GB494667A - Improvements in and relating to radiation-sensitive devices - Google Patents

Abstract

494,667. Electric signalling systems. RICKETS, W. J., and RAWLINGS, A. L. March 25, 1937, No. 8775. [Class 40 (i)] [Also in Group XL] An apparatus for detecting and indicating the presence of objects, for example aircraft, and locating their directions by means of infra-red or other invisible radiation, comprises in combination, an optical system 1, Fig. 1, forming an image of a field upon an opaque screen 2 having a slit 3, means, for example a reflector 4, for throwing the radiation passing through the slit on to a radiation-sensitive system, for example an electron multiplier 5, means for moving said image and slotted screen relatively to each other, a cathode ray tube 11, means for causing the line of oscillation of the electron beam of the tube to be altered in unison with the alteration of the relative position of the slit and image, and means for causing a high frequency oscillation of the electron beam with an amplitude or intensity proportional to the total radiant energy passing through the slit at each of its positions as detected by the radiation-sensitive system, whereby the luminous image or graph formed on the screen of the cathode ray tube serves as an indication in linear or polar coordinates of the position and to some extent of the relative magnitude of the objects sighted. Fig. 4a shows graphs that would be produced in polar co-ordinates by two aeroplanes. The direction of the optical apparatus may be adjusted to bring a graph in the centre of the screen of the cathode ray tube and then points in the direction of the object producing the graph. In Fig. 1, the slotted screen 2 and the line of oscillation of the cathode ray tube are rotated in synchronism. In a modification the slotted screen and the line of oscillation of the tube are reciprocated. And in another modification, Fig. 3, the slotted screen 2a is fixed, the image is reciprocated relatively to the screen by an oscillating mirror 12, and the line of oscillation of the tube 11 is reciprocated in synchronism by means of a Wheatstone device 14. The radiation-sensitive system may include an amplifier so biassed that radiations below a certain strength do not affect the indicating apparatus. The potentials applied to the cathode ray tube for producing the graphs may be modulated unidirectional potentials.