GB402181A - Improvements in or relating to television and the like systems - Google Patents

Abstract

402,181. Oscillographs. ELECTRIC & MUSICAL INDUSTRIES, Ltd., Hayes, Middlesex, and MANIFOLD, M. BOWMAN-, Heathcot, Worplesdon Station, Surrey..July 7, 1932, No. 19293. [Class 37.] A cathode ray is periodically deflected over a screen 4, Fig. 1, under the control of synchronising signals and is rendered innocuous to the screen by auxiliary apparatus when the deflection fails. A condenser 7 is charged slowly, and discharged periodically through a valve 5 when signals are applied to the latter. A saw-tooth voltage is thus applied to deflecting-plates 8, 9 in the cathoderay tube 1. A neon tube 10 is shunted across the condenser and discharges it when the voltage across it exceeds the normal owing to failure of the synchronising signals. The ray is thus kept in motion over the screen. The saw-tooth voltage may be applied to an amplifying valve, Fig. 2 (not shown), the anode current of which is passed through deflecting-coils, Fig. 3 (not shown). In Fig. 4, the safety circuit comprises a valve 15 with such a high positive potential on its cathode 16, that anode current only flows when the voltage on the condenser 7, to which the grid 17 is connected, becomes abnormally high. This current decreases the potential of a control electrode 19 to reduce the intensity of the ray. According to modifications : the saw-tooth voltage is applied to an amplifying valve, Fig. 5 (not shown) and the anode current passed through deflecting-coils, Fig. 6 (not shown) ; the plate of the auxiliary valve is connected to deflecting-coils, Fig. 7 (not shown). In Fig. 8, the deflecting-current in coils 13, 14 passes through a rectifier 25, the output from which energizes a relay 26 to apply a normal potential to a control electrode 41 from a battery 28. On failure of the deflecting current, a battery 29 supplies a higher negative potential to reduce the intensity of the ray. A modification using electrostatic deflection is described, Fig. 9 (not shown). To prevent the ray coming to rest before being extinguished on switching off, the cathode 2, Fig. 10, of the tube is positively biased from a potentiometer 35 connected to the rectifier 33 supplying anode potential to the tube, and the control grid 41 is negatively biased from a potentiometer 37 connected to the rectifier 44 supplying potential to the generator 23 of deflecting currents. The time constant of the former biasing-circuit is greater than the latter, so that the negative grid tends to remain high in the initial period after switching off the source 32. When the deflecting-circuit and the heating circuit of the cathode of the tube are controlled by a common switch, a resistance is inserted in the heating circuit so that, on switching on, the deflecting circuit operates at least as soon as a visible spot is formed on the fluorescent screen.