This charge is then converted electronically to a differential voltage signal, which is proportional to the acceleration that is parallel to the sensitive axis of the transducer. The pyroelectric charge appears in the poling axis i.e. The 200355 Accelerometers contain a piezoelectric sensing device, which generates charge when subjected to vibration. The operational principle of such sensors is similar to the other transducers, where the one form of energy is converted to another and stimulates an electric signal. We remember that certain piezo materials, especially all piezo ceramics, have the peculiarity that the remnant polarization varies with the temperature and the piezo element produces a charge. The piezoelectric accelerometers utilize the effect of certain materials to measure changes in mechanical variables such as shock or vibration dynamically rather than statically. Due to the compact design it is also a good choice when we want a high resonance for a wide frequency response.Ī possible drawback of the compression mode is the potential occurrence of the pyroelectric effect. The compression mode accelerometer is probably the most common design as it is most simple and has very good basic characteristics. These devices are well suited for taking high-frequency vibration data. Of course we have to omit the central bolt as well otherwise we have a short circuit from the mass to the base. A piezoelectric accelerometer can accurately measure signals between 1 Hz and 15,000 Hz. Hereby the sensing element becomes electrically asymmetric or single ended. One pole is then on the base and the other on the inertial mass. The final sensing element can then be calibrated by removing weight from the mass.Ī similar but simplified design we get when we omit the two insulators. This is why the mass is designed to be about 10 to 15% heavier than really required so all sensitivities come out high. If we want the final sensitivity to be in a closer tolerance than that, we can adapt the mass accordingly. In practice we see often up to 10% variation. All technical materials show a certain variation of their characteristics and so does the piezoelectric constant. Piezoelectric accelerometers have very low noise levels and are considered for both shock and vibration testing of all types. The sensitivity is only depending on the piezoelectric constant and the mass. Piezoelectric accelerometer Piezoelectricity Frequency Brel & Kjr, others, charge, transducer, acceleration png 600圆00px 151.47KB Accelerometer. That's why we want to place the sensing element always in the same orientation. It is also a good idea to have the phase of the signal identical over all individual sensors of the same type. However if we need the phase information, for example for balancing an engine the phase is of prime importance. If we are only interested in the magnitude of the vibration this is irrelevant. We remember that in a sinusoidal motion the acceleration is out of phase by 180° with respect to the displacement. In the case shown here the acceleration is a= A∙ sin ωt.
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