Patent GB-743701-A (GB)
Title: Improvements in or relating to remote control and supervision systems
Inventor: TERRY VICTOR JOHN
IPC: H04L12/40
Filed: 1951-02-26
Abstract: 743,701. Electric selective signalling. STANDARD TELEPHONES & CABLES; Ltd. Feb. 22, 1952 [Feb. 26, 1951], No. 4641/51. Class 40(1) The invention relates to precedence arrangements for a party-line remote control system using two twin lines 1, 2, Fig. 1. Each station, except one end station, e.g. the South End station is provided with a relay A so that when any one station transmits, it energizes the more northerly stations over line 1 and the more southerly stations over line 2, whereby the receivers at all other stations are energized and disable their associated transmitters. In the event of two stations initiating transmission simultaneously precedence is given to the more northerly station since it canenergize the receiver of the, more southerly calling/station whereas its own receiver is isolated from the more southerly stations by opening of its relay contacts a2. D.C. signalling. As shown in detail, Fig. 2 (complete) operation . of the.. sender key-NK, 1K, 2K,......SK, at any one station (only two intermediate stations being shown) energizes the associated relay NA, 1A, 2A,......, which connects the local battery 10 over line 1 to the lower winding of the receiver-line relays NR; 1R, 2R....... of the more northerly stations and over line 2 connects battery to the upper winding of the receiver relays of the more southerly stations. The receiver line relays at all stations other than, the transmitting station operate respective local slow-to-release relays ND, 1D, 2D,..:...SD which disable the associated senders for the duration of signal. The receiver line relays however respond to the line current which is pulsed by the transmitting station according to a predetermined code to select the desired station and effect the desired control-or-supervisory function in known 'manner. Should two stations initiate transmission simultaneously, the more northerly station takes precedence because it energizes the line relay of the more southerly initiating station over line 2 whereas its own receiver is .isolated from this more southerly station by operation of its A relay. An A relay is not required at the South End station. A.C. operation, Fig. 2 (Provisional), shows the circuit arrangements at each intermediate station, in a system using a speech signalling channel on which voice. frequency control and supervisory telegraph signals at the upper end of the speech band are superposed, the precedence arrangements being substantially similar to those of Fig. 1. The four wire circuit 1, 2 is interrupted by at least one line repeater between each substation and its neighbours so that the direction of transmission indicated by arrows holds, good for speech as well as for telegraphy signals. When a station initiates transmission, a code sender 17 operates in known manner- and through a relay B keys a V.F. oscillator 18 which sends the coded control or supervisory signal through a; hybrid coil 20 and unidirectional devices 7, 8 (rectifiers or amplifiers) to the lines 1. 2. The relay A is also actuated to remove, the short-circuit from low pass filters 3, 4 at contacts a1, a3 which disconnect the entry and exit points of 'lines 1, 2 at the transmitting, station with respect to the telegraph signals so that as shown in Fig. 1 the receivers at all other stations are operated over lines 1, 2. Speech may be transmitted to line at any time over the hybrid coil 20. At each receiving station signals; are passed via unidirectional devices 5, 6 to hybrid coils 9, 10, 11 which enable speech to be received from both directions whether the relay A is operated or not. As in Fig: 1 'telegraph signals pass along line 2 directly to a more southerly station receiver, via the hybrids 9, 11 a filter 12 for passing the V.F. only, and a V.F. detector 16 to a code detector. For more northly stations the circuit for the V.F: signal is, as in Fig. 1, by way of contact a2. When a telegraph V.F. signal is detected, at 15 the code sender 17 is disabled by the connection 19. In the event of two stations initiating signals simultaneously precedence is given to the more northerly station as in Fig. 1.