Calibration and accuracy requirements for vibro-acoustic power measurements

  • Ohlrich, Mogens (Project Manager)
  • Henriksen, Eigil (Project Participant)

    Project Details


    The piezoelectric transducer principle used in accelerometers and force transducers generally provides good linearity and fine overall characteristics both in frequency and dynamic range. In such applications the principle is associated with only small deviations from the true values in amplitude and phase, and these are usually of little importance in most vibration measurements. However, the deviations cannot be ignored in measurements of complex mobilities or impedances and in measurements of the vibratory power that sources inject into structures, or the power which is transmitted between connected structures. It has been found that very strict requirements are needed for power measurements, especially with respect to the phase accuracy at off-resonant conditions. The purpose of this project has been to examine the causes of uncertainties in measurements with accelerometers and force transducers. A small bias error associated with the piezoelectric principle has been identified and quantified. By the use of simple models it is shown that the structural damping of the transducers is responsible for a phase error, which by far is the most serious one in measurements of vibratory power.
    From results of the limited number of accelerometers and force transducers tested the phase errors are found to be in the order of one degree and half a degree, respectively. In dual channel measurements it is only the relative error between the measured force and acceleration that is important. For a set of sensors this bias error can be compensated for both in amplitude and phase, at least to first order, by performing a broadband absolute calibration using an ideal mass. What remains after such a correction is only small residual errors, which reflect the uncertainty of the calibration itself and differences in transducer mounting. The experimental results indicate that these uncertainties will be +/-1% for the relative amplitude error and +/-0.2 degree for the phase error.
    Effective start/end date01/06/199630/12/1997