Ultrasonic Measurements and Technologies

Transcription

1 Ultrasonic Measurements and Technologies

2 Sensor Physics and Technology Series Series editors: Professor K. T. V. Grattan Centre for Measurement, Instrumentation and Applied Physics City University London, UK Dr A. Augousti School of Applied Physics Kingston University Kingston-upon-Thames, UK The Sensors Physics and Technology Series aims to bring together in a single series the most important developments in the rapidly-changing area of sensor technology and applications. It will present a snapshot of the range of effort which is being invested internationally in the development of novel types of sensors. New workers in the area of sensor technology will also be catered for with an introduction to the subject through the provision of tutorial guides. Volumes may be sensor technology or applications oriented, and will present recent results from the cutting edge of research in a compact monograph format. Topics covered will include: optical sensors: free-space sensors optical sensors: guided wave sensors solid state sensors biosensors microwave sensors ultrasonic sensors process tomography control of networked sensors system control and data aquisition medical instrumentation infrared sensors chemical and biochemical sensing environmental sensing industrial applications Titles available: 1. Biosensors Tran Minh Cahn 2. Fiber Optic Fluorescence Thermometry K. T. V. Grattan and Z. Y. Zhang 3. Silicon Sensors and Circuits F. Wolffenbutte1

3 Ultrasonic Measurements and Technologies Stefan K o ~ i s Faculty of Electrical Engineering and Information Technology Slovak Technical University Bratislava, Slovak Republic and Zdenko Figura SONO Electric Nove Mesto nad Vdhom Slovak Republic CHAPMAN & HALL London Weinheim. New York Tokyo Melbourne Madras

4 Published by Chapman & Hall, 2-6 Boundary Row, London SEI 8HN, UK Chapman & Hall, 2-6 Boundary Row, London SEI 8HN, UK Chapman & Hall GmbH, Pappelallee 3, Weinheim, Germany Chapman & Hall USA, 115 Fifth Avenue, New York, NY 10003, USA Chapman & Hall Japan, ITP-Japan, Kyowa Building, 3F, Hirakawacho, Chiyoda-ku, Tokyo 102, Japan Chapman & Hall Australia, 102 Dodds Street, South Melbourne, Victoria 3205, Australia Chapman & Hall India, R. Seshadri, 32 Second Main Road, CIT East, Madras , India Published in co-edition with Ister Science Limited Ister Science Limited, StaromestskA 6, Bratislava, Slovak Republic Typeset by Forma Ltd., Bratislava, Slovak Republic First edition Chapman & Hall and Ister Science Limited Translation Milan Seberini Softcover reprint of the hardcover 1 st edition 1996 ISBN-13: DOl: / e-isbn-13: Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the UK Copyright Designs and Patents Act, 1988, this publication may not be reproduced, stored, or transmitted, in any form or by any means, without the prior permission in writing of the publishers, or in the case of reprographic reproduction only in accordance with the terms of the licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of licences issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to the publishers at the London address printed on this page. The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made. A catalogue record for this book is available from the British Library S Printed on permanent acid-free text paper, manufactured in accordance with ANSIINISO Z (Permanence of Paper)

5 Contents Preface ix INTRODUCTION 2 ULTRASONIC WAVES Propagation of ultrasound in solids. liquids and gases Reflection and transmission of an ultrasonic wave Refraction of ultrasonic waves Attenuation of ultrasonic wave motion Focusing of ultrasonic waves Radiation of ultrasonic energy References 28 3 ULTRASONIC TRANSDUCERS Capacitive transducers Physical principle of operation The design and qualities of an ultrasonic transducer Shape of the sensitive area and the scope of utilization The principle of a quasi-point transducer - a microphone The design and associated analytical solution for transducers Excitation and evaluation circuits Piezoelectric transducers Piezoelectric materials An equivalent circuit diagram of a piezoelectric transducer The quality coefficient Polymeric piezoelectric materials Magnetostrictive transducers Transducers operating with an electric discharge Introduction, classification and features of a discharge The electric spark - a source of ultrasonic waves 52

6 vi Contents Voltage supply for the electric spark Spark features A spark - a thennal source of sound Transducer design Safety of operation and conclusions regarding sparks A glow-discharge as a receiver of ultrasonic waves The principle of the discharge microphone The principle of the reciprocal transducer References 62 4 ULTRASONIC DIGITAL MEASURING METHODS Fundamental ultrasonic measuring methods Measuring methods using phase evaluation Pulse measuring methods Distance and level measurement Ultrasonic echo sounders Ultrasonic length meters Ultrasonic level meters Position measurement Plane coordinate pick-ups Pick-ups of spatial coordinates Further possibilities of dimensional measurements Some further methods of increasing the precision of a measurement Ultrasonic measurement of liquid flow velocity Measuring the thickness of materials Temperature and pressure measurement Temperature measurement Pressure measurement References NON-DESTRUCTIVE TESTING (NOT) Basic principles of ultrasonic NOT Ultrasonic methods in NOT Transmission method Pulse reflection method Resonance method The impedance method Holographic method 131

