US2355431A - Telephone or like system - Google Patents

Description

Aug. 8 1944. c. GILLINGS ETAL TELEPHONE on LIKE SYSTEM Filed Nov. 30, 1942 3 Sheets-Sheet 1 INVENTORS 1 CHARLES GlLLlNGS LAWRENCE JOHN MURRAY ATTORNEY Aug. 8, 1944. c. GILLINGS EIAL TELEPHONE OR LIKE SYSTEM Filed Nov 50, 1942 s Sheets- Sheet 2 Aug. 8, 1944.

Filed Nov. 30, 1942 3 Sheets-Sheet 3 CSri INVENTORSV CHARLES GILLINGS LAWRENCE JOHN MURRAY ATTORNEY Patented Aug. 8, 1944 Charles Gillings and Lawrence John Murray, Liverpool, England, assignors, by mesne, assignments, to Automatic Electric Laboratories, -Inc.,v

Ghicago, 111., a corporation of Delaware Application November 30, 1942, Serial No.467,316

In Great Britain January 30, 1942 16 Claims. 01. 179--22) The present invention relates to telephone systems and is more particularly concerned with small private automatic telephone systems,

It is the general object of the invention to provide an improved private automatic telephone system of the crossbar switching type.

The crossbar switches to which the present invention has application are of the type in which contact devices are arranged in rows and columns at right angles to the rows and in which the operation of any desired contact device is effected by a preparatory operation common to all contact devices in the same row as the desired contact device and by a holding operation common to all contact devices in the same column as the desired contact device, the arrangement being such that the only contact device operated is that which is subject to both a preparatory operation and a holding operation.

When one contact device has been operated the magnet or its equivalent which has effected the preparatory operation is freed and a second or further contact device can be operated provided such device or devices is or are in different columns and it is to crossbar switches of this type that the invention relates,

The invention is particularly concerned with small size exchanges and it is an object of the invention to control the preparatory and holding operations of the crossbar switch in a special manner particularly applicable to small size exchanges.

According to one feature of the invention the magnets of a crossbar switch mechanism which elfect the holding operations are individual to subscribers lines and are arranged to be operated after respective preparatory operations have been effected by equipment common to a number of subscribers lines to connect subscribers lines to link circuits.

According to a subsidiary feature of the invention the magnets which effect the holding operation are provided with contact springs which enable them to act as cut-off relays.

According to a further feature of the invention on the initiation of a call common equipment is adapted to select an idle link circuit and cause a preparatory operation of crossbar mechanism corresponding to such circuit to take place and to hunt subsequently for a calling line to cause the holding magnet individual thereto to operate and connect the calling line to the idle link circuit.

According to a further feature of the invention when impulse responding equipment has been operated in accordance with the number of a wanted line, common equipment is adapted to hunt for the link'circuit'over which the connection has been setup to cause a preparatory operation of the crossbar switch mechanism, whereupon a holding magnet individual to a subscribers line is operated from the impulse responding equipment to cause the said link circuit to be connected to the wanted subscribers line.

According to a further feature of the invention a common equipment is provided for effecting the preparatory operation of a crossbar switch mechanism and the operation of a holding magnet individual'to a calling line to connect up calling and called lines and a separate common equipment is provided for efiecting the preparatory operation of the crossbar switch mechanism and the operation of a holding magnet individual to a called line and is characterised in that arrangements are provided such that only one common equipment can operate at a time.

The invention will be better understood from the following description of one method of carrying it into effect, reference being had to the accompanying drawings comprising Figs, 1-4, Figs. 1-3 of which should be arranged side by side with Fig. 1 on the left to show typical circuits of a crossbar private automatic exchange, hereafter termed P. A. X, having a capacity of up to 20 lines, while Fig. 4 which is shown at the bottom of Fig. 3 shows a trunking diagram of the P. A. X.

Referring now to the trunking diagram of Fig.

