Glossary of Metal Detecting Terms
NOTE: Only basic metal detecting terms are included in this glossary. Excluded are the following terms: uncommon slang words and expressions, specific names of detector's functions and features that relate to a certain brand of metal detector(s) and treasure hunting equipment. If you do not see a term that you think is important, please let me know.
A
AIR TEST - A test to determine the maximum sensitivity a metal detector is capable of under ideal conditions. Various sized metal samples are held beyond the search coil bottom at varying distances to determine the limits of audio or visual response. Air tests are not accurate indicators of ground penetration ability, (see BENCH TEST).
ALKALINE - A grade of battery composition which sustains higher current drain and possesses a greater shelf life than basic carbon-zinc types.
ALL-METAL - A mode or control setting description associated with total acceptance of metal targets. Also related to the ground balance mode function.
AUDIO ID - Circuitry enabling the operator to make judgments on target conductivity levels based on sound. A voltage controlled oscillator is employed to produce multi-pitch audio responses.
AUTO TUNE (Automatic Re-Tuning) - Circuitry capable of continuously restoring threshold audio level. Used to control circuit drift caused by mineral interference in the All-Metal, Pinpoint or Ground Balance modes of operation. Rates of re-tuning speed may be preset or variable depending on design features.
B
BACK READING - False responses caused by rejected targets being too close to or in contact with the search coil bottom when the detector is operating in the discriminate mode.
BENCH TEST - Another form of air test used to define which discriminate settings accept or reject various target samples. Detector is placed upon a stationary and non-metallic rest, and samples are manually passed across the bottom of the search coil.
BLACK SAND - A form of negative ground mineralization found on beaches and in gold bearing regions. The major component of non-conductive ground, also known as magnetic iron oxide or magnetite (Fe304).
BODYMOUNT - An operator setup whereby the metal detector control housing is removed from the control shaft and attached to the body by straps or fixed upon a belt. This configuration lessens arm fatigue and promotes better maneuverability on land and in shallow water searching. Also called hip-mount.
C
CACHE - A hoard of valuables purposely buried or concealed.
CARBON-ZINC - The standard or basic grade of dry-cell battery.
COAXIAL - A search coil design having identical diameter transmit and receive windings stacked and aligned on the same axis. Advantages include a uniform detection pattern and resistance to 60 Hz AC electrical interference.
COIN DEPTH INDICATOR - A meter or visual display which measures the depth of coins and coin-sized targets in numerical increments. Targets which are larger or smaller than the circuitry is calibrated for will not be measured accurately.
CONCENTRIC - A search coil design having unequal winding diameters aligned on the same center. The most common style called concentric co-planar has all windings on the same plane. Recent designs have been configured elliptical. Concentric search coils are considered most compatible with the discrimination function.
CONDUCTIVE SALTS - The major component of the positive ground matrix. Wet ocean sand can cause false signals in the motion discriminate mode of operation and an increase or positive rise in threshold audio in an unbalanced non-motion all-metal mode.
CONDUCTIVITY - The measured amount of eddy current generation created on a metal target's surface, (see PHASE RESPONSE).
CONTROL HOUSING - The enclosure which contains detection circuitry, indicators, power source and related controls. Typically made of plastic or metal.
CONTROL SHAFT - Telescoping metal tubes to which the control housing, search coil, and isolator are attached.
CONVERTIBLE - A metal detector configuration in which the control housing can be temporarily detached for body-mounting.
COPLANAR - Orientation of search coil windings occupying the same horizontal plane.
CROSSTALK - Interference between two metal detectors operating in near proximity at the same transmit frequency.
CRYSTAL CONTROLLED OSCILLATOR - An oscillator utilizing a quartz crystal to sustain a stable transmit frequency.
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.
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.
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.
E
EDDY CURRENTS - Small circulating electrical 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.
FERROUS - Any material containing iron.
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 inartificial conditions.
