Capacitive position sensing system with resonant amplification
View Patent ↗At least one exemplary embodiment of the present invention includes a capacitive sensing system, comprising a sensing conductor coupleable to a grounded target by a gap capacitance C d , said grounded target separated from said sensing conductor by a gap having a width. The capacitive sensing system also comprises a circuit connected to said sensing conductor, an input signal having an input frequency f osc provided to said circuit through an input resistance R d , an output signal of said circuit having an output voltage varying linearly with the width of the gap when the impedance of the gap capacitance 1/(2πf osc C d ) approaches or exceeds the input resistance R d .
1. A system, comprising a delay element connected to an op-amp, said delay element comprising:
a stray capacitance C s between a guard conductor and a sensing conductor;
a stray capacitance C c between the guard conductor and a grounded shield;
an input resistance R d connected serially between an oscillating voltage input and said op-amp; and
a first variable resistance R c connected in series between an output of said op-amp and the guard conductor;
a resonant frequency of said system approximately equal to a frequency f osc of the oscillating voltage input.
2. The system of claim 1 , the sensing conductor capacitively coupleable to a grounded target.
3. The system of claim 1 , the sensing conductor coupleable to a grounded target by a gap capacitance C d .
4. The system of claim 1 , the sensing conductor capacitively coupleable to a grounded target, the grounded target separated from the sensing conductor by a gap having a width.
5. The system of claim 1 , wherein the guard conductor surrounds the sensing conductor.
6. The system of claim 1 , wherein a grounded shield surrounds the guard.
7. The system of claim 1 , the sensing conductor coupleable to a grounded target by a gap capacitance C d , wherein the guard conductor surrounds the sensing conductor and a grounded shield surrounds the guard.
8. The system of claim 1 , further comprising a buffer amplifier between an output of said op-amp, and a power input of said op-amp.
9. The system of claim 1 , further comprising a means for reducing parasitic capacitance between non-inverting input of said op-amp and a positive and negative power input of said op-amp.
10. The system of claim 1 , further comprising a second variable resistance connected to an output of said op-amp.
11. The system of claim 1 , wherein said op-amp is configured to provide a non-inverting gain.
12. The system of claim 1 , further comprising a means for providing a non-inverting gain from said op-amp.
13. The system of claim 1 , the sensing conductor coupleable to a grounded target by a gap capacitance C d , the grounded target separated from the sensing conductor by a gap having a width, an output signal of said system having an output voltage varying linearly with the width of the gap when an impedance of the gap capacitance 1/(2πf osc C d ) approaches or exceeds a resistance of said input resistor R d .
14. The system of claim 1 , further comprising a means for obtaining a measurement based on an output signal of said system.
15. The system of claim 1 , further comprising a means for making a determination based on an output signal of said system.
16. The system of claim 1 , further comprising a means for measuring a width of a gap between the grounded target and the sensing conductor based on an output signal of said system.
17. The system of claim 1 , further comprising a means for measuring displacement based on an output signal of said system.
18. The system of claim 1 , further comprising a means for measuring vibration based on an output signal of said system.
19. A system, comprising:
a stray capacitance C s arising between a guard conductor and a sensing conductor;
a stray capacitance C c arising between the guard conductor and a grounded shield;
an input resistance R d connected serially between an oscillating voltage source and a non-inverting input of an op-amp; and
a variable resistance R c connected in series between an output of the op-amp and the guard conductor;
wherein the sensing conductor is connected to the non-inverting input of the op-amp, and a resonant frequency of said system is approximately equal to a frequency f osc of the oscillating voltage input.