Study On Magneto-elastic Cable Tension Sensor Based On The Inverse Magnetostrictive Effect

Cable structure has been widely used in the space structure and bridge engineering due to its advantages of large span,small weight and easy construction.The steel cable is utilized as the main load bearing component in the cable structure.The structures are inevitable to suffer from the influence of natural and artificial factors during its service life.The steel cable tension may exceed the designed value,which will lead to the deterioration of structural health status and sometimes even result in the collapse of building structures.Hence,there are important scientific significance and application value to accurately realize the real-time on-line monitoring of steel cable tension.In this dissertation,based on the inverse magnetostrictive effect,the cable tension measurement of magnetic flux sensor using the ratio measurement method is discussed from several aspects,including the theoretical analysis,analogue simulation,test study and engineering application.The following are the main studies:(1)The excitation coil and induction coil of traditional magnetic flux sensor are indispensable for cable tension monitoring.In order to solve this problem and enhance the stability of cable tension measurement of magnetic flux sensor,the LR model of single-coil sensor system is established by the theoretical analysis and the measurement method of cable tension using single coil is proposed f'or the first time in this dessertation.The alternating voltage,impedance parameter and pulse current of single-coil sensor are selected as the measurement indicators for cable tension monitoring.Additionally,based on the LR model of single-coil sensor system,the transformer model of double-coil sensor systen is established and the ratio measurement method is presented for improving the sensor performance.(2)The finite element models of the non-sleeve and sleeve sensors are established and simulated to study the influence of the sleeve structure on the internal magnetic field distribution of the test specimen.In the elastic range of steel cable.an equivalent simulation method is introduced to simulate the change of the external tension by changing the permeability of the test specimen.This method simplifies the multi-field coupling problem and reduces the computational complexity of the model.Moreover.the influence of the length change of the external wire on the magnetic flux sensor output is analyzed by changing the external resistance value,which would prove the superiority of the ratio measurelent method.The finite element simulation results illustrate that the utilize of the sleeve structure not only improves the internal lagnetic flux density of steel cable,but also reduces the external magnetic field interference from different directions.In addition.there exists a good linear relationship between the proposed measurement parameter and the permeability of the test specimen and the utilization of ratio measurement method could make the measurement result more accurate.(3)After improving the theoretical system and the finite element model of the traditional magnetic flux sensor,the test of the measurement method of single-coil is carried out for the first time.Finally,the fitting curves between the measurement indicators and the external tension are obtained.The test results show that measurement indicators for cable tension monitoring have good linear relationships with the external tension under different excitation conditions.The use of the sleeve structure can improve the relative sensitivity and reduce the repeatability error of the sensor.Furthermore,the bypass structure is designed and the permeability transfer theory is proposed for the easy installation and utilization of the sensor.The test results verify the accuracy of the theoretical deduction in the bypass structure as well as the feasibility of the bypass structure used in the cable tension monitoring.(4)Based on the embedded hardware platform,the acquisition instrument of magnetic flux sensor with multi-channel is developed.The function modules of configuration,data acquisition and data display of the sensor parameters are integrated by using LabVIEW programming environment and the tension monitoring system of nagnetic flux sensor is established.The superiority of magnetic flux sensor and the stability of the monitoring system based on the ratio measurement method are verified by analyzing the calibration test data and measurement results in tensile process of the Guiyang Kailin city and Zhengzhou Olympic stadium.