FREQUENCY - The number of alternating current cycles per second (Hz) produced by the transmit oscillator.
VF = Voice Frequency = 30OHz-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).
G
GRIDDING - Rigid and disciplined search routes along predetermined boundaries used to thoroughly cover a metal detecting site in several directions. Markers or boundaries may be real or imaginary.
GROUND BALANCE - A condition or mode of operation in which the detector is adjusted to optimally reduce the interference that ground mineralization has on metal targets.
GROUND BALANCE (Manual) - A ground balance feature requiring manual adjustment by the operator.
GROUND BALANCE (Factory Preset) - A feature eliminating the ground control and operator manipulation. The metal detector is preset at the factory to an average range of non-conductive soils.
GROUND BALANCE (Self-adjusting) - A true automated ground balancing feature. The detector circuitry senses change in mineralization and compensates to sustain balance.
GROUND FILTER - Specialized sections of metal detector circuitry which separates the ground mineral effect from metal responses in the motion discriminate mode. Quality of design dictates the level of efficiency, sweep rate, depth penetration, and recovery time related to target separation.
H
HALO EFFECT - A conductive increase in target size as seen by the metal detector's electromagnetic field. The effect is caused by excessive target oxidation permeating the soil directly surrounding the target. Associated with long term burial or highly acidic soils.
HAMMERED SITE - A slang term for a metal detecting site that has been searched by metaldetectorists many times. Also called HUNTED OUT and POUNDED SITE.
HEADPHONES - Remote loudspeakers worn over the ears to enhance the operator's hearing ability and block ambient noise such as automobile traffic and ocean waves. A highly recommended alternative to the detector's speaker.
HEEL - The southern section of search coil behind the control shaft attachment point as viewed from above by the operator.
HERTZ (Hz) - Cycles per second (see FREQUENCY).
HOT ROCK - Any rock containing more non-conductive mineralization than the surrounding matrix to which the detector is ground balanced. Positive or false metallic responses can be heard from these rocks in the motion discriminate mode and a negative or null in audio threshold in the non-motion, all-metal ground balanced mode.
I
IB - An abbreviation which stands for induction balance. IB is a condition of zero current flow between transmit and receive windings prior to metal detection.
ISOLATOR - The lower most section ofnon-m etallic control shaft which attaches to the search coil and separates the metallic portion of the control shaft from the electromagnetic field.
K
KEEPER - A slang word for a good metal detecting find.
kHZ (Kilohertz) - One thousand cycles per second, (see FREQUENCY).
L
LCD - Abbreviation for Liquid Crystal Display. The basis for metal detector visual graphic display technology.
LED - Abbreviation for Light Emitting Diode. A lamp-like semiconductor used for visually indicating circuit functions such as target response and battery condition.
M
MATRIX - The total volume of ground penetrated by the electromagnetic transmit field containing minerals, metals, salts, rocks, moisture and organic matter.
MINERALIZED GROUND - Soil containing non-conductive and/or conductive properties which directly influence metal detector tuning and depth penetration.
MODE - A state of metal detector operation selected by the operator to accomplish a specific task.
MODULAR - A metal detector configuration in which the circuit board(s) can be easily removed and/or replaced for the purpose of repair or upgrade without replacing the entire metal detector.
MOTION DISCRIMINATOR - A detector requiring constant search coil motion to reduce the effect ground mineral interference has on its discriminate function.
MULTI-FREQUENCY - Metal detector circuitry employing multiple transmit frequencies to enhance the separation of ground mineral effect from target response to increase target identification accuracy.
N
NARROW RESPONSE - An audio target signal which is not wider than the physical size of the search coil.
NEGATIVE GROUND - Non-conductive soil matrix which has a negative or nulling effect on an air tuned audio threshold.
NEUTRAL GROUND - Soil with little or no non-conductive or conductive properties.
NICAD - A class of rechargeable battery having a nickel-cadmium composition.
