GB812332A - Improvements in or relating to ultra-sonic methods and equipment - Google Patents

Abstract

812,332. Ultrasonic inspection devices. LEWIS, E. M., and FOX, J. W. July 12, 1955 [April 12, 1954], No. 20146/55. Divided out of 812,331. Class 118 (2). Apparatus for the examination of material by ultrasonic oscillations in which two relatively movable directional probes are employed is provided with means to indicate the focus or out-of-focus condition of said probes. In a first embodiment observable auxiliary radiation is also directed by the probes and correct adjust. ment for this ensures adjustment for the ultrasonic energy. Two probes 10, 12 carry light projectors 11, 13 respectively (Fig. 1) and the intersection of the light beams indicates the point of focus of the probes. Alternatively a photo-cell 16, or battery of photo-cells, is held in place on the test specimen and its output used to indicate focus of the probes. Special polarizing screens or light filters 14, 15, 17 may be used. The output of the cell may light a lamp, sound an audible alarm or provide a marker pulse on the trace of a cathode-ray tube (C.R.T.). A second embodiment (Fig. 2) utilizes the reflection from acceptable minor discontinuities, e.g. in a weld, to establish correct focus. A trigger unit 20 controls an ultrasonic pulse generator 21 feeding a transmitting probe 22 applied to test specimen 23. A receiving probe 24 is connected to two amplifiers 25 and 26 in parallel. The amplifier 26 is the primary amplifier used for detecting flaws and it may have automatic gain control and/or swept gain. Amplifier 25 is set at a high gain for detection of the minor discontinuities. The outputs of both amplifiers are fed to a C.R.T. 27 having a timebase 28 synchronized from trigger unit 20. A gating circuit 29 ensures that amplifiers 25 and 26 operate on alternate pulses from generator 21, and also controls a step voltage generator 30 to deflect vertically alternate traces on the C.R.T. Thus separate indications are given of the signals from flaws and from the acceptable discontinuities to be used for focusing adjustment of the probes. Instead of the beam switching by generator 30 a double-beam C.R.T. may be used. The amplifier 25 may be gated to show only the minor reflections from the desired range. In a modification only one amplifier is used and the gating circuit 29 controls its gain appropriately for alternate pulses. A further embodiment (Fig. 3, not shown) utilizes different frequencies for detection of the minor irregularities and for detection or examination of flaws. The arrangement is as shown in Fig. 2 but with two ultrasonic pulse generators operating at the different frequencies but at the same pulse recurrence frequency. These are controlled by the gate circuit to emit pulses alternately. Display arrangements are as in the former embodiment.