STATIC MAGNETIC FIELD METAL DETECTOR

A static magnetic field detector senses the passage of ferrous or magnetic objects, employing a balanced pick up coil configuration providing substantial self-cancellation of spurious background signals. The pick up coils are disposed in a uniform static magnetic field and are cooperatively effective to sense the presence of such objects with respect to an extended passage way by reacting to the field distortion caused by the object to produce an alarm or control signal. Further reduction of the effects of spurious background signals is afforded by novel means for processing the signals generated within the detector coils providing filtering and threshold functions. An adaptive threshold control circuit provides automatic adjustment of the threshold level of object detection.