Circuit for capacitive sensor made of brittle material
First Claim
1. For use in combination with a differential pressure sensor assembly comprising first and second sensor sections each having a separate deflecting diaphragm mounted with respect to a sensor surface and initially substantially contiguous with such surface and capable of deflecting with respect to the surface to form separate internal chambers for each sensor section, means fluidly connecting the internal chambers, a quantity of substantially noncompressible fluid filling said chambers and said means fluidly connecting to bow the diaphragm relative to the respective sensor surface, whereby movement of one diaphragm in direction to reduce the volume of its associated internal chamber results in movement of the other diaphragm in direction to increase the volume of its internal chamber, means on the respective diaphragms and on the respective sensor surfaces for forming first and second sensing capacitors which vary in opposite sense as a function of differential changes in pressures acting on the diaphragms, the improvement comprising means for providing an output signal from such a pressure sensor assembly representing differentials in pressure acting on the diaphragms of the sensor elements of such a pressure sensor assembly including:
- means for sensing the capacitance values of the first and second sensing capacitors of such a sensor; and
means associated with such a sensor assembly for providing a signal F1 representing a change in density of the noncompressible fluid filling the internal chambers of such a pressure sensor assembly, and also coupled to the means for sensing for providing a signal F2 which is a function of the capacitances of the first and second capacitors of such a pressure sensor assembly and thus of the differential pressure on the sensor elements thereof, and which signal F2 is substantially zero when the sensed differential pressure is substantially zero, and for multiplying the signals F1 and F2 to provide the output signal.
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Accused Products
Abstract
Sensor circuitry for sensing changes in capacitance of separate sensor portions wherein in each of the sensor portions a separate plate will deflect in response to changes in parameter, for example changes in pressure, to thereby provide an output that relates to differential pressure. The specific example is in connection with sensor portions which are fluid filled and in fluid communication with each other so that a deflection of a plate on one of the sensor portions causes an opposite deflection of a plate on the other sensor portion. The circuitry provides a stable output regardless of some variation in sensor characteristics. Temperature induced variations in the dielectric constant and density of the fluid filling the sensor portions may all be compensated for in the circuitry. Preferably CMOS logic devices that provide a signal which exhibits a direct relationship to capacitive loading are used. The signal is sensed to modify the voltage applied to the CMOS device to achieve a desired relationship. The voltage or current output from the capacitors indicates the capacitive values of the sensor.
38 Citations
24 Claims
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1. For use in combination with a differential pressure sensor assembly comprising first and second sensor sections each having a separate deflecting diaphragm mounted with respect to a sensor surface and initially substantially contiguous with such surface and capable of deflecting with respect to the surface to form separate internal chambers for each sensor section, means fluidly connecting the internal chambers, a quantity of substantially noncompressible fluid filling said chambers and said means fluidly connecting to bow the diaphragm relative to the respective sensor surface, whereby movement of one diaphragm in direction to reduce the volume of its associated internal chamber results in movement of the other diaphragm in direction to increase the volume of its internal chamber, means on the respective diaphragms and on the respective sensor surfaces for forming first and second sensing capacitors which vary in opposite sense as a function of differential changes in pressures acting on the diaphragms, the improvement comprising means for providing an output signal from such a pressure sensor assembly representing differentials in pressure acting on the diaphragms of the sensor elements of such a pressure sensor assembly including:
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means for sensing the capacitance values of the first and second sensing capacitors of such a sensor; and means associated with such a sensor assembly for providing a signal F1 representing a change in density of the noncompressible fluid filling the internal chambers of such a pressure sensor assembly, and also coupled to the means for sensing for providing a signal F2 which is a function of the capacitances of the first and second capacitors of such a pressure sensor assembly and thus of the differential pressure on the sensor elements thereof, and which signal F2 is substantially zero when the sensed differential pressure is substantially zero, and for multiplying the signals F1 and F2 to provide the output signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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- 14. A measuring circuit for use in combination with a differential pressure sensor assembly comprising first and second sensor sections each having a separate deflecting diaphragm mounted with respect to a sensor surface to initially be substantially contiguous therewith and forming a separate internal chamber for each sensor section, means fluidly connecting the internal chambers and a quantity of substantially noncompressible fluid filling said chambers and said means fluidly connecting to bow the diaphragms away from their respective surface, whereby movement of one diaphragm in direction to reduce the volume of its associated chamber results in movement of the other diaphragm in direction to increase the volume of its chamber, means on the respective diaphragms and on the respective sensor section surfaces for forming first and second sensing capacitors which vary in opposite sense as a function of differences in pressure acting on the diaphragms, said circuit providing an output indicating the differential pressure value, and including excitation means for providing an excitation signal to each of said first and second capacitors of such sensor, means for sensing the capacitance of such first and second capacitors and for adjusting the excitation signal from the excitation means as a function of the capacitance of said first and second capacitors, detection circuit means coupled to the output of such first and second capacitors to provide a variable signal which is a function of the capacitance, zeroing circuit means connected to the excitation means and to the detection circuit means, said zeroing circuit including means for adjusting the voltage output signal to be zero when the first and second diaphragms are sensing equal pressures.
- 21. A circuit for use with a differential pressure sensor having first and second sensing capacitors which include deflecting diaphragms supported by a noncompressible fluid which is common to both diaphragms and wherein the sensing capacitors are at substantially zero setting when the pressure of the noncompressible fluid is zero, at least one of said sensing capacitors varying in response to pressure, said circuit including having means for exciting said sensing capacitors in series, means coupled to the capacitors to provide an output representing the quantity ##EQU38## wherein C1 and C2 represent the capacitance values of the first and second sensing capacitors, respectively, and means for providing a correction signal to the means for exciting the capacitors, said correction signal being a function of the series capacitance of the first and second sensing capacitors.
Specification