Weiwen Liu

Experimental Estimating Deflection of a Simple Beam Bridge Model Using Grating Eddy Current Sensors

A novel three-point method using a grating eddy current absolute position sensor (GECS) for bridge deflection estimation is proposed in this paper. Real spatial positions of the measuring points along the span axis are directly used as relative reference points of each other rather than using any other auxiliary static reference points for measuring devices in a conventional method. Every three adjacent measuring points are defined as a measuring unit and a straight connecting bar with a GECS fixed on the center section of it links the two endpoints. In each measuring unit, the displacement of the mid-measuring point relative to the connecting bar measured by the GECS is defined as the relative deflection. Absolute deflections of each measuring point can be calculated from the relative deflections of all the measuring units directly without any correcting approaches. Principles of the three-point method and displacement measurement of the GECS are introduced in detail. Both static and dynamic experiments have been carried out on a simple beam bridge model, which demonstrate that the three-point deflection estimation method using the GECS is effective and offers a reliable way for bridge deflection estimation, especially for long-term monitoring.

Design of Compensation Coils for EMI Suppression in Magnetostrictive Linear Position Sensors

This paper presents recent development on magnetostrictive linear position sensors (MLPS). A new compensation coil structure improves the EMI suppression and accuracy considerably. Furthermore, experimental results indicate that the new structure can improve the accuracy to ±0.13 mm nearly double the ±0.2 mm obtained with traditional structures. As another design continuation after the differential waveguide structure, this new structure is a practical and reliable implementation technique for the commercialization of MLPS.

Design and Analysis of a Differential Waveguide Structure to Improve Magnetostrictive Linear Position Sensors

Magnetostrictive linear position sensors (MLPS) are high-precision sensors used in the industrial field for measuring the propagation time of ultrasonic signals in a waveguide. To date, MLPS have attracted widespread attention for their accuracy, reliability, and cost-efficiency in performing non-contact, multiple measurements. However, the sensor, with its traditional structure, is susceptible to electromagnetic interference, which affects accuracy. In the present study, we propose a novel structure of MLPS that relies on two differential waveguides to improve the signal-to-noise ratio, common-mode rejection ratio, and accuracy of MLPS. The proposed sensor model can depict sensor performance and the relationship of sensor parameters. Experimental results with the new sensor indicate that the new structure can improve accuracy to ±0.1 mm higher than ±0.2 mm with a traditional structure. In addition, the proposed sensor shows a considerable improvement in temperature characteristics.

Analytical modelling for edge effects and impedance characteristics of the transverse eddy current displacement sensors with rectangular coils

Analytical method for eddy current evaluation is an attractive field of learning the concept of electromagnetic phe- nomena. This paper proposes an analytical approach to a transverse eddy current displacement sensor with a rectangular testing coil. Solving domain in the Cartesian coordinate system is limited to finite extents through imposing artificial boundaries at x and y axis, and solutions to the electromagnetic field are expressed as double series. Complete closed-form expressions based on second order vector potential for the electromagnetic field in each region can be obtained from the continuity conditions at the interfaces by mode matching. Closed-form expressions of the eddy current density as well as coil impedance related to the transverse displacement can thus be derived, and the calculated results show good agreement with the experimental results.

Analysis of technical requirements and the self-modification method for a combinatorial code grating eddy-current absolute-position sensor

In order to overcome the shortcomings of the low coarse-localization accuracy of a phase difference grating eddy-current sensor (PDGECS), a combinatorial code grating eddy-current sensor (CCGECS) is presented in this paper. A single-track code localization method is adopted in a CCGECS to realize the coarse localization of a grating eddy-current sensor (GECS). This method is used as a replacement of the multi-track phase difference localization method in a PDGECS. The measurement principle of a CCGECS is introduced in this paper. The relationship between measurement accuracy and main characteristic parameters of sensor is obtained by mathematical deduction and error analysis, which offers theoretical foundation for design and technical requirements analysis of a sensor. A simple and practical self-modification method is also introduced in this paper. Experimental results show that adoption of a single-track code localization method to realize the coarse localization has greatly improved the coarse-localization accuracy of a GECS, resolved the contradiction between the coarse-localization accuracy and the measurement range caused by the multi-track phase difference localization method, realized the absolute-position measurement for a larger range and at the same time reduced the technical requirements, which lays a solid foundation for mass production of a CCGECS.

Multi-parameters Optimization and Nonlinearity Analysis of the Grating Eddy Current Displacement Sensor

The grating eddy current displacement sensor (GECDS) for displacement or position measurement used in watertight electronic digital caliper was described. The parameters optimization of the sensor is essential for economic and efficient production. The purpose of this study is to determine the optimal combination of the sensor parameters and analyze the effects of these parameters on the nonlinearity of the sensor. The effects of the sensor parameters on nonlinearity are studied by finite element method (FEM). Multi parameter optimization is realized through orthogonal experimental design (OED) method combined with FEM.