| The basic task of realizing a smart power plant is the remote digitalization of the on-site basic equipment.Because only when the effective signals of bottom device can be digitally transmitted to the monitoring layer,management layer and decision-making layer,the upper application software and decision analysis system can make decisions more scientificly.There are a large number of base-type liquid level meters in power plants,which play an important role in the safety and economic operation of power plant units and in the comprehensive management of energy.Remote real-time monitoring of the level signal of the base equipment has become a new demand in the intelligent development of power plants.However,there are some problems in the current liquid level monitoring such as blurred images and the inability of automatically obtaining the liquid level data according to the image.Therefore,a new liquid level measuring system based on modern visual inspection technology has been developed,and the laboratory tests have been completed.The hardware cost of the system is low,which lays the foundation for the remote digitalization of the liquid level signal of the base type instrument.The main research content of this paper is as follows:(1)On the basis of studying the components and functions of the visual inspection system,the liquid level measurement system is composed of the lighting system,the optical camera system,the computer processing analysis system and the display recording system.In light of the environment of power plant,the characteristics of liquid level meter display and imaging requirements,LED is choosen as the type of light source of the system,and circular field diffuse as lighting scheme.Considering the integration of the system and the speed of video data transmission,a CMOS camera with USB interface is selected.(2)According to the characteristics of the base type liquid level instrument of the thermal power unit and the latest results of the visual inspection technology,the technical route for converting the display image of the base type instrument to the digital signal is determined.In order to eliminate the impact of the background as much as possible,firstly introduce the color threshold segmentation to determine the position of the display part in the image.To reduce measurement error,adapt inverse perspective transformation based on correspondence point control to correct the perspective distortion of images.Than apply the Canny operator to detect the edge of the liquid level interface,in the meanwhile adaptive median filter and histogram analysis are added to improve the adaptive performance of the algorithm.A window-search peak detection algorithm and a camera self-calibration method based on Lagrange interpolation are proposed.In combination with template matching,finally obtaine the level value at the interface.As tested,the algorithm improves the signal-to-noise ratio of the image and the positioning accuracy of the interface,ensuring the accuracy of level value.(3)Under the environment of Microsoft Visual Studio2015,based on C# programming language,have completed the software development of windows form application program of liquid level measurement system.The software can realize user parameter setting,camera automatic photographing,digital image processing,historical data storage,and the digitization and graphing of liquid level,ensuring that the operator can obtain accurate and intuitive level information at any time.(4)Taking the laboratory glass tube water level gauge as the test object,built a test bench.According to the evaluation index of the measurement system,experiments on system error,linearity,repeatability,stability,resolution and adaptability have been completed.As tested,the absolute error between the detection value and the reference value of the liquid level measurement system is within 1mm,the standard deviation is within 0.1mm,the linearity is 99.99%,and the resolution is 1mm,and realize improving the resolution of the liquid level gauge on the base of maintaining the accuracy level of the original instrument.Furthermore,the system has a good adaptability to illumination changes and visual direction changes within a certain range.To a certain extent,it solves the problem in existing water level monitoring software which is unable to automatically correct water level according to change of site environment and camera visual direction.The liquid level measurement system based on visual inspection technology has realized the remote digitalization of the base instrument signal in the power plant,and has the foundation of application in the industrial field.It is also applicable to the same type of liquid level measurement in the fields of petroleum,chemical engineering and other fields. |
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