GB621100A - Improvements in or relating to automatic telephone systems - Google Patents

Abstract

621,100. Automatic exchange systems. ERICSSON TELEPHONES, Ltd., and DRYSDALE, L. H. March 13, 1947, No. 6964. [Class 40 (iv)] In a two-motion selector of the rectangular release kind with provision for digit absorption, in order to allow the selector to be set correctly although at the beginning of a particular impulse train it may not have completed its release from a setting determined by a preceding impulse train, the setting of the selector is controlled by an auxiliary switch stepped by incoming impulses. As shown, the selector may absorb up to two digits and may discriminate between local and junction calls on the first, second or third digit. Relays A (not shown) and B operate upon seizure and the first digit is repeated by relay A to the stepping magnet of the auxiliary switch DS and goes also over a main exchange junction seized by an associated hunting switch. Dialling relay C operates on the first impulse of the train and completes a circuit to earth via a release alarm relay in wire 12 for the vertical magnet V which operates and holds over resistance YA, wiper DS3, wiper VW1 of an auxiliary bank VC of the selector until the succeeding impulse is received to advance the switch DS to its next position. The magnet reoperates over wire 12 and the action is repeated until the end of the train. The switch DS may be individual or may be common to a group of switches and in the former case may be used for multimetering. Discrimination. If the first digit is other than 4, a circuit is made over wiper VW2 and a terminal field TF for relay JD if the digit indicates a junction call or relay LD if it indicates a local call. Relay JD prevents operation of the vertical magnet by subsequent digits. Relay LD causes the selector to hunt over the selected level for a local second selector. Digit absorption. If the first digit is 4, a circuit is made over wiper VW2 for DA which makes a stepping circuit for the rotary magnet R to effect release, operates OA to rearrange the connections to the terminal field and homes the switch DS. A second digit coming in before the selector is fully restored resets the switch DS and the vertical magnet V is connected up by the relapse of DA when release is complete and then operates by self-interruption until it catches up the switch DS. If the vertical magnet V is still behind at the end of the train, C holds over an intermittent circuit in series with it. The connections to the terminal field may be further modified by OB if the second digit is absorbed. Specification 481,671 is referred to.