Method and apparatus for metal detection using a coil arrangement with several separate controllable regions

摘要

The method involves using multiple coil pairs (5-8) which are arranged in crosswise overlapping fashion in e.g. the uprights of a door frame. One coil pair set (5,6) is used for simultaneous transmission of a pulse sequence whose pattern varies with the position of the sending coil, the other coil pair (7,8) is used for reception of the pulse signals from the corresponding sending coil. The received signals are sampled in accordance with a corresponding pattern so that any metallic object in the doorway can be located from its effect on the reception. Each receiving pair has its own amplifier (16) and sample-and-hold circuit (17) connected to a multiplexer (18). Signals from the multiplexer are digitised (19) before sending to a microprocessor (20) and a display (21).