4 it will be seen that use is made of a single crossbar switch which is operated in conjunction with four connecting link circuits AL-DL. The crossbar switch comprises twenty vertical hold bars and their associated crossbar relays IKH2DKl-I and four pairs of horizontal operate bars and their associated crossbar relays AOP and ATP to DOP and DIP respectively. Each of the connecting link circuits ALDL has associated therewith such a pair of relays, an OP relay in operating serving to prepare for the connection of the calling party to a link, which connection is completed by the operation of the relevant one of the relays IKH2BKH provided individual to the subscribers lines; the IP relay of the link in question serves in similar manner for connecting it to the called party, The KI-I relay provided per subscribers line acts also as his cut-off relay so that each subscriber will only require a single individual line relay in addition. A two digit numbering scheme is employed on the line a single common equipment shown at the foot of Fig, 1 is provided which is accessibleto.

all subscribers over the wipers of a rotary'swi'tch of the self-interrupted drive step-by-step type,

which switch serves as a combined link hunter and line finder adapted first of all to connect with a free link and then to connect this link via the crossbar switch to the calling line.

links such as DL and it will be seen that each link is provided with a rotary switch adapted to receive the two-digit dialled numbers. In response thereto it will be understood that connection between the calling link and the called line is thereupon effected on the crossbar switch under control of further common equipment, shown at the foot of Figs. 2 and 3, which serves to ensure that only one connection can be in process of being set up on the crossbar switch at any one time and so prevents the possibility of multiple connection to aline. r

Furtherdetails of the operations will become apparent from the ensuing circuit description.

Referring to the general nomenclature of the various elements utilised in the circuits of Figs; 1-3, it will be seen that the number of contact units carried by each relay is shown underneath its designation, as for instance: B/B (Fig. 2), and are designated individually in small letters which in this instance will be bl, b2, etc. A slow-torelease relay is shown with a hatched portion at one end of the rectangle indicative thereof, while a slow-to-operate relay with a copper slug at the armature end of its core is shown with a cross at one end, such a relay being in some instances slow-to-release as well as slow-to-operate.

The contact units individual to the crossbar switch vertical and horizontal relays are indicated in the same manner, while the set of crossbar switch contacts proper which are closed at the intersection of any given pair of vertical and horizontal bars are designated OP/KH (Fig, 1) or IP/KH (Fig. 3), according to whether a connection is outgoing from a line to a link or incoming from a link to a line.

The various rotary switches such as that in the common equipment shown in Fig. 1 which is designated HFS are provided with driving ma nets such as HFM, each having a set of interrupter contacts such as him. The various sets of wipers and banks thereon are designated HFSI HFS2, etc.

Considering now the circuit operations, when a subscriber such as No. 11 calls, a loop is placed across the incoming negative and positive conductors (Fig. 1) to operate the associated line relay IR which thereupon at contacts Ir! connects a guard earth to the incoming test lead T, and at [r2 connects an earth on to the start lead H! extending into the common equipment.

Assume that an idle one of the connecting links AI DL is available, this earth will extend via the parallel-connected normally-made contacts of the B relays in the idle connecting links Figs?- 2 and 3 show circuits of one of the connecting of the board (contacts b8 of relay B in the connecting link DL shown in Figs. 2 and 3 being designated) and will extend over bank and wiper HFSI to bring up relay RA. This relay in operating at its contacts ml extends the earth over bank and wiper HFSZ to energise the switch magnet HFM in series with the magnet interrupter contacts him. The magnet in energising opens its contacts him and then releases, since its circuit is opened and the switch wipers are thereupon stepped from the home position I to sociated with the various links AL-DL, to short circuit and prevent the testing relay TK from operating. The wipers of switch I-IFS will therefore proceed to advance step-by-step until a free link is encountered, and assuming that link DL in Figs. 2 and 3 is the one concerned, then when the I-IFS switch wipers reach contact 5 connecting with this link an operating circuit will be completed for relay TK as follows: start earth, 128, icsZ, ral, winding of relay TK, normally-made contacts dopla0p|, banks and wipers I-IFS4 and HFS5, resting contacts b8 and n2 in the, link DL and the winding of relay D0? in parallel with resistance YH to battery. Relay TK in operating at its contacts tkl opens the HFM magnet driving circuit, while owing to the low resistance of this relay, relay DOP will operate in series therewith. Relay DOP in operating operates its associated horizontal bar on the crossbar switch in readiness for connecting with the calling line and at its own individual contacts d pI (Fig. 1) completes a holding circuit for itself independently of the banks HFS4 and HFS5, while at dopZ (Fig, 1) it recompletcs a self-interrupted driving circuit for magnet HFM independently of the operated contacts tk2,

