Moreover, we can go to the higher frequency range and evaluate the time data directly. In case of damage, physical properties are changed, leading to a change of the modal parameters, which are monitored by vibration-based SHM systems. Vibration-based methods are based on the fact that modal parameters like eigenfrequencies, mode shapes and modal damping are functions of physical properties like the distribution of stiffness or of mass. Within the toolbox of methods used for SHM, the two groups vibration-based methods and wave-based methods have emerged. It is closely linked to the third step, which aims at extracting the damage relevant information from the measured data via data analysis. Within this chapter, the second step “data acquisition” is focused. This reliability has to be ensured for all steps of the SHM process, which are, according to Farrar and Worden, (1) operational evaluation, (2) data acquisition, (3) feature selection and (4) statistical modeling for feature discrimination. With the help of application scenarios-including temperature variations-the advantages and disadvantages of the introduced methods of transducer inspection are presented, enabling an increased reliability of SHM systems.Īspects of reliability play a major role for the development of structural health monitoring (SHM) systems in working industrial applications. It is shown how a sensor fault can be detected before the SHM system indicates a (false) alarm. The authors show the effects of different transducer faults on the excited wave field, used for AU. An overview is given on the usage of piezoelectric transducers within SHM systems, their electro-mechanical coupling and its modeling as well as frequent faults of these devices and methods on how to inspect them and diagnose defects. Subsequent steps within the chain of SHM rely on the quality and reliability of these measurements. Especially for the use of acousto-ultrasonic (AU)-based methods or the electro-mechanical impedance (EMI) method, piezoelectric transducers are frequently used. In this chapter, we deal with the important first element of the chain, the sensor, which can undergo various faults and defects during its lifetime. In the chain from sensing to information extraction, there are many traps where errors can occur, which might lead to false alarms and therefore leave us with the impression of an unreliable system.
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