Patent ID: 8587301

Claim:
A method for operating a metal detection system that comprises a balanced coil system including a transmitter coil that is connected to a transmitter unit, which is adapted to provide transmitter signals having a selectable transmitter frequency, and a first and a second receiver coil that are adapted to provide output signals to a receiver unit, which are adapted to compensate one another in an event that the metal detection system is in balance and, in an event that a product is present in the balanced coil system, the receiver unit is adapted to provide an output signal that is forwarded to a signal processing unit, which is adapted to suppress at least components of a product signal and deliver signal components caused by metal contaminants contained in the product, comprising the following steps: a) for each of a plurality of metal contaminants, determining phase and magnitude of related signals for each of at least two transmitter frequencies and for at least two particle sizes of each of the metal contaminants; b) determining phase and magnitude of a product signal respectively for the product for the at least two transmitter frequencies; c) comparing information established for each of the metal contaminants and information established for the product respectively for the at least two transmitter frequencies; d) for each of the metal contaminants, determining a preferable transmitter frequency with which signal components for smallest sized particles of the contaminant differ most in phase and amplitude from the phase and amplitude of the product signal; and e) alternately applying the preferable transmitter frequency for each of the metal contaminants for measuring the product.