Implementation of capacitive fluid level sensor

Abstract

This paper describes the design and characterization of a fluid-level measurement system based on a grounded capacitive sensor. The sensor electrodes are constructed using affordable materials, such as a stainless steel rod. The interface circuit utilizes a common relaxation oscillator, which performs a capacitance-to-period conversion, and a microcontroller that carries out a period-to-digital conversion. Additionally, a cable with active shielding interconnects the sensor with the interface circuit over a level range of 150 cm. In some cases, mechanical solutions are sufficient. For example, a toilet float valve is suitable for shutting off water flow at a specific level. However, what if it could detect a fault, send an alert signal to a central monitor, and prevent a disaster like flooding by automatically shutting down the input water supply? In today’s increasingly resource- and energy-conscious world, mechanical systems are being replaced by more sophisticated electronic and electromechanical approaches that offer additional functionality and integration within a comprehensive system. Embedded microcontrollers, for instance, can perform tasks that mechanical systems cannot reasonably handle.