| 摘要 |
A transmit-receive type buried metal detector is described employing wide gating pulses to transmit a portion of the received signal through a gate means to an averaging means for reducing any noise in the signal. The gating pulses are centered on the received signal waveform at a centering position where a background signal component of such received signal is of minimum amplitude. As a result, equal positive and negative polarity portions of the background signal component are transmitted through the gate means during each pulse and are averaged to zero in order to eliminate such background signal from the output voltage of the averaging means. The background signal component may be produced by mineralized soil or by undesired metal objects located near the metal object sought to be detected. As a result, the mineral soil signal component or the background signal component of the undesired metal objects is eliminated from the output voltage of the averaging capacitor. This enables detection of the desired metal object in mineral soil or enables such desired metal object to be discriminated from undesired objects. A wide gating pulse greater than about 1/3 cycle and preferably equal to approximately 1/2 cycle of the oscillator signal, is used for improved noise rejection including random noise of high frequency and harmonics of 60 hertz power line frequency which are close to harmonics of the oscillator signal. |
