Linear capacitive sensor system

• US 4,386,312 A
• Filed: 04/24/1981
• Issued: 05/31/1983
• Est. Priority Date: 04/24/1981
• Status: Expired due to Term

• Current Assignee: Setra Systems Incorporated (Fortive Corp.)
• Original Assignee: Setra Systems Incorporated (Fortive Corp.)
• Inventors: Briefer, Dennis K.
• Primary Examiner(s): Krawczewicz, Stanley T.
• Application Number:
  US06/256,994
• Time in Patent Office: 767 Days
• Field of Search: 324/60 C, 324/60 R, 324/61 R, 324/162, 73/718, 361/283, 361/290, 361/291
• US Class Current: 324/661
• CPC Class Codes: G01D 5/2417 by varying separation
• CPC Class Codes: G01L 9/12 by making use of variations in capacitance , i.e. electric circuits therefor
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24

Abstract

A capacitive sensor system including a sensor with two fixed plate elements having opposed planar, electrically conductive surfaces serving as electrodes. The sensor further includes a movable, electrically conductive diaphragm positioned between the electrodes. At least one diode detector network is coupled across the electrodes. The diode detector networks each include a pair of oppositely directed series connected diodes with the junction between the diodes of each network being coupled to the diaphragm. In embodiments having only one diode detector network, the junction between the two diodes may be directly or capacitively coupled to the diaphragm. In embodiments having two such diode detector networks, the diodes of the second network are oppositely directed with respect to the corresponding diodes in the first network, and the junction between the diodes in the second network are capacitively coupled to the diaphragm while the junction between the diodes in the first diode network may be either directly or capacitively coupled to the diaphragm. The system further includes a coupler for coupling a constant amplitude a.c. signal across the electrodes of the sensor. The net d.c. voltage across the diodes of the diode detector networks is representative of the position of the diaphragm between the two sensor electrodes.

Claims

1. A capacitive sensor system comprising:

A. a capacitive sensor including first and second plate elements and means for coupling said first and second plate elements to first and second terminals, respectively, said plate elements having opposed, electrically conductive surfaces, said opposed surfaces being substantially parallel and spaced apart by a predetermined fixed distance, and including an electrically conductive diaphragm member positioned substantially parallel to and between said opposed surfaces, said diaphragm member being movable in the direction perpendicular to the plane of said opposed surfaces,

B. at least one diode detector network coupled across said first and second terminals, each of said diode detector networks including a pair of oppositely directed series connected diodes and means for coupling said series connected pair of diodes across said first and second terminals, and means for resistively shunting each of said diodes in said diode networks, and further including means for noninductively coupling the junction between said diodes to said diaphragm member, and

C. means for coupling a substantially constant amplitude a.c. signal across said first and second terminals,

whereby the net d.c. voltage across the diodes of said diode detector networks is representative of the position of said diaphragm with respect to said plate elements.

2. A system according to claim 1 wherein said second terminal is capacitively coupled to a ground reference potential, and

wherein said diode coupling means for one of said diode detector networks includes means for directly connecting said network across said first and second terminals, and

wherein said a.c. signal coupling means includes means for coupling a ground-referenced a.c. signal with a zero volt average value to said first terminal,

whereby the d.c. portion of the voltage at said second terminal corresponds to said net d.c. voltage.

3. A system according to claim 2 wherein said plate element coupling means directly couples said plate elements to the respective one of said first and second terminals.

4. A system according to claim 2 wherein said plate element coupling means capacitively couples said plate elements to the respective ones of said first and second terminals.

5. A system according to claim 1 wherein said second terminal is directly coupled to a ground reference potential, and

wherein said diode coupling means for a first of said diode detector networks includes means for directly connecting said first network across said first and second terminals, and

wherein said a.c. signal coupling means includes means for capacitive coupling said a.c. signal to said first terminal,

whereby the d.c. portion of the voltage at said first terminal corresponds to said net d.c. voltage.

6. A system according to claim 5 wherein said plate element coupling means directly couples said plate elements to the respective one of said first and second terminals.

7. A system according to claim 5 wherein said plate element coupling means capacitively couples said plate elements to the respective ones of said first and second terminals.

