An apparatus is disclosed for measuring one or more parameters of a variable
physical structure, at least one of the parameters being
fluid level, position, velocity or acceleration. The apparatus includes an electromagnetic sensing element comprising at least two
electrically conductive members that are electrically insulated from one another. A distributed
capacitance and a distributed
inductance are each formed along a length of the sensing element. The inductive
reactance is at least ten percent of the capacitive
reactance, thereby allowing the
capacitance to be distributed, rather than acting as a “lump
capacitance”. The distributed capacitance enables shaping of the electric and magnetic fields around the electromagnetic sensing element so that disturbance by nearby electromagnetic fields, conductors, and dielectrics is minimized. When the apparatus is configured as a
fluid level sensor, the capacitance is affected by the
permittivity and the level of the measured fluid. A
reference sensor can be used to compensate for changes in the
permittivity of the fluid. When the apparatus is configured as a
position sensor, the capacitance and / or
inductance are affected by the position of an
electrically conductive or
dielectric target. The position measurement can be differentiated to obtain measurements of velocity or acceleration. Electronic circuits for operating the sensing element are also shown.