6. A piezoelectric acceleration transducer, whose internal electronic circuit pr

Question

6. A piezoelectric acceleration transducer, whose internal electronic circuit produces an electric voltage proportional to the relative displacement between the outer box and the moving mass inside the pickup, has a natural frequency of 10 kHz and damping ratio of 0.05. Sensitivity of the electronic circuit is given as 1 V/mm.

a)Calculate sensitivity of the acceleration transducer in terms of mV/g at a frequency of 1 kHz and compare with the sensitivity at a lowest frequency 1 Hz.

b)Calculate sensitivity of the acceleration transducer in terms of mV/g at a frequency of 9.5 kHz.

c)Noting that highest useful frequency of an acceleration transducer is defined as the frequency at which the sensitivity is not larger than the sensitivity at the lowest frequency 1 Hz, e.g., by 5 %, determine the highest useful frequency of this acceleration transducer.

Explanation / Answer

A piezoelectric accelerometer with charge output can be regarded as either a charge source or a voltage source with very high impedance. Consequently, charge sensitivity or voltage sensitivity are used to describe the relationship between acceleration and output. In the individual characteristics sheet Metra states the charge sensitivity at 80 Hz and room temperature in picocoulombs per g or perms -2 (1 g = 9.81 m/s²). The sensitivity of accelerometers with IEP/LIVM output is stated as voltage sensitivity in millivolts per g or per ms-2 . The total accuracy of this calibration is 2 %, valid under the following conditions:

f = 80 Hz, T = 21 °C, a = 10 m/s², CCABLE = 150 pF, ICONST = 4 mA.

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