SE345521

1,219,203. Infra-red viewing. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 19 Feb., 1968 [20 Feb., 1967], No. 7986/68. Heading H4F. The Specification describes a device for converting an infra-red image into a visible image and also for determining the temperature of the object providing the image. In Fig. 1 which is a plan view, a mirror 3 oscillates about a vertical axis and scans the object (below and to rightout of Figure) through an angle of 0À15 rad at 15 c/s. and directs the scanned light on to a vertical array of 40 infra-red sensitive photodetectors 1 subtending a vertical angle of 0À1 rad. via forming means 2. The image is thus analysed in 40 x 40 x (0À15/0 10) = 2,400 elementary areas. The infra-red radiation falling on the detectors is chopped at 2000 times per second by toothed disc 4. The disc is mounted in a thermally isolated housing 8 and has its surface covered with a material emitting black radiation of the temperature of the housing 8. The radiation falling on the detectors is thus alternately at levels determined by the object temperature and by the housing temperature. With the obejct temperature To below that of the housing temperature Te, the output of the detectors varies as shown in Fig. 2 (solid line). To make To equal to Te radiation can be added to or subtracted from the object radiation by source 11 and semi-permeable mirror 10 or attenuator 9, respectively. The amount of radiation biasing thus needed gives an indication of the object temperature. To produce the visible image of the object, each detector is connected to a respective electro-luminescent diode in a vertical array 5, which are viewed via the reverse side of mirror 3.