Eriez Xtreme, Reference Manual

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H = smaller tunnel
dimension (typically height)
Figure 2
ELECTRICAL CURRENT LOOP
The most frequent problem encountered in metal detector installations is false tripping caused
by intermittent electrical current loops. The electromagnetic field dissipates in strength with
distance to a point that metal outside the “metal free” area will not cause false detections.
Since the field is time varying, it will generate small electrical currents in conductive paths
(metalwork) beyond the metal free area. These currents along with ground currents from
nearby equipment will not cause false tripping as long as they are constant. If the current is
disrupted, the resulting disturbance in the electromagnetic field may cause the metal detector to
false trip.
The schematic diagram shown in Figure 3 provides a simplified view of a typical metal detector
and conveyor. The arrows represent electrical currents. The bearings supporting the pulleys
and idlers turn, causing them to become “make and break” contact points.
MECH
15