| 摘要 |
A method of operation of a metal detector having a driver circuit 42 for establishing an alternating magnetic field in a coil system 40 so as to generate an output signal at a given frequency, comprises generating an adjustable balance signal; combining the adjustable balance signal with the output signal of the detector; and varying the adjustable balance signal so as to provide a compensated signal. The metal detector may be operable at a selected frequency though use of a plurality of switches arranged to alternatively connect the coil system across a potential difference, the operating frequency determined by the operation of the switches. The metal detector may be calibrated by incrementally scanning across its range of operating frequencies in the absence of an object in the detector, adjusting the balance signal, and storing the adjustments in a database or lookup table. The stored adjustments can be used when scanning a product (e.g. food) to detect metal. Harmonics in the balance signal, output signal or combined signal may be filtered. |
