3
how detectors work
Metal detectors create an electromagnetic eld,
which penetrates the ground. Metal objects
cause a change to this eld because they are
conductive. The detector senses this change
and sends a signal back to the control box,
alerting the operator.
Metal detectors can determine the size, shape
and composition of metallic objects beneath
the coil. Typically, the larger the object, the
easier it is to detect.
“BEEP!”
The 2nd generation X-Terra detectors continue to
incorporate Minelab’s proven VFLEX Technology.
VFLEX uses state of the art digital and mixed-signal
components to enhance standard single frequency
technology by replacing most of the analogue circuitry
with digital signal processing. The small amount of
analogue circuitry still employed has been very carefully
designed and calibrated to obtain the outstanding
sensitivity, stability and repeatability required to match
the performance of the digital processing.
This radical departure from traditional approaches to
metal detector design has been made possible by
advances in electronics that power personal digital
assistants, cell (mobile) phones and high-delity
portable audio equipment.
Precision VFLEX Signal
Standard VLF Signal
(Without VFLEX)
Power
Supply
Audio
Transmit
LCD ReceiveKeypad
Primary micro
(in control box)
Digital Signal ProceSSing
(DSP)
coDec Signal converSion
Analog Signal
Coil
Analog Signal
Transmit
Receive
SeconDary micro
(in coil)
SenSing + tranSmitting
coil tyPe, Size, frequency
Control Box
For the X-Terra user, this precision means dependable
performance and improved immunity to environmental
conditions such as ground mineralisation,
electromagnetic interference and temperature
variations.
VFLEX requires coils that are accurately constructed and
calibrated. Every time the detector starts up, the micro-
controllers in the control box and the coil establish
communication through a digital data link.
Information about the coil is sent to the control box, so
the detector ‘knows’ what type of coil is attached and
can set the appropriate operating parameters.
This optimises performance, and also makes the
detector ‘future proof’, in that it will be capable of
operating at dierent frequencies depending on the
electronic properties of the coil.
The frequency of a detector is
the number of times a signal is
transmitted into the ground, per
second (measured in Hertz - Hz).
1000Hz = 1kHz.
The X-Terra 705 has two basic coil congurations,
each with its own benets.
A Concentric coil is the
standard coil supplied
with the X-Terra 705
and is an all purpose
coil with excellent
pinpointing capabilities.
Double D coils are
available also. They
provide improved ground
rejection and have a
dierent detection prole.
The X-Terra 705 uses a single frequency
(7.5kHz) as it’s standard operating frequency.
This frequency has the ability to penetrate
deep into the ground and is the most suitable
for general purpose detecting.
The X-Terra 705 is also capable of operating at
frequencies of 3kHz and 18.75kHz, depending
upon the selection of appropriate accessory
coils (p. 48, 52).
The X-Terra 705 has two main detecting
modes: Coin & Treasure Mode (p.18) for general
purpose detecting and Prospecting Mode (p.
19) for detecting gold nuggets and relics.
The specialised Prospecting Mode has
improved Sensitivity and adjustable Iron Mask
Discrimination. It is the ideal mode when
searching for gold nuggets, small relics, and
some types of jewellery.
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