Tension measuring method

A tension measuring method for measuring a tension of a cable, comprising:

• installing a tension measuring reel having a cylindrical solenoid coil forming part on the cable to be measured;
• forming a first coil by winding a conductor around the solenoid coil forming part to form a first coil;
• measuring a magnetic hysteresis loop of the cable by supplying a current to the first coil to generate a magnetic field;
• and
• computing the tension of the cable using a parameter determined from the magnetic hysteresis loop,
• wherein the solenoid coil forming part has a first through hole along a center axis thereof,
• wherein a magnetic field sensor and a magnetic flux sensor are provided inside the first through hole,
• wherein the installing installs the tension measuring reel on the cable so that the cable is positioned inside the first through hole,
• wherein the measuring varies the magnetic field so that the magnetic hysteresis loop includes a near-saturation magnetization region, to measure the magnetic hysteresis loop using the magnetic field sensor and the magnetic flux sensor, and
• wherein the parameter used by the computing is one or more parameters selected from a group consisting of a magnetic flux or a magnetic flux density, a remanent magnetization, a coercivity, a magnetic permeability, and a hysteresis loss in the near-saturation magnetization region.