Volume charge density measuring system

A capacitive sensing system for testing a material sample, comprising:

• a sensor having a body and two electrical conductors, with a chamber disposed between said two electrical conductors for admitting said material sample, said chamber electrically insulated to inhibit electrical conduction between said two electrical conductors through said material sample;
• and
• a circuit, comprising:
• an oscillator circuit coupled to said two electrical conductors for producing a measurement signal having a frequency responsive to a capacitance defined by said two electrical conductors and a dielectric region between said two electrical conductors comprising said material sample in said chamber;
• an indicator circuit for displaying a measurement indication in response to said frequency of said measurement signal, said indicator circuit having a phase-locked loop for producing said measurement signal.

A capacitive sensing system for testing a material sample, comprising:

• a sensor having a body and two conductors, with a chamber disposed between said two conductors for admitting said material sample, said chamber electrically insulated to inhibit electrical conduction between said two conductors through said material sample;
• and
• a circuit, comprising:
• an oscillator circuit coupled to said two conductors for producing a measurement signal having a frequency responsive to a capacitance defined by said two conductors and a dielectric region between said two conductors comprising said material sample in said chamber;
• an indicator circuit for displaying a measurement indication in response to said frequency of said measurement signal, said indicator circuit having non-linearity compensation means for linearizing a non-linear response in said frequency to dielectric changes in said material sample.

A capacitive sensing system for testing a material sample, comprising:

• a sensor having a body and two electrical conductors, with a chamber disposed between said two electrical conductors for admitting said material sample, said chamber electrically insulated to inhibit electrical conduction between said two electrical conductors through said material sample;
• and
• a circuit, comprising:
• an oscillator circuit coupled to said two electrical conductors for producing a measurement signal having a frequency responsive to a capacitance defined by said two electrical conductors and a dielectric region between said two electrical conductors comprising said material sample in said chamber;
• an indicator circuit for displaying a measurement indication in response to said frequency of said measurement signal, said indicator circuit having temperature compensation means for negating effects of environmental temperature variations on said measurement signal.

A capacitive sensing system for testing a material sample, comprising:

• a sensor having a body and two conductors, with a chamber disposed between said two conductors for admitting said material sample, said chamber electrically insulated to inhibit electrical conduction between said two conductors through said material sample;
• and
• a circuit, comprising:
• an oscillator circuit coupled to said two conductors for producing a measurement signal having a frequency responsive to a capacitance defined by said two conductors and a dielectric region between said two conductors comprising said material sample in said chamber;
• an indicator circuit for displaying a measurement indication in response to said frequency of said measurement signal, said indication indicating only whether said frequency of said measurement signal is above or below a predetermined threshold.

A capacitive sensor for testing a material sample, comprising:

• an outer conductor having a longitudinal axis, an elongated, substantially tubular shape, and a plurality of fins;
• an inner conductor having a longitudinal axis, an elongated shape, and disposed coaxially within said outer conductor, said inner conductor having a plurality of fins spaced from and intermeshing with said plurality of fins of said outer conductor;
• and
• a body retaining said inner and outer conductors in coaxial orientation;
• and
• said inner and outer conductors arranged to define a chamber therebetween for admitting said material sample, said chamber providing electrical insulation to inhibit electrical conduction between said inner and outer conductors through said material sample.

A capacitive sensor for testing a material sample, comprising:

• two conductors spaced from and parallel to one another, each conductor of said two conductors having an elongated, substantially planar, bar-like shape;
• an elongated body retaining said two conductors and having a longitudinal axis;
• and
• said two conductors arranged to define a chamber therebetween for admitting said material sample, said chamber providing electrical insulation to inhibit electrical conduction between said two conductors through said material sample.

A method for using a capacitive sensor to test a material sample, said capacitive sensor including a body having a longitudinal axis and two conductors mounted in said body spaced from and parallel to one another with said longitudinal axis extending therebetween, said two conductors arranged to define a chamber therebetween for admitting said material sample, said chamber providing electrical insulation to inhibit electrical conduction between said two conductors through said material sample, said body having an inlet port disposed at a first end of said body for communicating said material sample into said chamber and an outlet port disposed at a second end of said body for communicating said material sample out of said chamber, said inlet and outlet port each having a flow axis defining a direction of flow of said material sample through said inlet and outlet port perpendicular to said longitudinal axis and not intersecting either of said two conductors, the method comprising the steps of:

• orienting said capacitive sensor above a body of liquid with said longitudinal axis perpendicular to a surface of said body of liquid and said flow axes of said inlet and outlet port parallel to said surface of said body of liquid;
• immersing said first end of said body in said body of liquid until said inlet port is submerged and said material sample fills said chamber;
• providing an electrical stimulus signal to said two conductors;
• and
• measuring an electrical response signal at said two conductors to said electrical stimulus signal when said material sample is present in said chamber.

