VIRTUAL CAPACITANCE METER BASED ON IMPEDANCE MODULUS MEASUREMENT

The capacitance can be calculated from the impedance modulus value of the object under test. It is possible, if a two-terminal network is represented by a series connection of a resistor and a capacitor and the reactance of the capacitor is considerably greater than the resistance (e.g. in a low-loss capacitor). In this case the error of the approximation can be omitted. A virtual realization of such meter has been presented in the paper. This one shows the idea of the signal processing in the quasi-balanced circuit. Quasi-balanced circuits are the AC circuits designated for impedance component measurements. Similar as the balanced circuits, the quasi-balanced circuits have a special status called a quasi-balance status. This is usually a phase shift between two selected signals of the circuits. The circuit is driven to the quasi-balance status by controlling of only one variable element and then the value of the measured impedance component can be calculated using the adjusted value of the variable element. The meter has been built with the application of the data acquisition card USB NI-6009, which has been controlled by a software programmed in the LabVIEW environment.