Experimental Research On Optimization Of Elasto-Magnetic (EM) Sensor Based On Ratio Measurement Method

In recent years,ferromagnetic materials have become more and more widely used in civil buildings and long-span structures.During the normal use of structures,structural health monitoring system is usually used to monitor the stress state of ferromagnetic components in structures.During the normal use of structures,it is necessary to use structural health monitoring system to monitor and measure the tension of bars.At present,the traditional steel cable force measurement methods,such as hydraulic method,fiber grating method,vibration frequency method,pressure sensor measurement method,strain gauge measurement method,have obvious defects,so their application in engineering is very limited.As a new type of sensor,elasto-magnetic(EM)sensor,based on magnetoelastic effect can measure the tension of bridge cables,external cables of prestressed structures and prestressed tendons without damage.Due to its good corrosion resistance,high tension measurement accuracy,strong overload protection ability,long life and other advantages,it has been widely used in engineering.However,in its practical application,the performance parameters of the magnetic flux sensor will be affected by the number of turns of the sensor coil,the number of layers,the diameter of enameled copper wire used and the design parameters and structural dimensions of the sensor in skeleton form.In addition,the pulse length of the excitation signal,the resistance of the external signal line and the temperature difference in the operating environment have a significant influence on the performance of the sensor.Therefore,to further explore the influence of the above factors on the output of the sensor is crucial to optimize its performance.To sum up,the main research contents of this paper are as follows:Chapter 1 firstly introduces the background and significance of the topic,and enumerates the basic principles and advantages and disadvantages of existing cable force measurement methods.The development history of magnetoelastic effect method and the research status at home and abroad are described as well.In the chapter 2,the basic principle of measuring cable force by magnetoelastic effect method is expounded in detail,and the theoretical formula of measuring by induction voltage integral method is introduced.The ratio of induction voltage integral to excitation current integral is proposed to measure cable force is given on this basis.Theoretical derivation shows that the induction voltage integral value and the ratio of the induction voltage integral value to the excitation current integral value have a linear relationship with the tensile force exerted on the steel member.In chapter 3,physical model experiments are carried out.Firstly,the sensor manufacturing process,the composition of the sensor system and the construction method of the experimental platform are introduced in detail.Secondly,the influence of excitation time,excitation coil length and external resistance on the sensor performance is investigated through experiments.Finally,it is proved that the ratio method can improve the relative sensitivity of the sensor.The experimental results show that the linear fitting degree of the sensor increases first and then decreases with the increase of excitation time.Increasing the length of the excitation coil can significantly increase the excitation time range of the sensor in normal operation,but the sensor's sensitivity decreases accordingly.Under experimental conditions,when the external resistance connected to the sensor system exceeds 18% of the resistance of the sensor itself,the sensitivity of the sensor begins to decline significantly.In chapter 4,the ambient temperature of the sensor and the bar to be measured is controlled by a constant temperature chamber,and the influence of temperature change on the output result of the sensor is explored.The experimental results show that: under the bar to be measured and the sensor system used in this experiment,a large temperature change has a significant impact on the output of the sensor,and the adverse effect of temperature cannot be ignored.Specifically,if the temperature on average 15 ? or more,the sensor output calculate the bar tension will produce at least about 1 KN deviation,compared with the full range of test measurement of 9KN,deviation rate ?11%.