The HFS switch wipers now advance step-bystep until they reach contact 6 which marks the commencement of the group of bank contacts 6-25 which connectv with the KI-I crossbar relays of the twenty subscribers lines on the board. In the present instance contact 6 corresponds to the calling line H, but if the calling line had been any other, such as 20, the switch HFS would continue to rotate its wipers until the contact 25 corresponding thereto was reached. In the present instance with wipers HFSA and HE'S-5 on contact 6 the start earth potential can extend through the low resistance testing relay RK and banks and wipers I-LFS-l and HFS5, operated line relay contacts 1T3, common lead I I to battery via resistance YB and relay RK thereupon operates.

to cut the magnet driving circuit at contacts rkZ. At rkl an operating circuit is completed for relay RKA and at rk3 an alternative locking circuit is completed for relay RA. Relay RKA in operating at contacts rkal opens the original operating circuit for relay RA so that; this relay is now dependent on relay RK, while at rkaZ an earth is extended forward over wiper and bank I-IFS3 to operate the vertical hold relay of the particular calling line in question, in this case relay IKH.

Relay IKH on energizing operates its associated a cut-oil relay and at its contacts Ikhl and Ikh2 disconnects relay IR from across the line and this relay therefore releases, While at Ikh3 a uard earth is maintained on the incoming test lead T independently of relay IR. Relay IR inreleasing at its contacts I11! and Ir3 opens the holding circuits of relays RK and TK, which release, and

relay RA follows immediately, while relay RKA commences to release slowly, the slow release period of this relay serving to maintain a holding circuit for relay IKH until a hold earth is returned from the connecting link taken in use. Relays TK and RK in releasing recomplete a driving circuit fo the magnet I-IFM and the wipers of switch HFS are thereupon rotated to the home position I, while relay DOP is released in the connecting link and in so doing releases its associated horizontal bar, but the crossbar contacts operated are now maintained held by the operated vertical bar. On release of relay RKA after its slow release period the common equipment is ready for further use by any other calling subscriber.

On operation of the crossbar contact OP/KH the subscribers loop is extended forward to operate relay A in the connecting link and this relay thereupon at its contacts aI brings up relay B in series with rectifier MBA and resistance YE to battery. Relay B in operating looks over its contacts bl, at 172 extends earth back to hold magnet IKI-I in the line circuit, at 175 completes an operating circuit for relay C over both it windings in series with the DS switch magnet DM, nonoperative in this condition, at b6 extends a guard earth over the incoming test lead to the common equipment so as to mark the link a busy and at 228 (Fig. 1), opens a point in the start circuit to the common equipment so as to prevent the starting up of this equipment at a time when all connecting links are busy. Relay C in operating at its contacts cl prepares an impulsing circuit for the magnet BM in series with its low resistance upper winding, the magnet being still nonoperative in series with the winding of relay B,

whil at 05 (Fig. 3) an operating circuit is completed for relay E from the earthed contacts b2 (Fig. 2). Relay E in operating at contacts eI (Fig. 2) connects the earthed centre winding of relay A up to common lead I2 extending to a dial tone source, whereupon dial tone is extended by induction through the windings of relay A on to the incoming speaking conductors.

The subscriber now dials the first digit of the required number, which digit may be either 1 or 2, and in case a subscriber should dial any other number as a first digit which would not be part of an allocated number on the board, then arrangements are made to return a busy tone.

Relay A responds to the digit dialled and on its first release an energising circuit is completed for magnet DM as follows: earth, contacts bl, aI, cI, low resistance upper winding of relay C, magnet DM to battery, the winding of relay B being short-circuited during this time, while the lower winding of relay C in series with resistance YF is similarly short-circuited. On the re-operation of relay A an energising circuit is recompleted for relay B and relay C now holds operated on both its windings in series with magnet DM.

