Process pressure measurement devices with improved error compensation

A pressure sensor, the pressure sensor comprising:

• a cell body having a concave first interior wall and a concave second interior wall generally opposite the first interior wall, wherein the first and second interior walls each include an edge region and a center region, the edge region surrounding the center region on each interior wall, the first and second interior walls defining an interior cavity;
• a conductive and deflectable diaphragm, the diaphragm coupled to the cell body between the first and second interior walls, the diaphragm separating the interior cavity into a first cavity and a second cavity,
• wherein the first cavity is defined by the first interior wall and the diaphragm, and the second cavity is generally opposite from the first cavity and defined by the second interior wall and the diaphragm, and
• wherein the first and second cavities each include a dielectric fill-fluid adapted to receive a pressure and exert a force on the diaphragm, and the diaphragm is deflectable in response to differences in the pressures received by the fill-fluids in the first and second cavities;
• a first conductive plate attached to the first interior wall generally within the center region, the first conductive plate capacitively coupled to the conductive diaphragm to form a first variable capacitor;
• a second conductive plate attached to the first interior wall generally within the edge region, the second conductive plate spaced-apart from the first conductive plate and capacitively coupled to the conductive diaphragm to form a second variable capacitor;
• a third conductive plate attached to the second interior wall generally within the center region and opposite the first conductive plate, the third conductive plate capacitively coupled to the conductive diaphragm to form a third variable capacitor;
• and
• a fourth conductive plate attached to the second interior wall generally within the edge region, the fourth conductive plate spaced-apart from the third conductive plate, the fourth conductive plate capacitively coupled to the conductive diaphragm to form a fourth variable capacitor.

A pressure sensor, the pressure sensor comprising:

• a cell body having generally opposite concave first and second interior walls at least partially defining an interior cavity;
• a deflectable diaphragm having a conductive portion, the diaphragm attached to the cell body to form a first cavity defined by the first interior wall and the diaphragm, and forming a second cavity defined by the second interior wall and the diaphragm,
• wherein the first and second cavities are each adapted to receive a variable pressure that exerts a force on the diaphragm, and the diaphragm is deflectable in response to differences in the pressures received in the first and second cavities;
• a first electrode coupled to the first interior wall and capacitively coupled to the conductive portion of the diaphragm to form a first variable capacitor;
• a second electrode coupled to the first interior wall and spaced-apart from the first electrode, the second electrode capacitively coupled to the diaphragm to form a second variable capacitor;
• a third electrode coupled to the second interior wall and capacitively coupled to the conductive portion of the diaphragm to form a third variable capacitor.

A process pressure transmitter, comprising:

• a transmitter electronics disposed within a housing, the transmitter electronics including a communications circuit coupled to a processing system;
• an analog to digital converter disposed within the housing, the analog to digital converter electrically coupled to the transmitter electronics;
• a pressure sensor comprising:
• a cell body having a first interior wall and a second interior wall generally opposite the first interior wall, the first and second interior walls defining an interior cavity;
• a deflectable diaphragm having a conductive portion, the diaphragm coupled to the cell body between the first and second interior walls, the diaphragm separating the interior cavity into a first cavity and a second cavity,
• wherein the first cavity is defined by the first interior wall and the diaphragm, and the second cavity is generally opposite the first cavity and defined by the second interior wall and the diaphragm,
• wherein the first and second cavities each contain a dielectric fill-fluid, each of the fill fluids adapted to receive a pressure and exert a corresponding force on the diaphragm, and the diaphragm is deflectable in response to differences in the pressures received by the fill-fluids in the first and second cavities, and
• wherein the first interior wall includes an edge region and a center region, the edge region surrounding the center region;
• a first electrode coupled to the first interior wall generally within the center region, the first electrode capacitively coupled to the conductive portion to form a first variable capacitor;
• a first lead wire electrically connected to the first electrode and extending from the cell body;
• a second electrode coupled to the first interior wall generally within the edge region, the second electrode capacitively coupled to the conductive portion to form a second variable capacitor;
• a second lead wire electrically connected to the second electrode and extending from the cell body;
• a third electrode coupled to the second interior wall generally within the center region of the second interior wall, the third electrode capacitively coupled to the conductive portion of the diaphragm to form a third capacitor;
• a third lead wire electrically coupled to the third electrode and extending from the cell body;
• a fourth electrode coupled to the second interior wall generally within the edge region of the second interior wall, the fourth electrode electrically coupled to the conductive portion to form a fourth capacitor;
• and
• a fourth lead wire electrically coupled to the fourth electrode and extending from the cell body;
• wherein the four lead wires are electrically coupled to the analog to digital converter.

A method of measuring differential pressure, comprising:

• applying a first process pressure to a first amount of fill-fluid on a first side of a deflectable diaphragm;
• applying a second process pressure to a second amount of fill-fluid on a second side of the deflectable diaphragm;
• measuring an amount of deflection of a center region of the diaphragm from a selected position;
• measuring an amount of deflection of an edge region of the diaphragm from the selected position;
• and
• subtracting the amount of deflection at the edge region from the amount of deflection at the center region.

A method of error compensation in measuring differential pressure with a sensor having a conductive and deflectable diaphragm, first and second electrodes on one side of the diaphragm, and third and fourth electrodes on another side of the diaphragm, wherein the four electrodes are each separately coupled to the diaphragm to form four capacitors, the method comprising:

• adding a first capacitance signal related to an electrical signal at the first electrode to a fourth capacitance signal related to an electrical signal at the fourth electrode to obtain a first sum;
• adding a third capacitance signal related to an electrical signal at the third electrode to a second capacitance signal related to an electrical signal at the second electrode to obtain a second sum;
• adding the first sum to the second sum to obtain a denominator;
• subtracting the second sum from the first sum to obtain a numerator;
• and
• dividing the numerator by the denominator.

A method of error compensation in measuring process pressure with a process measurement transmitter having a sensor generating a plurality of electrical signals representative of a first, second, third and fourth capacitance signals, the method comprising:

• subtracting the fourth capacitance signal from the second capacitance signal to obtain a first difference;
• subtracting the third capacitance signal from the first capacitance signal to obtain a second difference;
• subtracting the first difference from the second difference to obtain a numerator;
• and
• dividing the numerator by a denominator, wherein the denominator includes a first sum of the second and fourth capacitance signals subtracted from a second sum of the first and third capacitance signals.

A method of error compensation in measuring differential pressure with a sensor having a conductive and deflectable diaphragm, first and second electrodes on one side of the diaphragm, and a third electrode on another side of the diaphragm, wherein the three electrodes are each separately coupled to the diaphragm to form three capacitors, the method comprising:

• multiplying a first capacitance signal related to a first electrical signal at the first electrode by a third capacitance signal related to a third electrical signal at the third electrode and by a first constant to obtain a first value;
• dividing the first value by a second capacitance signal related to a second electrical signal at the second electrode to obtain a second value;
• subtracting the second value from the third capacitance signal to obtain a fourth value;
• subtracting the fourth value from the first capacitance signal to obtain a numerator;
• and
• dividing the numerator by the sum of the first capacitance signal, third capacitance signal and a second constant.