Minelab GPX-4000 Service Manual download pdf (Page 14)

22 23Detector Sounds

Threshold (Background sound)

This is the background sound produced by the

detector. When a target is detected, the Threshold

changes in volume and pitch. Listen to the Threshold

carefully. Concentration is an important part of

detecting. A very deep or small target may only give

a minor change to the Threshold.

(pg. 34)

Target Response (Metal Object Response)

This is a change in the tone (pitch) and volume of

the Threshold when a target is detected and not

discriminated (rejected).

Electrical Interference

The detector may also produce sounds when not

over the ground. These will not be target signals, but

signals caused from the surrounding environment.

The GPX-4000 has a Tune function to overcome

electrical interference. (pg. 32)

Ground Noise

The detector may also produce various random

signals caused by different minerals in the ground,

sometimes referred to as false signals. The GPX-

4000 has an automatic Ground Balance function to

overcome ground noise. (pg. 38)

Blanking

When sweeping over a rejected target, the Threshold

‘blanks’ (becomes silent) indicating that a target is

located underneath the coil, but has been rejected.

Blanking is a useful way of distinguishing between

desired and undesired targets. (pg. 59)

Low Battery

When the battery is low, a series of alarm signal

pulses are given at 1 minute intervals.

(pg. 62)

Targets

Buried metal objects are

referred to as targets.

Targets are comprised of

both ferrous and non-

ferrous metals.

The GPX-4000 is a ‘motion’

detector. This means it

must be moving over a

target to detect it.

Detecting Basics

The GPX-4000 will perform at its best when the coil

is kept close and parallel to the ground at all times.

This will increase detection depth and response to

small objects.

Practise sweeping the coil over the ground in a

side-to-side motion, while walking forward slowly at

the end of each sweep. Slightly overlap the previous

sweep to ensure full ground coverage. An average

sweep speed is four seconds from left to right to left.

A variation in coil height at the end of each swing

may cause confusing sounds and reduce detection

depth, so an even, flat sweep is desirable.

When using a Monoloop coil, more overlap is required

to ensure that targets at maximum depth are not

overlooked.

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Minelab GPX-4000 Service Manual Page 14

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