EEE lnfemvtional zyxwvutsrqponmlk Workshop zyxwvutsrqpo on zyxwvutsrqponm lotelligent Dam Acquisition and Advanced Computing System: Technology and Appbcationi 8-10 Scpmkr 2W3, Lviv, Ubaine Self-Calibration of Ultrasonic zyxw . . Transducers in an Intelligent Data ,. Acquisition System ' . . . . . : ,,, . Chris Papageorgiou, Theodore Laopoulos Electronics Lab. Physics Dept., Aristotle University of Thessdoniki, Thessaloniki, 54124, Greece, e-mail: papageorgiou@physics.auth.gr. zyxwv Abstract: The rapid growth. of powerful single-chip microcomputers for monitoring and data acquisition applications permits nowadays the design of advanced measuring systems. The work reported here is presenting an advanced on-line monitoring configuration in order to improve the performance and extend the lifetime of ultrasonic transducers by applying an automated testing and calibration technique. The operation of this instrumentation system is based on the fast measurement of frequency and amplitude, performed by the proposed configuration. The combination of this information with the time offlight of each pulse-train is then used to derive practically all characteristics of ultrasonic transducers. zyxwvuts Due zyxwvutsrqpon to its zyxwvutsrqponm low cost and small size, the system can be used either for characterization and classification of transducers, or as a selftesting and automated calibration section within any high performance ultrasonic system. Keywords: - Ultrasonic transducers, transducer calibration, transducer characterization 1. INTRODUCTION The use and the interest in air coupled ultrasonic transducers have increased in recent years. Ultrasonic transducers are widely used in a variety of applications and in technological areas with significant differences in performance characteristics, operating environment, specifications, etc. Ultrasonic instrumentation and measurement systems can he found in applications varying from underwater or industrial systems to medical imaging, nondestructive evaluation, and robotics. Piezoelectric transducers cannot be economically produced to generate either a controlled radiation pattem or a reproducible amplitude and frequency response. Transducer sensitivities and resonant frequencies tend to change with time and usage with an average life expectancy, which is sometimes limited to a few months of continuous use. With the advances made in zyxwvuts air transducer technology, there is a need for suitable calibration tools for characterization of airbome transducers. The increased usage of the transducers, results to an enhanced need for precise knowledge of the characteristics of the transducers and consequently for new precise methods to test'and evaluate their performance:.The more well known the operating characteristics of the transducers are, the more accurate the signal analysis will he. These characteristics must be verified for each transducer before installing it to a high performance system, and 'furthermore there must he established a test routine to check periodically transducers! operation. It is not surprising to find transducers that do not meet expectations or others that suffer from severe performance degradation (depending on the operating environment). Various methods have been proposed '. for ' measuring the performance characteristics of ultrasonic transducers, nearly all of them based on complicated systems from both; the hardware and the software point of view [I, 2, 3, 61. Unix workstations and spectrum. analyzers are used by a number. of t e a k ' together with certain mathematical calculations and advanced techniques like neural configurations and pattern recognition [I]. The aim is to identify and classify automatically ultrasonic transducers according to the value of certain characteristics of the transducers [l] or the echo signal [7]. Yet, there are two weak points to this approach; (1) the tests cannot be performed on site, as the system is operating and (2) a complicated and expensive test configuration is needed to perform the measurements and to analyze the data.' Further more not all of the measured characteristics are really needed for a proper evaluation of the transducer. operation. In most cases, once a certain type of ultrasonic transducer is chosen at the design and development phase building a prototype system, then only a small number of characteristics need to be measured for the evaluation routine. These characteristics ire basically the level of the transmittedreceived signal (sensitivity) and the resonance (peak) frequency. But even in cases where a more detailed analysis ,of the transducer is needed, nearly all information Cin be retrieved from measurements of the amplitude of the received signal (sensitivity of the transmitter receiver pair) .'vdrsus frequency and distance. This work presents a different approach based on the capabilities of modem DSP microcontrollers. The method implemented by this system is based on its capability of performing fast measurements of these Characteristics. The proposed microcontroller configuration (shown in fig. 1) is measuring the frequency and the amplitude of each period of the'incoming'signal, along with the'time of anival of each"period. These measured value6 ire then used to provide the desired characterizlion. of the transduce?. A description of this automated test configuration is given in the following, along some illustrative examples of the type of measuremnts that can be performed. . . ., .:, 2. SYSTEM OPERATION . , i, The ,characteristics of an automated system ,' for the evaluation of ultrasonic trans&" are presented in this section. The system is basically,intended, for evahation,of transducers operating in the range of.40kHz, but .it may also be,' used . for higher , freguency , .trbsducep;. with li,$ted accurac? or response time, due to $e 'operating frequency ' (clock) of. !he , ,digital - circuitry. This . .. .I. . 0-7803-81386/03/$17.00 WKI3 iEEE 2