Fortunately, not many pull tabs around any more! Unfortunately, gold and silver rings give a similar indication to an aluminum pull tab. But that particular coin will cause the same phase change every time. So a penny will give a different indication than a quarter, or a nickel. In addition, the size and conductivity of a nonferrous object will cause a particular phase change, as long as mass and composition are controlled. The phase change is in opposite directions between ferrous and nonferrous metals. Ferrous objects unbalance by pulling magnetic fields into them. The coils are arranged so that, with no metal present, the coupling cancels out to zero in the receive coil.įor conductive objects, eddy current induced in nonferrous metals repel the AC magnetic field, causing the receiver coil to no longer be nulled. An Induction Balance (IB) metal detector has a transmit and a receive coil.
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