| 摘要 |
The invention relates to a method for differentiating conductive and/or ferromagnetic objects (O) in a material stream (2), comprising the generation of an electromagnetic alternating field by means of exciting a coil (S) having a sinusoidal voltage (ue(t)) of a constant frequency (fM), the detection of an impedance change of the coil caused by an object (O) by determining at least one pair of values from a peak value (ÎM) and a phase shift (ΦM) of the coil current (iM(t)) for the excitation voltage (ue(t)) of the coil, and the determination of the material by comparing the peak values (ÎM) and the phase shifts (ΦM) to reference values, wherein the peak values (ÎM) of the coil current (iM(t)) are calculated at least one measuring phase angle (ΦM) by means of a limit comparator at a constant limit width (&Dgr;i), wherein the time (&Dgr;tM) between the limit entry point (p4) and the limit exit point (p6) of the coil current (iM(t)) is measured, and the increase of the current path (iM(t)) is calculated from the limit width (&Dgr;i) and the time measured (&Dgr;tM), and the peak value (ÎIM) is calculated from the increase of the sinusoidal current path (iM(t) and the frequency (fM) thereof.
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