Electromagnetic induction forma board thickness measuring method and its measurement equipment

摘要

PURPOSE:To achieve the enlargement of a measurable range and the enhancement of resolving power and to reduce the effect due to external noise, by detecting the fundamental wave of the input sine wave of an exciting coil showing significance to the change of a plate thickness from the frequency component of induced voltage. CONSTITUTION:An alternating magnetic field is applied to an object to be measured by an exciting coil 11 to generate an eddy current in the object to be measured. The fundamental wave output voltage value in the frequency component of induced voltage obtained in a detection coil 12 by said eddy current and the higher harmonic output voltage value of said fundamental wave show different significant differences to the change of the plate thickness of the object to be measured according to the magnitude of the value of the current applied to the coil 11. These signal components different in significant difference and the signal components showing no significant difference become noise to narrow the plate thickness measuring range of the object to be measured. Therefore, by detecting only the frequency component showing the most significant difference to a measuring condition, the frequency components becoming noise are removed to achieve the enlargement of a measuring range and the enhancement of dissolving power. At this time, action removing external noise is also obtained and the adverse effect thereof is reduced.