US1757446A - Telephone-exchange system - Google Patents

Description

May 6, 1930; E. G, WRiGHT T AL l,757,446

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ATTO/MQW Patented May 6, 1930 STATES EBMCND P. WRIGHT, F CROYDON, .TURN H. E. BAKER, 0F HAHPSTEAD, AND ALAN H. CAMERON, 0F BRONDESB'UBY, ENGLAND, ASSIGNOBS T0 WESTERN ELECTRIC COMPANY, INCORPORATED, 0F NEW YORK, N. Y., A CORPCBATION OF NEW YORK TEEPHONEEXCHANGE SYSTEM Application led Hay 10, 1928, Serial No. 276,734, and in Great Britain lay 10, 1927 This invention relates to telephone exchange systems and more particularly to systems of the character in` which' connections are extended between subscribers lines by 's means of machine switching apparatus under the control of common register senders. The invention is especially adapted for use in large multi-ofceexchange areas and the object thereof is to provide a system of simple lo character which utilizes all apparatus involved to the most economical degree and with the greatest surety of operation.

In the prior art, systems employing power driven switches of the panel or rotary type controlled by common register senders, and systems employing switches of the Strowger or step-by-step type controlled by so-called directors, have been disclosed for use in large multi-office exchange areas. The syszo tem of the present invention has been de signed particularly to simplify the connection extending selectors and the equipment of the common register senders to order that less apparatus may be required for maintaining adequate service and in order that the cost of maintenance may be reduced as much as possible.

In the embodiment of the invention disclosed herein by way of illustration, all switches employed in the exchange are of the single motion rotary type movable in one direction only. The calling lines are associable with' a first group selector by means of groups of link circuits each link circuit comprising a line finder and -a selector finder. Each link circuit has access through its selector finder to a group of rst selectors havin access in turn to a single register sender. ssociated with a group of link circuits is a distributor switch. Provision is made whereby, upon the initiation of a call in a group of calling lines, the distributor switch will select only an idle link, the selector finder of which has access to an idle first group selector in a group having access to an idle register sender. A single register sender is multipled directly before all first group selector trunks of a selector group and may be associated with anyone of the group selector trunks, no hunting :for an idle sender being required other than the hunting o eration of the link l'distributor switch, w ereby time is saved in associatin an idle sender with a calling line and additional switches are obviated.

The selector switches of each switching sta e except the rst,`are divided into groups an a minor or auxiliary switch is rovided common to the selectors of each suc group. The minor switches are directed b im vulses transmitted thereto over the estab ishe connection from the common sender and mark the groups of terminals, and in the case of the final selector the desired line terminal to which their associated selectors shall hunt. The selector switches therefore have no directed movement but only a single hunting movement to findV a terminal in the, group marked by the minor switch. The rst group selector is not provided with a minor switch but hunts to find an idle trunk in a group marked directly by the sender. Provision is also made that when a group selector hunts twice over its bank without finding an idle trunk in the group marked or the nal selector hunts to the terminal of the marked wanted line and inds the line busy, all switches beyond the first group selector are released, the finder is dismissed,` and a busy signal is transmitted from the first group selector to the calling line.

The minor switches may be made small and compactand therefore readily responsive to impulses transmitted thereto from the register sender. Further, since only one minor switch and the control relays therefor is required for a group of selectors, and the structure of the selector is extremely simple, only a rotary magnet and testing relay being necessary, an appreciable economy in equipment is realized. In addition since all selectors and minor switches are ofthe rotary single motion type, they may be mounted on hinged panels to either side of the mounting frame whereby, they may be swung out to enable ready access tothe cable connections extendincr thereto. By this arrangement an apprecia le saving in mountin space is attained.

Connections between o ces of the exchan e area are extended over two-wire ofiice trun s and provision is made at the outgoing ends of such trunks to mark an entire group busy if the minor switch and control relays common to the incoming selectors in which the distant ends of the trunks terminate is unavailable. This busy condition is controlled over the two-wire trunks of the group without the additional use of extra conductors in the inter-office cable.

