A Medium-Range Hygrometer Using Nano-Porous Thin Film of $\gamma$ - $\hbox {Al}_{2} \hbox {O} _{3}$

Present work deals with the development of a low-cost prototype RH meter for measuring humidity in the range of 1-10% RH. The sensor working on capacitive technique consists of porous thin film of γ-AI₂O₃ formed between the parallel gold electrodes. The film was fabricated by dipcoating of sol solution obtained from the sol-gel method. The pore morphology of the sensor has been characterized by XRD, FESEM and BET analysis. The electrical parameters of the sensor have been determined by Agilent 4294A impedance analyzer. Response (~ 10 s) and recovery (~ 16 s) times of the sensor are better than the commercial sensor utilized for calibration (Xentaur, USA, LPDT-100). A suitable signal condition circuit has been developed to convert the capacitance change into voltage signal. For direct display of the humidity, the output of the sensor has been linearized by diode function generation. The prototype instrument has the potential for measuring humidity in different applications.