Patent GB-806515-A (GB)
Title: Improvements relating to remote indicating systems
Inventor: DOBSON JOHN THOMAS
IPC: G01R17/08
Filed: 1955-02-28
Abstract: 806,515. Remote indicating systems: electric selective signalling. EVERSHED & VIGNOLES Ltd. Feb. 17, 1956 [Feb. 28, 1955], No. 5889/55. Class 40 (1). In a system for sending D.C. signals over one pair of lines between a plurality of transmitters at a first station and a plurality of receivers, each controlling an indicator whose reading remains constant between signals at the value last received, at a second station, the receivers are switched into circuit singly in sequence by a master switching device at the second station which, in the intervals between the disconnection of one receiver and the connection of the next, transmits a signal to the first station to select and connect in circuit the appropriate transmitter, the synchronism of the selection of transmitters and receivers being checked periodically. Telephone communication between the stations, and control of a selected variable from the second station, are provided. Operation.-As shown (Fig. 1) receivers R1- R4 are connected in turn across lines 20, 21, by the closing of contacts 11, 13, 15, 17 and the energization of relays AR, BR, CR, DR respectively by a master switch (Fig. 3) driven by a motor 10. When the master switch contacts 12, 14, 16, 18 are closed, relay IR pulls up to connect across the lines 20, 21, a battery 28 which supplies a stepping impulse through relay IT at the remote station and this repeats the impulse to a counting circuit (Fig. 2) to disconnect one of the transmitters T1-T4, supplied from a common power unit 22, and to connect the next in sequence across the lines. The transmitter signals stabilize through a dummy load resistor 24 before being fed to the relevant receivers when the master switch moves on. When master switch contacts 18 re-open, relay RR comes up, opening contacts rr and de-energizing, inter alia, relay AA. The consequent closing of contact aa2 energizes relay XT which operates to place a battery 33 in series with relay IT across the lines and to close contacts rr. The closing of master switch contacts 19 actuates relay E, thus energizing in series over the line relays F and IT, which latter initiates another cycle of transmitter selection. Checking synchronism.-If the selection of transmitters and receivers is out of step, battery 33 will not be in position to actuate relay F when relay E pulls up; consequently master switch motor 10 will be disconnected from its supply and will stop, and " alarm " lamp 35 and buzzer 36 will be operated (Fig. 2). Synchronism is restored by operation of a reset button 37 (Fig. 1) which sends stepping impulses to relay IT thus advancing the switching mechanism of Fig. 2. Control.-Control of a selected variable from the receiving end is achieved by stopping motor 10 when the relevant transmitter and receiver (as shown, T4 and R4) are in circuit and operating an earthed control key 43 to energize one of the two windings of a relay V which actuates one of the devices 58, 59 (Fig. 2) which serve to change the variable in opposite directions. Telephony.-Ringing devices 46, 47 (Fig. 1) are earthed on one side in use, the other terminal being connected by way of capacitors 48, 49 and 52, 53 respectively between the halves of the secondaries of transformers 50, 54 the primary circuits of which include telephone instruments 51, 55. Modifications.-Provision of recording and integrating devices and additional alarm relays is mentioned. Specifications 589,423 and 806,514 are referred to.