Capacitive pressure transducer

• US 4,388,668 A
• Filed: 12/03/1979
• Issued: 06/14/1983
• Est. Priority Date: 03/12/1976
• Status: Expired due to Term

• Current Assignee: Kaylico Corporation
• Original Assignee: Kaylico Corporation
• Inventors: Bell, Robert L., Kavli, Fred, Willing, Robert
• Primary Examiner(s): Goldberg, Elliot A.
• Application Number:
  US06/099,600
• Time in Patent Office: 1,289 Days
• Field of Search: 361/283, 73/718, 73/724, 65/43
• US Class Current: 361/283.4
• CPC Class Codes: G01L 9/0075 using a ceramic diaphragm, e.g. alumina, fused quartz, glass
• CPC Class Codes: G01L 9/0086 using variations in capacitance

Abstract

A capacitive pressure transducer comprising a pair of disc shaped members having planar surfaces made from an insulator material, one of the members being several times thinner than the other plate and flexible and constituting a diaphragm and the other thicker plate constituting a stationary plate. A thin conductive film is formed on the surface of each of the members to form the plates of the capacitor. A glass frit is applied on the marginal edge of each member and when the members are held in adjacent relationship, the assembly is fired to seal the two members together while spacing them a predetermined distance apart so that the two conductive plates are opposite each other and are separated by an open gap of a predetermined distance, the two conductive plates being insulated one from the other. Leads are electrically connected to the conductive plate of each disc through the fused glass frit. When pressure is applied to the member, the diaphragm member is displaced thereby changing the capacitance of the pressure transducer.

Claims

1. A pressure sensor for use over a predetermined pressure measurement range in environments subject to periodic high overload pressure comprising:

first and second ceramic insulating members having flat opposed surfaces, one of said members being relatively thin with respect to the other member and being flexible when exposed to pressure;

a thin electrically conductive plate deposited on each of said insulating members flat opposed surfaces facing one another;

means for establishing an open gap between said electrically conductive plates, said open gap ranging between 0.1 and 20 milinches, said means consisting of fused glass frit positioned around the marginal edge portion between said two members, said fused glass frit also hermetically sealing the space between said members to form a chamber;

said frit and insulative members being substantially similar materials from the standpoint of coefficient of thermal expansion; and

means including said members and said fused glass frit for permitting said electrically conductive plates to deflect toward one another without touching throughout said predetermined measurement range while allowing said plates to engage one another and bottom out under high overload pressure conditions, so that said pressure sensor is protected against impairment.

2. A pressure sensor as defined in claim 1 wherein the other said member is rigid.

3. A pressure sensor assembly as defined in claim 2 further comprising an electronic circuit mounted on the outside surface of the thicker member.

4. A pressure sensor assembly as defined in claim 1 wherein said plates are both made of alumina of about 96% purity.

5. A pressure sensor as defined in claim 1 wherein said conductive plates are gold and are screened and fired on said members.

6. A capacitive transducer for the accurate and economical measurement of pressure or the like, comprising a pair of essentially zero hysteresis nonconductive electrically insulative members, at least one of said electrically insulative members comprising an elastic diaphragm defining a substantially planar inner surface and having a substantially continuous solid cross-section, the other of said electrically insulative members defining a substantially planar inner surface and having a substantially continuous solid cross-section, said electrically insulative members being disposed in vertically aligned, stacked relationship with the marginal edge portion of said elastic diaphragm in overlying relationship with the other insulative member, and with said inner surfaces in spaced apart substantially parallel relationship to define a gap, seal means comprising a fired glass frit having a thickness ranging from about 0.1 millinch to 20 millinches bonding said overlying edge portions together in sealed relationship having a predetermined spacing and fixing said electrically insulative members in a parallel relationship, said frit and insulative members being of substantially similar materials from the standpoint of coefficient of thermal expansion, a planar layer of conductive material secured on each of said inner surfaces, each of said layers of conductive material comprising an extended conductive portion and a conductive path portion extending from said extended portion for connection to external electrical circuitry, said extended conductive portions on said inner surfaces being disposed in spaced apart parallel relationship to form a capacitor having a capacitance which varies according to the flexing of said elastic diaphragm toward the other member in response to pressure, with the gap being dimensioned between 0.1 millinch to 20 millinches.

7. A capacitive transducer as defined in claim 6 wherein said electrically insulative members are both made of ceramic material.

8. A capacitive transducer as defined in claim 6 wherein said electrically insulative members are both made of alumina.

9. A capacitive transducer as defined in claim 6 wherein said two electrically insulative members are both discs of ceramic of substantially the same diameters, both having flat and substantially parallel top and bottom surfaces.

10. A capacitive transducer as defined in claim 6 wherein said transducer includes means for permitting said diaphragm to bottom out when a pressure or force in excess of a predetermined pressure is applied to the transducer so as to avoid damaging stress on the transducer.

11. A capacitive transducer as defined in claim 6 wherein conductive means for connecting said conductive layers to external circuitry are provided to extend at least part way through said fired glass frit, whereby said glass frit seals around said conductive connecting means and avoids leakage.

