Abstract: A method and apparatus for detecting internal defects in a workpiece are disclosed which uses time inversion to invert echo signals received by a transducer from the workpiece with respect to the signal shape and its time distribution and retransmits the inverted signal onto the workpiece. The method involves transmitting an unfocused ultrasonic beam onto the workpiece, receiving an echo signal from the workpiece, storing the first echo signal and inverting the first echo signal from each transducer with respect to the signal shape and time sequence. The inverted signal is transferred to a memory and the aforementioned procedure is carried out for each of the inspection zones n on the workpiece. The stored, inverted first echo signals are then transmitted onto the workpiece, each inverted signal being transmitted onto the inspection zone n from which the non-inverted first echo signal was received.

Abstract: A method of selecting the ultrasonic transducers which are used in non destructive ultrasonic inspection apparatus consists of establishing under predetermined conditions the frequency spectra of the transducers under consideration, comparing these spectra with the frequency spectrum of a reference transducer obtained under the same predetermined conditions, and selecting only those transducers of which the frequency spectrum is substantially identical in form to that of the reference transducer.

Abstract: A method of measuring a characteristic, such as thickness, of a test part makes use of the variation in impedance of a coil in a senor caused by eddy currents generated as a result of the proximity of the test part. The sensor measures two orthogonal components of the complex impedance. In use the sensor is moved towards the test part until one component of the impedance reaches a predetermined value and the characteristic measured as the value of the other component. The first component is selected during calibration as that component which is most sensitive to variation in the distance between the sensor and the test part.

Abstract: An indicator for determining the sensitivity of a radiological defect testing device which simulates plane defects within a workpiece. Two or more tapered elements are placed side by side on a support such that parallel, adjacent sides define the plane defects. The elements are oriented such that the plane defect extends generally parallel to the direction of the radiation.