NiMH - A class of rechargeable battery having a nickel-metal-hydrate composition.
ON-FERROUS - Metal types not containing iron such as gold, silver, copper, aluminum, etc.
NON-MOTION - Any mode of operation which sustains target response without search coil motion.
NOTCH ACCEPT - A basic notch filter discrimination mode which eliminates all responses except those whose conductive properties fall within the range of the notch width.
NOTCH FILTER DISCRIMINATION - Specialized discrimination circuitry which selectively accepts or rejects a narrow conductive range of targets inside or outside normal discrimination settings, i.e. accepting nickel coins while rejecting targets higher in conductivity such as pull-tabs.
NOTCH LEVEL - The control used to position the notch width or "window" within the range of metallic conductivities.
NOTCH REJECT - A basic notch filter discrimination mode which rejects only those targets whose conductivities fall within the range of the notch width.
NOTCH WIDTH - A preset or adjustable range of conductivity positioned by the notch level setting - also known as NOTCH WINDOW.
NULL - A momentary disappearance of threshold audio as the search coil passes over a rejected target or a hot rock located with a ground balanced mode.
NUMISMATIST - A person specializing in the study and collection of coins, tokens, and currency.
O
OSCILLATOR - A metal detector circuit component which sends a specific current frequency generation to the transmit windings of the search coil to produce an electromagnetic field.
OVERLAP - The amount of scan advance not greater than the physical size of the search coil.
OVERSHOOT - False signals produced by an auto-tuned non-motion discriminate mode as the search coil passes too quickly past a rejected target. Excessive audio restoration by automatic re-tuning produces these false signals outside the target response periphery.
P
PHASE RESPONSE - The duration of time between target surface eddy current generation and resultant secondary electromagnetic field effect on the search coil's receive windings. Also called phase lag or phase angle and is directly related to target conductivity.
PINPOINTING - The act of aligning the center of target response width to the designated search coil center for accurate location and careful recovery.
PLUGGING - A method of target recovery by which a plug of soil is carefully cut and folded back to expose deeper targets which cannot be successfully recovered with other methods.
POSITIVE GROUND - Soil containing conductive minerals or wet salts that affect an air tuned audio threshold.
POUNDED SITE - A slang term for a metal detecting site that has been searched by metaldetectorists many times. Also called HAMMERED and HUNTED OUT SITE.
PRESET MARKINGS - Metal detector control panel markings which have been highlighted by the manufacturer as a guide to setting up the detector for average operating conditions.
PI - An abbreviation for Pulse Induction circuit technology. This type detector ignores both non-conductive and conductive minerals simultaneously by pulsing the receiver amplifier off before the response from wetted salts and iron oxides can reach the search coil winding. PI detectors are capable of extreme depth but are currently inept at rejecting elongated ferrous targets.
Q
QUICK RESPONSE - The measure of time it takes between metal sensing and full audio/visual response. Generally associated with all frequencies of TR detectors.
R
RECEIVE WINDING - The coil(s) of wire inside the search coil housing whose function is to accept the secondary electromagnetic field generated on a target's surface by eddy currents.
RECOVERY TIME - The duration of time it takes a metal detector to respond to the next target after responding to the previous. Detectors with slow recovery speeds often are unable to respond to all targets in close proximity when discrimination is used.
REJECTION - Non-acceptance of a target when operating in the discriminate mode indicated by a null in threshold audio or no change in silent operation.
RETUNING - The act of manually restoring threshold audio by means of an external switch, (see AUTO-TUNE).
S
"S" HANDLE - A metal detector control shaft designed with offsets which increase operator comfort by reducing arm and wrist fatigue.
SCAN - To complete a detection path of search coil travel or sweep.
SEARCH COIL - The search head or housing which holds both transmitter and receiver windings aligned in a specific configuration, (see COAXIAL; CO-PLANAR; CONCENTRIC; DOUBLE D) Also known as a search loop or coil.
