Pressure sensor with improved capacitive pressure transducer

• US 4,774,626 A
• Filed: 09/16/1987
• Issued: 09/27/1988
• Est. Priority Date: 05/05/1986
• Status: Expired due to Term

• Current Assignee: Sensata Technologies Incorporated (Sensata Technologies Holding Plc)
• Original Assignee: Texas Instruments, Inc.
• Inventors: Kawate, Keith W., Charboneau, Thomas J.
• Primary Examiner(s): Griffin, Donald A.
• Application Number:
  US07/097,002
• Time in Patent Office: 377 Days
• Field of Search: 361/283, 73/718, 73/724
• US Class Current: 361/283.4
• CPC Class Codes: G01L 9/0072 using variations in capacitance
• CPC Class Codes: G01L 9/0075 using a ceramic diaphragm, e.g. alumina, fused quartz, glass

Abstract

A pressure sensor comprises an improved capacitive pressure transducer having a first capacitor plate secured to a limited portion of a first surface of a relatively rigid ceramic substrate and having a diaphragm with an electrically conductive surface forming a second capacitor plate, the diaphragm being secured to the ceramic substrate at a location spaced inwardly from the periphery of that first substrate for disposing the second capacitor plate in spaced, overlying relation to the first capacitor plate to be movable in response to applied pressure for varying the capacitor formed by the plates. Support means bear against opposite surfaces of the ceramic substrate at the periphery of the substrate for mounting the transducer with the diaphragm thereof substantially free of mounting stresses to be exposed to a pressure force in a pressure zone to be monitored.

Claims

1. A pressure sensor comprising a capacitive pressure transducer having a ceramic substrate, a first electrically conductive capacitor plate secured to one surface of the substrate, a flexible ceramic sheet forming a diaphragm, a second electrically conductive capacitor plate secured to one surface of the flexible ceramic sheet, a mixture of a glass frit fusible at one temperature and of a plurality of elements with portions of a selected diameter of a material which retains its shape at said one temperature disposed between portions of said one surface of the ceramic substrate and the flexible ceramic sheet member for disposing the first and second capacitor plates in precisely spaced relation to each other as determined by the diameter of said element portions to form a capacitor, the glass frit being fused at said one temperature for securing the first and second capacitor plates in said precisely spaced relation to permit the second capacitor plate to be movable in response to application of pressure to an opposite surface of the flexible ceramic sheet for varying the capacitance of the capacitor in response to changes in pressures applied to the flexible ceramic sheet, and connector means for electrically connecting the first and second capacitor plates in an electrical circuit;

support means attached to the transducer forming a chamber between the support means and transducer for mounting the transducer to be exposed to a pressure in a zone to be monitored; and

electrical circuit means disposed in the chamber and electrically connected to said connector means for providing an electrical signal corresponding to said pressure changes;

the support means comprising housing means having an opening therein for exposing the flexible ceramic sheet of the transducer to said fluid pressure and seal means between the transducer and housing means sealing the electrical circuit means within the chamber from said fluid pressure.

2. A pressure sensor according to claim 1 further characterized in that said sealing means comprise a pliable film of organic material disposed in overlying relation to said flexible ceramic sheet of the transducer, and an O-ring gasket clamped between the housing means and a portion of the film overlying the flexible ceramic sheet in sealing relation to the transducer.

3. A pressure sensor according to claim 1 wherein said electrical circuit means includes means mounted in the chamber for calibrating the sensor.

4. A pressure sensor according to claim 3 wherein said electrical circuit means include discrete capacitor means and integrated circuit means forming hybrid circuit means in said chamber.

5. A pressure sensor according to claim 3 wherein said housing means has an opening therein permitting access to said electrical circuit means in said chamber for permitting calibration of the sensor.

6. A pressure sensor according to claim 1 wherein a metal guard ring is provided on said one surface of the ceramic substrate in surrounding relation to said first capacitor plate, and connector means connect said guard ring to said electrical circuit means to be held at substantially the same potential as the first capacitor plate.