8. A system according to claim 1 wherein said second terminal is directly coupled to a ground reference potential, and

wherein said diode coupling means for a first of said diode detector networks includes means for directly connecting said first network to said first terminal and for capacitively coupling said first network to said second terminal, and

wherein said a.c. signal coupling means includes means for capacitively coupling said a.c. signal to said first terminal,

whereby the d.c. portion of the potential difference between said first terminal and the diode coupled to said second terminal corresponds to said net d.c. voltage.

9. A system according to claim 8 wherein said plate element coupling means directly couples said plate elements to the respective one of said first and second terminals.

10. A system according to claim 8 wherein said plate element coupling means capacitively couples said plate elements to the respective ones of said first and second terminals.

11. A system according to claims 3 or 4 or 6 or 7 or 9 or 10 wherein the junction between the diodes of the first of said first diode detector network is capacitively coupled to said diaphragm.

12. A system according to claims 3 or 4 or 6 or 7 or 9 or 10 wherein the junction between the diodes of the first of said first diode detector network is directly coupled to said diaphragm.

13. A system according to claim 1 wherein said second terminal is directly coupled to a ground reference potential, and

wherein said diode coupling means for a first of said diode detector networks includes means for directly coupling said first network across said first and second terminals,

wherein said diode coupling means for a second of said diode detector networks includes means for directly coupling said second network to said first terminal and for capacitively coupling said second network to said second terminal,

wherein said a.c. signal coupling means includes means for capacitively coupling said a.c. signal to said first reference terminal,

whereby the d.c. portion of the voltage at the diode of said second network coupled to said second terminal corresponds to said net d.c. voltage.

14. A system according to claim 13 wherein the junction between the diodes of said first network is directly coupled to said diaphragm, and the junction between the diodes of said second network is capacitively coupled to said diaphragm.

15. A system according to claim 13 wherein the junction between the diodes of said first network is capacitively coupled to said diaphragm, and the junction between the diodes of said second network is capacitively coupled to said diaphragm.

16. A system according to claim 1 wherein said second terminal is capacitively coupled to a ground reference potential,

wherein said diode coupling means for a first of said diode detector networks includes means for directly coupling said first network across said first and second terminals, and

wherein said diode coupling means for a second of said diode detector networks includes means for capacitively coupling said second network to said first terminal and for directly coupling said second network to said second terminal, and

wherein said a.c. signal coupling means includes means for capacitively coupling said a.c. signal to said first reference terminal,

whereby the d.c. portion of the voltage at the diode of said second network coupled to said first terminal corresponds to said net d.c. voltage.

17. A system according to claim 16 wherein the junction between the diodes of said first network is directly coupled to said diaphragm, and the junction between the diodes of said second network is capacitively coupled to said diaphragm.

18. A system according to claim 16 wherein the junction between the diodes of said first network is capacitively coupled to said diaphragm, and the junction between the diodes of said second network is capacitively coupled to said diaphragm.

19. A system according to claim 1 wherein said second terminal is directly coupled to a ground reference potential,

wherein said diode coupling means for a first of said diode detector networks includes means for directly coupling said first network to said first terminal and means for capacitively coupling said first network to said second terminal, and

wherein said diode coupling means for a second of said diode detector networks includes means for directly coupling said second network to said first terminal and means for capacitively coupling said second network to said second terminal, and

wherein said a.c. signal coupling means includes means for capacitively coupling said a.c. signal to said first terminal,

whereby the d.c. portion of the potential difference between the diodes coupled to said second terminal corresponds to said net d.c. voltage.

20. A system according to claim 19 wherein said second terminal is directly coupled to a ground reference potential,

wherein said diode coupling means for a first of said diode detector networks includes means for directly coupling said first network to said first terminal and means for capacitively coupling said first network to said second terminal, and

wherein said diode coupling means for a second of said diode detector networks includes means for directly coupling said second network to said first terminal and means for capacitively coupling said second network to said second terminal, and

wherein said a.c. signal coupling means includes means for capacitively coupling said a.c. signal to said first terminal,

whereby the d.c. portion of the potential difference between the diodes coupled to said second terminal corresponds to said net d.c. voltage.

