Glossary of Metal Detecting Terms

Terminology Used in Metal Detecting & Treasure Hunting: from D to F

D

DEPTH PENETRATION - A metal detector's maximum capability to transmit an electromagnetic field through a mineralized ground matrix and signal the presence of a metal target. The detecting depth indication is based on the strength of the secondary magnetic field generated by the metallic targets. The Depth Penetration is the detector's DEPTH POTENTIAL affected by mineralization. The Depth Potential can be determined ONLY through empirical observation during an Air Test (Bench Test).

DEPTH POTENTIAL - A metal detector's maximum capability to transmit an electromagnetic field with a current search coil without being reduced by ground mineralization and/or improper levels of program settings including ground balance.

DETECTING DEPTH RANGE (also called OPERATIONAL DEPTH RANGE) - the Depth Penetration that is reduced by high levels of Discrimination and/or Sensitivity (or other features responsible for it depending on a metal detector used), or poor Ground Balance of a metal detector.

DETECTION PATTERN - The perceived shape or footprint of effective electromagnetic field transmission directly related to search coil winding configuration.

DETUNING - A method of desensitizing threshold audio tuning which reduces the target signal width for accurate pinpointing. Achieved in a non-motion, all-metal mode of operation by re-tuning threshold audio within the target response area.

DISCRIMINATION - Circuitry and the mode of operation in which audio or visual responses from undesired metal objects are intentionally eliminated.

DISCRIMINATION PATTERN (Accepted) - On the detector's display, the range of accepted targets is represented by the white (clear) area on the Conductivity (1-dimensional) scale or on a Conductivity/Ferrous Content (2-dimensional) scale of Discrimination.

DISCRIMINATION PATTERN (Rejected) - On the detector's display, the range of rejected (undesirable) targets is represented by the black area on the Conductivity (1-dimensional) scale or on a Conductivity/Ferrous Content (2-dimensional) scale of Discrimination.

DOT DISCRIMINATION - Can be applied only to the Minelab's revolutionary 2-dimensional discrimination circuitry which is capable of selectively accepting or rejecting a specific target. The target's conductivity/ferrous content coordinates correspond to a graphic square that can be of three changeable sizes, can be colored white for Accept or black for Reject, and can be placed anywhere inside the 2-dimensional discrimination pattern on detector's LCD. For instance, dot discrimination will accept gold rings of certain conductivity while rejecting targets of the same conductivity but of different ferrous content such as nickel coins and pull-tabs. The 1-Dimensional discriminators of other regular metal detectors are not capable of doing that. The best they can do is to reject a narrow range of targets by NOTCH DISCRIMINATION (see further in the list) which still rejects all targets of the same conductivity.

DOUBLE BEEP - Two positive audio signals in rapid succession generally associated with elongated ferrous objects such as nails or coins on edge.

DOUBLE D - A search coil design with two "D" shaped windings configured back to back giving it a long and narrow detection pattern from "toe" to "heel". This type of search coil is generally employed in high mineral locations where the discriminate function is considered secondary.

DRIFT - Unstable threshold tuning levels caused by temperature extremes, battery strength, and rapid changes in mineralization.

DUAL-FREQUENCY (see also FREQUENCY) - This is when a metal detector is designed to operate on two frequencies of alternating currents which are generated by the transmit oscillator and passed through the transmitter coil. As using only two frequencies, the low one and the high one, is not 100% effective in achieving both a good sensitivity to small targets and good detecting depth, Dual-Frequency metal detectors have a little advantage over the single-frequency machines. Only the Multi- detectors made by Minelab get the job done effectively. Two manufacturers, Fisher and White's, make the dual-frequency metal detectors.

DUAL VOLTAGE TECHNOLOGY (DVT) - Minelab's patented technology is implemented in the GPX series of metal detectors. DVT transmits two different voltage levels from the search coil. This has an advantage of improved ground balance, increased sensitivity to small targets and increased operational depth range.

E

EDDY CURRENTS - Small circulating electric currents generated when an electromagnetic field contacts the surface of a metal object. Secondary electromagnetic fields are generated by these currents and picked up by the search coil's receive windings. This causes an inductive imbalance to occur between the transmit and receive windings which is relayed to the detector circuitry producing an audio and/or visual response.

ELECTROMAGNETIC FIELD - An invisible electrical field emanating in force primarily from the top and bottom sides of a search coil. This field is generated by the flow of alternating oscillator frequency current around the search coil's transmit winding, (see DETECTION PATTERN).

ELLIPTICAL - An oval search coil housing shape containing either the Double D (2D) or concentric winding configuration.

F

FAINT SIGNAL - A minimal target response generally associated with deeply buried objects or targets very small in physical size.

FALSE SIGNAL - A positive signal incorrectly thought to be metallic and desirable. Caused by ground minerals, tuning overshoots, ground voids, hot rocks, electrical interference and detector malfunctions.

FARADAY SHIELD - A continuous metal foil wrapping around search coil windings used to reduce electrostatic interference caused by contact with wet vegetation on the search coil housing exterior.

FBS (see also MULTI-FREQUENCY) - Full Band Spectrum is a new technology used by the Minelab Explorer II, SE Pro, and E-Trac metal detectors. FBS combines Minelab's multiple frequency BBS (Broad Band Spectrum) technology with a powerful microprocessor to give: greater detecting depth, high sensitivity over a wide range of targets, less interference from electromagnetic sources, and more accurate identification of target characteristics.

FERROUS - Any material containing iron. If a metal object is attracted to a magnet, it is called ferrous. If not, it is called non-ferrous such as gold, silver, copper, aluminum, etc.

FERROUS OXIDES - Particles of oxidized iron which make up the non-conductive or negative ground mineral matrix, (see BLACK SAND).

FIELD TEST - An outdoor test conducted to evaluate metal detector performance and operational characteristics under real conditions of metal detecting.

FREQUENCY - The number of alternating current cycles per second (Hz) produced by the transmit oscillator. A metal detector's electromagnetic operating frequencies are measured in kiloHertz (kHz). Low signal frequencies penetrate the ground deepest, but sensitivity to smaller targets is low. Higher frequencies have a more shallow detecting depth but high sensitivity to small targets.
VF = Voice Frequency = 300Hz-3kHz, VLF = Very Low Freq.= 3-30kHz, LF = Low Freq.= 30-300kHz

FREQUENCY SHIFT - A feature designed to reduce crosstalk interference by altering the transmit frequency of the metal detector, (see CROSSTALK).



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