GB516136A - Improvements in or relating to electrical communication transmission systems - Google Patents

Abstract

516,136. Repeating systems. STANDARD TELEPHONES & CABLES, Ltd., and HODGSON, K. G. June 21, 1938, No. 18422. [Class 40 (iv)] In an electrical communication system including two terminal stations and a plurality of intermediate unattended stations, one of the terminal stations is a control station, each station is associated with a signal current of a particular -frequency, and, in addition, one or - more signal currents of frequencies differing from the first-mentioned frequencies are associated with two or more unattended stations. Means are provided at each unattended station for varying the strength of the signal currents associated with it when a fault occurs. With such arrangement, both the station and the part of the apparatus at fault can be ascertained at the control station. At an unattended station, the supervisory lines 1, 1<SP>1</SP>, 2, 21, Fig. 2, are shunted through relay contacts by series resonance circuits L1, C1, L2, C2, and L3, C3 tuned to three frequencies associated with the station. Relay J is operated when the main amplifier is in operation. Relay S is operated when a spare amplifier is in operating condition and relay H is normally unoperated but operates when the spare amplifier is switched into service. Relay FS, however, is normally operated and releases when the spare amplifier fails. Relay MF is normally operated and releases when the power supply fails. Failure of the main amplifier releases relay J, connects L1, C1 across the lines and blocks the corresponding frequency which is peculiar to the station. Failure of the spare amplifier connects L2, C2 across the lines, and failure of the power supply connects L3, C3 across the lines. At the control station each signal is filtered out, amplified and made to operate a relay. Absence of any signal frequency causes the corresponding relay to release and complete an alarm circuit. Time delay devices may be included in the circuit at an unattended station so that when a fault occurs the corresponding frequency is only interrupted for a predetermined time. In this case the corresponding relay 24, Fig. 6, at the control station releases and closes contacts 25 for a predetermined time when the fault occurs. Relay 28 then operates to light a lamp 26 to operate an audible alarm 27 and to lock itself in operated condition. The alarm is reset by separating the contacts 32 by means of a push button: A suitable circuit for the operation of the relays in Fig. 2 is described in Specification 513,162. Specifications 446,225 and 477,875, [Group XXXV], also are referred to.