GB237952A - Improvements in or relating to thermionic indicating means responsive to light variations - Google Patents

Abstract

237,952. Dowling, J. J. April 11, 1924. Light, control of signalling and other apparatus by.-Thermionic indicating means responsive to light variations comprises an interrupted beam of light falling on a photo-electric cell operatively associated with a thermionic amplifier so arranged that the indicating means is rendered operative, if the cell is not effected by the regularly interrupted light beam, by a relay under the control of the valve system and of a battery independent of the valve system. Fig. 1 shows a light beam source 1, rotating disc 4 with apertures 3, lenses 2, 6 influencing a selenium cell 7 connected to an audio-frequency amplifier to affect a moving coil relay 12 having a biasing current from battery 17 and a regulating resistance 18. The light rays may be brought to a focus by the lens 6 in front of a screen or diaphragm 11 arranged in front of the cell 7. Fig. 4 shows a modified amplifier in which the cell 7 is arranged in series with an equal resistance 47 and the potential is applied to the grid of the valve through a condenser 45. In a further modification a clockwork or other mechanically driven switch is employed to disconnect the batteries except for a brief period at intervals so as to economise battery power. In this modification the moving coil relay influences a second relay so arranged that the signal or indication given by the apparatus is unaffected by the current interruption. The apparatus may be employed to detect haze or fog and a colour screen or cells sensitive to special regions of the spectrum may be used. It is also applicable to detecting smoke or turbidity in liquids or for recording the passage of objects. A recording galvanometer may be used instead of, or in addition to, the relay 12.