| 摘要 |
A housing 10 is open at both ends for the flow of material therethrough. Extending around the housing are a central primary coil 18 flanked by two secondary coils 20, 22 connected in series opposition. The primary coil is excited with an oscillatory signal which also provides a reference signal to a phase detector which detects a component of the signal across the secondary coils generated when there is conductive metal in the housing. The detected signal is differentiated to provide an indication only when there is moving metal. Conductive straps 12 and 14 are disposed either side of the coils to shield them from moving metal outside the housing. |
