Metal Detecting Terminology
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Air Test : A test performed by moving various sized metal samples beneath the metal detector search coil to check the detector's features and target response. This test is not an accurate indicator of ground depth penetration capability.
Audio ID : See Tone ID.
Audio Response : See Target Response.
Body Mount : A configuration whereby the control housing is separated from the control shaft and fastened to the operator's body lessening arm fatigue and expanding usability for shallow water hunting. Also known as hip mount.
Coil : See Search Coil.
Concentric : A search coil configuration using one or more transmit and one receive windings having unequal diameters aligned on a common center; most recently arranged on the same plane and called coplanar concentric.
Detection Pattern : The densest or strongest region of the search coil’s electromagnetic field where detection occurs. Its shape is balloon and changes in size directly proportional to target surface area.
Detuning : Adjusting the audio threshold into the null or less sensitivity tuning zone. Also a method of narrowing a target signal width manually for precise pinpointing. This is accomplished by retuning to audio threshold over the target response area.
DISC : See Discrimination.
Discrimination : Adjustable circuitry which ignores or nulls audio responses from a specific conductivity range allowing positive responses to be heard from metals higher in conductivity above the discriminate control setting. Designed primarily to eliminate audio response from trash metals. See also Motion Discriminator.
Double D or 2 D : See Wide Scan.
Eddy Currents : Small circulating currents produced on the surface of metal by the transmitted electromagnetic field. These currents then produce a secondary electromagnetic field which is then detected by the search coil receiver windings resulting in inductive imbalance between the windings.
Electromagnetic Field : An invisible force extending from top and bottom of the search coil created by the flow of alternating oscillator frequency current around the transmit winding. See also Detection Pattern.
Faraday-Shield : A metal foil wrapping of the search coil windings or metallically painted search coil housing interior for the purpose of eliminating electrostatic interference caused by wet vegetation.
Ferrous Oxide : An oxidized particle of iron which generally becomes nonconductive and makes up the natural negative ground mineral matrix. Hematite, which is also iron oxide (Fe203) will respond as positive or metallic. See also Black Sand.
Frequency : The number of complete alternating current cycles produced by the transmit oscillator per second. Measured in cycles per second. VLF Very Low Frequency = 3 to 30 kHz; LF Low Frequency = 30 to 300 kHz;MF Medium Frequency = 300 to 3000 kHz; HF High Frequency = 3 to 30 MHz.
Ground Balance - Factory Preset: A feature which eliminates the manual ground balance control and its adjustment from the operator's setup procedure. This adjustment is performed internally by the factory to optimize operation over an average range of nonconductive soils.
Ground Balance - Manual Adjusted: A feature requiring a manual control adjustment procedure to neutralize the effects of negative minerals in the search matrix.
Ground Balance - Self Adjusting: A feature which senses change in ground mineral content and continuously readjusts the ground balance while in operation. Sometimes called Ground Tracking or Automatic Ground Balance.
Head : See Search Coil.
Hip Mount : See Body Mount.
Hot Rock : A rock which contains a higher concentration of nonconductive ground minerals than the surrounding matrix to which the detector is balanced. A metallic (positive) response will be heard in the motion and non-motion modes and a null or negative drop in threshold is heard in the all-metal, ground balance mode over these rocks.
Isolator : A nonmetal stem which attaches the search coil to the control shaft eliminating metallic interference in the detection pattern. On some detectors, the entire lower shaft is made of a nonmetal substance.
LCD or Liquid Crystal Display : Used on a metal detector as a graphic visual indicator same as a meter/needle indicator.
Loop : See Search Coil.
Meter : A detector component that provides visual information to aid in target identification. Meters feature either an LCD or needle indicator which may display intensity of signal, target depth, target identification, type of metal, or battery condition.
Notch Discrimination : Filtering circuitry which allows a "window" of desirable targets to be accepted within the entire rejection range of unaccepted targets, i.e., rejecting nails, foil and pull tabs while accepting nickels and gold rings of the same conductivity. This circuitry can also be adjusted to reject all metal targets while accepting only a specific conductivity range.
Null : The zone just below audible threshold in metal detector tuning. This also refers to the momentary drop or quiet response of threshold sound as the search coil passes over a discriminated or rejected target.
Overshoot : A common false signal heard as the search coil passes over a rejected target when using a no-motion All Metal mode in conjunction with automatic retuning. Excessive tuning restoration pushes the audio above threshold level creating a positive response at the edges of target detection periphery.
Phase Response : The length of time between eddy current generation sustained on a metal's surface and the resultant secondary electromagnetic field effect on the search coil’s receive winding. Related to target conductivity.
Pinpointing : Finding the exact target location with respect to a search coil’s designated center. Accomplished by interpreting the centers of audio response width in perpendicular directions or scans. See also Detuning.
PI or Pulse Induction : A mode of operation where the transmitter circuit pulses an electrical current into the ground before it quickly shuts down. The eddy cur rents dissipate immediately from poor conductors such as wet salt sand and ground minerals. Metals hold eddy cur rents because they are better conductors. When the receiver circuit comes on, it picks up the returning signal from metal; the eddy currents in the ground minerals have already disappeared.
RF-Two Box : A radio frequency detector having its own transmit and receive windings separate and in an orthogonal configuration. This detector is capable of deep large object detection while naturally ignoring small targets such as nails and individual coins.
Search Coil : A circular (or other shaped) plastic housing containing single or multiple transmit and receive windings (wire coils) in a specific configuration. A search coil emits and receives signals from the ground and metal targets. Also called loop, coil or head.
Sensitivity : The capacity of a metal detector to perceive changes in conductivity within the detection pattern. Generally, the more sensitivity a detector can smoothly provide, the more depth it will achieve in sensing targets.
Surface Mount : The art of mounting electronic components on the surface of a printed circuit board rather than using the "through board" method. This allows more technology in a much smaller space and with much higher tolerances.
Target Response : See Signal.
Test Garden : A mapped plot of buried targets at various depths to aid in learning characteristic target responses and in comparing metal detector performances under a given ground mineral content. Also called test plot or test bed.
Threshold : Continuous tone that establishes a reference point for tuning the detector to ground balance it. The threshold tone also establishes the minimum sound level for deep targets in the discriminate mode.
TR or Transmitter-Receiver : Term describing method of operation of early detectors. Some manufacturers still produce this type of detector. Electromagnetic field distortion caused by mineralized ground interferes with depth penetration as this type of detector does not ground compensate. It does balance conductive salt water effects so, it is primarily used in salt water and on low mineral salt water beaches or low mineral inland locations.
VLF or Very Low Frequency : See Frequency.
Wide Scan : A coplanar search coil with two "D" shaped transmit and receive windings positioned back to back and overlapping. This search coil type is capable of detecting a target across at least its full diameter. Also called Double-D or 2-D.