Patent GB-645889-A (GB)
Title: Improvements in or relating to telephone and like systems
IPC: H04Q1/18
Filed: 1947-12-31
Abstract: 645,889. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Dec. 31, 1947, No. 35117. Convention date, June 12, 1942. [Class 40 (iv)] The outlets of the final selector multiple and the contacts of the tens and units digit switches in the register-controller are connected to various characterizing D.C. potentials, the selection being controlled by a detector as described in Specification 617,100 responding to a potential difference in the correct direction greater than a predetermined value. The Specification describes the final selection stage of the 3-digit P.A.B.X., of which the group selection stage is described in Specification 645,069. Reception of the tens digit (e.g. 2). At the end of the hundreds digit, relays A, B, Fd, Fig. 4, are operated and the latter completes a circuit over which the power magnet S10 of the tens digit switch is actuated by the impulsing relay AS, Fig. 5. Relay LM energizes for the duration of the impulse train. Providing relay H has pulled up indicating the completion of the group selection and switch S10 has moved from its normal position, relay C operates to disconnect the test potentials corresponding to the hundreds digit from the detector and to remove the locking ground for relays K, L, which together with relays M, N, release, thus setting up the conditions required in the registercontroller before a numerical selection. Relay C also completes a circuit over brush c of the group selector GS for relay AF which busies the final selector by removing the idle potential rt from brush d. Relays JT, H release, the latter removing one short-circuiting earth from the operating circuit of relay D. The winding of relay C is connected to one or more contacts of wiper c of the switch S 10 to ensure that there is a sufficient time lag between the setting in motion of the switch S10 and the final selector. When the earthed wiper c moves off these contacts or when at the end of the digit LM releases to operate relay SD and remove the earth from the wiper c, relay D pulls up and holds in series with relay C to close the circuit for the power magnet FS which rotates the final selector. Relay SD prepares the register controller for reception of the units digit. One end of the test wire containing the detector, which comprises a cold cathode tube, is now connected over brushes t, a of the link-finder LS and the group selector GS, respectively, to the wiper t of the final selector FS, which steps over contacts connected to tappings on a potentiometer P, and the other end over the wiper a of the switch S10 to the tapping 11. The tappings on the potentiometer are equally spaced at intervals of potential of, say, " p," the minimmn potential difference to which the detector responds being 2p. When the selector reaches contact 20 connected to.the tapping 9, the cold cathode tube detector fires and energizes relay GT, which breaks the circuit of the power magnet FS and operates relay K to disconnect the detector from the wiper a of the switch S10. Relay LC pulls up to extinguish the detector and relay GT releases and removes the short-circuiting earth from relay L which operates and locks in series with relay K and connects the test wire to wiper b of the switch S10 at the potential of tapping 10. The potential difference p across the signalling wire being insufficient to fire the detector, relay JT operates over its high resistance winding from the battery and resistance r1 on a break,contact of relay M, and slow-operating relay H follows. False selection. If, after the digit 2 has been dialled the selector overshoots contact 20 owing to, e.g., dirty contacts, the detector is fired by a potential difference of 3p when the selector reaches contact 30. Relays K, L operate as described above and the test wire is connected to the wiper b. The detector is then fired immediately again by a potential difference 2p, and relay GT pulls up to complete a circuit for the operation of relay M, which breaks the circuits for relays JT, H and reverses the test wire connections by connecting the selector end of the wire to the tapping 18 and connecting the other end to the brush t of the final selector. The detector is extinguished by the operation of relay LC and GT releases to allow relay N to pull up and hold in series with M. Relay LC releases and the selector is rotated to the last contact, i.e., 09, connected to the tapping 20, where it is stopped by the actuation of relay GT due to the detector firing. Relay K falls back, LC operates to extinguish the detector, and relays L, M, N, LC release to restore the conditions existing after reception of tens digit and a fresh selection is made. Reception of the units digit (e.g., 4). The third train of impulses from relay AS actuates the power magnet Su of the units digit switch Su. On the release of relay LM and providing relay H has operated to indicate the completion of the tens digit selection, relay A is shortcircuited by earth on the wiper c of switch Su and falls back. Relay LC pulls up and relays JT, H, B release. Relay M pulls up and holds in series with M, relay LC releases, and the selector is rotated. The connections of the ends of the test wire have now been reversed, the selector end being connected over wiper a of the switch Su to the tapping 17 and the other end to the brush t of the final selector. When the selector reaches contact 24, the brush t is at the potential of the tapping 19, and the detector fires to operate relay GT and stop the selector. Relay ES pulls up to remove the short-circuiting earth from BF, which completes the line connections between the group selector and final selector, and the c wire is connected to wire III in the register-controller for the testing of the selected line. If the unit digit is 0 the switch Su is stepped to its last contact and as soon as relays M, N pull up and A, B, LC release, as described above, the test wire being connected at one end over the wiper a of the switch Su to the tapping 18 and at the other end over the wiper b to the tapping 20, the detector fires and GT operates followed by ES to prevent further rotation of the selector and to indicate cornpletion of the selection. Group hunting. Adjacent outlets of the final selector may form a group, the relay CO of each outlet removing the marking potential when that outlet is busy, so that the selector passes to the next outlet of the group.