10
Loop Effect
Besides observing rules for metal-free areas, precautions should be taken to prevent the occurrence of loop effect. Loop effect
is caused by an electrical loop in the conveyor, which is allowed to make intermittent contact (see Figure 10). This loop, when
closed, can produce a large electromagnetic field. When the loop opens, the field collapses very rapidly, causing the detector's
field to be disturbed. This results in false detections. Loops can be caused by rollers whose bearings make intermittent
connection, or any metal which crosses the conveyor frame that is not securely fastened (e.g.: transfer plate, loose cross
member, electrical conduit, retracting reject or flap gate reject).
Metal Free Area
Loop Effect Area
Roller
Cross Members
Legs
Side Panel
Bearing
Figure 10
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