Level detector

Claim 1

A level detector, comprising: a level detecting capacitor for placement in a container of dielectric fluid wherein the level of the dielectric fluid is to be detected, said level detecting capacitor including a pair of substantially coextensive electrodes, the electrodes being separated by a predetermined distance; an impedance element connected in series with said level detecting capacitor; an oscillating circuit means for applying an alternating voltage having a constant angular frequency to said level detecting capacitor by way of said impedance element so as to provide signal voltages; and an amplifying circuit means for substantially linearly amplifying voltage drops at said impedance element so as to output a signal corresponding to the level of said dielectric fluid, wherein said level detecting capacitor includes an outer cylinder and an inner cylinder disposed concentrically with respect to the outer cylinder, the outer cylinder constituting an external electrode to which said alternating voltage is supplied from said oscillating circuit means, and the inner cylinder being hollow and concentrically disposed inside the outer cylinder, said inner cylinder constituting an inner electrode from which signal voltages are transmitted to said amplifying circuit means; said level detecting capacitor further comprising a top cap and a bottom cap disposed at opposite longitudinal ends of said level detecting capacitor, said bottom cap having at least one hole for restricting the flow of fluid into and out of said level detecting capacitor to thereby operate as a mechanical low-pass filter, said top cap being substantially cup-shaped and arranged so as to snugly receive one of said opposite longitudinal ends of said outer cylinder, said top cap further comprising a centrally disposed projection which is partially received in said inner cylinder so as to secure said inner cylinder at said predetermined distance from the outer cylinder.