Development of virtual humidity sensor system

This paper presents the development of an active bridge based virtual humidity sensor system, where the capacitive humidity sensor and a reference capacitor forms two arms of the bridge. The bridge is excited by an AC voltage source of 1 kHz with amplitude of 200mV (rms). The amplitude of the input and output voltages and their phase difference are measured by National Instruments (NI) LabVIEW virtual instruments (VI) blocks through NI data acquisition (DAQ) card. The governing equations for evaluating the capacitance and resistance of the sensor are implemented by Virtual Instruments blocks to directly display the measured values. The sensor capacitance is also measured with Agilent Impedance Analyzer and accuracy of measurement for pure capacitance is found to be 1 %.