The common register-sender for controlling the setting of the minor switches is provided with a group of four registers which respond to impulses dialed by calling subscribers. The first two office code series of impulses are registered on two of these registers and are then transferred to translator switches. The third office code series of impulses is registered directly on one of the translator switches. Following the transfer of the code registrations to the translators the registers upon which they were initially registered are restored and are later employed, together with the two other registers, to register the numerical digits of the wantedline number. As soon as the ofiice code has been completely registered the sender proceeds to transmit series of impulses for extending the connection from the calling line to the office in which the wanted line terminates. For this purpose a sending switch is employed which assumes a plurality of settings as directed successively from a plurality of banks of one or the other of the translators,lterminals of the sending switch being multipled to points in the banks of the translators with resistances interpo` lated between such contact points. The arrangement is such that when the sending switch has advanced to the point marked by a translator bank the direction of current f'low through a relay will be reversed to mark the end of the selecting stage. There tht` code registered 0n a translator indicates that the connection must be extended through more than three selecting stages to reach the desired oiiice the translator is advanced one step following the completion of selections controlled through the three stages and in its advanced position controls selections through three additional stages.

In order that the apparatus ofthe exchange may at all times be maintained in proper con dition for rendering efficient service a routine test circuit is provided for association with the common minor switches and control circuits serving groups of selectors at any switching stage. This test circuit may, at the option of an attendant, be rendered effective and will continue as long as desired to select idle minor switch control circuits and to test their operation, operating suitable alarm signals when any such circuit is found to function improperly.

Provision is also made for automatically hunting for any line of an office on which a calling condition exists for more than a predetermined period without the establishment of a connection, such a. condition arising through a permanent abnormal ground on the calling line or through the neglect of the calling subscriber to dial a number after lnitiating a call. When such a line is thus selected the number thereof is displayed on an indicator.

A clearer understanding of the invention will be obtained from a consideration of the following detailed description in connection with the drawings in which:

Fig. 1 shows a link circuit and preselecting arrangement;

Fig. 2 shows a portion of the first group selector;

Fig. 3 shows the remainder of the first group selector and a portion of the sender;

Figs. 4, 5, 6, 7 and 8 show the remainder of the sender; 4

Fig. 9 shows a second group selector;

Fig. 10 shows a testing arrangement for testing the control equipment of the group selector shown in Fig. 9;

Fig. 11 lshows a relay arrangement for the outgoing end of a two-wire inter-office trunk;

Fig. 12 shows a selector at the incoming end of a two-wire trunk;

Fig. 13 shows a final selector;

Fig. 14 shows the common control equipment for the selector of Fig. 13;

Fig. 15 shows an arrangement for selecting and identifying a calling line on which a permanent signal condition exists;

Figs. 16 and 17 show a final selector and control equipment for connecting with private branch exchanges; and

Fig. 18 shows the manner in which the remaining figures should be arranged.

A brief summary of the operation of the system as a whole will first be given.` The initiation of a call by a subscriber at substation 101 causes distributor switch 130 to hunt for a link circuit having access. to a group of first group selectors served by a register sender which is idle. When such a link circuit, forexample link 100, has been found the selector finder 120 is operated to find an idle selector in the group. The line finder 110 is then operated to connect the calling line to the selector and the distributor switch is advanced to the next link. When the calling line is connected through. the sender is associated therewith and with the selector by means of relay 203. There is such a relay for each first group selector and the sender is connected in multiple to the contacts of such relays in all of the selectors which it serves.

The called line designation is then recorded in the sender. The first digit of the office code is recorded on register 52() and transferred to translator 600. The second digit y is recorded on register 510 and transferred to translator G50. The third digit is recorded directly on translator 600. Registers 520 and 510 are then restored to normal and the numerical digits are recorded on registers 540,530, 520 and' 510 in succession.

