Capacitance manometer having a relatively thick flush diaphragm under tension to provide low hysteresis
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United States of America Patent
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Jan 4, 2005
Grant Date -
Sep 30, 2004
app pub date -
Mar 25, 2003
filing date -
Mar 22, 2003
priority date (Note) -
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Abstract
A capacitance diaphragm gauge (CDG) for measuring pressure includes a flush diaphragm mounted to a body structure via a shim or other raised perimeter portion. The diaphragm and the shim are welded to the body structure while the diaphragm is maintained at an elevated temperature. Contraction of the diaphragm as it cools pretensions the diaphragm to substantially reduce hysteresis effects. An electrode advantageously includes two portions with one portion providing excellent bonding characteristics and the other portion having temperature characteristics corresponding to the body structure and the diaphragm. An alternative CDG includes two identical electrodes with a first electrode positioned proximate to the center of the diaphragm and with a second electrode positioned proximate to the perimeter of the diaphragm. The second electrode provides a second capacitance signal that is used to compensate for changes in capacitance between the diaphragm and the first electrode caused by temperature changes.
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