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A piezoelectric accelerometer consists of the sensor case, piezoelectric measuring element and seismic mass. Accelerometers can be based on various principles, but compression and shear are particularly popular. In both cases sensor elements are preloaded between the seismic mass and the base. The compression principle entails the sensor element being loaded in compression under acceleration, whereas with the shear principle shear forces produce the corresponding sensor signals. As this seismic mass is constant, in accordance with Newton's second law (F = m•a) the force acting on the measuring element corresponds to the acceleration. The quartz element produces an electric charge that is proportional to the force and hence to the acceleration. A piezoelectric accelerometer is generally AC-coupled and unsuitable for measuring static accelerations, for example in a centrifuge. To get around this drawback, Kistler developed the K-beam accelerometer with a capacitive silicon measuring element in order to measure truly static accelerations. The long-term stability, lower mass, higher rigidity and hence higher natural frequency of the compression-type accelerometer have made it outstandingly successful. However, rather than resting on these laurels, Kistler has developed a new type of accelerometer that uses quartz measuring elements cut to produce the shear effect. Along their shear-sensitive axes these elements are only sensitive to shear force and not to normal pressure. The quartz element for shear also yields twice the electric charge of its longitudinal or compression counterpart. This has made it possible to manufacture smaller seismic systems and hence a lighter and more compact accelerometer. The measuring element of this piezoelectric accelerometer also generates an electric charge that is proportional to the force and hence to the acceleration. Typical Accelerometer Applications: - Monitoring vibration of rotating machines such as pumps and turbines
- Modal analysis in vehicle and aircraft development
- Shock measurement in crash tests
- Seismic measurement in tunneling
- Monitoring of machine tools and general
vibration measurement in the laboratory
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