Magnet DM will not hold in thi condition and thereupon releases to advance its wipers from contact I'to contact 2. On the advancement of the DS wipers to contact 2 an immediate operating circuit is completed for relay N (Fig. 3) via wiper and bank D83 and contact 174 to battery via resistance YJ and this relay at its contacts nI (Fig. 2) opens the dial tone circuit and at its contacts 113 (Fig. 2) opens the holding circuit for relay C in series with magnet DM and at the same contacts short-circuits the lower winding of relay C so that if there should be no second impulse of the train, then relay 0 will release after a slow release period governed by the short-circuiting of its lower winding and will prepare the switch US for receiving the second digit. In like manner relay B holds operated during each break impulse and it will be mentioned here that the presence of the metal rectifier MBA in the energising circuit of relay B serves to prevent the slowing up of the operation of magnet DM which would otherwise result by the direct connection of a comparatively low value non-inductive resistance in parallel with its winding; neither the magnet DM nor relay 0 will moreover hold operated in series with relay B.

If digit 1 is dialled by the calling party, then relay A will remain operated after the first impulse, while relay N will also remain operated over wiper DS3 in position 2 and contacts 114 to battery. Relay C therefore commences to release slowly and on its release the impulsing circuit is opened at contacts cI (Fig. 2) and earth is extended over contacts b3 and c3 (Fig.3) and wiper and bank D82 to bring up relay AD which in a manner to be later described causes the DS switch to be advanced to contact 4 in readiness for being set by the second dialled digit on to one of the contacts 5-44 giving access to any one of the subscribers having the first digit (1.!

If 2 is dialled as a first digit then switch DS will be in position 3 when relay C releases and in this case relay BD will be operated to cause the switch DS to be advanced to contact I5 in readiness for being subsequently set in response to the second digit on a desired one of the contacts I5-25 giving access to the subscriber in the second group of ten on the board.

If 3 is dialled as a second digit, then the DS switch wipers will be set to position 4 in which case there will be no holding circuit for relay N which will release. As contacts n3 the shortcircuit is removed from relay C which will now remain operated on both its windings in series with magnet DM (non-operative) and earth will be extended over contacts M and c3, wiper and bank D82, and contacts adii, 1x15, sd2 and g2 to battery via the left-hand winding of relay G which operates. 'Ihereupon a locking circuit for this relay is completed over the make-first light contacts gI and at g! the holding circuit for relay E is opened. On release of relay E busy tone is connected up over lead I3 and contacts 94 and eI to the centre winding of relay A which busy tone is thereby extended to the calling party.

If any of the numbers 4-4) are dialled then the DS switch will be set to one of the positions 5-I I whereupon relay N will hold operated over wiper and bank D53 and relays C and E will therefore release in turn. On release of relay C earth via the winding of relay N will extend via contacts b3 and 03 to operate relay G with the above described results.

Assuming that digit fl has been, dialled, then relay AD in operating at its contacts adl (Fig. 2) locks to the earthed contacts b2 (Fig. 2) and at contacts adi and ad3 (Fig. 2), completes a self-v interrupted driving circuit for. magnet DM from the earthed low resistance winding of relay N via wiper and bank BS2 so that the switch advances its wipers to contact 4 where the driving circuit is opened; at wiper and bank DS3 the main holding circuit for relay N is now opened sinc contacts bl are operated andthis relay now releases so as at contacts n3 (Fig. 2) to reoperate relay C in readiness for the dialling of the second digit. Similar remarks apply if relay BD has been operated, the only difierence being that the DS wipers will be re-positioned to contact l5 before relay N is released to re-prepare the impulsing circuit.

Returning to the consideration of the selection of a called subscriber in the first group of ten lines, the second digit dialled advances the DS switch wipers to one of the contacts 5-ld, relay N being operated as before when the DS switch moves from position 3. At the end of the second train of impulses relays A, B, C, E, N and AD will be already operated and relay C commences to release slowly. On release of relay C after its slow release period, earth is extended over contacts g3, slc3 and 02 (Fig. 2), operated contacts add, bank and wiper DSl, operated contacts 111 and common lead 46 to operate relay FS in the final switching control equipment FSC common to the various connecting links and which serves to control the testing of the wanted line and at the same time to ensure that only one connecting link out of the four provided can perform 2. called line testing operation at any one time. Relay FS in operating at contacts I32 completes a selfinterrupted driving circuit for the magnet SCM of the switch SC in the common switching control equipment, and this switch thereupon rotates its wipers in search of a marking indicating the calling connecting link, in the present instance link DL, which is marked on bank S03 (Fig. 3) by means of a resistance marking battery via resistance YG, contacts g5, s7c4, c4 and dill, and bank and wiper BS6. It will be seen that leads from the 1' our connecting links AL-DL make repeated appearances on the banks SCl-SC3 and when switch SC reaches any one of the multipled contacts on bank SC3 corresponding to the calling link DL, relay FK operates and cuts the driving circuit at contacts jlcl. At i702 an operating circuit is completed for relay FKR which at its contacts ficri extends earth over wiper and bank SCZ to hold relay E independently of contacts 05, while if at this time no other out-going call is in process of being coupled to a free link as will be indicated by the operation of relay TX. in the common equipment of Fig. 1, and therefore provided that the operation of the cross bar switch has not been initiated by another call,

