Frequency optimizing metal detector

Abstract

A metal detector (10) which uses a metallic test sphere (5) to pass with the product through the detector head (2) at periodic intervals. The frequency generator (21) which generates the signal sent to the oscillator coil (11) is capable of operating on numerous frequencies in the 50 kHz to 2 MHz range. The product is passed through the detector head (2), with and without the sphere (5) present, for each of the operating frequencies. The detected signal from the product and the product with metal is characterized for each of the operating frequencies. In this manner the frequency which produces the highest ratio of product with metal present signal to product signal without metal present can be identified. A second version of the metal detector (40) uses a frequency synthesizer (43) which may be rapidly scanned through a range of frequencies while the product is passing through the detector head (41). The signal produced by the product for each frequency can then be identified and stored in a controller (49), thereby establishing a threshold value for the product at each frequency. During a subsequent metal detection step, a signal above the threshold at any frequency indicates the presence of metal. A third version (63) of the metal detector simultaneously and continuously operates on two or more frequencies. When product passes through the search head 60, the amplitude and phase of the received signals (65) are measured and recorded for each of the operational frequencies. A controller (94) establishes threshold levels for the product. If any threshold for the product is exceeded at any frequency, metal is present.