A basic capacitive liquid level sensor works on the principle of measuring changes in capacitance to determine the level of a liquid in a container. Capacitance is the ability of a capacitor (two conductive plates separated by an insulating material) to store an electric charge, and it is influenced by the distance between the plates.
Here's how a capacitive liquid level sensor generally works:
Sensor Construction: The sensor consists of two conductive plates placed in close proximity to each other. These plates can be made of metal or a conductive material, and they are separated by an insulating material (often referred to as the dielectric).
Empty State: When there is no liquid in the container, the two plates are close together, and the capacitance between them is at its baseline value. This baseline value may be predefined during calibration.
Liquid Filling: As the liquid is poured into the container, it comes in contact with one of the conductive plates (usually the bottom plate). The liquid acts as an additional dielectric material, altering the overall capacitance of the sensor.
Capacitance Change: When the liquid level rises and covers more of the bottom plate, the effective distance between the two plates (i.e., the distance between the bottom plate and the liquid surface) increases. This results in an increase in capacitance.
Signal Processing: The capacitive sensor is connected to signal processing circuitry, which measures the capacitance and converts it into an electrical signal. This signal is then processed to determine the liquid level.
Calibration: To accurately determine the liquid level, the sensor needs to be calibrated initially. Calibration involves measuring the capacitance values at different liquid levels in the container to establish a reference curve or table that relates capacitance to the corresponding liquid level.
Liquid Level Determination: Once the sensor is calibrated, subsequent measurements of capacitance are compared with the reference curve or table to calculate the liquid level accurately.
Advantages of capacitive liquid level sensors include their ability to detect both conductive and non-conductive liquids, their simplicity, and their reliability. However, they can be affected by factors such as the dielectric constant of the liquid, temperature, and the presence of contaminants on the sensor plates. Therefore, it's important to choose appropriate materials and design the sensor for the specific application.