earth will be extended over contacts tlci and fkrl to bring up relay ICS. Relay ICS in operating at its contacts icsl extends earth over wiper and bank SC! to bring up the horizontal bar relay DIP associated with the connecting link DL and at contacts i032 (Fig.1) opens the start circuit to the equipment common to the various subscribers lines to prevent the taking into use of this common equipment and therefore of the crossbar switch by another outgoing call during the switching through from the link DL to the called subscriber in question. On operation of relay DIP the associated horizontal bar is operated to prepare for connection to the called line on the crossbar switch and at the same time the earth extended from the contacts fkr2 (Fig. 3) over wiper and bank S02 is diverted over contacts dipl and e5, (relay E now commencing to release slowly due to its slug), into the upper winding of the switching relay SK, and thence via wiper DS4 in one of the positions 5l4 on to the test lead T of the required caled line.

Assuming that the called line is free, a resistance marking battery will be connected to lead T in which case relay SK will operate and will lock on its lower winding via contacts ski and SM to the earthed contacts 192. At contacts sk3 (Fig. 2) the start earth to the common switching control equipment FSC is removed. If no other connecting link should be set to switch through, relay FS in the common equipment releases and in turn releases relays FK, FKR and ICS. At contacts sk4 (Fig. 3) the marking on the bank S03 is removed and the circuit of relay FK is opened at a further point. If however at this time another connecting link should be already set to switch through to a called line, relay FS will remain operated but relay FK will release and will be followed by FKR. and ICS. Switch SC will then rotate in search of the marking corresponding to such other connecting link; if no other connecting link should be waiting, then on release of relays FS, FK, FKR and ICS switch SC will remain in the position it has taken up until it is required for another call.

At contacts slc5 (Fig. 3) earth is extended over wiper and bank BS5 to operate the vertical bar relay KH corresponding to the called line. Relay K operates its associated vertical bar to close a set of crossbar contacts such as IP/KI-I (Fig. 3) which extend the connecting link DL to the called line and at its own contacts disconnects the line relay from across the called line. Owing to relay FKR (Fig. 2) in the common equipment being slow to release, it will be noted that the horizontal bar relay DIP is maintained operated at least until the vertical bar relay has operated and when relay DIP releases, the crossbar contacts IP/KI-I are maintained closed by the vertical bar. On the release of relay E after its slow release period, the called subscribers bell is rung in the following manner: ringing current extends over common lead !5 from the earthed ringing current generator through the winding of the ring trip relay F and contacts e2 and f4 on to the negative line, a return circuit from the positive line being completed over contacts f5 and resistance YC to battery. During the ringing of the called subscribers bell ringing tone is returned to the calling party by the connection of a ringing tone source via common lead l4 and contacts f1, SM, 94 and el to the centre winding of relay A.

When the called subscriber answers, relay F operates and at contacts 4 and f5 trips the ringing and extends the lines through. At fl it completes a local locking circuit for itself to earth via contacts sits and 122, while at f2 and 3 it connects the called subscribers battery feeding relay SD across the lines, while at f! the ringing tone circuit is opened.

