A basic capacitive liquid level sensor operates on the principle of capacitance, which is the ability of a system to store an electric charge. In this type of sensor, changes in capacitance are used to detect and measure the level of a liquid in a container. The sensor consists of two main components: a probe and a reference electrode.
Here's how the working principle of a basic capacitive liquid level sensor can be explained:
Probe and Reference Electrode: The sensor includes a probe (also known as the sensing electrode) and a reference electrode. These electrodes are typically made of conductive materials like metal. The probe is positioned inside the container or tank where the liquid level needs to be measured, while the reference electrode is usually located outside the container, often serving as a ground reference.
Dielectric Medium: The liquid in the container serves as a dielectric medium, which is a substance that can store electrical energy in an electric field. The dielectric constant of the liquid (a measure of how well it can store electric charge) plays a crucial role in determining the capacitance of the sensor.
Capacitance Changes: When the container is empty or has a low liquid level, there is a relatively larger gap between the probe and the liquid. In this state, the capacitance between the probe and the liquid is lower because the electric field lines between them are less concentrated due to the larger gap.
As the liquid level rises and comes into closer proximity with the probe, the effective gap between the probe and the liquid decreases. This leads to an increase in the concentration of electric field lines, resulting in a higher capacitance.
Capacitance Measurement: The sensor's electronics continuously monitor the capacitance between the probe and the reference electrode. This is typically done using an oscillator circuit. As the liquid level changes, the capacitance changes correspondingly. These changes in capacitance are converted into an electrical signal that can be processed by the sensor's electronics.
Calibration and Output: To convert the measured capacitance into an understandable liquid level measurement (in percentage, millimeters, or other units), the sensor needs to be calibrated based on the known properties of the container and the liquid being measured. The calibration process involves determining the relationship between capacitance and liquid level.
Output Display: The calibrated measurement is then displayed on an output interface, which could be a digital display, analog output, or even a communication interface like 4-20mA current loop or Modbus, depending on the sensor's design and application.
In summary, a basic capacitive liquid level sensor detects changes in capacitance between a probe and a reference electrode caused by the presence and level of a dielectric liquid medium. By measuring and interpreting these changes, the sensor can provide accurate information about the liquid level in a container.