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Variable capacitance accelerometer Phase Shift


I am using a Variable Capacitance accelerometer. After a few tests I have realized the accelerometers' damping is causing the phase shift of the high frequency components. Is there any way to evaluate what the phase shift is of particular frequencies in the full accelerometer frequency response bandwidth?


Some applications require accelerometers with high sensitivity. High sensitivity is frequently related to relatively significant movement/displacement of the accelerometer seismic mass - i.e. the accelerometer seismic mass has a relatively soft suspension. In order to generate a high sensitivity output a softer mass-spring system is required, and this is made possible by lowering the resonant frequency, and a lower resonant frequency is more easily excited, which can be a problem in some applications. To avoid this effect damped accelerometers were developed.

Since every vibration transducer can be considered as a single degree of freedom mechanical system, its theoretical frequency response (sensitivity and phase) can be calculated. We just need the information about the weight of seismic mass, stiffness of transducer mechanism and the damping ratio.

In practice the information about the mass of the seismic mass are impossible to obtain. Only the information about the approximate accelerometer resonance and damping are indicated in the accelerometers' datasheet. Also every VC accelerometer is provided with a calibration certificate showing its frequency response.

Having that information we may try to evaluate the phase response of the VC accelerometer, using this excel file. To do that you will need to follow a few easy steps.

  • Enter the resonance and damping ratio values into the green cells.
  • Modify them in such a way as to have the blue plot becoming as similar as possible to the curve in accelerometer calibration certificate

Once this is done, the red curve will provide an approximate phase response of the accelerometer.

Should exact information about the accelerometer phase shift be needed, the accelerometer may be ordered with an additional calibration defining not only its amplitude response, but also its phase response.