Metal Detector Terms Part iii

Neutral Ground: Soil that has no nonconductive or conductive mineral properties. Lacks mineralization using a metal detector.

No-Motion: Refers to any mode of operation that does not require searchcoil motion to trigger target response. Also called non-motion.

Notch Accept: Operation whereby all target responses are “tuned-out” except those the instrument is adjusted to accept in the notch “window.”

Narrow Response: A target that produces an audio response so short that pinpointing is almost not needed.

Negative Ground: Soil that contains non-conductive minerals which have a negative or nulling effect on an air-tuned threshold.

Ni-Cad or Nickel-Cadmium: A rechargeable type of battery cell.

Non-Ferrous: Not of iron. Metals of the precious class (i.e., gold, silver, copper, etc.)

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 pulltabs 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.


Notch Width: A finite discrimination range of target conductivities (“window”) at the chosen notch level.

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 searchcoil passes over a discriminated or rejected target.

Notch Level: A control used to select the target level or target conductivity which the notch filter will act upon.

Notch Reject: Operation whereby all targets within the notch width at chosen notch level will be “tuned-out.”

Overlap: The amount of searchcoil swing advance not greater than the searchcoil’s physical diameter.

Overshoot: A common false signal heard as the searchcoil 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 searchcoil’s receive winding. Related to target conductivity.

Pinpointing: Finding the exact target location with respect to a searchcoil’s designated center. Accomplished by interpreting the centers of audio response width in perpendicular directions or scans. See also Detuning.

Positive Ground: Soil which contains conductive minerals or moist salts which have a positive or upward effect on an air-tuned threshold.

PI or Pulse Induction: A mode of operation where the transmitter circuit pulses an electrical current into the ground be fore 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.

Quick Response: A short time period between metal sensing and peak audio/ visual indicator indication usually associated with all frequency ranges of TR detectors.

Rejection: An indication of target nonacceptance by a null in threshold or broken sound while operating in a discriminate mode.

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.

Scan: Refers to 1) the effective searchcoil detection width or 2) searchcoil movement over the ground.

Scrubbing: The searchcoil is pressed and held in contact with the ground while searching to maintain even audio threshold. With newer detectors, this technique is used to gain depth.

Searchcoil: A circular (or other shaped) plastic housing containing single or multiple transmit and receive windings (wire coils) in a specific configuration. A searchcoil emits and receives signals from the ground and metal targets. Also called loop, coil or head.

Searchcoil Cable: An electrostatically shielded cable of conductors (wires) which convey signals to and from the searchcoil and control housing.

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.

Signal: An audio response or visual indication alerting the operator that a target has been detected.

Signal Width: The total distance of ground an audio signal is sustained during search- coil travel or scan.

Silent Search: Refers to detectors capable of producing a target signal while operating below the threshold audio. Also called silent operation.

Scuff Cover: A protective cover for the searchcoil bottom. Also called coil cover or skid plate.

Slow Motion: A description of searchcoil speed required to operate the motion discriminate mode.

Stability: The ability of a metal detector to maintain manually adjusted tuning thresh- old under the effects of outside interference. See also Drift.

Surface Area: Refers to the area of a target closest to the searchcoil where eddy current generation can take place.

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.

Sweep: The motion employed in moving the searchcoil across the ground.

Target: Refers to any object that causes an audio or visual response in a detector.

Target Masking: When large sizes or high concentrations of trash metals drive the threshold into the null zone suppressing weaker, positive responses from deeper or smaller targets.

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.

Tone ID: Circuitry producing different audio tones for each target’s conductivity range, i.e., low tone for nickel, high tone for coins.

Ten-Turn: A control which can be manually rotated ten times to cover the full electrical range of the function. Usually associated with tuning or ground balance function.

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.

TH’er,TH’ing: Universal word contractions for treasure hunter and treasure hunting. Also known as Metal Detectorist.

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/TR: A class of detector that can operate in both the All Metal, Ground Balance mode and the No-Motion Discriminate, Non-Ground Balance mode.

Wide Response: A target that produces an audio signal over an area wider than the searchcoil diameter.

Wide Scan: A coplanar searchcoil with two “D” shaped transmit and receive windings positioned back to back and overlapping. This searchcoil type is capable of detecting a target across at least its full diameter. Also called Double-D or 2-D.

Zero Discrimination: Used to describe detectorswhose discrimination control allows the acceptance of all metals at zero setting.

Visual ID: A feature in which a visual indication is produced to help identify the target.

Visual Indicator: A meter, LCD or LED that signals a target’s presence.

VLF or Very Low Frequency: See Frequency.

VLF/DISC: Term associated with detectors capable of mineral-free operation in both the Discriminate and All Metal modes.