Research On Calibration Technique Of Measuring Dust Concentration System

In order to effectively reduce the impact of dust particles emitted from industrial production, it is of great practical significance to measure and limit the concentration of dust. With the continuous development of science and technology, there are a lot of methods to measure the dust concentration, including the light transmission method, which uses the theory of extinction light as the measurement principle. When a beam of monochromatic light is irradiated to the dust area, due to the dust particle absorption and scattering of light intensity, it would cause attenuation of the output light intensity in a certain degree, and the regional dust concentrations value can be measured by the attenuation degree of the output intensity. As the dust concentration measurement system is implemented by photoelectric conversion, the result of the dust concentration is showed by voltage, rather than direct value of dust concentration in reality. Therefore it is necessary to be calibrated. The actual dust concentration measured by the calibration is the key point of the measurement system. The accuracy of the calibration results directly affects the accuracy of the measurement system.This paper aims to research on calibration technique of measuring dust concentration system. Based on the measuring principle, it mainly studied on the following two aspects:On the one hand, the purpose is to select effective suitable media for calibration. Because it is difficult to simulate a uniform dust environment with high concentration, we select medium with better transmittance to make dust uniformly distributed in it and then the standard concentration samples were made to simulate the dust area. Considering the characteristics of the medium, the light transmittance and the operability of the sample preparation, calibration research is made on three final kinds of media, which are water, gelatin and PMMA. On the other hand, the purpose is to obtain the relationship between concentration and voltage. This part mainly studied the calibration method of the system. After modeling and analyzing the system transfer function, two methods are used to calibrate the system. There are two methods to obtain the function relation between concentration and voltage:the calibration of unknown K parameter method and data fitting method are two methods. Calibration unknown K parameter method can obtain the relationship beiween voltage and concentration through calibrating the unknown parameter K in transfer function; Data fitting method is used to obtain the functional relationship between the concentration and the voltage of the experimental data directly. In this paper, several data fitting methods are compared and square fitting method is finally used in the calibration.At last, a lot of calibration experiments are carried out. The three different medium made of standard sample concentration was measured. Based on the measured data, the relationship between the concentration and voltage was obtained by calibration of unknown K parameter method and least square fitting method, and the result of these two kinds of experiments were compared. In order to verify the accuracy and reliability of the calibration results, the concentration results are tested by calculating the relative error. The final results show that using gelatin as medium by least square method obtain function calibration method is excellent, and the relative error size is within the error range calibration allows. Experimental results verify the feasibility and correctness of the method of calibration.