21. A system according to claim 19 wherein said second terminal is capacitively coupled to a ground reference potential,

wherein said diode coupling means for a first of said diode detector networks includes means for capacitively coupling said first network to said first terminal and means for capacitively coupling said first network to said second terminal, and

wherein said diode coupling means for a second of said diode detector networks includes means for capacitively coupling said second network to said first terminal and means for directly coupling said second network to said second terminal, and

wherein said a.c. signal coupling means includes means for directly coupling said a.c. signal to said first terminal,

whereby the d.c. portion of the potential difference between the diodes coupled to said first terminal corresponds to said net d.c. voltage.

22. A system according to claim 1 wherein said second terminal is capacitively coupled to a ground reference potential,

wherein said diode coupling means for a first of said diode detector networks includes means for capacitively coupling said first network to said first terminal and means for capacitively coupling said first network to said second terminal, and

wherein said diode coupling means for a second of said diode detector networks includes means for capacitively coupling said second network to said first terminal and means for directly coupling said second network to said second terminal, and

wherein said a.c. signal coupling means includes means for directly coupling said a.c. signal to said first terminal,

whereby the d.c. portion of the potential difference between the diodes coupled to said first terminal corresponds to said net d.c. voltage.

23. A system according to claim 22 wherein said second terminal is directly coupled to a ground reference potential,

wherein said diode coupling means for a first of said diode detector networks includes means for directly coupling said first network to said first terminal and means for capacitively coupling said first network to said second terminal, and

wherein said diode coupling means for a second of said diode detector networks includes means for directly coupling said second network to said first terminal and means for capacitively coupling said second network to said second terminal, and

wherein said a.c. signal coupling means includes means for capacitively coupling said a.c. signal to said first terminal,

whereby the d.c. portion of the potential difference between the diodes coupled to said second terminal corresponds to said net d.c. voltage.

24. A system according to claim 22 wherein said second terminal is capacitively coupled to a ground reference potential,

wherein said diode coupling means for a first of said diode detector networks includes means for capacitively coupling said first network to said first terminal and means for capacitively coupling said first network to said second terminal, and

wherein said diode coupling means for a second of said diode detector networks includes means for capacitively coupling said second network to said first terminal and means for directly coupling said second network to said second terminal, and

wherein said a.c. signal coupling means includes means for directly coupling said a.c. signal to said first terminal,

whereby the d.c. portion of the potential difference between the diodes coupled to said first terminal corresponds to said net d.c. voltage.

25. A displacement sensor system, comprising

a capacitive sensor including a pair of fixed elements with spaced parallel electrically conductive surfaces aligned along an axis substantially normal to said surfaces defining therebetween a continuum of parallel equipotential surfaces and a movable element mounted for axial displacement midway between said fixed elements having an electrically conductive surface substantially parallel to the surface of said fixed elements, a first capacitor half being formed by said movable element and one of said fixed elements and a second capacitor half being formed by said movable element and the other one of said fixed elements,

means for applying a nonrectified a.c. signal across said capacitive sensor such that nonrectified a.c. signals appear across both said capacitor halves,

detector means for shifting the baseline of that portion of the a.c. signal developed across one capacitor half in accordance with its amplitude, and for shifting the base line of and inverting that portion of the a.c. signal developed across the other capacitor half in accordance with its amplitude, and

output means coupled to said detector means for combining the opposed baseline shifted a.c. signals to produce a d.c. output signal representing the differential amplitudes of the a.c. signals across said capacitor halves caused by displacement of said movable element.

26. The system of claim 25, wherein said detector means includes

a pair of oppositely directed, series connected diodes, the junction between corresponding ends of said diodes being electrically coupled to said movable element, the other ends of said diodes being electrically coupled to said fixed elements respectively.

27. The system of claim 26, wherein said output means includes means for reproducing net d.c. voltage across said diodes.

28. The system of claim 27, wherein said detector means further includes

another pair of oppositely directed series connected diodes having reversed polarity relative to said one pair of diodes, the junction between corresponding ends of said diodes in said other pair being electrically coupled to the junction between said diodes in said one pair, the other ends of said diodes in said other pair being electrically coupled to the other ends of said diodes in said one pair.

29. The system of claim 28, wherein said output means further includes means for reproducing the net d.c. voltage across said diode pairs.