Pressure sensor

• US 5,517,073 A
• Filed: 07/19/1994
• Issued: 05/14/1996
• Est. Priority Date: 03/19/1992
• Status: Expired due to Fees

• Current Assignee: Unisia Jecs Corporation (Hitachi, Ltd.)
• Original Assignee: Unisia Jecs Corporation (Hitachi, Ltd.)
• Inventors: Ohkuma, Shigeo
• Primary Examiner(s): Budd, Mark O.
• Application Number:
  US08/277,026
• Time in Patent Office: 665 Days
• Field of Search: 310/315, 310/338
• US Class Current: 310/315
• CPC Class Codes: G01D 3/036 on measuring arrangements themselves
• CPC Class Codes: G01D 5/24 by varying capacitance
• CPC Class Codes: G01L 23/10 by pressure-sensitive members of the piezoelectric type
• CPC Class Codes: G01L 9/008 using piezoelectric devices piezoelectric resonators G01L9/0022; surface acoustic waves G01L9/0025
• CPC Class Codes: G01L 9/085 with temperature compensating means non electric temperature compensating means G01L19/04

Abstract

A pressure sensor comprises a movable structure which is movable in accordance with a pressure applied thereto. A piezoelectric transducer is employed against which a pressure is applied when the movable structure is moved. The transducer has opposed electrodes between which a voltage is generated when the transducer is pressed. The capacitance between the opposed electrodes increases with increase of temperature. A dielectric member is arranged in the vicinity of the piezoelectric transducer. The dielectric member has opposed electrodes the capacitance between which decreases with increase of temperature. The piezoelectric transducer and the dielectric member are electrically connected in series.

Claims

1. A pressure sensor for detecting pressure in a high temperature environment, comprising:

a cylindrical casing having a diaphragm portion, said diaphragm portion including a cylindrical portion and a closed end integrally connected to one axial end of said cylindrical portion, said cylindrical portion having a thin wall such that said cylindrical portion axially expands and contracts together with said closed end upon being exposed to an external pressure;

a transmission rod received in said cylindrical casing, said transmission rod being engaged at one end with said closed end so that said transmission rod is axially moved upon expansion and contraction of said cylindrical portion of the diaphragm portion;

a stopper fixed in said cylindrical casing in such a manner as to define a given clearance between the stopper and the other end of said transmission rod;

a piezoelectric plate member having opposed electrodes;

a dielectric plate member having opposed electrodes, the capacitance characteristic of said dielectric plate member relative to a temperature being opposite to that of said piezoelectric plate member, said dielectric plate member being directly placed on said piezoelectric plate member in such a manner that one of the electrodes of said dielectric plate member is mated with one of the electrodes of said piezoelectric plate member;

said piezoelectric plate member and said dielectric plate member forming a unit, said unit being located in said given clearance in such a manner that when, due to the axial movement of the cylindrical portion of the diaphragm portion, said transmission rod is moved toward and away from said stopper, said unit is compressed and relaxed in a direction along which said piezoelectric plate member and said dielectric plate member are aligned; and

means for establishing both a first electrical connection between the other electrode of said piezoelectric plate member and an external electric device and a second electrical connection between the other electrode of said dielectric plate member and said external electric device.

2. A pressure sensor as claimed in claim 1, wherein said piezoelectric plate member and said dielectric plate member are annular in shape.

3. A pressure sensor as claimed in claim 1, wherein said piezoelectric plate member is constructed of lead titanate.

4. A pressure sensor as claimed in claim 3, wherein said dielectric plate member is constructed of strontium titanate.

5. A pressure sensor as claimed in claim 1, wherein a voltage is established between said first electrical connection and said second electrical connection, said voltage being substantially proportional to the axial movement of said transmission rod.

6. A pressure sensor as claimed in claim 5, wherein the proportional relationship between said voltage and said axial movement of said transmission rod is substantially constant for all operational temperatures.

7. A pressure sensor as claimed in claim 1, further comprising tightening means for assuring a tight mechanical connection between said piezoelectric plate member and said dielectric plate member.

8. A pressure sensor as claimed in claim 7, wherein said tightening means comprises:

a lower plate constructed of electrically and thermally insulated material, said lower plate being put on the other end of said transmission rod;

a contact plate constructed of conductive material, said contact plate being put on said lower plate and supporting said piezoelectric plate member and said dielectric plate member; and

an upper plate constructed of conductive material, said upper plate being tightly sandwiched between said dielectric plate member and said stopper, said stopper being constructed of a metal.

9. A pressure sensor as claimed in claim 8, wherein said contact plate, said piezoelectric plate member, said dielectric plate member, said upper plate and said stopper are substantially annular in shape.

10. A pressure sensor as claimed in claim 9, wherein said contact plate is integrally formed with a rod portion, said rod portion extending in a direction away from said transmission rod through aligned openings respectively formed in said piezoelectric plate member, said dielectric plate member, said upper plate and said stopper.

11. A pressure sensor as claimed in claim 10, wherein said rod portion has an insulating tube disposed thereabout.

12. A pressure sensor as claimed in claim 11, wherein said rod portion has an upper part connected to a lead cable.

13. A pressure sensor as claimed in claim 1, wherein said stopper is a cylindrical screw operatively engaged with an internal thread formed on an inner cylindrical surface of said cylindrical casing.

14. A pressure sensor as claimed in claim 1, wherein said closed end of the cylindrical portion of said diaphragm portion has a thickness greater than that of the wall of said cylindrical portion.

15. A pressure sensor as claimed in claim 1, wherein said closed end of the cylindrical portion of said diaphragm portion has a thickness smaller than that of the wall of said cylindrical portion.

16. A pressure sensor as claimed in claim 1, wherein said cylindrical casing has an upper end closed by an upper cover.

17. A sensor operating in a high temperature environment, comprising:

a piezoelectric plate member having opposed electrodes;

a dielectric plate member having opposed electrodes, a capacitance characteristic of said dielectric plate member relative to a temperature being opposite to a capacitance characteristic of said piezoelectric plate member, said dielectric plate member being directly placed on said piezoelectric plate member in such a manner that one of the opposed electrodes of said dielectric plate member is mated with one of the opposed electrodes of said piezoelectric plate member, said piezoelectric plate member and said dielectric plate member forming a unit; and

means for establishing both a first electrical connection between the other of the opposed electrodes of said piezoelectric plate member and an external electric device and a second electrical connection between the other of the opposed electrodes of said dielectric plate member and said external electric device.

18. A sensor as claimed in claim 17, wherein said piezoelectric plate member and said dielectric plate member are annular in shape.

19. A sensor as claimed in claim 17, wherein a voltage is established between said first electrical connection and said second electrical connection, said voltage being substantially proportional to a phenomenon being sensed by the sensor, wherein the proportional relationship between said voltage and said sensed phenomenon is substantially constant for all operational temperatures.

20. A sensor as claimed in claim 17, wherein the sensor is a pressure sensor, and when the unit is compressed in response to a pressure a voltage between said first electrical connection and said second electrical connection is produced, said voltage being substantially proportional to said pressure for all operational temperatures.

21. A sensor as claimed in claim 18, wherein the sensor is a pressure sensor, and when the unit is compressed in response to a pressure a voltage between said first electrical connection and said second electrical connection is produced, said voltage being substantially proportional to said pressure for all operational temperatures.