Immediately following the reception of the third digit the sending switch 850 is actuated. A distributing rack `810 is provided comprising a plurality of resistances 811 to 823 connected between battery and ground. The normal terminal of brush 854 of the sendlo ing switch is connected to ground and the succeeding terminals are connected to the distributing rack at points between succeeding resistances. The terminals of brushes 602, 603 and 604 of translator 600 and brushes 654, 653 and 652 of translator 650 are cross connected to distributing rack 810 in accordance with the routing corresponding tothe setting of the translator. A circuit is established including brush 854 and translator 2g b rush 602, or 652 according to which translator is effective and switch '850 is advanced under the control of an interrupter until brush 854 reaches a. terminal beyond that connected to the point marked by the translator setting so that the direction of current flow in the circuit is reversed. When this occurs relay 708 which is included in this circuit is operated, stopping the sending switch andpreparing the circuit for the next selection. Due to the intimate relation between the sender and the first group selector the sending switch 850 is itself employed as the minor switch for that selector and the setting `01E the sending switch marks the group ot' terminals within which selector 300 is to hunt. Due to the large number of trunks outgoing Vfrom a first group selector, this selector made up of two, or possibly more switch structures,with two operating magnets 301 and 302 and two testrelays 209 and 210. while discrimination between the switches is made by the setting of the sending switch.

When the first group selector has been positioned, the sending switch becomes effective to control the sending out of impulses to the second group selector. Minor switch 910 is positioned in response to these impulses and marks a group of terminals over which the second groupl selector 900 hunts. Translator 600 provides for three selections while translator,650 provides for as many as six selections in order to pick a group of trunk outgoing to a desired oliice. Only two selectors have been shown, it being assumed that subsequent selectors would be essentially duplicates of the second group selector 900.'

The first numerical digit controls the setting of minor switch 1210 whereupon switch 1200, is operated to select an intermediate b selector which is not shown. This intermediate selector in turn picks a final selector. Two types of final selectors may be employed, that shown in Figs. 13 and 14 serving indi- .vidual lines. The minor switch. 1400 is po sitioned once for the tens digit after which the final selector hunts for the group of ten lines marked b the minor switch. The minor switch is t en restored and re-operated in response to the units digit and the inalV selector hunts for the called line so marked. The final selector shown in Figs.'16 and 17 will ,serve either individual lines or groups of .to a private branch exchange the final selector first hunts for the terminal marked by the minor switch 1710 and then hunts for an I idle branch exchange trunk. The final selector applies ringing current to the wanted line and completes the connection.

The operation ofthe circuits will now be discusse in more detail. Owing to thelarge number of contacts controlled by certain relays, these contacts will be referred to according to their numerical position counting from the relay out. 'For example, the innermost contact ofrelay 203vwill be called the 1st front contact .of that relay and the outermost contact will be called the 12th front contact. Only single motion rotary switches are employed as pointed out above. Three types of switches may be distinguished depending on the number of terminals to which each brush has access. For example, the selector switches and the translators have 100 sets of terminals each; the register switches and minor switches have 11 sets of terminals, while the sending switch constitutes a class by itself having 25 sets of terminals.

When the subscriber at substation 101 initiates a call by removing his receiver from the switchhook he completes a circuit from battery through the winding of line relay 102, outer left back contact of relay 103, over the substation circuit, back to ground at the inner left back contact of relay 103. Relay 102 in operating` connects ground to conductor 125 for initiating the extension of the line to an idle first group selector. 1t also connects battery through the Winding of relay 103, and in parallel therewith through resistance 132 and the right back contact-oitl relay 103, to terminal 117 to identify the calling line to the line finder 110. Y

The connection of ground to conductor 125 completes a circuit over the outer right ack contact of relay 122, conductor 133, winding of relay 104to battery. Relay 104 in operating prepares a circuit from battery through the right winding of relay 105, right frontcontact of relay 104 to brush106 to test the link circuits for availability. It also completes a circuit from battery through uit

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