Friday, September 17, 2010

Metal Detectors Glossary IV

Pulse Induction (PI):   pulse-induction metal detectors use the same coil(s) to both transmit and receive. A PI metal detector works by sending quick and powerful electrical pulses through its coil-usually about 100 pulses per second-each one creating a brief magnetic field. When a pulse ends, this field reverses polarity and collapses, causing a reflective pulse to run through the coil. If a conductive metal is present, the reflective pulse will take longer to disappear. PI metal detectors make excellent beach detectors because of their ability to ignore ground mineralization; ground minerals are poorer conductors than metals, and are thus less likely to interfere with the returning signal of a pulse-induction metal detector.
Relic Hunting:    relic hunting refers to metal detecting in quest of objects that possess historical (and sometimes also economic) value.
Scrubbing:   scrubbing or scraping is a metal detecting technique in which the detector coil is kept in direct contact with the ground. This helps a detectorist to gain deeper readings, though it can have a detrimental effect on the search coil, which is why many detectorists use search coil covers.
Sweep:    the motion a detectorist employs when using a metal detector, so-called because it usually resembles the side-to-side movement used when sweeping a floor.
Threshold:   the threshold is essentially status quo for the listening detectorist. The threshold is a continuous, faint tone that provides an audible reference point for ground-balancing a detector. It also determines the minimum sound level for pinpointing targets, including deep targets in discriminate mode.
Very Low Frequency (VLF):   a very low frequency metal detector, or VLF detector, features a search coil with an outer transmitting loop and an inner receiving loop. The receiver coil is shielded from the transmitter coil's magnetic field, but it detects the magnetic fields emanated by objects in the ground.
Wheat Penny:   a wheat penny or wheatie is a penny that was produced between 1909 and 1958. The reverse of the coin featured two stylized wheat stalks. The wheat penny is one of the many types of coins that can be found using a coin detector.
Widescan (Double D or 2D):   in contrast to concentric search coils, widescan search coils are coplanar, i.e. their transmit and receive windings are positioned back-to-back in the form of two Ds. This gives widescan metal detector coils a larger search area and also minimizes the effect of ground minerals.

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