Conversation now proceeds between the calling and called parties, and at the end of conver-' sation the connection will remain held until the calling party hangs up; when this occurs relay A releases and brings down relay B which in turn releases relays SK, F, SD and AD or BD as the case may be. A homing circuit is now completed for the switch DS over the following path: earth, low resistance winding of relay N, wiper and bank D83, resting contacts b4 and b1 (according to the particular bank contacts being wiped over), magnet interrupter contacts dm, magnet DM to battery and switch DS thereupon drives its wipers through to the home position I. Relay N remains operated during this time due to its slug and at its contacts 122 (Fig. 2) maintains the idle marking battery circuit open during the homing of the switch. When the switch reaches the home position the circuit of relay N is opened and this relay releases and the connecting link is free for further common use. Returning again to the testing of the called line it will be remembered that this is efiected by relay SK during the slow to release time of relay E. If the called line should prove to be busy, then relay SK will not operate and on release of relay E the operating earth for relay SK 'will extend tionof one of a plurality of holding magnets arranged in another of. the coordinate directions, a plurality of subscribers lines corresponding respectively to said holding magnets, each line being connected in multiple to all contact sets under the. control of its corresponding holding magnet, a'plurality, of link circuits corresponding respectively to said selecting magnets, each link I circuit being connected in multiple to all contact over contacts skZ and e4 to operate relay G on its right-hand winding and this relay thereupon looks over its make-first light contacts gl to the earthed contacts 172. Relay G in operating at its contacts 93 and 95 (Figs. 2 and 3) opens the start and marking circuits to the common switching control equipment FSC so as to release this for further common use and at its contacts g4 (Fig. 2) completes a circuit for returning busy tone from common lead I3 to the calling party.

It will have been noted that the equipment FSC is not taken into use from a connecting link until the completion of the dialling of the two digits on that link, that is to say, until the link is in readiness for testing the required called line. This arrangement is adopted so that if a a subscriber should take into use a link and should then delay to dial for a short interval during which time a second link is taken into use by another calling party, then if the dialling operations of both subscribers should overlap it will not be possible for the two connecting links simultaneously to operate on the crossbar switch, since the equipment FSC which controls the test ing of a called line from a link can only be associated with one link at a time, which in this instance will be the link on which the dialling operations are first completed.

As regards the supervision arrangements, if a subscriber takes into use a link and should then fall to dial, the continued glowing of the permanent glow lamp (PG Fig. 3) over a circuit extending to earth over contacts 96, be, ad5 and D2 will give a visual indication to this effect; by the insertion of a suitable delayed operation relay in the battery feeding path common to these circuits a delayed alarm could be brought into operation if any link was held too long. If a subscriber should set up a call to another party on the board and should then hold the connec-- tion after the called party has hung up, the called subscriber held lamp CSH (Fig. 3) will be lit and a delayed alarm could be brought into operation if desired in similar manner as for the permanent glow lamp PG,

What we claim as new and desire to secure by Letters Patent is:

1. In a telephone system, a crossbar switch wherein any contact set in a coordinately arranged field of contact sets may be operated through the temporary operation of one of a plurality of selecting magnets arranged in one of the coordinate directions and, during the period of operation of said selecting magnet, the operasets under the control of its corresponding selecting magnet, equipment common to said lines and also commonto said link circuits operated responsive to a calling condition on any line to search for said: calling line and foran idle link circuit, said equipment efiective, when they are found to operatethe selecting magnet corresponding to saididle link circuit and the holding magnet corresponding to said calling line,- said two operated magnets effective conjointly to con.-

trol one of said contact sets to complete a connection' between said calling line and said idle linkcircuit.

2. In a telephone system, a crossbar switch "wherein any contact set in a coordinately arbeing connected in multiple to all contact sets under the control of its corresponding holding magnet, a plurality of link circuits corresponding respectively to said selecting magnets, each link circuit being connected in multiple to all contact sets under the control of its corresponding selecting magnet, means for seizing any one oi said link circuits and transmitting thereto impulses indicative of a wanted one of said subscribers lines, equipment common to saidlink circuits effective to search for the seized link circuit and, when it is found, to temporarilyoperate the selecting magnet corresponding thereto, and means for then operating the holding magnet corresponding to said wanted line while said selecting magnet is temporarily operated, said two opera ated magnets efiective conjointly'to control one of said contact sets to complete a connection between said wanted line andsaid seized link circuit.

