Capacitive phase shift proximity detector
First Claim
1. Proximity detector with capacitive antenna for detecting the presence of a foreign body in the surroundings of said antenna, comprising:
- a variable radio frequency oscillator producing a first electrical signal,a transmission circuit comprising said capacitive antenna and to which said first signal is applied,a reception circuit forming, with said transmission circuit, a selective coupler for picking up a second electrical signal at the frequency of said oscillator,detection means comprising a phase comparator circuit for comparing the phases of said first and second electrical signals and producing an output signal in response to a variation of the phase shift between said signals resulting from detuning of said transmission circuit, anda feedback circuit driven by said output signal from said comparator circuit and controlling said oscillator in order to make the frequency of said first signal vary in the sense which tends to tune said transmission circuit by cancelling out said variation of the phase shift, said feedback circuit comprising an integrator circuit with a high time constant compared to the range of relative speeds of movement of the antenna with respect to said foreign body to be detected.
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Accused Products
Abstract
This detector comprises a variable radio frequency oscillator (1) producing a first electrical signal, a transmission circuit (3) with a capacitive antenna to which said first signal is applied, a reception circuit (6) forming, with the transmission circuit (3), a selective coupler for picking up a second electrical signal at the frequency of the oscillator, and a circuit (9) for comparing the phases of the first and second electrical signals and producing an output signal in response to a variation of the phase shift between said signals due to the presence in the surroundings of the antenna of a foreign body to be detected.
The detector further comprises a feedback circuit (13) driven by the output signal of the comparison circuit (9) and controlling the oscillator (1) in order to make the frequency of the first signal vary in the sense which tends to cancel out said variation of the phase shift.
42 Citations
12 Claims
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1. Proximity detector with capacitive antenna for detecting the presence of a foreign body in the surroundings of said antenna, comprising:
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a variable radio frequency oscillator producing a first electrical signal, a transmission circuit comprising said capacitive antenna and to which said first signal is applied, a reception circuit forming, with said transmission circuit, a selective coupler for picking up a second electrical signal at the frequency of said oscillator, detection means comprising a phase comparator circuit for comparing the phases of said first and second electrical signals and producing an output signal in response to a variation of the phase shift between said signals resulting from detuning of said transmission circuit, and a feedback circuit driven by said output signal from said comparator circuit and controlling said oscillator in order to make the frequency of said first signal vary in the sense which tends to tune said transmission circuit by cancelling out said variation of the phase shift, said feedback circuit comprising an integrator circuit with a high time constant compared to the range of relative speeds of movement of the antenna with respect to said foreign body to be detected. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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Specification