GB527441A - Improvements in automatic telephone systems - Google Patents

Abstract

527,441. Automatic exchange systems. ELECTRIC RESEARCH PRODUCTS, Inc. April 12, 1939, No. 11063. Convention date, April 13, 1938. [Class 40 (iv)] In a system in which numerical selection by the subscriber is performed by means of keys each of which controls the application of alternating current of a characteristic frequency to the line, the selecting currents are derived from a harmonic producer which is fed with the fundamental frequency from the exchange. Preferably the harmonic producer is a toroidal coil on a permalloy core. The tuned selecting circuits made up by depressing the keys are divided into two groups, one of which uses the whole, and the other only a part of the inductance 161. In the system shown a calling subscriber is extended in known manner to a group selector S which is associated with a register-sender in which a fundamental frequency generator 200 is permanently connected to the in-impulsing circuit and in which line relay 209, release relay 214 and the first relay 300 of a number of digit distributing relays pull up. A tone signal goes back from 215. When any of the digit keys is operated the telephone set is disconnected arid transformer 164 is connected up in its place. Alternating current from the source 200 then excites the harmonic producer and one of the harmonics is selected by the depressed key and transmitted back over the line to .energize the corresponding receiving relay such as 217. This energizes a common relay 218 and an individual auxiliary relay such as 219 which locks and energizes the corresponding relay or group of relays in the A register. When the key is released, the receiving relay and the common relay 218 and shortly afterwards the auxiliary relay fall back, but before the relapse of the latter the register relay or relays lock up over relay 303 which releases the fiist digit distributing relay 300 and energizes 304 to connect up the next register. The remaining digits are registered in the same way.. The relay registers may operate as described in U.S.A. Specification 1,862,549.