GB779690A - Improvements in or relating to supersonic devices for measuring workpieces - Google Patents

Abstract

779,690. Ultrasonic gauging. SIEMENSREINIGER-WERKE AKT.-GES. Aug. 31, 1955 [Aug. 31, 1954], No. 25046/55. Class 118 (2). Apparatus for determining the thickness of workpieces by multiple echoes of an ultrasonic pulse comprises a pulse transmitter, a pulse receiver, and an automatic device for measuring the time within which a predetermined constant number of echo pulses are received. A rectangular pulse generator 7 provides synchronizing pulses 20 (Fig. 2), the leading edge 21 of a pulse causing a transmitter 2 to generate a pulse 22 which is fed to transducer 3. Echo pulses 23 from the workpiece 4 are received by receiver 5, amplified, limited and demodulated to produce a series of rectangular pulses 24. The initial large pulse 25 is due to direct reception and may interfere with the first one or two echo pulses, hence the rear edge 26 of a pulse 20 is used to activate a step-down counter 6 which proceeds to count the next light echo pulses. The first of these eight echo pulses initiates a rectangular pulse 27 in a generator 7 and the eighth pulse terminates it. This rectangular pulse 27 feeds a sawtooth voltage generator 8 which produces a sawtooth 28 having the same base length as pulse 27 and hence its peak voltage is dependent upon the time taken to receive the eight echo pulses. A peak voltage valve voltmeter 9 may therefore be calibrated directly in thickness. The varying velocity of sound in different workpiece materials may be allowed for by adjusting the generator 8 to give a different slope to the sawtooth 28. In a modification (Fig. 3, not shown), the rear edge of the synchronizing pulse besides activating a counter also triggers an adjustable calibrated pulse generator, the pulses from which are passed to a second counter. The eighth pulses from both the echo pulse counter and the calibrated pulse counter are fed to a coincidence amplifier which operates a relay to signal when coincidence occurs. The calibrated pulse generator frequency is adjusted to the desired thickness of workpiece and the signal indicates automatically if the actual thickness of the workpiece agrees with the desired value. Reference has been directed by the Comptroller to Specification 708,413.