Envec Mess-und Regeltechnik Gmbh + Co.

Lukas Klausmann

Frank Hegner

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 c.sub.sp, 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 C.sub.p and a pressure-independent capacitance C.sub.r are produced. Then, using the equation c=(C.sub.p -C.sub.r)/C.sub.p =k.sub.1 (p-p.sub.0)+k.sub.0, at room temperature and under a vacuum (=p.fwdarw.0) a first zero value c.sub.n1 =-k.sub.1 p.sub.0 +k.sub.0 is determined by means of a capacitance zero-point measuring device having the zero-point measuring error F.sub.n. A second zero value c.sub.n2 =-k.sub.1 p.sub.0 '+k.sub.0 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 .delta.c.sub.n between the first and second zero values .delta.c.sub.n =c.sub.n1 -c.sub.n2 =-k.sub.1 .delta.p.sub.0 is formed, and the value .delta.c.sub.n /c.sub.sp is compared with the value F.sub.n /c.sub.sp. It is also possible to make use analogously of the zero-point temperature coefficient.

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Lorrach, Germany

Lukas Klausmann