Capacitive pressure transducer with cut out conductive plate

• US 4,207,604 A
• Filed: 04/20/1978
• Issued: 06/10/1980
• Est. Priority Date: 12/02/1976
• Status: Expired due to Term

• Current Assignee: Kavlico Corporation (Sensata Technologies Holding Plc)
• Original Assignee: Kavlico Corporation (Sensata Technologies Holding Plc)
• Inventors: Bell, Robert L.
• Primary Examiner(s): Goldberg, E. A.
• Application Number:
  US05/898,518
• Time in Patent Office: 782 Days
• Field of Search: 361/278, 361/283, 361/280, 73/724
• 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 cnductive 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 continuous pressure measurement range in environments subject to periodic high overload pressure comprising:

first and second ceramic insulating members having flat opposed parallel 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 parallel surfaces facing one another, one of said plates defining a plurality of spaced apart non conductive cutout areas;

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; 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 bottom out under high overload pressure conditions, so that said pressure sensor is protected against mechanical impairment and means including a cut-away central portion of the plate deposited on the thicker of said members for preventing electrical engagement of said two plates when said plates bottom out under high overload pressure conditions.

2. A pressure sensor comprising:

first and second ceramic insulating disc-shaped members having flat opposed surfaces, one of said members being relatively thick in comparison with the other of said members;

thin electrically conductive plates ranging from 1500 to 2500 angstroms in thickness formed on each of said insulating members and facing one another in a parallel relationship, said plates being formed in a plurality of concentric sections comprising an inner central section and an outer section separated from each other by a non-conductive area, the inner central section of said thicker insulating member defining a central non-conductive cut-out portion and a plurality of symmetrical non-conductive cut-out portions spaced away from said central portion; and

glass frit means positioned on the outer margins of at least one of said members for establishing an open gap between said thin conductive plates, of between 0.001 and 0.002 inches while sealing said gap area to form a chamber.

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

first and second ceramic essentially zero hysteresis insulating members having flat opposed surfaces, one of said members having a thickness less than the other member and being flexible when acted upon by a pressure;

an electrically conductive circular plate formed on each of said insulating members, said plates facing one another in a spaced-apart parallel relationship, said plate on the thicker of said insulating members defining a plurality of arcuate non-conductive cutout areas in said plate and also defining a central circular nonconductive cutout area in said plate;

a conductive guard plate surrounding said plate on said thicker member, said guard plate being spaced apart from said conductive plate by a concentric nonconductive area;

means for establishing an open gap between said flat conductive plates, of between 0.00145 to 0.00165 inches, said means comprising fused glass frit between said two members, said fused glass frit also hermetically sealing the space between said member to form a chamber containing said plates; and

means including said members and said fused glass frit for permitting said plates to deflect toward one another without touching throughout said predetermined measurement range and to permit said plates to bottom out under high overload pressure conditions, so that said transducer is protected against electrical and mechanical impairment.

4. A capacitive pressure transducer comprising, in combination, a pair of planar surfaced essentially zero hysteresis nonconductive electrically insulative members, one of said electrically insulative members comprising a flexible diaphragm, the other of said electrically insulative members comprising a rigid member, said electrically insulative members being disposed in vertically aligned, stacked relationship with marginal edge portions in overlying relationship and with said inner surfaces in spaced apart parallel relationship to define a gap, seal means comprising a fused glass frit having a thickness ranging from 0.001 to 0.002 inches bonding and spacing said overlying edge portions together in sealed relationship to form a sealed chamber, a planar layer of electrically conductive material secured on each of said inner surfaces, each of said layers of conductive material comprising a central circular conductive portion and a co-planar conductive path portion extending from said central portion through said seal means and to the marginal periphery of said insulative members for connection to external leads, the central conductive portion of said conductive material on the inner surface of said rigid member defining a plurality of symmetrical cutout nonconductive areas, said central conductive portions on said inner surfaces being disposed in vertically aligned spaced apart parallel relationship to form a capacitor having a capacitance which varies according to the flexing of said elastic diaphragm in response to pressure, with the gap and diaphragm being constructed to enable said diaphragm to bottom out when a pressure in excess of a predetermined pressure is applied to the transducer.