GB687098A - Improvements in automatic telephone systems - Google Patents

Abstract

687,098. Automatic exchange ystems. GENERAL ELECTRIC CO., Ltd., and ROUSSEAU, J. E. Nov. 9, 1951, No. 26330/51. Class 40 (iv). To identify a subscriber from whose line circuit, Fig. 1, a call has been extended through a selector, Fig. 2, to an operator's position, Fig. 3, where the operator plugs into a jack JA, the operator depresses a key (not shown) to apply a positive potential over the ring connection and thereby operate a relay MA which applies positive battery and a high-frequency A.C. signal to the P wire. A non-linear resistance NL in the calling subscriber's line circuit becomes conductive and passes the signal to an amplifier - receiver VA which is common to a group of lines and is tuned to receive the signalling frequency used, so that a relay D is energized to bring up a relay DA. Meanwhile a relay S has been energized to start a switch G stepping, and a relay MB has operated slowly to remove the positive battery from the P wire before it can operate the subscriber's meter M. Relay D releases and a relay DB operates in series with relay DA to mark in contact bank G1 the contact corresponding to the group containing the calling line. The switch G is stopped on this contact by the operation of a relay T, and a relay ST is energized over wiper G2 to complete a stepping circuit for a switch F. Relay T releases and the switch G steps on. The amplifier-receiver VA being now connected to wiper F1, relay D operates when the switch F reaches the calling line, which is still marked by the A.C. signal on the P wire. A relay DC is energized to stop the switch F and connect the P wire to a code circuit of known type which sends a code of voice-frequency impulses identifying the line to apparatus associated with the operator's cord circuit, relay ST being released at the end of the impulse train. The calling subscriber's number is displayed in known fashion to the operator who then releases her key to initiate release of the identification equipment. In a modification (not shown), the start circuit for the switch G is directly controlled by the operator who may thereby delay an identification cycle until she is ready to receive notification of the calling subscriber's number.