Patent ID: 8890516

Claim:
A tension measurement apparatus for measuring a tension of a long magnetic element, comprising: a cylindrical magnetizer arranged to surround a portion of the magnetic element to direct-current magnetize the magnetic element in a longitudinal direction up to a range of approach to saturation magnetization, and a magnetic sensor arranged in proximity to said magnetic element at a central region in the longitudinal direction of a magnetic domain to detect a spatial magnetic field intensity in a neighborhood of a surface of said magnetic element, said tension measurement apparatus configured to measure tension acting on the magnetic element based on the spatial magnetic field intensity detected by said magnetic sensor, wherein said magnetic sensor is arranged at an inner circumferential side of said cylindrical magnetizer, and wherein said magnetizer includes at least a pair of permanent magnets facing each other by different magnetic poles, spaced apart along the longitudinal direction of the magnetic element, and the pair of permanent magnets being arranged to sandwich said magnetic sensor, wherein said cylindrical magnetizer is arranged so that a length of a magnetic domain has a ratio equal to or less than 3 to the diameter of said magnetic element.