How is capacitance principle used to measure level?
A storage vessel is made to behave like an electrical capacitor by installing an insulated electrode on it. The sense electrode and the tank wall form the two electrodes of the capacitor with the material as the dielectric. The capacitance C of a parallel plate capacitor can be calculated by the following formula: Where C is the capacitance in Farads, K is the dielectric constant, A is the electrode area and D is the distance between the electrodes. After installation of the probe, area of electrode and the distance between them remain constant. With a change in level the dielectric varies from air to that of the material. The dielectric constant for air is 1 whereas that of other materials is always more than 1. A change in the level therefore causes a change in the value of the capacitance. The measurement of the capacitance therefore affords a method of measuring the level indirectly.
