| 摘要 |
PURPOSE:To enable secure defect detection by limiting the output of a signal supply means and controlling the defect presence/absence decision level of a 2nd detecting means to a low level when the level of a supply monitor signal exceeds a prescribed upper-limit value. CONSTITUTION:A test signal T1, i.e. the output of an amplifier 22 which amplifies the reference signal S10 of the AC output of a reference signal generator 21 to a prescribed level for the potential of a shield tape 2a and has its gain controlled with a control signal T1 supplied through a switch 23a is supplied to a brush 5 connected to the starting terminal of a coated core 1a through a slip ring 4. Here, when the level of a signal Ri exceeds the level of a reference signal S30 set previously in an upper-limit setter 26, it is judged that a dangerous voltage is applied to the conductor of the core 1a, and a switch 23a is turned off to hold the gain of the amplifier 22 at a prescribed upper limit. At the same time, a switch 23b is turned on and a control signal T2 is applied to an amplifier 30, which decreases in its gain to lower the level of a reference signal S40, thereby lowering a slice level.
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