GB470846A - Improvements in apparatus for the remote detection or location of sources of radiantenergy - Google Patents

Abstract

470,846. Infra-red ray detectors. WOOD, R., MOSLEY, L., and DUNKLEY, H. Dec. 21, 1935, No. 35440. [Class 40 (iii)] [Also in Group XXXVI] An infra-red ray detector comprises a pair of thermo - electric current generators of minute mass, on to one of which rays from a distant radiator are focused by means of a parabolic mirror and /or lens, while the other is completely shielded from such rays by being mounted in a shielding enclosure, the currents generated by the two thermo - electric devices being normally balanced so as to compensate for ambient and background temperature effects and means being provided for detecting thermo-electric current generated when infra-red rays are focused on the unshielded generator. The device comprises a casing 1 having a hinged front shutter 2 and rotatably mounted upon a vertical pillar 6 which is itself rotatable about a vertical axis, being supported in a pedestal bearing 9 and provided with a hand wheel 10. Pointers and scales are provided for indicating the angular position of the casing. Within the casing there is secured a parabolic reflector 13 at the focus of which is arranged a thermocouple 14, while a second thermo-couple 15, also provided in the casing, is surrounded by a shield 16 formed with openings so as to expose the thermo-couple to the ambient temperature. The thermo-couples are reversely connected in the adjacent arms of a Wheatstone bridge network, the two opposite arms of which are formed by a potentiometer with a sliding contact. The current from the thermo-couples is taken from a diagonal of the network to a low-frequency valve amplifier, the current to the amplifier being rendered intermittent either by means of a commutator or by an electromagnetically-operated make-and-break in the circuit. The thermo-couple 15 serves to compensate for changes in the ambient temperature, but when infra-red rays from an obstacle such as an aircraft, iceberg or other object fall on the thermo-couple 14, a current is obtained in the output circuit of the amplifier which operates a telephone receiver, current meter or a lamp, bell or other indicator. The direction of the obstacle can be found by the use of one instrument and its position can be located when more are employed. To improve the range of the apparatus, the thermo-couples may be replaced by thermopiles or the absorption of a thermo-couple increased by blackening it. Fluorspar or rock salt lenses may be used for focusing the infra-red rays in addition to or in place of the reflector 13 and the directional effects of the detector may be enhanced by locating the thermo-couples at the end of a tube of length chosen in accordance with the accuracy required. The thermo-couple is preferably formed by beating a strip of Eureka wire to a thinness of less than <1>/500 mm. and copper plating the strip. Specifications 5887/13 and 147,482, [both in Class 97 (iii)], are referred to.