Study On Sensitivity Limit Mechanism Of Sky Screen

The detection sensitivity as a characterization parameter of detection capabilities of sky screen is an important indicator in evaluating the performance of sky screen. The detection sensitivity of sky screen in the plains regions is obviously different from in plateau regions, and it changes significantly with the sky brightness changing at different time on the same day in the same area, so the sensitivity scope, especially the sensitivity limit needs to be clearly known in practical use and engineering design. In this paper, researches on mechanism of sensitivity limit in theory, analysis of influencing factors as well as influence rules about the sensitivity limit and putting forward an accurate calibration method for sensitivity have been achieved. The results of research possess important guiding significance for the use and design of sky screen. The main contents are as follow:1) The structure and working principle of sky screen were analyzed, and the working model of sky screen has been built by mathematical equations for the first time. Two kinds of description methods of detection sensitivity of sky screen have been studied and compared, which are the times of the bullet diameter and minimum relative ratio of luminous flux detected by sky screen. Calculation formulas for detection limit height of sky screen and the outputted signal voltage at random point in effective ballistic trajectory have been derived. Furthermore, the detection sensitivity limit model of sky screen has been established, and detailed derivation process was given. The experimental results show that the mechanism and the sensitivity limit models constructed are correct and practical.2) The main factors about detection sensitivity of sky screen such as characteristics of photoelectric sensor, the optical system parameters, sky brightness, the comparator threshold voltage and magnification of the signal processing circuit, and those influence rules were analyzed. Relationship curves of detection sensitivity of sky screen and light characteristics, voltage-current characteristics and spectral characteristics of photoelectric sensor and sky brightness have been gotten through a way of theoretical analysis and experimental verification. And the basis of how to choose the parameters such as slit size, focal length, the comparator threshold voltage and the magnification of circuit reasonably were given. The results of research provide guidance for the user and engineering design.3) A kind of inversion algorithm about demarcating sensitivity of sky screen has been putted forward. The range of sensitivity and the sensitivity limit can be demarcated quickly from the fitting curve about ballistic height and the voltage of the signal which is fitted out by firing and the sensitivity limit model of sky screen. Error analysis and experimental results with 4.5mm gas cartridge indicate that the calibration precision is less than 1% for the relative error, which can meet the practical needs.4) A kind of artificial light for sky screen used indoor was designed, and the conditions of sensitivity of sky screen working on the background of artificial light were analyzed through the experiment.