To virtually eliminate false rejects, a "Faraday Screen," located between the detector coil
system and the product being inspected, filters out signals that can interfere.
Metal detectors with newly designed detector coil
systems for enhanced sensitivity detect all types of metal (nonferrous, ferrous and stainless steel) in a moving stream of resin pellets or powder.
Conductive products, such as tablets containing iron, generate a significant disturbance in the detector coil
current--a phenomenon known as `product effect'--even when completely free of metallic contamination.
This demagnetizes a "window" in the magnetized fluid and the window is discerned by the detector coil
as a momentary drop in output signal.