Liquid Level Measurement System Based On Subpixel Edge Detection

In the process of chemical reagent blending,medical pharmaceutical constant volume and food automated production,it is necessary to detect the liquid level of the reagent solution,the result of which is often required to satisfy absolute non-contact,high-precision and continuous measurement and other standards.However,the liquid level measurement method has currently existed such problems like the lower intelligence,the inaccuracy of the transparent reagent level measurement,the poor closed contact measurement form and so on.Owing to its high sensitivity and good reliability,the CCD image sensor based on photoelectric technology has become a research hot spot in the field of measurement at present.Therefore,the design and development of a new transparent reagent level measuring device based on CCD has important value and significance for the chemical and pharmaceutical industries.In view of the above problems and requirements,the linear CCD measurement technology and optical imaging theory are used to building the transparent reagent level detection system that has features such as high precision and non-contact transmission in this paper,the detection device of which consists of beam emitter,CCD receiver and PC software.The laser with uniform light intensity and strong directionality of light is selected as the light source of transmitting end,and the single-line laser light is converted into a parallel beam by a lens combination according to the alignment characteristics of the linear array CCD pixels.When the parallel beams pass through different media,the light intensity changes greatly at the critical point of different media.The changed parallel beam carries the liquid level information to the receiving end and is collected by the linear array CCD.The liquid level signal collected by the line CCD is a one-dimensional digital image signal.Firstly,the liquid level signal noise is filtered.Secondly,the Canny pixel edge detection operator is used to extract the liquid level edge feature region.Finally,improved image sub-pixel edge detection algorithm is used to determine the liquid level edge pixel coordinate,the error analysis is performed on the detection algorithm,and the liquid level height compensation value is obtained for fast,high-precision measurement of transparent or translucent reagent levels.The driving circuit of linear array CCD is designed by using FPGA chip.The hardware circuit includes ADC,USB driving circuit,low-pass filter and correlative double sampling signal processing circuit.The upper computer software is built on the platform of Lab VIEW,which can detect the relevant measurement data in real time.In the end,the device has been tested experimentally and the data obtained by different experimental methods are analyzed by Origin data analysis software.After many experiments,the measurement device ranges is 5 ?25mm,the error is less than 7.5?m,and finer is better than 1.5%.The detection system can be used not only for liquid level measurement of transparent reagents,but also for size measurement of objects.It has the advantages of high accuracy,intelligence,compact,easy installation,utility and so on.It makes the detection device have important theoretical significance and practical application prospects.