초록 ▼

A capacitive sensor includes a tubular outer conductor, a tubular inner conductor coaxial with the outer conductor, and an electrically insulated chamber between the inner and outer conductors. The material sample to be measured is introduced into the chamber. The sensor is shielded against electric

A capacitive sensor includes a tubular outer conductor, a tubular inner conductor coaxial with the outer conductor, and an electrically insulated chamber between the inner and outer conductors. The material sample to be measured is introduced into the chamber. The sensor is shielded against electric fields to maximize measurement accuracy. The shielding completely encloses the chamber during operation and may include a removable cap, a valve, or a screen made of a conductive material. A measurement circuit connected to the sensor includes a reference oscillator that oscillates at a constant frequency and a test oscillator that oscillates at a frequency determined by the sensor capacitance. A circuit displays a value representing the sensor capacitance in response to the frequency difference between the test oscillator frequency and the reference oscillator frequency.

대표청구항 ▼

[ What is claimed is:] [1.] A capacitive sensor for testing a material sample, comprising:an outer conductor having an elongated, substantially tubular shape with a longitudinal axis and first and second ends, and made of an electrically conductive material;an inner conductor having an elongated, su

[ What is claimed is:] [1.] A capacitive sensor for testing a material sample, comprising:an outer conductor having an elongated, substantially tubular shape with a longitudinal axis and first and second ends, and made of an electrically conductive material;an inner conductor having an elongated, substantially tubular shape with a longitudinal axis and first and second ends, and made of an electrically conductive material;a chamber electrically insulated from said inner and outer conductors having an elongated, substantially tubular shape with a longitudinal axis and first and second ends, said chamber disposed between said inner and outer conductors and coaxially aligned with said inner and outer conductors;said outer conductor having an opening in communication with said chamber, said outer conductor defining a shield against penetration by an electric field, said shield completely enclosing said chamber but for said opening in said outer conductor; anda valve attached to said opening and having a movable sealing member made of conductive material electrically coupled to said outer conductor, said sealing member selectably movable to open and close said opening.