Research On The Method And Application Of Temprature Monitoring And Measurement Based On The CCD Image Sensoring Principle

Temperature is one of the important parameters in the high temperature heat treatment field. The real-time and accurate measurement of temperature field is an effective mean for improving product quality, preventing industrial accident, conserving energy and reducing environment pollution. The conventional contact sensor such as thermocouples would not meet the demands of industry development because of the drawback of single-point and intrusive measurement. The uncontact temperature measurement using a CCD image sensor is a new technique that integrates electronics, heat transfer theory and image processing technique, and attracts the attention of the researchers on account of its obvious advantages like quick response, uncontact measurement and wide available range. The method now is still in research and experimental stage. The main factors limiting the technology application include low measurement accuracy, narrow measurable temperature scope, weak real-time processing ability and poor portability.In the paper, the basic principle of CCD is analyzed and a prototype system of temperature measurement using a linear CCD sensor is presented firstly. The system is able to get the radiation image gray-level at a single wavelength by loading the filter in front of the CCD and then calcuates point temperature or uniform temperature field of radiation object by applying the two-color theory. Then the method of wavelength selection and its effect on the measured results are discussed combined with the experimental. In view of the multi-sensor characteristic of temperature output at varity wavelength combinations, an algorithm of adaptive weighted real-time data fusion is presented. It improves the accuracy of temperature measurement and efficiency of system operation.Combining the digital imaging processing technique and two-color temperature measurement method, a novel instrumentation system is built for whole temperature field monitoring using a color matrix CCD camera. On the basis of analyzing the advantages and the disadvantages of the conventional methods, a two-color temperature measurement system with a single camera is designed. The system can capture the three monochrome images synchronically by using a splitting/filtering optical path, which reduces the system error. The relationship is deduced between the radiation temperature and pixel gray-level, and then a temperature expression is given based on the two-color theory. To meet measurement needs, an industrial black-body furnace is made for system calibration and experimental research.To improve the accuracy of temperature measurement and easy to be used in engineering application, the system's potential error sources are analyzed and the corresponding solution are given. Aiming at the error aroused by CCD spectral response bandwidth, a digital filtering method is proposed to get gray-level output at single wavelength by applying the thought of CCD spectral responsed curve tracing and the digital image discretization technique. The system simulates the filter effect with an algorithm to accomplish the temperature measurement using CCD camera without any external filtering optical path. Besides, the radiation image captured by CCD camera involves much unknown noise from bug dust, environment light and optical device. For this problem, an algorithm of multiple wavelet images de-noising based on improved Generalized Cross Validation (GCV) law is adopted to purify the radiation image and reduce measuring error.The issue on the dynamic temperature measurement scope is discussed. The CCD sensor's photo-behavior results in measurable temperature range too narrow to show the whole temperature field accurately. For solving the problem, a gray-level fitting algorithm is presented to establish an expression about RG gray-level to estimate the virtual gray-level on the saturation pixel. Increased gray-level ratios will extend the range of temperature measurement. To decrease the fitting error, the algorithm mentioned above is corrected through analyzing the curve of gray-level ratio.Two application tools have been developed for convinent to apply the temperature measurement system into industrial field. One is a FPGA(Field Programmable Gate Array)-based portable real-time temperature measurement system. The system, using a FPGA chip to implement data acquisition, temperature calculation and showing, is suitable for getting real-time results of simple point temperature or mean value of temperature zone. The other one is a PC-based monitoring system of temperature field, which is applied to monitor and analyze combustion temperature field with the powerful image processing function including image acquisition, algorithm processing, gray-level analysis and temperature field showing, etc. The two tools provide technique support for the over-all monitoring of heat-treatment processing, improving combustion efficiency, saving energy source and reducing pollution.