Broken wires inspection for coated steel belts in elevator system using MFL method

Coated steel belts (CSBs) are becoming widely used in elevator systems due to their good performance. The reliability and safety of the belts are the most important factors for elevator operation. The difficulties for the belts testing are the small diameter of the rope and high lift-off distance during magnetic flux leakage (MFL) inspection, which will result in a fairly weak signal with low SNR. This paper presents hardware and software methods for overcoming the problems. By comparing two kinds of magnetic sensors, Hall and giant magneto-resistance (GMR) sensors, GMR sensors were used and differential sensing mechanism was designed to detect broken wires (BWs) from one side of the flat belt. Further, data processing method based on local variance was developed to enhance SNR. Novel equipment was developed and used for CSBs inspection in elevators. Experimental results show that the equipment could be applied to detect broken wires of coated steel belts successfully and has good sensitivity and reproducibility.