GB842241A - Improvements in or relating to sonic thickness measuring apparatus - Google Patents

Abstract

842,241. Ultrasonic inspection devices. MAGNAFLUX CORPORATION. Sept. 24, 1958 [Oct. 31, 1957], No. 30544/58. Class 40(7). [Also in Group XXXVI] Apparatus for direct indication of material thickness comprises means for visually indicating the values of the frequencies at which a sweptfrequency oscillator, connected to an electroacoustic transducer coupled to the material, is loaded, a first scale graduated in thickness, a second scale of markings corresponding to the harmonic relation between oscillator frequencies and adjustable to align the visual indications with those markings, and means responsive to the movement of the second scale to effect relative movement between a marker and the first scale whereby that marker indicates on the first scale the material thickness. Rotor plates 15 of oscillator 13 capacitor 14, 15 are continuously rotated by motor 16 to give a designated variation of frequency with rotation angle (see Group XXXVI). The motor shaft rotates neon 21 energized by trigger 26 when an oscillator peak loading occurs due to resonance in test material 12 excited by crystal transducer 11. Points opposite thickness scale 23 are illuminated through arc 32 by the neon and scale 24 is rotated so that adjacent markings thereon are aligned over adjacent illuminated points; the index 31 on scale 24 is then opposite the actual material thickness on scale 23. Filter 28 rejects oscillator frequences but passes the relatively low frequency "loading" pulses to amplifier 27. In a second embodiment amplifier 27 provides vertical deflexion of a cathode-ray beam in an oscilloscope whose time-base is synchronous with oscillator frequency sweep and associated scales are aligned with the display produced, Figs. 6-9 (not shown).