| 摘要 |
PURPOSE:To measure exactly the thickness even if irregularity is generated on the surface of an insulator, by calculating the respective signals from a pair of eddy current type distance detectors and other distance detecting means which has been installed between said detectors. CONSTITUTION:A pair of eddy current type distance detectors 3A, 3B consist of eddy current sensors 1A, 1B and rollers 2A, 2B, respectively. Also, an optical distance detector 6 is provided between them in the upper part of an insulator 5, and they are connected as one body to each other by an arm 7. In this state, signals corresponding to distances L1, L2 between tips of the sensors 1A, 1B and the reverse side of a steel pipe 4, a signal corresponding to a distance L3 between the tip of the detector 6 and the surface of the insulator 5, and a signal corresponding to a distance L4 between the tip of the detector 6 and one of the sensors 1A, 1B, which have veen detected, respectively, by a pair of detectors 3A, 3B are inputted to an operator 8. In this way, thickness of the insulator 5 is calculated continuously in accordance with an expression [L4+(L1+L2)/2)-L3. In this regard, in said expression, a detection error at the time when a device has been inclined against the steel pipe 4 is reduced by deriving an average of the distances L1, L2.
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