SEARCH COIL CABLE - A cable of electrostatically shielded wires which carries circuit board oscillator current frequency to the search coil and phase related target information back to the control housing.
SENSITIVITY - The measure of a metal detector's capacity to sense changes in conductivity throughout the pattern of detection set forth by the search coil configuration, (see AIR TEST).
SIGNAL - A visual and/or audio response which alerts the operator to the presence of a metal object (see FALSE SIGNAL).
SIGNAL WIDTH - The ground distance measure of search coil travel in which target audio is sustained. Signal width is directly proportional to target size and ferrous content when operating in a non-motion all-metal mode.
SILENT OPERATION - A search mode which does not use constant threshold audio tuning to maintain sensitivity.
SKID PLATE (Coil Cover) - A non-metallic cover placed on the search coil bottom for protection against abrasion.
SLOW MOTION - The rate or class of search coil sweep speed necessary to efficiently operate the motion discriminate mode.
SLOW RESPONSE - The measure of time associated with metal sensing and peak audio/ visual response. Generally associated with PI type detectors.
STABILITY - The quality of a metal detector circuit to resist external sources of thermal and electrical interference, (see DRIFT).
SURFACE BLANKING - A feature designed to eliminate the response from nondiscriminated targets lying within a predetermined depth. Based on signal intensities usually associated with shallow depths.
SWEEP - The width and/or speed rate of search coil scan.
T
TARGET - Any buried or hidden object to which a metal detector responds.
TARGET MASKING - The overriding or interfering effects large or numerous rejected targets have over desirable targets in close proximity.
TARGET SEPARATION - The ability of a metal detector to respond to individual targets within a closely spaced group.
TEN-TURN - Any control requiring ten revolutions of the indicator knob to cover the adjustment range of its function, (i.e. ground balance).
TEST GARDEN - A plot of targets intentionally buried by the detectorist. Arranged by size, depth, and composition for learning characteristic responses and comparing metal detector performances in a controlled environment.
THRESHOLD - The minimum audio level of tuning adjusted for optimum sensitivity.
TH'er - An abbreviation for Treasure Hunter, an enthusiast in a hobby of metal detecting and treasure hunting. Also called a Metaldetectorist or Detectorist.
TOE - The northern section of search coil above the control shaft attachment point as viewed from above by the operator.
TONE CONTROL - An adjustment used to regulate the audio frequency or sound pitch to operator preference. Also used to contrast target response with external ambience.
TONE ID - Audio identification of a target based on a principle of relationship between the target's conductivity and the tone's pitch: the higher the conductivity, the higher the tone, i.e. the lowest pitch tone for iron, the highest pitch tone for silver.
TRANSMIT WINDING - The coil of wire which generates and transmits the primary electromagnetic field from within the search coil housing into the soil matrix.
TR (Transmitter/Receiver) - A class of metal detectors operating in a broad range of radio frequencies (i.e. VLF/TR; VF/TR) utilizing the inductive balance principle of metal detection.
V
VCO (Voltage Controlled Oscillator) - Oscillator circuitry which is driven by target voltage to produce varying audio pitch and/or visual display responses for target identification and pinpointing.
VISUAL ID - A metal detector feature which provides the operator with a probable target identity reference in terms of relative conductivity. Indications can be a metered needle movement or LCD display.
VLF - Very Low Frequency (see FREQUENCY).
VLF/TR - A metal detector class designation meaning a transmitter/receiver type detector operating in the very low frequency range.
VOLUME CONTROL - A metal detector control which regulates the loudness of target response.
W
WIDE RESPONSE - An audio target response associated with an all-metal non-motion mode which is wider than the physical size of the search coil.
WIDE SCAN - A description of any search coil capable of producing a target response across its full dimension.
Z
ZERO DISCRIMINATION - Describes a discrimination control characteristic which accepts ferrous metals at its minimum setting, (see ALL-METAL).
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