Selective high temperature humidity sensing using fast impedance spectroscopy on Titania sensors

A new method and device for the selective measurement of humidity at high temperature is presented. It consists of a TiO2 sensor element and a Fourier-based impedance spectrometry (FobIS) device with a dynamic range from 100 Hz to 100 kHz. For selective humidity detection we use an electrical equivalent circuit model presented earlier [1]. In this model, the humidity can be attributed to a constant phase element describing the ionic conduction of humidity related species. In this work, we can demonstrate that humidity can be quantified at 320 degrees C in the range from 80 to 450 mbar with an accuracy of 12 mbar with this approach. Furthermore, we can show that the circuit element for ionic conduction is not dependent on reducing gas tested with 1000 ppm ethanol. The response to ethanol, however, contributes to an ohmic resistor describing the electronic conductance within the TiO2. With compensation of reducing gas, humidity can be quantified with an error of 13 mbar.