Glossary of Metal Detecting Terms
Terminology Used in Metal Detector Instruction Manuals and Among Metaldetectorists
NOTE: Metal detecting terms used in the instruction manuals and among metaldetectorists are included in this glossary. Excluded are the uncommon slang words and expressions. If you do not see a term that you think is important, please let me know.
A
AIR TEST (see also BENCH TEST and FIELD TEST) - A test to determine the maximum sensitivity a metal detector is capable of under artificial 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.
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.
ALLOY - A substance which is composed of two or more metals (an alloy may also include non-metals).
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.
BBS (see also MULTI-FREQUENCY and FBS) - Broad Band Spectrum is a multi- technology used by the early Minelab metal detectors (Explorer XS, Sovereign and Excalibur). BBs circuit automatically transmits from 17 to 28 frequencies simultaneously. BBS preceded the newer FBS technology of Minelab.
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.
BFO - Beat Frequency Oscillation is the oldest technology used in metal detectors. BFO metal detectors have two coils of wire. One large coil is located in the search coil of the detector, the other small coil of wire - a "receiver" coil, is located within the System Control Pack or Control Box. Each coil of wire is connected to an oscillator that produces pulses of current. These pulses of current pass through the coils generating radio waves. A "receiver" coil housed within the Control Box receives the radio waves and makes a series of tones based upon the waves' frequencies. When the detector's search coil passes over any metallic object, a magnetic field called Eddy Currents is created around the object. As this magnetic field causes interference with the frequency of the radio waves generated by the search coil, the tone produced by the receiver is also changed.
BFO metal detectors are the cheapest (under $100) and designed mainly as toy detectors for kids. Because the BFO technology is the easiest and cheapest to make, it has its limitations when compared to other types. For example, poor ability in distinguishing between different types of metals is one of them. BFO technology is also still used in cheap hand-held devices.
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. Body Mount is also called Hip-Mount.
"BUTTERFLY" Search Coils - These search coils are a variant of the DD Search coils' open design with a butterfly-like shape.
C
CACHE - A hoard of coins or other valuables purposely buried or concealed. Also called Coin Cache.
CAMLOCK - Lever which releases or locks detector's assembly components (shafts or stems).
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 two transmit coils (windings) and one receive coil of unequal 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. More on search coils here.
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 (also CONTROL BOX) - The enclosure which contains detection circuitry, indicators, power source and related controls. Control housing provides user access to functions via the Control Panel. Typically made of plastic or metal.
CONTROL PANEL - The front of the Control Box housing the display screen and providing press-button or knob access to all of the detector's operating functions.
CONTROL SHAFT - Telescoping metal tubes to which the control housing, search coil, and isolator are attached. Also called Medium Shaft.
CONVERTIBLE - A metal detector configuration in which the control housing can be temporarily detached for body-mounting (hip-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.
