| 摘要 |
A monitoring circuit is provided for a metal detector which includes a metal sensor for producing a sensor signal in response to the passage of a metallic object through a rotating apparatus and a tachometer for producing a tachometer signal at a frequency proportional to the rate of rotation of the rotating apparatus. In accordance with the invention, the monitoring circuit comprises an adjustable tracking filter responsive to a predetermined control signal for tracking the frequency of the sensor signal in a predetermined fashion and a control circuit responsive to the tachometer signal for producing the control signal.
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