Patent GB-723997-A (GB)
Title: Automatic telecommunication exchange systems
Inventor: JOHNSON BENJAMIN BERTIE
IPC: H04Q3/00
Filed: 1953-03-18
Abstract: 723,997. Automatic exchange systems. TELEPHONE MANUFACTURING CO., Ltd. March 18, 1953 [March 28, 1952], No. 8022/52. Class 40 (4). [Also in Group XXXVII] In a relay selector or cross-bar switch in which the contacts to be operated are selected by one of a number of auxiliary finger-magnets, the operating relay once operated is maintained by residual magnetism until restored by current in the reverse direction. An exchange system is described in which the call finders and connectors are constituted by a number of such relay selector units. Certain of the control relays are also of the same character so that the current consumed is reduced to a minimum. Construction of relay selector. The core 1 carrying the energizing winding 12 may be of hard steel so that it remains magnetized after the current is cut off, or alternatively it may be made of soft iron and provided with a backward extension la surrounded by a permanent biasing magnet 12a. The armature 13 carries a transverse operating member 17. The contacts to be operated are selected by 5 finger-magnets 32 arranged in an upper row of two and a lower row of three, the pole-pieces of those in the upper row being of greater length to compensate for their remoteness from the horizontal limb of the L-shaped support 31. The armatures 33 which hang from a plate 36 carry fingers 44 the ends of which are provided with a pin 45 extending between upturned lugs 54. When a finger-magnet is energized, the pin 45 comes beneath an operating bar 25 and allows it to be lifted by the operating member 17 to close contacts 21, 22. With the elementary circuit shown, the magnet 12 is energized by current in one direction over contacts ss, a and closes contact mo, and is maintained until it is restored by current in the reverse direction when contact a changes over. In the case of a cross-bar switch, the operated finger-magnet would control a selecting bar to select all the sets of contacts in a column. 20-line exchange, Figs. 2-7. The line finders, Fig. 2, and connecters, Fig. 5, each comprise two selective relay units such as that shown in Fig. 1 and a change-over relay. Each subscriber's line comprises four wires, two for conversation and two for signalling and ringing. Assuming that the subscriber SL12 calls, line relay L12 responds and connects up relay LA serving the particular 5-line group and the appropriate finger-magnet FM(MO) 1 in each of the line finders. Relays LB . . . LD are disconnected, and the start relay, e.g. SSA, of the first idle finder-connector link energizes. Feed relay A pulls up, and, dependent on LA, connects up the appropriate operating magnet MO. Relay RT, also of the residual magnetism kind, operates. The calling line is now connected to relay A, cut-off relay K12 pulls up and L12 restores followed by LA, FM(MO)1 and SSA. The digit keys SK1 . . . 5 connect earth to wire Q alternatively through oppositelypoled rectifiers RF(+)1, RF)-)1, with or without resistance R7, or directly. Relays X . . . Z respond in the manner shown in Fig. 9 and control corresponding relays TX . . . TZ which lock in series with DC and energize the appropriate finger-magnets FM(UX), FM(UY) of the connectors. In response to a second keying operation, relays X . . . Z control operating magnets UX, UY and switching relay UZ to complete the desired connection, TX . . . TZ and DC being released. If the line is idle, relay E energizes over the cut-off relay, e.g. K21, and connects up H which switches through and applies ringing current, ringing tone being fed back to the caller and E being shunted out. Back-bridge relay D energizes upon reply and restores RT by reversal, thus cutting off ringing current. Relay H holds by residual magnetism until restored by reverse current in its right-hand winding when D falls back. If the wanted line is busy, E is inoperative and RT is restored at once by the release of DC, so that buzzer relay BY operates to send back busy tone. When both parties hang up, the finder magnets are restored by A and the connector magnets by D.