Patent GB-967762-A (GB)
Title: Improvements in or relating to ultrasonic inspection apparatuses
IPC: G01N29/06
Filed: 1962-06-25
Abstract: 967,762. Ultrasonic inspection. REALISATIONS ULTRASONIQUES. June 25, 1962 [June 26, 1961], No. 24293/62. Heading H4D. In an ultrasonic inspection system comprising an electro-acoustic transducer 2, Fig. 1, transmitting pulses E, Fig. 2 (b), through a coupling medium to the object 9 under inspection, and energized by ultrasonic frequency electric pulses generated by an oscillator 1, under the control of a synchronizer 3, an echo receiving amplifier 13 taking its input from the transducer 2 and feeding its output to a control means also fed with pulses from the synchronizer 3, the control means generates a first vertical sweep voltage V1, Fig. 2 (e), proportional to the speed of the pulses in the coupling medium between a time coincident with the transmission of a pulse E, or with a pulse E D  delayed by a known amount from pulse E, and the time up to the return of the first echo A, and a second vertical sweep voltage V2, proportional to the speed of the pulses in the object, between the time of return of echo A and the desired end of the vertical sweep W, said first and second vertical sweep voltages being fed to the vertical sweep generator 5 of a C.R.T. 6 having vertical and horizontal shift plates and associated sweep generators 5 and 7. The horizontal scan generator 7 also controls the movement of the transducer across the object, such that the C.R.T. displays a vertical television type scan depicting an intensity modulated cross-sectional view of the object with the dimensions of the coupling medium and object in true relationship. The control means comprises a first bi-stable device 17 triggered from a zero to a V1 potential by a pulse E D , delayed from the synchronizing pulse E by delay means 4, and returned to zero potential by a threshold signal from a threshold amplifier 19 and the vertical sweep generator 5, indicating the end of the vertical scan and a second bi-stable device 18 triggered from a zero to a V2 potential by echo pulse A, via shaping amplifier 20, buffer stage 21 and differentiating C/R circuit 22/23, and returned to zero potential by the said threshold signal. The two thus produced pulse signals V1 and V2 are fed over lines 15 and 16 to the vertical sweep generator 5, comprising a Miller type integrator, to produce the sawtooth waveform of Fig. 2 (a) for application to the vertical sweep plates of the C.R.T. Where the top surface of the object 9, Fig. 4, is not normal to the incident ultrasonic beam, refraction occurs and the pulse when inside the object follows a path having vertical and horizontal speed components Vy=V2 cos (r-i) and Vx=V2 sin (r-i) V2 where r=sin<SP>-1</SP> (- sin i). As the transducer V1 moves over the object a distance #x, a change in the time of return of the front face echo pulse A occurs equivalent to the distance #y. For constant values of #x, #y and therefore the changes in time of return, represent tan i from which the values of Vy and Vx may be calculated. The thus calculated values of Vy and Vx can be converted into corresponding vertical and horizontal sweep velocities signals for application to the C.R.T. during the period after the reception of echo pulse A, for the true internal representation of an object having a sloping upper surface. A circuit for carrying out such a process is indicated in dotted lines in Fig. 1 and in detail in Fig. 5, with associated waveforms in Fig. 6. Delayed sync. pulses E1/E4, Fig. 6, and top surface echo pulses A1/A4 trigger bi-stable device 21, Fig. 5, to produce waveform (d). This is integrated in means 39, to produce waveform (e). Waveform (e) is then passed to a double peak threshold detector 40 to produce waveform (f) having amplitudes equal to the maximum of the previously detected sawtooth. This is then differentiated by C/R circuit 41/42 to produce waveform (g) formed of pulses having amplitudes representing the difference in the amplitudes of adjoining flat sections of waveform (f), which in turn represents the difference in the peak height of adjoining sawtooths in waveform (e), which in turn represents the difference in the echo return times for consecutive transmitted pulses, which is proportional to #y and tan i. Waveform (g) is passed into symmetrical amplifier 43 which reproduces waveform (g) together with its inverse waveform (h). To separate out the negative values of tan i from the positive values, waveforms (g) and (h) are separately added to the widened positive pulses of the waveform (d2) produced by differentiating waveform (d) 21a at the inputs of double peak threshold detectors 44 and 45, to produce the dotted waveforms (i) and (j). These stepped waveforms are then converted into sawtooth deflection signals having slopes proportional to the amplitude of waveforms (i) or (j), in Miller integrators 46 and 47. These deflection voltages are then applied either directly to the horizontal deflection plates of the C.R.T. representing V2 tan i or, after suitable processing, are applied representing V2 sin (r-i). A signal representing the differences of waveforms (i) and (j) is taken from the tapping between resistors 51 and 52 and is applied via amplifier 53 to the vertical sweep generator 5, Fig. 1, to vary the vertical deflection speed during the required period. As before, the vertical deflection speed may be merely made proportional to tan as a rough approximation or may be made proportional to cos (r-i) for an exact representation.