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

Nan Li,Jiabin Jia,Yunjie Yang,Mingchen Cao,Xiaojun Yu

doi:10.1109/access.2019.2929585

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.

Highlights

Water film in all forms (moisture, hidden water, water droplets, etc.) always exists in specific industrial processes and some key parts of instruments
Water film in all forms always exists in specific industrial processes and some key parts of instruments
Because the capacitance measured by the designed sensor is approximately 1pF–3 pF, the change in capacitance caused by the increasing thickness of the water film is approximately 0.1 pF–0.5 pF

Summary

Introduction

Water film in all forms (moisture, hidden water, water droplets, etc.) always exists in specific industrial processes and some key parts of instruments. The coplanar capacitive sensing technique is studied for application to the thickness detection of a water film on an insulation surface. Because the capacitance measured by the designed sensor is approximately 1pF–3 pF (this mainly depends on the geometry and size of the electrodes), the change in capacitance caused by the increasing thickness of the water film is approximately 0.1 pF–0.5 pF (this depends on the geometry and size of the electrodes).

Results

Conclusion