High Sensitive Capacitive Sensing Method for Thickness Detection of the Water Film on an Insulation Surface

Abstract

Water films are always formed on the outer or inner surfaces of materials in industrial processes and some key parts of instruments because of complex working environments (moisture and hidden water). This situation may lead to inaccurate measurement results or even unsafety process for instrument operation. Therefore, it is important to reliably detect and quantify the formed water films. A coplanar capacitive sensor and an AD7745-based measurement system were designed for the first stage of this paper. A glass tank and a specific power ultrasonic humidifier were then added to construct the experimental platform. To verify the feasibility of the designed coplanar capacitive sensor, the thickness of the water films was set to change from 0 to 1.5 mm with a 0.1-mm interval. The experimental results based on the self-developed system were compared with the results simulated by COMSOL, and the results derived from Agilent 4294A (an impedance analyzer). The results indicated that the coplanar capacitive sensor could be used to detect and evaluate the thickness of the water film. The resolution of AD7745-based measurement system for water film thickness detection is less than 0.1 mm.

Dual excitation self-balancing capacitance measurement method based on frequency adjustment

“…medium thickness. The use of the AD7745 system is mentioned in [30] for measuring capacitance changes. For the AD7745 sampling chip, the measured capacitance ranges from −4 pF to +4 pF, with a measurement accuracy of 4 fF.…”

Liquid level measurement using a single electrode capacitive sensor made of carbon nanotube-paper composite

“…This arrangement achieved a resolution of 0.1 mm [21], although the larger electrodes were necessary to cover the entire lateral surface. When sensors were placed at the bottom, the electrodes were positioned underneath the container to measure both the liquid level and dielectric properties [27][28][29][30]. Interdigitated electrodes (IDEs) were implemented beneath a microfluidic device to measure the liquid level [28].…”

“…When sensors were placed at the bottom, the electrodes were positioned underneath the container to measure both the liquid level and dielectric properties [27][28][29][30]. Interdigitated electrodes (IDEs) were implemented beneath a microfluidic device to measure the liquid level [28]. The microscale gap between the electrodes allowed for differentiation among three different liquids, namely distilled water, glycerol, and tetraethylene glycol.…”

“…The fringing effect [17] resulted in greater sensitivity with a smaller gap but reduced the dynamic range. Conversely, a larger gap provided a larger dynamic range at the expense of resolution [28][29][30][31]. Assuming a capacitive sensor comprised of a single electrode with an infinite gap, the dynamic range could be significantly expanded due to the diverging electric field [32].…”