Gravity fall metal detection systems are designed specifically for the inspection of free-falling powders and granular products in non-pressurized applications with different reject devices depending on the application. Most metal detectors can detect objects about 4-8ʺ (10 – 20 cm) deep. In ideal conditions, a mid-range metal detector can reach 12-18ʺ (30-45 cm) underground. Some specialized detectors can go as deep as 65' (20 m). The operation of metal detectors is based upon the principles of electromagnetic induction. Metal detectors contain one or more inductor coils that are used to interact with metallic elements on the ground.