where M'(z) is linked to the magnetic energy thus increases the permeability, M" (z) is linked to the energy loss by eddy current in the specimen like the core in the
detector coil, and G is the gain.
The application of radio frequency pulses cause the nuclei to rotate around the alignment axis at a rate that is characteristic of its molecular environment, known as "frequency." When the radio frequency is applied to the sample, the precession around the alignment axis induces a current that is captured by a
detector coil as a Free Induction Decay (FID) signal.
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.
According to the company, this new generation of metal detectors is now more sensitive, especially in applications with strong product effects and external 'noise' Depending on the size of the
detector coil, metal particles of 01 0.15mm in diameter can be filtered out.
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.
Engineers mounted a primary electrical coil above the metal to induce eddy currents in the aluminum, and a secondary
detector coil below it.
Sure enough, Hertz was able to detect small sparks jumping across the gap in his
detector coil.
This is when conductive products generate a significant disturbance in the
detector coil current.
