Three false reject sources
False rejects are one of the most overlooked costs in metal detection. They usually come from three sources: product effect, where salty or moist products generate signals similar to metal when the phase angle is set poorly; environmental interference from inverters, motors, radios or moving metal nearby; and sluggish reject mechanisms or unstable air supply that blow good products away. Isolate each factor to locate the cause.
Product learning and phase
Reducing false alarms starts with proper product learning and phase adjustment so the unit recognizes the signal of good products. Keep the installation away from strong interference sources and ensure good grounding. Check air pressure, delay and reset status of the reject device regularly. For lines with many product types, store parameters for frequent products and recall them at changeover.
Realistic false reject goal
Zero false rejects is not a realistic target. A reasonable goal is a stable, acceptable false reject rate while ensuring real contaminants are not missed. Keep a log of false rejects by frequency and batch to judge whether the problem lies in product, environment or mechanism, then improve accordingly. This works better than simply lowering sensitivity.