GB1103591A - Improvements in or relating to analysing and/or sorting arrangements - Google Patents

Abstract

1,103,591. Photo-electric analysis and sorting apparatus. NATIONAL RESEARCH & DEVELOPMENT CORPORATION. Feb. 19, 1965 [Feb. 25, 1964], No.7713/64. Heading G1A. An arrangement for analyzing and/or sorting a continuous flow of a mixture of pieces of two or more different solid materials comprises means for subjecting the pieces of the mixture to ionizing radiation e.g. X-rays or y-rays, and detectors which operate to determine the amount of scattering or absorption of radiation by the materials of the mixture at two or more energy levels in order to provide an indication of the composition of the mixture or a control to sort the materials. The embodiments described utilize an X-ray tube source, the energy levels used being determined by the detector circuitry, but y-rays may be used by providing a number of sources of different radiation energies. The apparatus operates on the principle that the ratio of its outputs at two (or more) energy levels in the presence of one material is appreciably different from the ratio in the presence of the other material(s). In a first embodiment Fig. 1 a mixture of flints and pieces of chalk is examined, being carried to the test area by a conveyer 1. The bodies fall past the flared collimator 3 of an X-ray tube, and a line of detectors which may be scintillation or proportional counters, arranged across the width of the beam. Each counter is connected to a pulse analyzer and amplifier, where pulses are divided into two pulse height channels A, B, each channel feeding an integrator 7, e.g. a diode pump inte- grator, a D. C. amplifier 8, and then to a common polarized relay. A control signal is also taken from one of the channels to feed back into the X-ray tube supply in order to reduce the tube current when necessary and prevent overloading of the detection system. When a body to be sorted out of the stream, which normally falls down past the fingers 13, passes particular detectors in the detector array, signals from the latter cause relays to be operated to energize an actuator 11 to prevent deflection of fingers 13 corresponding to the particular detectors affected. Other embodiments include apparatus to record the composition of a mixture Fig. 2 (not shown), in which the conveyer passes through the X-ray beam, and apparatus to record the composition of a liquid slurry or airborne powder, carried through the beam within a duct Fig. 3 (not shown). A mixture of more than two materials may be examined to investigate composition, measure constituent quantity, or sort out one or more components, a number of sorters, as in Fig. 1, being provided. For each detector in the array, the number of pulse height channels is at least the same as the number of constituents, signals being fed to an analog computer and store and/or comparator circuit, where the signals are compared with a standard measurement for the mixture. If the mixture is fed to the test area by a narrow conveyer, test objects may be examined sequentially, necessitating only one detector. A theoretical explanation of the principles involved is given.