| 摘要 |
PURPOSE:To enable the detection of metal free from effect of noises by changing the intensity of DC magnetic field cyclically to selectively fetching the unbalanced signal alone with the frequency the same as that of changes in the magnetic field. CONSTITUTION:This detector is made up of a transmission coil 2 for generating a magnetic field, a magnetic field detector comprising first and second receiving coils 3a and 3b receiving the magnetic field and a detection means which obtains an unbalanced signal detected due to metal in material W to be inspected to output a metal detection signal. Then, a transmission coil 2 is operated to generate a magnetic field changing cyclically only in the intensity thereof without changing the direction of magnetic line of force and receiving coils 3a and 3b selectively fetch the unbalanced signal having the frequency component with the frequency equivalent to changes in the magnetic field generated from a magnetic field generator and the metal detection signal is outputted by the unbalanced signal. |