12. A capacitive transducer as defined in claim 6 wherein said other electrically insulative member is substantially thicker than said elastic diaphragm.

13. A capacitive transducer as defined in claim 12 wherein printed circuit means are mounted on said other, thicker electrically insulative member, and wherein electrically conductive means extending at least part way through said glass frit electrically connect said circuit means to said conductive layers.

14. A capacitive transducer as defined in claim 6 wherein said electrically insulative members are both made of glass.

15. A capacitive transducer as defined in claim 6 wherein both of said members are relatively thin diaphragm members.

16. A capacitive transducer as defined in claim 6 wherein said fired glass frit extends for a substantial distance parallel to said members and perpendicular to the edges of said members and bonds and seals said members together in spaced apart relationship with one-another over this substantial distance around the periphery of each of said members.

17. A capacitive transducer as defined in claim 6 wherein spacer means are embedded within said glass frit around the periphery of said members, and wherein said spacer means is formed of particles of higher temperature glass.

20. A capacitive transducer as defined in claim 14 wherein said electrically insulative members are both made of ceramic material.

21. A capacitive transducer as defined in claim 14 wherein said electrically insulative members are both made of alumina.

18. A capacitive transducer for the accurate and economical measurement of pressure or the like, comprising:

a pair of essentially zero hysteresis nonconductive electrically insulative members, at least one of said electrically insulative members comprising an elastic diaphragm defining a substantially planar inner surface and having a substantially continuous solid cross-section, the other of said electrically insulative members defining a substantially planar inner surface and having a substantially continuous solid cross-section, said electrically insulative members being disposed in vertically aligned, stacked relationship with the marginal edge portion of said elastic diaphragm in overlying relationship with the other insulative member, and with said inner surfaces in spaced apart substantially parallel relationship to define a gap;

a planar layer of conductive material bonded onto each of said inner surfaces, each of said layers of conductive material comprising a broad area conductive portion and an integral continuous conductive path portion extending outwardly from said extended portion for connection to external electrical circuitry;

seal means comprising a fired glass frit having a thickness ranging from about 0.1 millinch to 20 millinches bonding said overlying edge portions together in sealed relationship having a predetermined spacing and fixing said electrically insulative members in a parallel relationship, said frit and insulative members being of substantially similar materials from the standpoint of coefficient of thermal expansion, and said fired glass frit sealing over said outwardly extending conductive path portions, whereby external connections may be made to said conductive path portions outside of the central area enclosed by said glass frit; and

said broad area conductive portions on said inner surfaces being disposed in spaced apart parallel relationship to form a capacitor having a capacitance which varies according to the flexing of said elastic diaphragm toward the other member in response to pressure, with the gap being dimensioned between 0.1 millinch to 20 millinches.

19. A capacitive transducer for the accurate and economical measurement of pressure or the like, comprising;

a pair of essentially zero hysteresis nonconductive electrically insulative members, at least one of said electrically insulative members comprising an elastic diaphragm defining a substantially planar inner surface and having a substantially continuous solid cross-section, said electrically insulative members being disposed in overlying relationship with one another, and with said inner surfaces in spaced apart substantially parallel relationship to define a gap;

a planar layer of conductive material bonded onto each of said inner surfaces, each of said layers of conductive material comprising a broad area conductive portion and a conductive path portion extending outwardly from said extended portion for connection to external electrical circuitry;

seal means comprising a fired glass frit having a thickness ranging from about 0.1 millinch to 20 millinches bonding said two insulating members together around the outer periphery of said broad area conductive portions, with said electrically insulating members having a predetermined spacing and being fixed in a parallel relationship, said frit and insulative members being of substantially similar materials from the standpoint of coefficient of thermal expansion, and said fired glass frit sealing over said outwardly extending conductive path portions, whereby external connections may be made to said conductive path portions outside of the central area enclosed by said glass frit; and

said broad area conductive portions on said inner surfaces being disposed in spaced apart parallel relationship to form a capacitor having a capacitance which varies according to the flexing of said elastic diaphragm toward the other member in response to pressure, with the gap being dimensioned between 0.1 millinch to 20 millinches.

22. A capacitive transducer as defined in claim 19 wherein said two electrically insulative members are both discs of ceramic of substantially the same diameters, both having flat and substantially parallel top and bottom surfaces.

23. An accurate and inexpensive transducer for use over a predetermined pressure or force measurement range in environments subject to periodic high overload pressures or forces comprising:

first and second insulating plates having flat opposed surfaces, at least one of said plates being relatively thin, and both of said plates having substantially flat parallel surfaces on both sides;

thin conductive layers formed on said insulating plates members and facing one another;

means for hermetically sealing the space between said insulating plates and for mechanically bonding said plates together in spaced apart substantially parallel relationship with a gap between said conductive layers of between 0.1 thousandth and 20 thousandths of an inch, said means for sealing and bonding including a layer of fused glass frit between said plates and extending around the periphery of said thin conductive layers; and

said frit and insulating plates being substantially similar materials from the standpoint of coefficient of thermal expansion; and

whereby inexpensive stock material which is flat on both sides, may be employed to produce a rugged high precision pressure transducer which can withstand repeated flexing and overload without impairment or loss of the hermetic seal.

