Abstract
An ultrasonic thickness gauge is constructed which can be conveniently applied to the practical measurements of the thickness of plates and tubes. The instrument which indicates the spectrum of thickness resonances on the cathode ray oscillograph is composed of variable inductance sweep oscillator and vibrator of X-cut quartz plate, and equipped with measuring device to give measures of every 0.1mm for arbitrary materials. As the results of tests performed on the plates of mild steel, aluminum, brass and glass, accuracy of less than 0.01mm can be expected for those plates of nearly 5mm thick and with fair quality.
Abrupt change of thickness at the back and geometrical irregularities such as small holes and flaws cari be detected not only as the lowering of resonance intensity but as the decisive change of resonance spectrum. In suchjrregular position, resonances due to the lateral propagation of elastic wave is responsible for the spurious resonances. In practical inspection, ultrasonic thickness gauge can take charge of the ultrasonic flaw detector, provided the resonance spectrum can be carefully investigated.