. 3. In a telephone system, a crossbarswitch wherein any contact set in a coordinately arranged field of contact sets may be operated through the temporary operation of one of a plurality of selecting magnets arranged in one of the coordinate directions and, during the period-of operation of said selecting magnet, the operation of one of a plurality of holding magnets arranged in another o'f the coordinate directions, a. plu-. rality of subscribers lines corresponding respectively to said holding magnets, each line being connected in multiple to all contact sets under the control of its corresponding holding magnet, a plurality of link circuits corresponding respectively to said selecting magnets,'each link circuit being connected in multiple to all contact sets under the control of its corresponding selecting magnet, a hunting switch common to all of said lines effective to temporarily operate different ones, of said selecting magnets at difierent timesj and, at each of said times, to operate someone of said holding magnets while the operated selecting magnet remains temporarily operated, whereby one of said contact sets. is operated to connect one of said subscribers lines to one of said link circuits, said holding magnet effective to maintain said contact set operated after said selecting magnet has ceased to be operated.

4. In a telephone system, a crossbar switch wherein any contact set in a coordinately arranged field of contact sets may be operated through the temporary operation of one of a plurality of selecting magnets arranged in one of the coordinate directions and, during the period of operation of said selecting magnet, the operationof one of a plurality of holding magnets arranged in another of the coordinate directions, a plurality of subscribers lines corresponding repectively to said holding magnets, each line being connected in multiple to all contact sets under the control of its corresponding holding magnet, a plurality of link circuits corresponding respectively to said selecting magnets, each link circuit being connected in multiple to all contact sets under the control of its corresponding selecting magnet, means'for temporarily operating any one of said Selecting magnets and, while it is operated,

operating any of said holding magnets, said two operated magnets effective conjointly to operate one of said contact sets thereby tocomplete a connection between the line corresponding to the operated holding magnet and the link circuit corresponding to the operated selecting magnet, said holding magnet effective to maintain said contact set operated after said selecting magnet has ceased to be operated, as individual line relay normally connected to each subscribers line, and contacts on each holding magnet for disconnecting from the line corresponding to that magnet the line relay normally connected thereto.

5. In a telephone system, a crossbar switch including two groups of lines, a magnet for each line, and mechanism for completing a connection between any line of one group and any line of the other group responsive to the concurrent operation of the magnets for those two lines; and equipment controlled over any one of the lines ofsaid one group, first to search-for an idle line of said other group and operate the magnet for that line, and then, while maintaining such magnet operated, to search for said one line of said one group and operate the magnet. for that line.

6. In a telephone system, a crossbar switch including two groups of lines, a magnet for each line, and mechanism for completing a connection between any line of one group and any line of the other group responsive to the concurrent operation of the magnets for those two lines, a plurality of relays corresponding respectively to'the lines of said one group, each saidlrelay being normally connected .to its corresponding line and at times'operated thereover; means responsive to an operation of any one of said relays for operatin the magnet for a'line of said other group and, while it is operated, operating the magnet for the line of said one group which corresponds to the operated relay, and contacts on said last magnet effective upon operation thereof to disconnect the operated relay from its corresponding line.

7. In a telephone system, a crossbar switch, a plurality of subscribers lines terminating in said switch, a plurality of switch operating magnets in said switch corresponding respectively to said lines, a plurality of link circuits terminating .in said switch, equipment common to said lines ef-,

'fective response to a calling condition on any line to search for and seize an idle one of said link circuits, means in said equipment for operating the magnet corresponding to the calling line thereby to connect the calling line to the seized link circuit, means then effective to release said common equipment, and means in said seized link circuit thereafter controlled over said calling line for maintainin said magnet operated.

8. In a telephone system, a crossbar switch, a plurality of subscribers lines terminating'in said switch, a link circuit also terminating in said switch, said switch including a plurality of switch operating magnets corresponding respectively to said lines, equipment common to said magnets effective to operate the differentv ones of said magnets at difierent times, each magnet effective when operated to connect its associated line to said link circuit, and means in said link circuit then controlled over the line connected to ,said link circuit for maintaining. said magnet operated independently of said equipment.

9. In a telephone system, a cross bar switch, a plurality of subscribers lines terminating in said switch, a plurality of switch operating magnets in said switch corresponding respectively to said lines, a plurality of link circuits terminating in said switch, equipment common to said lines effective responsive to a calling condition on any line to search for and seize an idle one of said link circuits, and means in said equipment for then operating the magnet corresponding to the calling line thereby to connect the calling line to the seized link circuit.

