| 摘要 |
PURPOSE:To securely and easily detect a defect in insulation between an upper and a lower skin metallic plate by detecting the voltage difference between two couples of rolls varying exceeding a specific preset value. CONSTITUTION:A couple of current supply rolls A1 and A2 connected to a constant current source 11 are made of conductive materials and contact the upper and lower skin steel plates 1 and 1' between stands 10a and 10b. Further, two couples of conductive voltage detection rolls B1 and B2, and C1 and C2 are provided on both sides of the rolls A1 and A2 and contact the skin steel plates 1 and 1' respectively. Further, the couple of voltage detection rolls B1 and B2, and C1 and C2 are connected to the inputs of differential amplifiers 13B and 13C. The outputs of the amplifiers 13B and 13C are inputted to a differential amplifier 15 and the force proportional to the difference between both voltages is compared by a comparator 17 with a specific value; when it is judged that the force exceeds the specific value, the correspond-part of the steel plate 3 is marked and a warning lamp illuminates.
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