Wide Range RH Detection with Digital Readout: Niche Superiority in Terms of Its Exceptional Performance and Inexpensive Technology

In this paper we report alumina based capacitive humidity sensor having exceptional sensing performance in wide range RH segment (10% - 90%). The developed sensor has an improvement of accuracy, reliability, and economic efficiency; apart from fast response and recovery time (~s), negligible baseline drift and high selectivity for moisture. The sensing mechanism was discussed based on their microstructures, such as surface area and mesopore volume. In general, at low humidity, surface area and water adsorption play the dominant role, while at high humidity, mesopore volume and capillary condensation become important. Standard characterization techniques such as AFM, FESEM, BET, XRD and impedance spectroscopy were employed for micro-structural and electrical characterization of RH sensor. The nano porous alumina film undergoes a huge change in dielectric upon adsorption of moisture, ensuing large change in capacitance. Additionally, a prototype RH meter has been developed with digital readout for humidity. The interface circuit was based on capacitor-to-duty cycle (CDC) converter. The proposed digital circuit has the advantage of performing adaptive measurements as a function of resolution and bandwidth. The prototype instrument can be used for sub ppm level moisture detection where stability and response are completely unaffected even in highly toxic ambience viz. 4% ammonia and 4% chlorine.