PURPOSE:To measure the thickness with the propagation time of ultrasonic waves and reduce noises by generating transversal ultrasonic waves in a conductive material through the mutual ds and detecting the eddy currents by the vibrating force thereof and magnetic fields. CONSTITUTION:An ultrasonic wave generating coil 6 is provided near a donductive material 1 an ultrasonic pulse power source 7 to induce eddy currents 8 in parallel with the surface. On the other hand, magnetic fields 5 in the perpendicular direction are generated in the conductive material 1 by magnetic field generators 2 thru 4, and the pulse-form motion 9 in the same direction as the surface is induced by the mutual action with the eddy currents 8. This moving force advances thereafter in the perpendicular direction shown by an arrow 10 and reflects and turns back like an arrow 11 upon arriving at the other surface of the material 1 and becomes parallel moving force tpon arriving at the neighborhood of the surface, inducing eddy currents 13. The eddy currents 13 are detected with a detecting coil 14, is subjected to amplification and detection in a circuit 15 then to counting in a circuit 19 and are converted to the thickness of the conductive material 1 by a time-thickness conversion circuit 20. The thickness is then displayed 21. In this way, the thickness may be measured.
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