Evaluating the Reliability of Low-Cost Level Sensors in Real-World Applications: A Comparison of Inductive and Capacitive Approaches

This thesis aims to investigate and compare the application of two distinct level sensors, one capacitive and the other inductive, for measuring the amount of water inside a coffee machine’s reservoir. The main objective is to evaluate their reliability and sensitivity in a real-world application context. The first part of the work introduces the operating principles and technical characteristics of both sensors. Inductive sensors, including variable inductance and LVDT types, and the management of eddy currents are described in detail. Subsequently, the operation of capacitive sensors is discussed, focusing on their ability to detect variations in the electric field and formulas that relate capacitance to liquid level. The document proceeds with a description of the sensor integration process into the system and the calibration phases. Various hardware and firmware modifications will be illustrated to improve the entire measurement system. The thesis concludes with a careful analysis of the results of both sensors and a subsequent comparison, also considering the strengths and weaknesses of both measurement systems. What is the purpose of a sensor that measures the entire filling range of the tank? There are several reasons why such a sensor might be beneficial in a coffee machine. The primary purpose is driven by the increasing popularity of long-form beverages in recent years, particularly in Nordic countries. Therefore, the sensor’s role would be to verify the presence of an adequate quantity of water in the tank before starting beverage dispensing, thereby preventing the water from running out during the process. A second crucial application is linked to the machine’s cleaning process. Specifically, prior to initiating the descaling cycle, the user is required to add a specific amount of water to the tank. In this context, the sensor would serve to accurately check the tank’s exact water level before the cleaning procedure begins.