previously traced for the operation of the hold magnet 203. 'Magnet 203 completes the connection of the line 20| to the link 23| and locks itself in a circuit from battery 242, through the front contact and winding of said magnet, conductor 203, closed contacts of the switch 200, conductor 2-33 to ground potential which in the meantime has been connected to this conductor in the well-known uve'potentiai of battery Ian is impressed upon the manner. The operation of magnet 203 releases relay 202.

After an interval following the closure of the main discharge gap of tube 228 the slow-operate relay 2|5 opens its contacts and severs the discharge circuits of the tubes 228 and 2 I0. There upon these tubes deionize, and the magnet 24| and relay 2|3 release. Also the relay 2|5 restores its armature and recloses its normal contacts. the line 20| to the link 230 and is held by ground potential on the sleeve conductor of said link.

Preference for the diierent trunk groups to which the calling lines have access is automatically varied in accordance with the load imposed The connection is now established fromv upon these groups by controlling the sensitivity l of the starting gaps of the tubes associated with the horizontal links in the line switches'. The circuits for obtaining this preferential control are disclosed more in detail inFig. 1. In this figure each of the ten primary line switches on each frame, such as the ten switches |e|0| on the lower frame, corresponds to the switch 'Y start cathodes H8, |42, |43, |44.y Similarly, the full negative potential of battery |4| is impressed upon the start cathodes I9, |45, |46|41, and the same is true for the other groups of trunks. When, however, the trunk in one of these groups is taken for use, such as the trunk |48 of the group |06, ground potential is applied to the test conductor thereof, and current now ows over a circuit traceable from the negative pole of'battery |30, resistor |29, contacts of relay |20, conductor |20, resistor |24, conductor ||6 through the contacts of switch |02, conductor |40 over the busy ground connection |49 to the opposite pole of battery |30. The voltage drop in the common resistance |29 lowers the potential on the start cathodes of all other tubes serving this group of trunks |06. Therefore, when the next call appears in vthe switch |00, and the same ls true in the other primary line switches, the negative potential on the-cathode ||8 of the tube |09 applied to the start anode |50 from the battery ample, the No. 0 horizontal link I6 of the switch |00 extends to the secondary switch |02, which has access to all ten of the trunks in the'group |06. TheNo.` 9 horizontal link ||1 of the switch |03 extends to the No. 9 secondary switch |03,

which has access to the ten trunks of the tenth l group |01. Similarly the eight intermediate horizontal links of the switch |00 extend respectively to the. eight intermediate secondary switches, which in turn have access tothe eight intermediate groups of trunks. The same relation between the horizontal links, the secondary switches and the trunk groups existv for the second frameof switches and also for other frames not shown.

The test conductors of the ten horizontal links |5|, is less than the voltage impressed across the starting gaps of the other nine tubes. For instance, the voltage applied to the gap of tube is the sum of the full negative potential of battery I4| impressed upon the cathode ||9 and the full positive potential of battery |5| impressed of the primary switch |00 appear respectively in the start cathodes ||.8||9 of the ten associated discharge tubes |09| And the same is true of the horizontal links of all other pri'- -mary switches. The No. 0 horizontal link of each No. 9 horizontal links H1, |3l, |32, |33which.

When all trunk groups |06|01 are idle, all test conductors are free from ground potential, and no current flows through any of the ten common resistors |29|40. Therefore, the full negaupon the anode |52. Therefore, the tube |09 isless sensitive than the other nine tubes, and the probability is that some one of the other nine tubes will discharge and cause the extension of the call over the corresponding into the associated trunk group thus preventing a second call from going int'o the group |06 which already has one call.

Whenever two or more trunks in any group are in use simultaneously a corresponding heavier current flows through the common resistor |29, and the negativepotential on the start cathodes of the associated tub'es is lowered correspondingly. Thus as a-gvroup becomes more and more loaded the tubes which cause the routing of calls into this group become less and less responsive with the result that'subsequent calls are automatically directed into trunk groups having lighter loads.

When all of the trunksof a group, such as group |06, become busy, a chain circuit of any renders all tubes serving this group inoperative.4 This condition prevails until 'some one of the well-known type may be utilized to cause the operation of the common group relay |28. This relay opens the voltage supply circuit |20 and trunks in the busy group becomes idle, at which time the relay |28 releases to render the group What is claimed is:

1. The combination in a selecting system of groups of lines,` switches, one for each group, for establishing connections with said lines, devices having dinerent degrees of sensitivity for selecting said switches for operation, and means for varying the sensitivity of said devices to vary the selectability of said switches in accordance with the extent to which the associated line groups are used. Y

2. The combination in a selecting system of groups of' lines, switches, one for each group, for establishing connections with said lines, devices having diiierent degrees of sensitivity for selecting said switches for` operation, and means for vlowering the sensitivity of said devices to reduce the selectability of said switches in proportion to the increased use of the associated groups of lines.

3. The combination in a selecting system of groups of lines, switches for establishing connections with said lines, discharge devices, one. for each of said groups, a source of voltage for 1 ber of connections established with' the corresponding group of lines.

4. The combination in a selecting system of groupsv of circuits, discharge devices, one for each group for controlling the extension of connections to said groups, means effective as the numberof busy circuits in any group increases for decreasing correspondingly the responsiveness of the associated discharge device to increase the l preference for other groups of said circuits.

6. The combination in a selecting system oi! a Vplurality of group of lines, switches having access to said lines, a plurality of groups ot discharge tubes, each group serving to cause the -extension of connections to a particular one oi.'

said groups of lines, a source of voltage, supply circuits, one for each group o! tubes for applying voltage from said source to said tubes, and means for lowering the voltage applied to any particular group oi' tubes in proportion to the number of connections establishedyto the lines of the corresponding group. f

7. The combination in a selecting system ot a plurality of groups of lines, switches having access to s aid lirfes, a plurality ol" groups of discharge tubes, each group serving to Acause the extension of connections to a particular one of said groups of lines, a source ot voltage, supply circuits, .one for each group of tubes for applying voltage from said source to said tubes, means for lowering the voltage applied to any particular group of tubes in proportion to the number ot connections established to the lines ot the corresponding group, and means for opening the supply circuit of any group of tubes when all of the lines in the associated group are busy.

NATHAN I. HALL.