10. In a telephone system, a crossbar switch, a plurality of subscribers lines terminating in said switch, a plurality of switch operating magnets in said switch corresponding respectively to said lines, a plurality of link circuits terminating in said switch, equipment common to said lines effective responsive to a calling condition on any line to search for and seize an idle one of said link circuits, means in said equipment for then operating the magnet corresponding to the calling line thereby to connect the calling line to the seized link, and means in the seized link thereafter controlled over the calling line to operate any desired other one of said magnets thereby to connect any desired other one of said lines to said link circuit to extend a call thereto.

11. In a telephone system, a crossbar switch, a plurality of subscribers lines terminating in said switch, a plurality of switch operating magnets in said switch corresponding respectively to said lines, a plurality of link circuits terminating in said switch, equipment common to said link circuits operated responsive to a calling condition on any one of said lines to search for an idle link circuit and, when one is found, to condition said switch to complete a connection between the calling line and that link circuit, means for then operating the magnet corresponding to said calling line thereby to cause said switch to complete said connection, means in said link circuit forreceiving information indicative of any particular wanted line, other equipment common to said link circuits operated to search for said link circuit and, when it is found, to condition said switch to complete a connection between said link circuit and said Wanted line, and means for then operating the magnet corresponding to said wanted line thereby to cause said switch to complete said last connection.

12. In a telephone system, a crossbar switch,

a plurality of subscribers lines terminating in said switch, a plurality of switch operating magnets in said switch corresponding respectively to said lines, a plurality of link circuits terminating in said switch, equipment common to said link circuits operated responsive to a calling condition on any one of said lines to search for an idle link circuit and, when one is found, to condition said switch to complete a connection between the calling line and that link circuit, means for then operating the magnet corresponding to said calling line thereby to cause said switch to complete said connection, means in said link circuit for receiving information indicative of any particular wanted line, other equipment common to said link circuits operated to search for said hnk circuit and, when it is found, to condition said switch to complete a connection between said link circuit and said wanted line, means for then operating the magnet corresponding to said wanted line thereby to cause said switch to complete said last connection, and means for preventing said first common equipment and said other common equipment from operating at the same time in the event that another call is initiated before said last connection is completed.

13. In a telephone system, a crossbar switch, a plurality of subscribers lines terminating in said switch, a plurality of switch operating magnets in said switch corresponding respectively to said hnes, a plurality of link circuits terminating in said switch, means for seizing any idle one of said link circuits and transmitting thereto impulses indicative of a wanted one of said lines, and means in said link circuit for thereupon operating the one of said magnets which corresponds to said wanted line, thereby to connect said wanted line to said link circuit.

14. In a telephone system, a crossbar switch,

a plurality of subscribers lines terminating in said switch, a plurality of switch operating magnets in said switch corresponding respectively to said lines, a plurality of link circuits terminating in said switch, means for seizing any idle one of said link circuits and transmitting thereto impulses indicative of a wanted one of said lines, equipment common to said link circuits then operated to search for said seized link circuit and, when it is found to condition said switch to complete a connection between the seized circuit and said wanted line, and means in said link circuit for thereupon operating the one of said magnets which corresponds to said wanted line, thereby to connect said wanted line to said link circuit.

15. In a telephone system, a crossbar switch, a plurality of subscribers lines terminating in said switch, a plurality of switch operating magnets in said switch corresponding respectively to said lines, a plurality of link circuits terminating in said switch, means for characterizing any one of said link circuits, equipment common to said link circuits operated to search for a characterized link circuit and to prepare said switch to extend a connection to said characterized circuit, and means in said equipment eifective, while said switch is thus prepared, to operate any particular one of said magnets thereby to complete the prepared connection to said characterized link circuit from the line associated with that magnet.

16. In a telephone system, a crossbar switch, a plurality of subscribers lines terminating in said switch, a plurality of switch operating magnets in said switch corresponding respectively to said lines, a plurality of link circuits terminating in said switch, equipment common to said lines and to said link circuits operated at times to prepare said switch to extend a connection to one of said link circuits and thereafter operated while said switch is thus prepared to operate any particular one of said magnets thereby to complete the prepared connection to said one link circuit from the line associated with that magnet.

CHARLES GILLINGS. LAWRENCE JOHN MURRAY.

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