Ultrasonic system for measuring dimensional or stress change in structural member
First Claim
1. An ultrasonic method for measuring dimensional change of a structural member comprising the steps oftiming the generation of paired acoustic pulses transmitted into said member at one end for reflection from its other end in a path along the direction in which dimensional change is to be measured, said timing being controlled by a variable oscillator adjusted for coincidence between the second reflection received at said one end of the first pulse of a pair with the first reflection received of the second pulse of said pair,measuring the frequency fo of said oscillator for the condition of reflected pulse coincidence with no dimensional change in said member, and storing the frequency fo for comparison,measuring the frequency f of said oscillator for the condition of reflected pulse coincidence with a dimensional change in said member, anddetermining the difference between said frequency fo and said frequency f as a measure of the extent of said dimensional change.
0 Assignments
0 Petitions
Accused Products
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, fo, for the unstressed condition of the member yields a measurement of its stress. The change (fo - f) is compared with a predetermined value, Δf, while stressing in order to adjust stress to that value. Initial and final conditions may be stored for comparison with subsequent stress measurement data.
-
Citations
18 Claims
-
1. An ultrasonic method for measuring dimensional change of a structural member comprising the steps of
timing the generation of paired acoustic pulses transmitted into said member at one end for reflection from its other end in a path along the direction in which dimensional change is to be measured, said timing being controlled by a variable oscillator adjusted for coincidence between the second reflection received at said one end of the first pulse of a pair with the first reflection received of the second pulse of said pair, measuring the frequency fo of said oscillator for the condition of reflected pulse coincidence with no dimensional change in said member, and storing the frequency fo for comparison, measuring the frequency f of said oscillator for the condition of reflected pulse coincidence with a dimensional change in said member, and determining the difference between said frequency fo and said frequency f as a measure of the extent of said dimensional change.
-
5. An ultrasonic method for measuring a dimension of a structural member comprising the steps of
timing the generation of paired acoustic pulses transmitted into said member at one end for reflection from its other end in a path along the direction in which dimension is to be measured, said timing being controlled by a variable oscillator adjusted for coincidence between the second reflection received at said one end of the first pulse of a pair with the first reflection received of the second pulse of said pair, determining the frequency fo of said oscillator for the condition of reflected pulse coincidence in said member of predetermined dimension in said member, measuring the frequency f of said oscillator for the present condition of reflected pulse coincidence in said member, and determining the difference between said frequency fo and said frequency f as a measure of the change of said dimension relative to said predetermined dimension.
-
6. An ultrasonic method for measuring stress of a structural member comprising the steps of
timing the generation of paired acoustic pulses transmitted into said member at one end for reflection from its other end in a path along the direction in which stress is to be measured, said timing being controlled by a variable oscillator adjusted for coincidence between the second reflection received at said one end of the first pulse of a pair with the first reflection received of the second pulse of said pair, measuring the frequency fo of said oscillator for the condition of reflected pulse coincidence with no stress in said member, and storing the frequency fo for comparison, measuring the frequency f of said oscillaator for the condition of reflected pulse coincidence with a stress in said member, and determining the difference between said frequency fo and said frequency f as a measure of the extent of said stress.
-
10. A method for measuring the ultrasonic transit time of a pulse through a structural member without regard to the transit time through coupling media comprising the steps of double pulsing an ultrasonic transducer coupled to a structural member at a pulse pair rate adjusted so that the second reflected echo of the first pulse of a pair coincides with the first reflected echo of the second pulse of the pair, whereby the pulse rate so adjusted is an accurate measure of the round trip transit time of an ultrasonic pulse through said member.
-
11. Apparatus for measuring dimensional change of a structural member comprising
a signal controlled variable oscillator, means for timing the continual generation of paired acoustic pulses transmitted into said member at one end for reflection from its other end in a path along the direction in which dimensional change is to be measured, said timing means being controlled by said variable oscillator to produce said paired pulses at an interval for coincidence between the second reflection of the first pulse of a pulse pair received at said one end with the first reflection of the second pulse of said pulse pair received at said one end, phase sensitive coincidence detection means for detecting any phase difference between the second reflection of the first pulse of said pulse pair with the first reflection of said second pulse of said pulse pair and for producing said signal proportional to any phase difference detected, means for applying said signal to said oscillator to reduce any phase difference detected toward zero, means for storing an initial frequency fo of said oscillator for the condition of reflected pulse coincidence with no dimensional change in said member, means for measuring the frequency f of said oscillator for the condition of reflected pulse coincidence with a dimensional change in said member, and means for determining the difference between said frequency fo and said frequency f as a measure of the extent of said dimensional change.
-
14. Apparatus for measuring a dimension of a structural member comprising
a signal controlled variable oscillator, counting means for timing the continual generation of paired acoustic pulses by counting cycles of said variable oscillator, means for transmitting said paired acoustic pulses into said member at one end for reflection from its other end in a path along the direction in which dimension is to be measured and for receiving reflected pulses at said one end, means for controlling said variable oscillator for coincidence between the second reflection received of the first pulse of a pair with the first reflection received of the second pulse of said pair, and means for determining the frequency of said oscillator for the condition of reflected pulse coincidence in said member as a measure of dimension of said member.
-
16. Apparatus for measuring stress of a structural member comprising
a controlled variable oscillator, means responsive to said oscillator for continually generating a timed pair of acoustic pulses, means for transmitting said paired acoustic pulses into said member at one end for reflection from its other end in a path along the direction in which stress is to be measured and for receiving at said one end reflections of said acoustic pulses from said other end, phase control means for continually controlling the frequency of said oscillator to continually adjust the time between acoustic pulses of each pair for coincidence between the second reflection received at said one end of the first pulse of a pair with the first reflection received at said one end of the second pulse of said pair by a feedback signal, means for measuring the frequency fo of said oscillator for the condition of reflected pulse coincidence with no stress in said member, and storing the frequency fo for comparison, means for measuring the frequency f of said oscillator for the condition of reflected pulse coincidence with a stress in said member, and means determining the difference between said frequency fo and said frequency f as a measure of the extent of said stress.
Specification