| 摘要 |
PCT No. PCT/CA95/00300 Sec. 371 Date Feb. 5, 1997 Sec. 102(e) Date Feb. 5, 1997 PCT Filed May 23, 1995 PCT Pub. No. WO95/32438 PCT Pub. Date Nov. 30, 1995A non-contact capacitive proximity detector includes a sensing plate and detection circuitry electrically coupled to the sensing plate. The detection circuitry comprises an oscillator electrically connected to the sensing plate and signal conditioning circuitry electrically connected to the oscillator. The signal conditioning circuitry includes a coupling capacitor C1, an envelope demodulator, a first comparator, a delay circuit and a second comparator. When an object is within a predetermined proximity to the sensing plate, the capacitance of the capacitor constituted by the sensing plate and the proximal object is at a level which causes the oscillator to generator an oscillating signal having a sufficient magnitude. The oscillating signal generated by the oscillator is applied to the envelope demodulator by way of the coupling capacitor. The envelope demodulator generates an envelope of the oscillating signal and applies the envelope to he first comparator. The first comparator in turn generates a logic high output which is fed to the delay circuit. The delay circuit in turn passes the logic high output to the second comparator after a predetermined amount of time has elapsed causing the second comparator to generate a logic high output representative of the presence of than object within a predetermined proximity to the sensing plate. When the object is removed from the sensing plate outside the predetermined proximity, the output of the proximity detector changes allowing the proximity detector to serve as a removal detector.
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