These types of transmitters take their name, and a good portion of their operating principle, from capacitors, the electrical circuit element that can temporarily store energy for use by the circuit.
Capacitors work by storing energy between two electrodes that are insulated from one another. A dielectric (non-conductive) medium is placed between the two electrodes to help store the electrical charge. With more dielectric medium comes the ability to store more energy.
Capacitance level transmitters use the liquid stored in a tank or other container as a dielectric medium between two or more electrodes. When there’s more liquid, the energy capacity of the capacitor circuit increases. When there’s less liquid, the energy capacity of the capacitor decreases.
By measuring the changes in the capacitance value of the circuit created by the electrodes and the liquid between them, capacitance level transmitters can estimate the current fill level of a container.
To ensure accuracy, however, it’s important to calibrate the sensor by testing it with the container both at maximum capacity and at zero capacity before starting regular use. Additionally, the dielectric constant value of the liquid being measured should be accounted for.