Ultrasonic system for measuring dimensional or stress change in

Details Ultrasonic system for measuring dimensional or stress change in Ultrasonic system for measuring dimensional or stress change in

1976-04-01

1977-03-29

Gill, James J.

Measuring and testing

Liquid analysis or analysis of the suspension of solids in a...

Content or effect of a constituent of a liquid mixture

73 88F, G01N 2900

Patent

active

040142086

ABSTRACT:
An ultrasonic system for measuring dimensional change in a structural member, and particularly change in a fastener due to tensile stress, utilizes means for double pulsing a transducer to transmit an acoustic pulse into the member at one end for reflection from its other end with a period between paired pulses selected to cause the second echo received of the first pulse to coincide with the first echo of the second pulse. A VCO is employed with a digital counter to time the period between paired pulses, the interval between successive paired pulses, and the time of a predetermined number of pulse pairs. The latter timing is used to alternatively shift the frequency of the VCO high and low to cause the first echo of the second pulse to be offset in phase from the coincidence position it might have at the central frequency. Phase detection and integration of the echo pulse coincidence during alternately high and low frequency offsets produces a phase-sensitive feedback signal to the VCO to drive its central frequency toward precise coincidence. Comparing the central frequency, f, with an initial frequency, f.sub.o, for the unstressed condition of the member yields a measurement of its stress. The change (f.sub.o - f) is compared with a predetermined value, .DELTA.f, while stressing in order to adjust stress to that value. Initial and final conditions may be stored for comparison with subsequent stress measurement data.

REFERENCES:
patent: 3427868 (1969-02-01), Charbonnier et al.
patent: 3759090 (1973-09-01), McFaul et al.
patent: 3918294 (1975-11-01), Makino et al.

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