| 摘要 |
<p>Metal Detection Apparatus Metal detection apparatus includes an oscillator coil 102 driven by an oscillator 101, which induces in detector coils 103, 104 equal and opposite E.M.F.s such that a nominally zero output is produced at terminals D.E. When metal is detected the E.M.F.s in coils 103, 104 move out balance to produce a voltage at D.E., which is detected by circuit IC11 and fed to output circuits 111. Drifts in the nominally zero output at D.E. are corrected by combining quadraphase balancing signals on lines 109, 110 with the detector coil output by means of amplifier IC10. The combined signal from IC10 is fed to phase sensitive detectors IC1, IC2 which respectively detect the quadraphase components of the combined signal from IC10. The outputs of IC1, IC2 are stored by capacitor circuits 112, 113 and used to adjust variable capacity diode bridges 106, 107 which adjust the amplitude of the balancing signals to maintain a nominally zero output from IC10 when metal is not being detected. The capacitor circuits 112, 113 have a long time constant so that the balancing signals are not adjusted to cancel out the detection of metal, but circuits IC5, IC6, IC13 switches the stores 112, 113 to provide a shorter time constant after metal has been detected in order to restore the circuit rapidly to a balanced condition. Additionally, the circuits IC5, IC6, IC13 disconnect the capacitor circuits from the phase sensitive detectors IC1, IC2 for a given time when metal is detected so as to restore the circuit rapidly to a balanced condition after detection of the metal.</p> |
