Study On Stress Measurement Method Of Steel Cable Based On Magneto-elastic Effect

Steel cables have been widely used in industrial fields such as bridges, buildings, traction machinery and equipment because of its light weight, good flexibility performance, high tensile strength, load transfer, long distance, etc. As the most important bearing component in these structures, cable force is the important indicator to evaluate the health status. Traditional methods such as hydraulic cable force measurement method and pressure sensors cannot be achieved due to in-service cable force measurement and monitoring, has gradually been replaced by new cable force measurement method. Magnetic-elastic effect on cable force measurement technique has good dynamic response, high accuracy, simple sensor structure, low cost, long life, easy calibration, etc., more and more widely used in domestic and foreign steel bridge cable force measurement / monitoring fields. However, the traditional magnetic-elastic cable force sensor structure exists some applying difficulties at the time of in use on in-service steel cable tension, because the sensor is unified calibration and hard to install. By now, select the sensor parameters there is a certain blindness, lack of existing sensors for presence, provide a reasonable basis for sensor design parameters and to propose new evaluation criteria and even sensor structure has important practical value and significance. The paper summarizes the basis of the current deficiencies in the domestic magneticelastic sensor at the cable force measurement technology, the optimization of the operating point of the sensors and the excitation signal waveform and frequency selection are playing in a single-pass magnetic sensor design. Then proposed flexible magneticelastic sensors and placed-type cable force sensor structure, designed the measurement system including excitation system, signal conditioning module circuit and postprocessing methods, carried out test for each sensor, they are as follows: 1. According to the current magnetic-elastic cable force measurement technology and its sensor structure, find the existing deficiencies and defined the purpose of this paper. 2. From the basic characteristics of a ferromagnetic material, analyzes the ferromagnetic magnetostrictive effect, according to the thermodynamic equilibrium conditions, from the energy point of view to explore the mechanism of magneticelastic effect and clarify the effect of cable force measurement method based of magnetic-elastic effect.3. The initial magnetization curves of the cable are obtained in experimentally 50 MPa and 100 MPa stress, propose that the work point should be made in the near saturation magnetization area, proposes to use a square wave signal as the excitation source based on ferromagnetic properties ropes. Then establishment of a two-dimensional axisymmetric traditional magnetic elastic cable force sensor simulation model to analyze the cable distribution of magnetic flux density to optimize the sensor coil sleeve design parameters and the senor has been designed, experimental verification of the correctness of the model test results show that the cable through the relative permeability and cable force show a linear relationship. 4. Design the magnetic-elastic cable force measurement system, in which the measurement system excitation modules MAX038 chip design a square wave signal generator, the method to achieve power through TDA2050 audio chip; signal conditioning modules mainly related to the induction signal pre-amplification and filtering, AD620 amplifier circuit based on the input pins of chip design and bypass capacitor in parallel to achieve a pre-filtering process; designed a complete software implementation of the post-processing of the signal of the low pass filtering, integration processing and adjustment of the zero line. Developed three reconfigurable magnetic-elastic cable force sensors: a single-pass magnetic-elastic sensors, flexible magnetic-elastic sensors and placed-type magnetic-elastic sensors to solve the shortcomings of the traditional type magnetic-elastic sensor mounting difficulties. 5. The performance of the three sensor cable to carry out a complete force measurement test. Single-pass magnetic-elastic sensors because of its induction signal is strong enough, so the measurement system does not include the preamplifier circuit. Clarifies the random signal source and a reasonable filtering methods, the integrator signal can remain stable in the long acquisition process. Then introduction of a new physical quantity Re(B x) to measure stress, by placing sensors developed to achieve the cable force measurement results higher linearity. The test results show that the flexible magnetic-elastic sensor is not only solve the problem of the conventional magnetic-elastic sensors installed, but also shows the absolute highest sensitivity.