| 摘要 |
<p>A metal detector circuit comprising an oscillator (14) capable of sensing any type of metal in motion over a predetermined frequency. The oscillator supply voltage is derived from a feedback correction circuit (30) which compensates for stationary metal as well as metal moving in a lower frequency past the sensing coil (10) of the oscillator by adjusting the supply voltage of the oscillator to make up for Q losses. The higher frequencies are blocked by a DC time constant (low pass filter) and the sensor coil (10) is able to see through stationary metal and detect a moving metal target on the other side thereof. The amplitude of the modulated signal from the oscillator remains nearly constant throughout its detection range by this supply voltage feedback correction circuit (30). The detection circuit also provides a reliable output signal indicating when the sensor portion is damaged due to an open or shorted coil circuit.</p> |
