Non-Contact Liquid Level Measurement Using Optical Interferometry and Neural Networks

Measurement of liquid levels inside containers is an important task in a number of industrial and scientific processes. In applications such as fuel monitoring, pharmaceutical industries, wastewater treatment, and food processes, the knowledge of the liquid level is of primary concern. Furthermore, the advent of new technologies and a growing number of applications require exploration of new sensors and techniques aiming at content level measurement. Over the years, several methods have been proposed to achieve this objective with pros and cons according to the specific area. At first glance, those methods can be grouped in mechanical [1], capacitive [2], [3], electromagnetic [4], [5], acoustic [6], ultrasonic [7], optical fiber sensors [8], or self-mixing interferometry [9], among others. A relevant condition of these techniques is whether they are invasive or not; for instance, transducers or sensors attached to the container or even immersed in the liquid can be unacceptable in certain applications in the pharmaceutical or food processing industries. A brief description of the principle of operation of each technique is as follows.