| 摘要 |
PURPOSE:To detect a metal in high sensitivity with a simple detecting circuit by arranging >= a pair of hall devices to which a bias current having the same frequency as an alternating field is supplied, in an advancing direction of a body to be inspected in said magnetic field. CONSTITUTION:An AC source 13 supplies alternating current to the hall devices 11a-11b through an alternating field generator 10 and phase shifters 14, 15. The bias current of each hall device is in-phase and anti-phase at the devices 11a, 11b respectively against the magnetic field, and is shifted by 90 deg. and 270 deg. at the devices 12a, 12b. If magnetic metal is contained in the body W to be inspected, a difference occurs in the outputs of the devices 11a, 11b, and an output from an arithmetic amplifier 16B is compared with a fixed voltage by a comparator 18B through a low-pass filter 17B to detect the metal. If nonmagnetic metal is contained in the body W, since the phase of the magnetic field is varied and the phases of the output voltages of the devices 12a, 12b are varied, said metal can be detected similarly by adding these output. |