26. An accurate, inexpensive and rugged pressure transducer as defined in claim 23, 24 or 25 wherein said plates are formed of insulating material having substantially zero hysteresis selected from alumina, fused silica or glass.

24. An accurate and inexpensive transducer for use over a predetermined pressure or force measurement range in environments subject to periodic high overload pressures or forces comprising:

first and second insulating plates having flat opposed surfaces, at least one of said plates being relatively thin, and both of said plates having substantially flat parallel surfaces on both sides;

thin conductive layers formed on said insulating plates members and facing one another;

means for hermetically sealing the space between said insulating plates and for mechanically bonding said plates together in spaced apart substantially parallel relationship with a gap between said conductive layers of between 0.1 thousandth and 20 thousandths of an inch, said means for sealing and bonding including a layer of fused glass frit between said plates and extending around the periphery of said thin conductive layers;

said frit and insulating plates being substantially similar materials from the standpoint of coefficient of thermal expansion; and

said space between said plates being substantially evacuated;

whereby inexpensive stock material which is flat on both sides may be employed to produce a rugged high precision pressure transducer which can withstand repeated flexing and overload without impairment or less of the hermetic seal.

25. An accurate, inexpensive and reliable transducer for use over a predetermined pressure or force measurement range in environments subject to periodic high overload pressures of forces comprising:

first and second insulating plates having flat opposed surfaces, at least one of said plates being relatively thin, and both of said plates having substantially flat parallel surfaces on both sides;

thin conductive layers formed on said insulating plates members and facing one another;

means for hermetically sealing the space between said insulating plates and for mechanically bonding said plates together in spaced apart substantially parallel relationship with a gap between said conductive layers of between 0.1 thousandth and 20 thousandths of an inch, said means for sealing and bonding including a layer of fused glass frit between said plates and extending around the periphery of said thin conductive layers;

said frit and insulating plates being substantially similar materials from the standpoint of coefficient of thermal expansion;

said space between said plates being evacuated; and

means for making external connections to said transducer including extensions from said thin conductive layers extending at least part way through said fused glass frit;

whereby inexpensive stock material which is flat on both sides, may be employed to produce a rugged high precision pressure transducer which can withstand repeated flexing and overload without impairment or loss of the hermetic seal.

27. An accurate and inexpensive transducer for use over a predetermined pressure or force measurement range in environments subject to periodic high overload pressures or forces comprising:

first and second ceramic insulating plates having flat opposed surfaces, at least one of said plates being relatively thin, said plates both being cylindrical disks having substantially flat parallel surfaces on both sides;

thin conductive layers formed on said insulating plates members and facing one another;

means for hermetically sealing the space between said insulating plates and for mechanically bonding said plates together at the outer edge of at least one of said plates in spaced apart substantially parallel relationship with a gap between said conductive layers of between 0.1 thousandth and 20 thousandths of an inch, said means for sealing and bonding including a layer of fused glass frit between said plates and extending around the periphery of at least one of said plates;

a pair of generally circular sealing gaskets mounted at the upper and lower peripheral edges of the transducer; and

a metal housing enclosing said transducer and engaging said sealing gaskets, said housing having a circular opening facing one of said plates through which a part of one of said sealing gaskets extends.

28. A capacitive transducer as defined in claim 27 wherein conductive means for connecting said conductive layers to external circuitry are provided to extend at least part way through said fused glass frit, whereby said glass frit seals around said conductive connecting means and avoids leakage.

29. A capacitive transducer as defined in claim 27 wherein the other insulating plate is substantially thicker than said one plate.

30. A capacitive transducer as defined in claim 29 wherein printed circuit means are mounted on said other, thicker insulating plate, and wherein electrically conductive means extending at least part way through said glass frit electrically connect said circuit means to said conductive layers.

31. A capacitive transducer as defined in claim 27 wherein said electrically insulating plates are both made of alumina.

32. A pressure sensor according to claim 29 including an evacuation bore through the thicker of said ceramic insulating plates.

33. A pressure sensor according to claim 27 wherein each of said electrically conductive layers has a thickness ranging from 1500 to 2500 angstroms.

34. A pressure sensor according to claim 27 wherein said first and second ceramic insulating plates are discs having flat opposed surfaces, and the thin conductive layers formed on said insulating plates and facing one another are formed in a plurality of concentric sections comprising an inner central section and an outer section separated from each other by a nonconductive space.

35. A pressure sensor assembly as defined in claim 27 further comprising an electronic circuit mounted on the outside surface of the thicker plate.

36. A capacitive transducer as defined in claim 27 wherein both of said insulating plates are relatively thin diaphragm members.

37. A capacitive transducer as defined in claim 27 wherein spacer means are embedded within said fused glass frit around the periphery of said members, and wherein said spacer means is formed of particles of higher temperature glass.

38. A capacitive transducer as defined in claim 27 wherein said transducer includes means for permitting said plates to bottom out when a pressure or force in excess of a predetermined pressure is applied to the transducer so as to avoid damaging stress on the transducer.