To make accurately calculable a stress to be applied to a gas pipe by providing a correcting means based on conductivity of an object to be measured for an electromotive force value captured by a detecting coil, and evaluating the stress based on the corrected force value.
In a magnetostrictive sensor 1, an exciting core 3 on which an exciting coil 2 is wound and a detecting core 5 on which a detecting coil 4 is wound are disposed in a mutually intersecting state, and an interval detecting coil 6 is wound on the core 3. With this configuration, an AC current is given to the coil 2, electromotive force values detected by the coils 4 and 6 are taken up as DC signals by a synchronous detector at each period decided by receiving a command from a clock device, and processed by an evaluating means having a CPU. Conductivities are previously measured for different objects to be measured by a conductivity input means, and selectively input based on manufacturing year or method of a cast steel tube C. The AC current given to the coil 2 which is scarcely affected by an influence of a surface state of the object is selected.
HAYAKAWA HIDEKI
SAITO TEI
ENOKI KOICHI
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