Three-phase excitation circuit for compensated capacitor industrial process control transmitters
AssigneeRosemount Inc.
InventorRongtai Wang
Life of this patent
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Abstract
A capacitor industrial process control transmitter includes a three-phase excitation circuit to charge a sensing capacitor and a compensation capacitor of the transmitter and transfer charges to an integrator. The sensing capacitor is charged during the first phase. During the second phase, the voltage to the sensing capacitor is reversed, and the charge on the sensing capacitor is pumped to the integrator. Also, the compensation capacitor is charged with the reversed voltage during the second phase. During the third phase, the voltage to the compensation capacitor is changed, and the charge on the compensation capacitor is pumped to the integrator.
Claims21
A pressure sensor having first and second capacitors each responsive to pressure and to sensor hysteresis, the sensor comprising:
- a charging circuit having a first charging level having a first polarity, a second charging level having a second polarity opposite the first polarity and third charging level that is intermediate the first and second charging levels;
- a sensing circuit that is a sigma-delta capacitance-to-digital circuit providing a digital output representative of the pressure;
- and
- a switch circuit selectively coupling the first and second capacitors to the charging circuit to charge the first and second capacitors, and selectively coupling the first and second capacitors to the sensing circuit to transfer charge from the first capacitor based on the first and second charging levels and to transfer charge from the second capacitor based on the second and third charging levels.
An industrial process control transmitter comprising:
- a pressure sensor having first and second capacitors each having a capacitance responsive to pressure and to sensor hysteresis;
- a charging circuit having a first charging level having a first polarity, a second charging level having a second polarity opposite the first polarity and third charging level that is intermediate the first and second charging levels;
- a sigma-delta capacitance-to-digital circuit providing a digital output representative of an analog input;
- a switch circuit selectively coupling the first and second capacitors to the charging circuit to charge the first and second capacitors and selectively coupling the first and second capacitors to the capacitance-to-digital circuit to transfer an analog signal from the first capacitor based on the capacitance of the first capacitor and the first charging level and to transfer an analog signal from the second capacitor based on the capacitance of the second capacitor and the second and third charging levels;
- and
- a transmitter output circuit responsive to the digital output to generate a standardized transmitter output adapted for coupling to a remote receiver.
A process of operating a pressure sensor having first and second capacitors each responsive to pressure and to sensor hysteresis, the process comprising steps of:
- (a) charging the first capacitor to a first polarity during a first phase;
- (b) pumping a charge on the first capacitor to a sigma-delta capacitance-to-digital circuit during a second phase that is mutually exclusive from the first phase;
- (c) charging the second capacitor to a second polarity opposite the first polarity during the second phase;
- and
- (d) pumping a charge on the second capacitor to the sigma-delta capacitance-to-digital circuit during a third phase that is mutually exclusive from the first and second phases.
Dependencies are inferred from the claim text.