In recent times the areas of application of direct current systems are being expanded. This may lead to increased risk of electric shock. The subject of investigations described in this paper is a non-linear model of the resistance of the human body under the conditions of direct current electric shock. The aim of the study was to determine the approximate model of the human body resistance at a hand-to-hand DC flow, which may be useful for assessing the effects of the electric shock. The investigations were carried out on three subjects using the hand to hand current path. Experimental studies were conducted within a voltage range of up to 80 V, while the analytical form of the identified model enables extrapolation of the obtained results to a wider range of touch voltages. The identified models allow to evaluate the shock hazard within a voltage range of up to 1500 V. The adopted shock hazard criterion was the probability of ventricular fibrillation of 5 %. The result of the studies was a direct correlation between maximum allowable duration of shock and the touch voltage determined for the three subjects on the basis of the relationship between shock duration and the touch current specified in the IEC report, and of non-linear models of resistance identified on the basis of experimental studies. It was demonstrated that for touch voltages of up to 650 V the fibrillation phenomenon should not occur when the shock duration is shorter than 10 seconds.

LASER TRIANGULATION IN 3-DIMENSIONAL GRANULOMETRIC ANALYSIS TRIANGULACJA LASEROWA W TRÓJWYMIAROWYCH POMIARACH SKŁADU ZIARNOWEGOThe measurement of the particle size distribution plays an important role in mineral processing. Due to the high costs and time-consumption of the screening process, modern machine vision methods based on the acquisition and analysis of recorded photographic images. But the image analysis methods used so far, do not provide information on the three-dimensional shape of the grain. In the coal industry, the application scope of these methods is substantially limited by the low reflectivity of the black coal particle surface. These circumstances hinder proper segmentation of coal stream surface image. The limited information contained in two-dimensional image of the raw mineral stream surface, makes it difficult to identify proper size of grains partially overlapped by other particles and skewed particles. Particle height estimation based on the shadow length measurement becomes very difficult in industrial environment because of the fast movement of the conveyor belt and because of spatial arrangement of these particles, usually touching and overlapping. Method of laser triangulation connected with the movement of the conveyor belt makes it possible to create three-dimensional depth maps. Application of passive triangulation methods (e.g. stereovision) can be impeded because of the low contrast of the black coal on the black conveyor belt. This forces the use of active triangulation methods, directly identifying position of the analyzed image pixel. High contrast of the image can be obtained by a direct pointwise laser lighting. For the simultaneous identification of the entire section of the raw material stream it is useful to apply a linear laser (a planar sheet of the laser light). There have been presented basic formulas for conversion of pixel position on the camera CCD matrix to the real-word coordinates. A laboratory stand has been described. This stand includes a linear laser, two high-definition (2Mpix) cameras and stepper motor driver. The triangulation head moves on the rails along the belt conveyor section. There have been compared acquired depth maps and photographic images. Depth maps much better describe spatial arrangement of coal particles, and have a much lower noise level resulting from the specular light reflections from the shiny fragments of the particle surface. This makes possible an identification of the coal particles partially overlapped by other particles and obliquely arranged particles. It enables a partial elimination or compensation of image disturbances affecting the final result of the estimated particle size distribution. Because of the possibility of the reflected laser beam overriding by other particles it is advantageous to use a system of two cameras. Results of the experimental research confirmed the usefulness of the described method in spite of low reflectance factor of coal surface. The fast detection of changes in particle size distribution makes...

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