560,732. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., GILLINGS, C., and MURRAY, L. J. Dec. 31, 1942, No. 18581. [Class 40 (iv)] Each group selecting stage comprises a crossbar switch of link-circuit type or the equivalent pair of cross-bar switches performing the functions of a number of selectors and having an individual control circuit comprising step-bystep switches. In the layout shown in Figs. 1 to 3, each line in an 800-line group has access over one of 40 20/6 primary cross-bar switches such as PSU1 and any of 6 20/10 secondary switches such as SSU1 to 60 first selector units and two primary switches share the same trunks. In busier groups, however, 400 lines may form a group, the trunks from all the primary switches being individual, and in still busier groups, the primary switches may have 10 instead of 20 inlets. As shown in Fig. 2, the first selector units such as GSU1 comprise 10/200 link circuit type switches with the 200 outlets in groups of 20 but in practice, each unit comprises two switches with their hold magnets connected in pairs to provide the equivalent to a link-circuit type switch. There may be further stages of this type. The penultimate selector units such as 1PGSU1, which contain the feed circuits and signalling arrangements, are link-type switches and have 90 outlets in 5 groups. The final selectors give access to from 200 to 1000 lines and consist of primary and secondary switches over which a connection is set up between a wanted line marked over a by-path and the penultimate selector. In the 400-line unit shown, the primary switches such as FPS1 give access to 10 lines and share with another primary switch six trunks to secondary switches such as FSS1 each of which has 20 inlets and 12 trunks outgoing to penultimate selector stages. The 72 routes from a given calling line are divided into four groups of 18 which each lead to a particular penultimate selector unit. The final selector control circuit is taken into use direct by the control circuit of the penultimate selector. Non-numerical switching. When a subscriber calls, his line relay R brings up the start relay 1S or 2S characteristic of his 10-line group and marks the position corresponding to the line in bank HS2 (or HS1). Switch SGS then hunts under control of TK for a secondary switch which has idle outlets and also has the inlet from the calling primary group idle and switch HS hunts for the position of the calling line under control of RK. On the operation of the latter, the select magnet such as 1PP of the calling line is energized in the primary switch. On the operation of TK, the start relay SSR of the selected secondary switch is enabled to operate and switch SSU thereupon hunts for an idle one of its 10 outlets. When this is found, SK, SKR pull up and the corresponding select magnet, e.g. 1SP is energized and then the pull-down and hold magnets such as 1SH in the secondary switch corresponding to the calling primary switch and 1PH in the primary switch corresponding to the seized secondary switch. Cut-off relay K operates in series with GS at the first selector and the other operated relays and the select magnets fall back, the hold magnets remaining energized over the c wire. First selector. This, as indicated in the opening paragraph comprises an incoming and an outgoing cross-bar switch. The select magnet 1GSP corresponding to the incoming trunk is energized in the incoming switch over the loop and locks up extending the loop to A which is followed by B, BB, C, 1GSR. GS is released. A repeats the first digit to the magnet TOM. Relay N pulls up when the switch goes off normal and at the end of the digit C falls back and energizes the select magnet such as 1GTP of the selected group of trunks in the outgoing switch. Switch AOM or BOM, according as the digit was 1 to 5 or 6 to 0, then hunts under control of KR for an available trunk in the group. For a trunk to be available it must be idle, as indicated by battery encountered by wiper AOS4 &c., and the outgoing switch cross-bar with which connection is made to it must be idle also as indicated by the condition of the contacts 1gth1 to 20gth1 of the corresponding pull down magnets. When such a trunk is found, KR, KRR and pull-down and hold magnets corresponding to this trunk in the incoming and outgoing switches, e.g. 1GSH, 1GTH, are energized. Relay A is released and its relapse is followed by that of the select magnets and the other energized relays except the off-normal relay N. Homing circuits are made for the step-by-step switches and finally N falls back. Registration of hundreds, tens and units digits-marking wanted line. On the seizure of an incoming trunk of the penultimate selector, the corresponding impulse and release relays 1A, 1B and select magnet 1PGP pull up and also the relays BA, HC in the control circuit. In response to the hundreds digit, switch HDS selects the 200 line group and energizes the corresponding select