Design Of Sensors For Measuring Evenness

Yarn evenness is an important index of measuring the quality of textile, and a comprehensive reflection of spinning technology and mechanical properties. In the textile industry, the quality of yarn is based on the index. So it is very important to detect the yarn evenness accurately for controlling the quality of yarn.In the thesis, author discussed the basic knowledge of evenness, the development of the domestic and international evenness tester, the advantages and disadvantages of various detection methods, and the measurement mechanism of the tester. According to the requirements and characteristics of detecting the yarn, author analyzed the influence of different structures and sizes on the performance of sensor by use of the finite element simulation software ANSYS, and optimized the sensor based on the simulation data.Then author designed the high frequency AC unbalanced bridge circuit to detect the tiny variation of capacitance caused by the fiber and compensate for fluctuations of ambient temperature.The phase-sensitive demodulator circuit was designed to convert the amount of fiber into DC voltage signal. The function of the capacitance sensor and detecting circuit was verified through experiments,and the performance was analyzed based on the experimental data. Finally, author analyzed the error of the sensor and correction method, and designed compensation circuit based on programmable capacitor to solve the problem of the drift, which could adjust the balance automatically and prevent the saturation of output voltage amplitude.