A method for calibrating a capacitive sensor system, said capacitive sensor system including a sensor for measuring an electrical response signal and a circuit having a display for providing a perceptible indication in response to said electrical response signal, said sensor having a body and two electrical conductors spaced from each other with a chamber disposed between said two electrical conductors for admitting a material sample, said chamber providing electrical insulation to inhibit electrical conduction between said two electrical conductors through said material sample, the method comprising the steps of:

• admitting a calibration material sample having a first predetermined volume charge density into said chamber;
• providing an electrical stimulus signal to said two electrical conductors;
• measuring a first electrical response signal at said two electrical conductors to said electrical stimulus signal when said calibration material sample is present in said chamber, whereby a first data point is defined by said first electrical response signal with respect to said first predetermined volume charge density;
• admitting a calibration material sample having a second predetermined volume charge density into said chamber;
• providing said electrical stimulus signal to said two electrical conductors;
• measuring a second electrical response signal at said two electrical conductors to said electrical stimulus signal when said calibration material sample is present in said chamber, whereby a second data point is defined by said second electrical response signal with respect to said second predetermined volume charge density;
• computing a compensation function in response to said first and second data points;
• admitting into said chamber a low-scale reference material sample having a substantially zero volume charge density;
• providing said electrical stimulus signal to said two electrical conductors;
• measuring a low-scale electrical response signal at said two electrical conductors to said electrical stimulus signal when said low-scale material sample is present in said chamber, said circuit providing a low-scale compensated signal in accordance with said compensation function in response to said low-scale electrical response signal;
• adjusting said circuit until said display provides a low-scale indication in response to said low-scale compensated signal;
• admitting into said chamber a high-scale reference material sample having a volume charge density greater than zero;
• providing said electrical stimulus signal to said two electrical conductors;
• measuring a high-scale electrical response signal at said two electrical conductors to said electrical stimulus signal when said high-scale material sample is present in said chamber ,said circuit providing a low-scale compensated signal in accordance with said compensation function in response to said high-scale electrical response signal;
• and
• adjusting said circuit until said display provides a high-scale indication in response to said high-scale compensated signal.

A method for calibrating a capacitive sensor system to measure a velocity of a fluid material, said capacitive sensor system including a sensor for measuring an electrical response signal and a circuit having a display for providing a perceptible indication in response to said electrical response signal, said sensor having a body and two electrical conductors spaced from each other with a chamber disposed between said two electrical conductors for admitting said fluid material, said chamber providing electrical insulation to inhibit electrical conduction between said two electrical conductors through said fluid material, the method comprising the steps of:

• moving said fluid material through said chamber at a first constant velocity;
• providing an electrical stimulus signal to said two electrical conductors;
• measuring a low-scale electrical response signal at said two electrical conductors to said electrical stimulus signal when said fluid material has said first velocity;
• adjusting said circuit until said display provides a low-scale velocity indication in response to said low-scale electrical response signal;
• moving said fluid material through said chamber at a second constant velocity greater than said first constant velocity;
• providing said electrical stimulus signal to said two electrical conductors;
• measuring a high-scale electrical response signal at said two electrical conductors to said electrical stimulus signal when said fluid material has said second constant velocity;
• and
• adjusting said circuit until said display provides a high-scale velocity indication in response to said high-scale electrical response signal.

A capacitive sensor for testing a material sample, comprising:

• an outer conductor having an elongated shape with a longitudinal axis and first and second ends, and made of an electrically conductive material;
• an inner conductor having an elongated shape with a longitudinal axis and first and second ends, and made of an electrically conductive material;
• a chamber for holding said material sample, said chamber electrically insulated from said inner and outer conductors, said chamber having an elongated 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;
• and
• a sealing member made of an electrically conductive material coupled mechanically and electrically to said outer conductor in selectably openable sealing engagement with said opening.

A capacitive measurement circuit for a capacitive sensor having a capacitance, comprising:

• a test oscillator circuit for producing a test signal having a test frequency in response to said capacitance of said capacitive sensor;
• a reference oscillator circuit for producing a reference signal having a predetermined reference frequency;
• a D-type flip-flop having a clock input and a D input, said clock input receiving one of said test signal and said reference signal, and said D input receiving the other of said test signal and said reference signal;
• and
• a display for displaying a measurement indication in response to an output of said flip-flop.

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, said chamber having a 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;
• and
• a screen made of a conductive material, said screen disposed in said opening and electrically coupled to said outer conductor.