The principle of operation of capacitive transducers is based upon the familiar equation for capacitance of a parallel plate capacitor.
(i) change in overlapping area A,
(ii) change in the distance d between the plates, and
(iii) change in dielectric constant
These changes are caused by physical variables like displacement, force and pressure in most of the cases. The change in capacitance may be caused by .change in dielectric constant as in the case in measurement of liquid or gas levels.