Vehicle detector with series resonant oscillator drive
First Claim
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1. An oscillator circuit for producing an oscillator signal having a frequency which is a function of inductance of an inductive sensor, the oscillator circuit comprising:
- an inductive load which includes the inductive sensor;
a capacitive impedance connected to the inductive load to form a resonant circuit;
means for sensing current flowing through the inductive load; and
means for supplying the oscillator signal to the resonant circuit as a function of the current sensed.
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Abstract
An inductive sensor is driven by a series resonant oscillator circuit to produce an oscillator signal having a frequency which is a function of inductance of the inductive sensor. An inductive load, which includes the sensor, is connected in series with a capacitive impedance. Power to the series resonant circuit formed by the inductive load and the capacitive impedance is controlled as a function of current in the series circuit as sensed by a current sensor. A detection system provides a detector output based upon the frequency of the oscillator signal.
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Citations
21 Claims
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1. An oscillator circuit for producing an oscillator signal having a frequency which is a function of inductance of an inductive sensor, the oscillator circuit comprising:
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an inductive load which includes the inductive sensor; a capacitive impedance connected to the inductive load to form a resonant circuit; means for sensing current flowing through the inductive load; and means for supplying the oscillator signal to the resonant circuit as a function of the current sensed. - View Dependent Claims (2, 3, 4, 5)
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6. An oscillator circuit for producing an oscillator signal having a frequency which is a function of inductance of an inductive sensor, the oscillator circuit comprising:
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an inductive load which includes the inductive sensor; a capacitive impedance connected in a series path with the inductive load; current sensing means for sensing current in the series path; amplifier means having first input terminal and an output terminal, for providing the oscillator signal at its output terminal as a function of a first feedback signal received at its first input terminal;
the series path being connected to the output terminal; anda first feedback circuit for providing the first feedback signal as a function of current sensed by the current sensing means. - View Dependent Claims (7, 8, 9, 10, 11, 12)
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13. A detector system which uses an inductive sensor which exhibits changes in inductance as a function of presence of an object, the system comprising:
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an inductive load which includes an inductive sensor; a series resonant oscillator circuit, for driving the inductive load with an oscillator signal, which includes a capacitive impedance connected in a series path with the inductive load, current sensing means for sensing current flowing through the inductive load, and means for controlling the oscillator signal as a function of current sensed by the current sensing means so that frequency of the oscillator signal changes as a function of changes in inductance of the inductive load; and means for providing a detector output based upon the frequency of the oscillator signal. - View Dependent Claims (14, 15, 16)
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17. A detector system which uses an inductive sensor, the system comprising:
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an inductive load which includes the inductive sensor; an oscillator circuit for supplying an oscillator signal having a frequency which is a function of inductance of the inductive sensor, the oscillator circuit including means for sensing current flow through the inductive load, and means for controlling the oscillator signal as a function of the current sensed so that the inductive load receives a constant AC current drive despite changes in inductance of the inductive sensor; and means for providing a detector output based upon the frequency of the oscillator signal. - View Dependent Claims (18, 19, 20)
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21. A vehicle detector for use with an inductive sensor which changes inductance in response to presence of a vehicle, the vehicle detector comprising:
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an input circuit connected to the inductive sensor; a series resonant oscillator connected to the input circuit for providing a constant AC current drive signal to the inductive sensor, the series resonant oscillator producing an oscillator output signal which is a function of current through an inductive load formed by the input circuit and the inductive sensor and which has a frequency which is a function of the inductance of the inductive sensor; means for measuring frequency of the oscillator output signal; and means for providing a detector output signal based upon the frequency measured.
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Specification