Influence and compensation method of wire resistance on measurement accuracy of elasto-magnetic sensors for tension monitoring of prestressed strand

Elasto-magnetic (EM) methods have been widely adopted in civil engineering for the tension monitoring of cables, hangers, and prestressed strands due to their noncontact and nondestructive properties. However, in practical applications, variations in the installation positions of EM sensor often lead to significant differences in wire length. This results in changes in wire resistance, which can affect the measurement results. Therefore, in this study, we developed a multiphysics coupling finite element model to systematically analyze the influence of wire resistance on the output signals and measurement results of EM sensors. A tension calibration experiment was conducted to verify the effectiveness of the simulation results and assess the influence of wire resistance on the measurement results. To mitigate the resistance effects, constantan wire resistors were used to compensate for wire resistance. The experimental findings indicate that compensation reduced the full-scale relative error of the EM sensor from (−9.1% to 7.2%) before compensation to (−4.9% to 4.5%) afterward, thereby enhancing the measurement stability and accuracy. Finally, EM sensors with resistance compensation were applied to an external prestressing reinforcement project for a prestressed concrete bridge. Measurement results with a relative error of less than 4% were obtained during the tensioning process. Long-term tension monitoring was performed. The results demonstrate that EM sensors with resistance compensation can provide accurate and stable tension measurements, thereby supporting the reliability of this approach for real-world applications.