magnet such as 1PTP over contacts of off-normal relay NN. At the end of the digit, HC falls energizing CB and COS or DOS, according as the digit was 1 to 6 or 7 to 0 as indicated by the condition of HD, hunts under control of CK for an idle one of the eight control circuits of the required 200-line section of the final stage. CK on operating is followed by CKR, CKZ and the impulse circuit is thus extended over wire 62. Other circuits made to the control circuit cause the operation thereon of SA, SB, DC and, if the hundreds digit was even, EH. If the latter relay is operated, the units switches UAS, UBS at once drive to their second normal positions. The tens digit sets DDS, off-normal relay ND arranging for the relapse of DC at the end of the digit so that the units digit sets UAS or UBS, according as the tens digit was 1 to 5 or 6 to 0 (UC having been operated on the first step of DDS). At the end of the digit, UC falls and brings up SGA. Provided that none of the other control circuits is marking at this moment, FZ pulls up to lock them out and energizes the select magnet 1FPP of the wanted line. Testing for a through route between the penultimate selector and the wanted line. FZ also connects battery over wire 64 to wires 66 to 71 of which there is one for each of the 18 trunks outgoing from the penultimate selector to the 200-line group of the selected line provided that the link by which connection is made to the corresponding trunk is not in use as indicated by the unenergized condition of the corresponding pull-down and hold magnet PTH. This battery is extended over such of the wires as also correspond to trunks to which access is possible via links in the secondary switches, as indicated by the condition of the pull-down magnets 1FSH to 3FSH in each of the 6 secondary switches concerned. Only one trunk runs from each secondary switch to the primary switch containing the wanted line and if this trunk is busy further extension of the battery towards the primary switch is prevented at contacts such as 1fph2 of the hold magnets controlling connection between the primary and secondary switches. If there is a through route, however, the battery extends to one or more of the select magnets FSP controlling access to the wanted primary switch which have been marked by a ground connection over DDS3 or DDS4. These are arranged so that, only one is able to remain energized and it locks up and energizes OFB which, with the layout shown, is common to 400 lines. Assuming 1FSP of FSS1 to be operated, OFB energizes SR, Fig. 20, which is individual to FSS1, and connects up relays 1SW .. 3SW which correspond respectively to the 1st, 2nd, and 3rd trunks between FSS1 and each of the penultimate selectors. The relay or relays corresponding to possible connections between FSS1 and the penultimate selector over which the marking operation is taking place, as indicated by the condition of the pull-down magnets FSH, FSS1 and PTH in the penultimate selector, now pull up, only one being able to remain energized. This relay locks up and energizes the corresponding pull-down and hold magnet FSH and prepares the circuit of the corresponding magnet PTH in the penultimate selector. Busy test and signal. Completion of connection. On the operation of the marking relay FZ, ZC pulls up sluggishly and if the select magnet 1FSP in the secondary switch has been energized the corresponding pull-down and hold magnet 1FPH in the primary switch is operated. The connection is thus extended back to the penultimate selector but is open there. ZC also energizes ZA and connects test relay SK via the tens and units switches to the private wire of the wanted line. At the same time ZB is operated and disconnects SA which interrupts the test circuit after a short interval. If the line is busy, SK does not operate and, on the relapse of SA, ground over resistance YAN, Fig. 22, is connected to relays KD, GE, Fig. 12. Only GE operates energizing 1SE which sends back busy tone and releases PGP to initiate release of the control group and the final selector switches. If the line is idle, SK causes full ground to be sent back to KD, GE and both relays operate. As a result, 1SD and the prepared pull-down and hold magnet 1PTH are energized and lock to the private wire. 1J is operated and the select magnet 1PGP is released. Ringing tone is sent back and ringing current is sent forward over 1F. The latter on the reply of the called party completes the connection back to the called side feed and supervisory relay 1D. Metering. 1D energizes 1SE, which applies a booster impulse to the c-wire, and releases 1J which terminates the impulse after an interval. The switch is guarded over MRE while 1J is operated and 1SE is unoperated. Release of control circuit. The initial circuit for the pull-down magnet 1PTH includes relay ZD and this relay locks up and releases OFB which releases SR, ZC. At the same time the release of 1PGP releases BA, CB, CKZ, ZB