Method for producing capacitive ceramic absolute pressure sensors sorted in zero-point long-term stability defect classes
First Claim
1. A method for producing capacitive alumina-ceramic absolute pressure sensors sorted in high-precision zero-point long-term stability defect classes which comprises the following steps:
- forming a disk-shaped substrate having an annular first electrode near the edge of the substrate and a circular second electrode near the center of the substrate, the first electrode being electrically insulated from the second electrode,forming a diaphragm having a third electrode;
forming an absolute pressure sensor by tightly joining the outer edge of the substrate to the outer edge of the diaphragm using an active brazing ring, a chamber being formed between the substrate and the diaphragm, the first electrode facing the third electrode making a virtually pressure independent reference capacitance, and the second electrode facing the third electrode making a pressure-dependent capacitance;
determining a measured-value span for the absolute pressure sensor;
determining a first zero value for the absolute pressure sensor in a first condition having a first gas at a first temperature and under a near-vacuum pressure using a high-precision capacitance zero-point measuring device having a guaranteed zero-point measuring error;
storing the absolute pressure sensor in a second condition having at least one of a second gas, a second temperature and a second pressure, the second gas having a lower molecular weight than the first gas, the second temperature being greater than normal room temperature, the second pressure being greater than normal atmospheric pressure;
after the storing step, determining a second zero value for the absolute pressure sensor in the first condition using the high-precision capacitance zero-point measuring device;
calculating a pressure sensor ratio by dividing the difference between the first zero value and the second zero value by the measured-value span of the absolute pressure sensor;
calculating a reference ratio by dividing the guaranteed zero-point measuring error of the high-precision capacitance zero-point measuring device by the measured-value span of the absolute pressure sensor;
selecting a minimum value which is greater than the reference ratio;
comparing the pressure sensor ratio to the minimum value; and
classifying the absolute pressure sensor into the high-precision zero-point long-term stability defect classes based on the comparison between the pressure sensor ratio and the minimum value.
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Abstract
In this method for producing capacitive alumina-ceramic absolute pressure sensors sorted in high-precision zero-point long-term stability defect classes referred to a measured-value span csp, the sensors are firstly produced conventionally: a substrate is provided with an annular first electrode and, at the center, a circular second electrode insulated from the first; a diaphragm is provided with a third electrode, and the substrate and diaphragm are joined tightly together in a vacuum by the mutually facing electrodes, at an outer edge through the interposition of an active brazing ring with the formation of a chamber, with the result that a pressure-dependent capacitance Cp and a pressure-independent capacitance Cr are produced. Then, using the equation c=(Cp -Cr)/Cp =k1 (p-p0)+k0, at room temperature and under a vacuum (=p→0) a first zero value cn1 =-k1 p0 +k0 is determined by means of a capacitance zero-point measuring device having the zero-point measuring error Fn. A second zero value cn2 =-k1 p0 '"'"'+k0 is determined for each sensor by means of the same measuring device after the sensors have been stored in a gas during a period t in such a way that the pressure and/or temperature of the gas was raised, or its molecular weight was lowered, with respect to normal atmospheric conditions. Then the difference δcn between the first and second zero values δcn =cn1 -cn2 =-k1 δp0 is formed, and the value δcn /csp is compared with the value Fn /csp. It is also possible to make use analogously of the zero-point temperature coefficient.
31 Citations
8 Claims
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1. A method for producing capacitive alumina-ceramic absolute pressure sensors sorted in high-precision zero-point long-term stability defect classes which comprises the following steps:
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forming a disk-shaped substrate having an annular first electrode near the edge of the substrate and a circular second electrode near the center of the substrate, the first electrode being electrically insulated from the second electrode, forming a diaphragm having a third electrode; forming an absolute pressure sensor by tightly joining the outer edge of the substrate to the outer edge of the diaphragm using an active brazing ring, a chamber being formed between the substrate and the diaphragm, the first electrode facing the third electrode making a virtually pressure independent reference capacitance, and the second electrode facing the third electrode making a pressure-dependent capacitance; determining a measured-value span for the absolute pressure sensor; determining a first zero value for the absolute pressure sensor in a first condition having a first gas at a first temperature and under a near-vacuum pressure using a high-precision capacitance zero-point measuring device having a guaranteed zero-point measuring error; storing the absolute pressure sensor in a second condition having at least one of a second gas, a second temperature and a second pressure, the second gas having a lower molecular weight than the first gas, the second temperature being greater than normal room temperature, the second pressure being greater than normal atmospheric pressure; after the storing step, determining a second zero value for the absolute pressure sensor in the first condition using the high-precision capacitance zero-point measuring device; calculating a pressure sensor ratio by dividing the difference between the first zero value and the second zero value by the measured-value span of the absolute pressure sensor; calculating a reference ratio by dividing the guaranteed zero-point measuring error of the high-precision capacitance zero-point measuring device by the measured-value span of the absolute pressure sensor; selecting a minimum value which is greater than the reference ratio; comparing the pressure sensor ratio to the minimum value; and classifying the absolute pressure sensor into the high-precision zero-point long-term stability defect classes based on the comparison between the pressure sensor ratio and the minimum value. - View Dependent Claims (2, 3, 4)
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5. A method for producing capacitive alumina-ceramic absolute pressure sensors sorted in high-precision zero-point long-term stability defect classes which comprises the following steps:
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forming a disk-shaped substrate having an annular first electrode near the edge of the substrate and a circular second electrode near the center of the substrate, the first electrode being electrically insulated from the second electrode, forming a diaphragm having a third electrode; forming an absolute pressure sensor by tightly joining the outer edge of the substrate to the outer edge of the diaphragm using an active brazing ring, a chamber being formed between the substrate and the diaphragm, the first electrode facing the third electrode making a virtually pressure independent reference capacitance, and the second electrode facing the third electrode making a pressure-dependent capacitance; determining a measured-value span for the absolute pressure sensor; determining a first zero-point temperature coefficient value for the absolute pressure sensor at a first temperature and a second temperature in a first condition having a first gas under a near-vacuum pressure using a high-precision capacitance zero-point temperature coefficient measuring device having a guaranteed temperature coefficient measuring error, the first temperature being different from the second temperature, one of the first temperature and the second temperature being equal to room temperature; storing the absolute pressure sensor in a second condition having at least one of a second gas, a raised temperature and a second pressure, the second gas having a lower molecular weight than the first gas, the raised temperature being greater than normal room temperature, the second pressure being greater than normal atmospheric pressure; after the storing step, determining a second zero-point temperature coefficient value for the absolute pressure sensor at the first temperature and the second temperature in the first condition using the high-precision capacitance zero-point temperature coefficient measuring device; calculating a pressure sensor ratio by dividing the difference between the first zero-point temperature coefficient value and the second zero-point temperature coefficient value by the measured-value span of the absolute pressure sensor; calculating a reference ratio by dividing the guaranteed temperature coefficient measuring error of the high-precision capacitance zero-point temperature coefficient measuring device by the measured-value span of the absolute pressure sensor; selecting a minimum value which is greater than the reference ratio; comparing the pressure sensor ratio to the minimum value; and classifying the absolute pressure sensor into the high-precision zero-point long-term stability defect classes based on the comparison between the pressure sensor ratio and the minimum value. - View Dependent Claims (6, 7, 8)
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