| 摘要 |
A method and apparatus for cancelling cyclically recurring noise induced in a magnetic metal detector (10) by movement of ferrous machine parts (1, 2, 4, 6) in the field of the detector provides for periodically sampling the output of the metal detector (10), delaying (16) each sample for the duration of one cycle of the cyclically recurring noise, and subtracting the samples taken in one cycle from the output of the metal detector during the following cycle. The delay is accomplished by a delay line or shift register (16), or by storing the samples under microprocessor control (100). If the noise has a first component occuring at a first rate and a second component occuring at a second rate, cancellation of both components may be accomplished. |
