| 摘要 |
PURPOSE:To perform a simultaneous inspection of a trouble part when an induction heating of a material to be heated is conducted, by a method wherein an AC power is applied to a parallel circuit in which a capacitor is connected in parallel to a heating coil surrounding the material to be heated to discriminate the resonance frequency of the parallel circuit. CONSTITUTION:A frequency of a parallel circuit 4 or a frequency of an AC power from an AC power source 5 is detected by a frequency detecting circuit 13. In case a normal part 1a of an electroseamed steel pipe being of a material 1 to be heated is positioned in a coil 2, a frequency f1 of an AC power applied to the parallel circuit 4 is, for example, 1-10KHz, and in case an abnormal part 1b such as cracks exists in the material to be heated, the frequency of the parallel circuit 4 is reduced to, for exmaple, 10% lower frequency f2. Thus, if a comparision circuit 16 becomes below a frequency L corresponding to a reference voltage level set by a reference level setting means 15, an indicator 17 indicates the presence of the abnormal part 1b in the material 1 to be heated. |
