Hey, we all have to start from somewhere. Here at Crawfords Metal Detectors, we are more than just a shop, we are detectorists too who like nothing more than to get out there in the fields. We want you to get the most from our exciting hobby, so before you make your first metal detecting purchase, read our little guide below and then get give us a call (01724 845608) and ask the questions the glossy ads never seem to answer. METAL DETECTOR GUIDE
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A test performed by passing metal samples of various sizes under the detector's search coil to check target responses.
This test is not an accurate indicator of ground depth penetration.
A type of battery characterised by the ability to sustain longer periods of current drain and greater storage life than standard carbon-zinc batteries.
Describes any mode or control setting that allows total acceptance of metal targets.
Usually associated with ground balance mode.
Circuitry producing different audio tone for each target's conductivity range, eg low tone for iron, high tone for coins.
Circuitry which continuously retunes the detector's threshold to the initially tuned audio level at a preset rate after drift and/or target rejection.
A false signal caused by a rejected target coming within one inch of, or contacting, the bottom of the search coil when operating in the discriminate mode.
An air test to determine at what approximate discriminate settings various metal samples are rejected or accepted.
The test is conducted in non-metallic area.
One of the most extreme components of non-conductive, negative ground minerals.
Also called magnetite and magnetic iron oxide.
A method of fastening the detector's control box to expand usability for shallow water hunting. Also known as hip mount.
Standard dry cell batteries.
Coin Depth Indicator
A visual indicator, used in conjunction with calibrated circuitry, to show depths, in inches or centimetres, of buried coins.
A search coil configuration using one or more transmit, and one receive, winding having unequal diameters aligned on a common center,
most recently arranged on the same plane and called coplaner concentric.
Wet salt sand which produces a positive rise, or metallic response on an air tuned threshold.
The measure of a metal target's ability to allow eddy currents to generate on its surface.
The densest or strongest region of the search coilselectromagnetic field where detection occurs.
It is balloon shaped and changes in size directly in proportion to target surface area.
Adjusting the audio threshold into the null or less sensitive tuning zone.
It is also a method of narrowing a target's signal width manually for precise pinpointing.
This is accomplished by returning to audio threshold over the target response area.
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 unwanted metals.
A loss of threshold tuning stability caused by temperature change, battery condition, mineral content, and/or detector design.
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.
An invisible force extending from top to bottom of the search coil and created by the flow of alternating oscillator frequency current around the transmit winding.
A metal foil wrapping of the search coil windings for the purpose of eliminating electrostatic interference caused by wet vegetation.
Descriptive of any iron bearing material.
An oxidised particle of iron which becomes non-conductive and makes up the natural negative ground mineral matrix.
Hematite, which is also an iron oxide, will respond as positive or metallic.
The number of complete alternating current cycles per second produced by the transmit oscillator.
Measured in Hertz (Hz).
A state of operation in which specialised circuitry can be adjusted to ignore the masking effect that iron ground minerals have over metal targets.
Ground Balance (Factory Preset)
A feature which eliminates the manual ground balance control and its adjustment from the operators set up procedure.
This adjustment is performed internally by the factory to optimise operation over an average range of non-conductive soils.
Ground Balance (Operator Adjust)
A feature requiring a manual control adjustment procedure to neutralise the effects of negative minerals in the search matrix.
Complex circuitry found in motion type detectors which separates mineral signals from metal signals,
allowing the metal signal to be further processed by the discrimination circuitry.
A rock which contains a higher concentration of non-conductive 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 metalground balance mode over these rocks.
Liquid Crystal Display. Type of screen used on a metal detector as a graphic visual indicator.
Light Emitting Diode.
A semiconductor which produces an illuminated visual response.
Has the appeance of a small lightbulb.
Any soil that contains conductive or non conductive components.
The abillty of a detector to operate on more than just one frequency.
True simultaneous multi frequency can use a number of frequencies all at the same time.
Some multi frequency machines can only use a single frequency at any one time, but will allow you to switch from one frequency to another as you choose.
Soil that contains non-conductive minerals which have a negative or nulling effect on air-tuned threshold.
Soil lacking non-conductive or conductive mineral properties.
It lacks mineralisation.
Nickel Cadmium. A rechargeable battery.
Not of iron; metals including gold, silver, copper, lead, tin, brass, bronze, etc.
Mode of operation that does not require search coil movement to trigger target response.
Operation whereby all target responses are tuned out except those the instrument is adjusted to accept in the notch window.
Circuitry which allows a desirable window of targets to be accepted within the rejection range of unaccepted targets.
A control used to select the target level of conductivity which the notch filter will act upon.
Operation whereby all targets within the notch width (at the chosen notch level) will be tuned out.
Zone just below audible threshold in detector tuning.
The term also refers to the momentary drop, or quiet response, of threshold audio as the search coil passes over a discriminated or rejected target.
The amount of search coil swing advance not greater than the search coil's physical diameter.
Finding the exact target location with respect to a search coil's designated centre.
Accomplished by interpreting the centres of audio response width in perpendicular directions or scans.
Pulse Induction. A metal detector with a transmitter circuit that pulses an electric current into the ground before quickly shutting down.
The eddy currents dissipate immediately from wet salt sand and other ground minerals because they are poor conductors.
Because they are better conductors, metals hold the eddy currents, and when the receiver circuit comes on, it picks up the returning signals from metal objects.
Radio frequency detector with 2 separate coils, the detector is capable of detecting large, deep objects while naturally ignoring small targets such as nails and individual coins.
The effective search coil detection width. Also refers to search coil movement over the ground.
Search technique in which the search coil is pressed and held in contact with the ground in order to maintain an even audio threshold.
With newer detectors, this technique is used to gain depth.
A circular (or other shaped) plastic housing containing single or multiple transmit and receive wingdings in a specific orientation or configuration to emit and receive signals from ground and targets.
Also called a loop,coil or search head.
Search Coil Cable
An electrostatically shielded cable of conductors (wires) which convey signals to/from the search coil and control housing.
The measure of capacity of a 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.
(= silent operation) A detector capable of producing a target signal while operating below the threshold audio.
A protective, sacrificial plastic cover placed on the search coil bottom to protect it from damage and wear.
Also known as a Coil Cover.
A description of search coil speed required to operate the motion discriminate mode.
The motion employed in moving the search coil across the ground.
Occurs when large pieces, or high concentrations, of trash metals drive the threshold into the null zone, suppressing weaker responses from deeper or smaller targets.
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.
An audible reference point for tuning the detector in order to ground balance it.
The threshold tone also establishes the minimum sound level for deep targets in the discriminate mode.
Transmit/Receive. The term used to describe an early type of detector, still produced by some manufacturers. Electromagnetic field distortion caused by mineralised ground interferes with depth penetration because this type of detector does not ground compensate.
It does however balance salt water effects.
Therefore, it is primarily used for searching in salt water and on low mineral salt water beaches.
Visual indication used to identify targets.
Very Low Frequency.
Term associated with detectors capable of mineral free operation in both the discriminate and all metal mode.