7 Contents vii The acoustic emission method 5.3 Special methods Imaging of defectoscopic signals Special ultrasonic method 5.4 Design and construction of NDT instrumentation Ultrasonic probes 5.5 References MEASUREMENT OF POSmON AND AIR FLOW BY PULSE METHODS 6.1 A pulse method of coordinate measurement using a reference transducer, positioned at the coordinate origin Measurement of coordinates using point microphones Measurement of coordinates using cylindrical transducers Measurement of spatial coordinates 6.2 Measuring air flow Principle of measurement Measurement of a planar vector of the air flow Measurement of a spatial vector of the flow velocity 6.3 Measurement of the position and flow with a single instrument Measuring flow in a plane Measuring flow in space 6.4 Measurement of wind velocity Measurement of the velocity of wind in a plane Measurement of the velocity of wind in 3D 6.5 References ULTRASONIC INSTRUMENTS: CASE STUDIES 7.1 Two-dimensional sensors for planar coordinates 7.2 Robot grip position tester 7.3 Instruments for measuring air flow 7.4 Ultrasonic measurement of thickness 7.5 Distance and level measurement 7.6 Ultrasonic flow gauges 7.7 Ultrasonic defectoscopy (NDn 7.8 References INDEX 211

8 Preface An impulse for writing this book has originated from the effort to summarize and publicise the acquired results of a research team at the Department of Automation of the Faculty of Electrical Engineering and Informatics, Slovak Technical University in Bratislava. The research team has been involved for a long time with control problems for machine production mechanisms and, in recent (approximately 15) years, its effort was aimed mostly at the control of electrical servosystems of robots. Within this scope, the members of the authors' staff solved the State Research Task Ultrasonic sensing of the position of a robot hand, which was coordinated by the Institute of Technical Cybernetics of the Slovak Academy of Sciences in Bratislava. The problem was solved in a complex way, i.e. from a conceptual design of the measurement, through the measurement and evaluation system, up to connection to the control system of a robot. Compensation of the atmospheric influence on the precision of measurement, as well as on the electroacoustical transducers, were important parts of the solution. The solution was aimed at using the ultrasonic pulse method which enables the measurement of absolute 3D position coordinates, contrary to the relative position measurements by the incremental pick-ups which are standard robotic equipment. The selected configuration of transducer arrangements and the coordinate calculation method enables us to compensate fully for the influence due to variations of parameters of the ambient medium, such as temperature, humidity, etc., except for air flow which has a vector character. However, in the environments where robots work, the air flow has a considerable influence on the precision of a measurement. Therefore, correction of this effect was attempted by introducing an auxiliary measurement of the air flow vector. The measurement method was selected with respect to full utilization of the given configuration of transducers, together with the appropriate electronic circuits of individual measurement channels. On mutual exchange of two measuring channels (with reciprocal transducers), another phase of measurement is carried out (in the

9 x Preface first phase, the coordinates are measured). After evaluation of that second phase, the individual terms of the flow vector are calculated, using particular algorithms. Then correction of the coordinates measured in the first phase follows. As a by-product of solving the task of the air-flow measurement, a possibility of its utilization as a self-standing, separate instrument for airflow measurements, (e.g. the wind, for meteorological purposes), can be considered. By extension of the calculation algorithm, it is also possible to calculate the air temperature from the measured readings. For the purpose of this book, this problem was elaborated by Pavol Bystrian-sky, M.S., PhD, in parts 6.2 and 7.3. An important problem of electroacoustical transducers for generating spherical pulse waves, which is necessary for picking up the spatial coordinates, was described by Miroslav Toman, M.S., PhD in parts 3.1 and 3.4. The problems of control and evaluation of the measurement process for the purpose of testing the trajectories of the robots motion was described by JUlius Oravec M.S. in part 7.2. In order to extend the problems in the book, the authors' team was joined by Zdenko Figura, M.S., PhD, a former long-term chief of the Ultrasonic Division of the Research Institute for Mechanization and Automation Control in Nove Mesto nad Vahom, who at present is a manager of SaNa Electric Ltd. He deals with ultrasonic sensors, especially with applications in machinery, electrotechnical, chemical, and civil engineering technology. He has put together Chapter 2 on the physics of ultrasonic waves; furthermore, he elaborated parts 3.2, and 3.3, of Chapter 3 (on ultrasonic transducers) and parts 4.2, 4.4, 4.5 and 4.6 of Chapter 4 (on ultrasonic techniques). He also wrote chapter 5 on non-destructive testing (NDT) completely and he contributed to Chapter 7 in parts 7.4 to 7.7 (examples of ultrasound applications). Other parts of the book were written by the leader of the authors' team, Assoc. Prof. Stefan Kocis, M.S., PhD, who wishes to express his sincere thanks to the co-authors for their contribution to the manuscript. The leader of the authors' team especially wants to thank the authors' employers for enabling them to acquire the information necessary for writing the manuscript.