Capacitance level instruments operate on the basic principle of the variation of the electrical capacity of a capacitorformedbythesensor,thevesselwallandthedielectricmaterial. A capacitor is made of two conductive plates which are isolated from each other by a dielectric. The storage capability of a capacitor is directly dependant on the plates areas (A), their distance (d) and the dielectric constant of the material between the plates (ε).

C = kεA/d

C is the value of capacitance, expressed in Farad.

k is a constant with a value of 0.225 or 0.0885 depending on the units used.