Capacitive position sensor and sensing methodology
First Claim
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1. A sensor for determining the position of a reciprocating member, said sensor comprising:
- a fixed electrode support structure comprising a fixed electrode and a guard electrode, said fixed electrode being electrically isolated from said guard electrode; and
a movable electrode, said movable electrode positioned to move in direct proportion to the movement of said reciprocating member;
wherein said fixed electrode and said movable electrode form a capacitive structure, said capacitive structure having a variable capacitance which is directly proportional to the instantaneous position of said reciprocating member;
wherein said fixed electrode and said movable electrode are cylindrical in shape; and
wherein said fixed electrode is formed from plastic and further comprises at least one area of conductive plating.
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Abstract
A simple and robust variable coaxial capacitive sensor and detection method for monitoring the position of a rapidly reciprocating member such as a piston or displacer in a free piston Stirling engine. The coaxial capacitor of the present invention in a preferred embodiment thereof is configured to modulate capacitive electrode area rather than inter-electrode spacing and as a result a highly linear transfer function can be achieved. Also disclosed are detection methods which derive and process signals in connection with applications which have small sensor capacitance variations while suppressing stray capacitance error.
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Citations
26 Claims
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1. A sensor for determining the position of a reciprocating member, said sensor comprising:
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a fixed electrode support structure comprising a fixed electrode and a guard electrode, said fixed electrode being electrically isolated from said guard electrode; and a movable electrode, said movable electrode positioned to move in direct proportion to the movement of said reciprocating member; wherein said fixed electrode and said movable electrode form a capacitive structure, said capacitive structure having a variable capacitance which is directly proportional to the instantaneous position of said reciprocating member; wherein said fixed electrode and said movable electrode are cylindrical in shape; and wherein said fixed electrode is formed from plastic and further comprises at least one area of conductive plating. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A sensor for determining the position of a reciprocating member, said sensor comprising:
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a fixed electrode support structure comprising a fixed electrode and a guard electrode, said fixed electrode being electrically isolated from said guard electrode; and a movable electrode, said movable electrode positioned to move in direct proportion to the movement of said reciprocating member; wherein said fixed electrode and said movable electrode form a capacitive structure, said capacitive structure having a variable capacitance which is directly proportional to the instantaneous position of said reciprocating member; wherein said fixed electrode and said movable electrode are cylindrical in shape; and further comprising a phase lead compensation network for correcting low-pass filter phase lag.
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12. A capacitive position sensor comprising:
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a fixed electrode support structure comprising a fixed electrode and a guard electrode, said fixed electrode being electrically isolated from said guard electrode; and a movable electrode, said movable electrode positioned to move in direct proportion to the movement of a reciprocating member; wherein said guard electrode is driven at a potential which is the same as that of said fixed electrode; and wherein said fixed electrode and said movable electrode are cylindrical in shape; and wherein said guard electrode and said fixed electrode are driven by a constant voltage source generating a constant amplitude triangle modulating wave. - View Dependent Claims (13, 14, 15, 16, 17, 18)
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19. A capacitive position sensor comprising:
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a fixed electrode support structure comprising a fixed electrode and a guard electrode, said fixed electrode being electrically isolated from said guard electrode; and a movable electrode, said movable electrode positioned to move in direct proportion to the movement of a reciprocating member; wherein said guard electrode is driven at a potential which is the same as that of said fixed electrode; wherein said fixed electrode and said movable electrode are cylindrical in shape; and wherein said guard electrode and said fixed electrode are driven by a voltage source generating a constant amplitude sine modulating wave. - View Dependent Claims (20, 21, 22, 23, 24)
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25. A capacitive position sensor comprising:
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a fixed electrode support structure comprising a fixed electrode and a guard electrode, said fixed electrode being electrically isolated from said guard electrode; and a movable electrode, said movable electrode positioned to move in direct proportion to the movement of a reciprocating member; wherein said guard electrode is driven at a potential which is the same as that of said fixed electrode; wherein said fixed electrode and said movable electrode are cylindrical in shape; and further comprising a constant amplitude current source and a voltage follower, said voltage follower adjusting voltage to ensure that the potential at said guard electrode is essentially the same as the potential at said current source.
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26. A capacitive position sensor comprising:
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a fixed electrode support structure comprising a fixed electrode and a guard electrode, said fixed electrode being electrically isolated from said guard electrode; and a movable electrode, said movable electrode positioned to move in direct proportion to the movement of a reciprocating member; wherein said guard electrode is driven at a potential which is the same as that of said fixed electrode; wherein said fixed electrode and said movable electrode are cylindrical in shape; and further comprising a phase lead compensation network for correcting low-pass filter phase lag.
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Specification