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Physical Science, Measurement and Instrumentation, Management and Education - Reviews, IEE Proceedings A

Issue 3 • Date March 1987

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Displaying Results 1 - 10 of 10
  • NDT: an integral part of engineering

    Page(s): 237 - 238
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    Freely Available from IEEE
  • Computers in ultrasonic NDT

    Page(s): 239 - 248
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    The paper reviews the various aspects of the development of ultrasonic NDT techniques made possible by the use of computers. Computerised control of scanning rigs, data collection, analysis and display are described. The advantages of whole waveform collection and analysis are discussed, as are some of the associated problems and their solutions. It is concluded that the use of computers has added flexibility in the use of equipment, it has permitted optimisation of the scanning of specimens, offered greater data storage possibilities and given greater scope in the analysis and display of data View full abstract»

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  • Efficient data acquisition in automated ultrasonic inspection

    Page(s): 249 - 256
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    The large volumes of data resulting from automated ultrasonic inspections illustrate the difficulties of efficient data acquisition and analysis. Consequently, all the available inspection systems impose a compromise between the quantity and the quality of data that they collect and the maximum possible speed of inspection. The paper introduces the problems of ultrasonic data acquisition and assesses several techniques so far employed in inspection systems. A further technique is then described in which only the minimum data required by ultrasonics specialists for defect detection, sizing and characterisation are gathered in a single high-speed scan. This is a technique which is presently being investigated so that the plotting and analysis may be carried out rapidly by discarding data which would otherwise obstruct the interpretation process. The technique requires intelligent discrimination of the features contained in the baseband envelope of the ultrasonic signal. A high-speed signal preprocessor which will implement this technique is under development and is known as the digital ultrasonic signal conditioner (DUSC); its design and applications are described View full abstract»

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  • Investigation of the 1-D inverse born technique

    Page(s): 257 - 265
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    An ultrasonic digital signal processing technique which can be used to size isolated inhomogeneities in an otherwise homogeneous medium is examined. The technique is known as Born inversion and is theoretically valid for application to weak scatterers. However, accurate radius predictions have also been obtained experimentally for strong scatterers (voids). The technique was examined using synthetically generated ultrasonic signals from weak and strong scatterers, as well as experimental data from voids in high strength metals, to ascertain the application limits of the algorithm and to investigate why the technique is insensitive to different classes of scatterer. It was found that the part of the frequency spectrum used in the inversion routine has a very similar profile for weak and strong scatterers. Accurate sizing using Born inversion is only obtained if the bandwidth of the interrogating probe is adequate. However, the probe bandwidth requirements depend on the size of the flaw being examined, which is not known a priori. A methodology is presented which determines whether the match of flaw size to probe bandwidth is suitable. This has proved critical in obtaining accurate size estimates from the inversion. View full abstract»

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  • Computer-controlled manipulator system for autonomous inspection

    Page(s): 266 - 278
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    The paper describes research carried out in the Mechanical Engineering Department at University College London with the aim of investigating the feasibility of introducing automation into remote structural inspection. The work concentrates on the problems associated with building up a mathematical model of structures made from cylindrical components by gathering tactile information using a computer-controlled manipulator. The results are of particular relevance to the inspection of offshore structures, pipelines, and nuclear plants. Experiments have been carried out in the laboratory, both using a three-degrees-of-freedom electrohydraulic manipulator fitted with a tactile sensor and by using a graphical simulation of a similar manipulator with enhanced capabilities. The paper describes the development of the hardware and software that was needed to carry out the experiments and discusses several methods of using tactile data to deduce the shape and size of cylinders. The experiments that were carried out are described and the results of sensitivity studies into the effects of measurement noise are presented. Finally, the main achievements of the research are summarised and possible extensions to the work are discussed View full abstract»

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  • Electromagnetic ultrasonic transducers and systems for in-service inspection of gas pipelines

    Page(s): 279 - 282
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    Electromagnetic ultrasonic transducers (EMUS) do not need liquid couplants; they can be designed to operate at elevated temperatures; they can be scanned at high speeds; and they can be designed and fabricated for a much wider variety of wave modes than piezoelectric probes, especially for modes with tangential polarisation. A disadvantage is the larger insertion loss than that of piezoelectric transducers. However, using an optimised layout of probes and transmitting and receiving electronics yields sufficient power and signal/noise ratio for pipe testing and many other industrial applications. The paper describes the general state of the art and the results of optimisation for in-service inspection of gas pipelines. In particular, the optimisation of linearly polarised shear-wave transducers for vertical and oblique incidence is presented. View full abstract»

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  • NDT applications of scanning acoustic microscopy

    Page(s): 283 - 289
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    The scanning acoustic microscope is becoming an important new tool for nondestructive testing. The paper concentrates on the current application of the technique and recent developments in instrumentation relevant to the NDT field: an area not well covered in the literature View full abstract»

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  • Consequences of resonant surface-wave excitation on contrast in reflection scanning acoustic microscope

    Page(s): 290 - 300
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    The scanning acoustic microscope (SAM) is a confocal imaging system that is very similar in structure to the scanning optical microscope. The purpose of the paper is to show that when surface-wave excitation is the predominant contrast mechanism, the imaging performance cannot be described within the same framework that is used to explain image formation in the scanning optical microscope. The paper explains that concepts such as the optical transfer function and the point spread function, which rely for their usefulness on the linear superposition of object features, are not applicable because surface-wave excitation is a resonant phenomenon. The paper shows how the images expected in acoustic micro-graphs can be severely perturbed by resonance in the specimen. It is therefore important that these effects are understood so that acoustic images are correctly interpreted. The specimen is modelled in the simplest possible manner to account for surface-wave excitation so that the features unique to imaging in the reflection acoustic microscope can be demonstrated View full abstract»

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  • Three-dimensional finite-element modelling in eddy-current nondestructive testing

    Page(s): 301 - 306
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    Eddy-current nondestructive testing is increasingly used in industry as a means of noninvasive detection of flaws in metals that are electrically conducting. Various computer modelling techniques have been used in the past for simulating different NDT processes. This contribution is concerned with the prediction of electromagnetic fields in the vicinity of a surface flaw using a general three-dimensional finite-element eddy-current program. Fields are modelled in terms of either the magnetic vector potential A or a magnetic scalar potential. Some experimental and calculated results are presented that suggest that the program could be used in its present form for a certain range of NDT problems. Some areas where further improvement would be desirable are highlighted View full abstract»

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  • Book review: Review of Progress in Quantitative Nondestructive Evaluation, Volumes 5A and 5B

    Page(s): 307 - 308
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    Freely Available from IEEE