The amplification of the charge amplifier A0 near infinity, and consequently the input voltage Ui amounts to almost zero and the current i equals zero ,too, for any voltage U2 on the amplifier output . The current supplied during the loading of the piezoelectric sample then the charge the capacities Ci and Cp, where Cp is a parallel capacity of the amplifier power supply conductors and input circuits . The current at the same time flows to capacity C0 connected in the feedback amplifier. In which case i=ic and voltage U2 equals :
U2 = Q/C0 = Q.kq
According to (15) , an operation amplifier with amplification freater than 10^4 is used in the connection , whereby the influence of the capacities Ci + Cp on the measurement accuracy is determined by the same relation and is smaller than one ten-thousandth of the relation Co/( Ci+Cp ). the influence of the capacities Ci+Cp on the accuracy of the meausurement of the piezoelectric charge constant dij thus can be omiited.
The piezoelectric charge constant d33 for the cylinder is calculated by the following equation.
d33= U2 / F3. kq