Abstract: An improved method for elastomagnetic(EM) effect-based tension measurement is presented using harmonic analysis technique(HAT). The magnitudes of odd harmonics of EM signals are extracted to calculate the total harmonic distortion(THD), which is commonly used in electrical engineering area to represent the extent of the distortion of sinusoidal signals. The value of THD is applied for tension characterization. The EM signals are acquired by a EM sensor which is made of two coaxial solenoid coils, and then are alternatively processed in time and frequency domain. The advantages of the two signal processing methods are compared to find that the HAT is much more succinct. The determined characteristic parameters of calibration equation, such as linear regression and slope, tend to be stable as the number of orders for statistics increases. Moreover, the obtained calibration equation has better parameters, for example, the linear regression is larger than 0.996. The mentioned techniques are then applied for measuring the tension of high voltage transmission line, the experimental results testify that there is a significant linear relationship between THD and the applied tension. When the value of THD is equal to 1, the relative errors of estimated forces, which are calculated from calibration equations corresponding to various statistical harmonic orders, are less than 3％ (a maximum of 2.4％ for seven-wire steel strand and a maximum of 2.9％ for high voltage transmission line). This study provides a new characterization and data processing method for EM-based tension measurement technology.

Key words: elastomagnetic, harmonic analysis, tension measurement, total harmonic distortion