Table 1 - Parameters of PZT (PZ27) piezoelectric material The measurement error is the ratio between the relative acceleration and the absolute acceleration minus 1 ([(d2 y -1), and (12) is written as: z/dt2 dt2 Parameters Internal impedance of accelerometer (C) Piezoelectric constant (d) tan δ Value 7.835*103 at 1 Khz 5*102 0.01585 Unit pf pC/N - In the following, we will express the relative sensitivity as a function of the measurement error. The piezoelectric sensor sensitivity is expressed by: The solution of this equation is shown by: 2 z 2 2 1 00 y 22 2 (10) S 1 0 dC. . c 0 1 2 2. . the expression of displacement z according to natural frequency of sensor, the damping rate and the relative frequency of the vibratory movement [23]. To express the measurement error, (10) becomes: