| 摘要 |
<p>PURPOSE: To provide a metal detector which is highly sensitive and unlikely to malfunction by subjecting an input signal to differential amplification, outputting the signal, converting the polarity of part of this output so that it becomes a feedback signal during the period of reception of both or one of switches, and feedbacking the signal to the input of a receiver either electrically or mechanically. CONSTITUTION: An output of an amplifier (receiver) 3 is separated into positive and negative components by semiconductor switches 4 for use in a synchronizing amplifier and is input to a differential amplifier 5. As a result, noises or the like that have commercial frequency components and are input to a detecting coil 1 are greatly damped. An output of the differential amplifier 5 is smoothed through a filter 6 and converted to a detection output. The detection output has its phase and gain adjusted by a feedback compensation circuit 7 and is input to one of the switches 4; the output is input to the other switch with its polarity reversed through an inverting amplifier, and its polarity is converted so that even if the switches 4 are changed from one to the other, negative feedback is always possible. This feedback signal is divided by resistances 13, 2 and feedback to the input of the amplifier 3 so that its drift is corrected.</p> |
