GB286011A - Improvements in or relating to electric signalling or control systems - Google Patents

Abstract

286,011. Reyrolle & Co., Ltd., A., and Willoughby, R. Nov. 29, 1926. Duplex telegraphs.-In a duplex telegraphy system, two relays which are respectively controlled by switches at the remote stations and are connected at each end of the line circuit, are associated with resistances in such a manner that the relays may, if desired, be operated simultaneously. Relays G, A located at the control and sub-station respectively are connected in series over the line wire C and resistances J, D with a battery E, and are respectively controlled by switches F, M. When the apparatus is in the condition shown, current flows in a circuit containing the relays G, A and resistances J, D. This current is not sufficiently strong to energize the relays but a measure of the battery power may be given by an instrument O shunted across the resistance J. To operate the relay A, the switch M is closed to short circuit, over the auxiliary contact N, part of the winding of relay G and the resistance J. 'The current is thereby increased and the relay A operated, the energization of relay G being, however, insufficient to cause operation. If now the switch F is closed to short circuit the resistance D, the current is still further increased to cause operation of relay G. Upon operation of the relay G the resistance L is inserted across a portion of the winding of relay G and the resistance J so causing a reduction of current which however is of sufficient strength to hold both relays in their operative positions. If the switch F is opened the current is reduced and the relay G is de-energized, the relay A however remaining operative. If, on the other hand, the switch F remains closed and the switch M is opened, the relay G remains energized whilst the relay A de-energizes. In this manner a relay at one station may be operated or de-energized by its distant control switch irrespective of the condition of the relay at the other station and its corresponding switch. Instead of an earth return between the stations as shown, a second line wire may be employed. In a modfication the line C may be connected to the tapping point of the relay G and the resistance L and contacts N to the end of the relay coil. The Provisional Specification states that the system may be supplied with alternating current, reactances being used instead of resistances.