The Precise Broadband Impedance Measurement System Based On Piezoelectric Devices

This thesis has presented a wideband high-precision impedance test system basedon the piezoelectric devices, which has taken the adaptive sweeping and switchingalgorithm, and can be able to achieve the divided collection and testing. Its bandwidthranges from20kHz to2MHz with its stepping accuracy0.1Hz and impedanceaccuracy0.001.Theoretically, the admittance circle theory has been deduced in detail from theequivalent circuit model of the piezoelectric device near the resonance state. Then it wasused to construct a voltage-current test method to get the impedance. In the algorithmresearch part, this thesis has done the following work. First, as the signals of highfrequency were too small to acquire. To solve this problem, the switching resistor-sampling and the adaptive frequency-sweeping algorithm have been introduced.Second, this thesis has focused on explaining these principles which turned to be rightfinally by a experimental comparison between our system and the other instruments,and it has proved the rationality of this algorithm.In the hardware, the system consists of three major components. The first part wascomposed by DDS, AD8369controllable gain, seventh-order elliptic filter. The secondpart is impedance matching module, constituted by the transformer coil and thesampling resistor switch networks. The last part was the phase amplitude discriminatormodule consisted by divide acquisition, RMS, ADC and AD8302etc. In addition, it hasalso made a detailed elaboration to the power protection, optical isolators, and serialcommunications and so on.In this thesis, the control system of the C software has been developed inWINAVR-2010development environment. The AD9850driving codes, the closed loopgain control procedures, the sampling resistor switch programs, the adaptive sweepprogram, the RMS control procedures, the collection frequency selection procedure, theADC voltage and current acquisition, the digital filtering and the correlation analysismethod based on voltage and current phase were compiled completely. Then theobtained amplitude ratio and phase difference of the voltage and current were put to thehost computer by the RMS232serial communication get the piezoelectric impedancecharacteristic and admittance circle and the further ceramic relevant parameters. Theexperimental results have showed that this set of device hardware and software systemsis reliable and the algorithm is suitable.