The Simple Virtual Impedance Spectroscopy Based on USB DAQ Card

The paper presents a virtual impedance spectroscopy based on a USB Personal DAQ/3000 card. A virtual spectroscope consist of a sine voltage generator (analog output of DAQ card), smoothing filter and two-channel voltage recorder - two analog inputs of DAQ card. The impedance of the tested object is measured indirectly using voltage samples on the object and a reference resistor, which is used to measure the current. All operations connected with signal generation, registration both voltage and current signals and also determination of the object impedance and its components has been developed in LabVIEW environment. In the paper a justification of the frequency band width of the signal depending on the maximum sampling frequency of DAC and the parameters of the used smoothing filter is presented. When the used DAQ card in analog input has only a single ADC therefore alternating sampling of both signals (voltage and current) must be used, therefore the additional signal phase shift proportional to signals frequency and sampling period occur. A simple and effective method of correction of this effect is proposed. In order to carry out experimental research, a research stand was developed. The uncertainty of the measurement results was investigated by A and B methods. Determined on the basis of the analysis of the uncertainty values of the measurement results show that using a relatively simple measurement DAQ card it is possible to build a virtual impedance spectroscopy of a few tenth percent relative combined standard uncertainty.