Patent GB-510551-A (GB)
Title: Improvements relating to electrical signalling systems
IPC: H04Q9/04
Filed: 1938-02-09
Abstract: 510,551. Electric signalling systems. EVERSHED & VIGNOLES, Ltd., and MARCHMENT, W. T. Feb. 9, 1938, Nos. 4111/38 and 1802/39. [Class 40 (i)] [Also in Group XL] In a system for the remote indication of the condition of a number of devices, the transmitter comprises, a distributer synchronized with an A.C. supply so that the time of passage from one contact to the next, is equal to that of one ,or more half cycles, the A.C. supply being also used to provide signalling impulses, whereas the receiver comprises a synchronous distributor controlling separate discharge tubes, or a synchronous rotating discharge tube observed through a fixed shutter with a number of slots, or a fixed circular tube observed through a synchronous rotating shutter: with a single slot. In the system shown in Fig. 1, transmitting and receiving distributers D1, D2 are driven through reduction gearing by synchronous motors M1, M2 connected to the supply S, the speed of the distributers being such that the wipers move from one contact to another in the duration of a half cycle, the peaks occurring when the wipers are centred and zero current when they pass from one contact to the next thereby avoiding sparking. The half cycles are transmitted over the line in cases where, switches 1-15 are closed, and result in discharge of a corresponding tube N1-N15 at the receiver. Synchronism is checked by a pulse transmitted by wiper 16 of a contact member SC driven at “ the speed of the distributer and should flash a tube N16 at the receiver. The motor M2 of the receiver is adjusted for synchronism by bodily rotation by handle 22. The tubes N1-N16 are tested by direct connection to supply S over switch 23. In modifications, Figs. 2 and 3 (not shown) the receiver comprises a discharge tube rotated synchronously with the transmitter and observed through radial slots in a fixed disc, or a fixed circular discharge tube observed through a single radial slot in a rotating disc, a fixed indicating scale or dial being provided. In the above arrangements, the signals comprise positive or negative half cycles but in the modification shown in Fig. 4 using high resistance lines, weak signals, and a thermionic valve receiver, the signal pulses are rectified before transmission and a pulse of opposite polarity is used for synchronising. At the transmitter, transformers 33, 39 and oscillator rectifiers supply positive and negative pulses for signalling and synchronizing respectively, safety resistances 31, 37 being provided in case the motor stops with wiper Wl bridging a signalling contact and the synchronizing contact SC which in this case is included in the distributer..At the receiver, valves 34, 35 are negatively biassed over resistance 36 by a voltage derived from transformer 46, rectifier 45 and smoother 47, the plate of the valve 34 being connected over tubes N1-N15 and the signal contacts of the distributer to H.T. supply derived from transformer 48 and rectifier 44 which is also connected to the plate of valve 35 over the synchronism contact and indication tube N16. Synchronism is adjusted by rotating the distributer relatively to the wiper. The discharge tubes may be maintained in continuous discharge by the impulses by associated condenser-resistance combination 42, 43 having a relatively large time constant. Specification 516,841 is referred to.