KNOWLEDGE BASE ARTICLE

Zero Voltage Transmission (ZVT) Technology

GPZ 7000 Tips for Better Ground Balance
Achieving good ground balance is imperative to successful gold prospecting; without it, false
signals from mineralised ground can mask gold signals. While most gold prospectors are familiar
with the ground balance process used with PI detectors, such as the GPX Series, the new technologyof the GPZ 7000 requires a new technique. This article describes advanced ground balancing
methods for obtaining optimum performance and gives tips for maximum detecting success.

How NOT to ground balance the GPZ 7000

How to ground balance the GPZ 7000

Using the GPX Series ground balance method for PI technology

Using the GPZ 7000 ground balance method for ZVT technology

The most common method of ground balancing
on GPX Series detectors is several cycles ofraising and lowering the coil between up to a
few tens of centimetres and down to a few
centimetres above the soil surface. This is usually
done whilst pressing and holding a groundbalance button until the audio is no longer
affected by the coil up and down movement, or at least until the audio
signal variation is lessened and stabilised. Thereafter, the groundbalance button is released and searching for targets by swinging thecoil side‑to‑side commences. With this technique only one aspect of
the ground balance ‘mathematics’ is varied to achieve the best value
for ground balance.

The best way to ground balance initially afterswitch on, is to press and hold the Quick‑Trak
trigger while sweeping the coil in a typicalside‑to‑side search motion at the recommended
coil operating height above the soil surface,e.g. 2–3 centimetres or whatever the soil
saturation or terrain will allow*. At the sametime, move forward at a slightly faster thannormal walking speed, so as to cover as much different ground as
possible in the first 10–12 seconds.

It is important to realise that the ground balancing operation of
the GPZ 7000 is different to PI metal detectors.
The GPZ 7000 uses new ZVT technology that analyses many moreground parameters and needs to be physically ground balanced bymoving the coil in a different way.
(Refer to Minelab KBA 24 for further information on ZVT technology.)

Why is the GPZ 7000 different?
What happens with ZVT technology when ground balancing
After the GPZ 7000 is switched on, and the Quick‑Trak trigger ispressed, the detector calibrates itself to the local ground conditions
within several seconds of moving the coil over the ground. This initial
fast calibration involves several different aspects of the detector
being calibrated, not just the single parameter as described above.
Upon further searching, the ground balance continually tracks or‘updates’ the primary soil ground balance data moderately quickly,
but the additional parameters calibrated during the initial groundbalancing are far more slowly updated. These extra measurements also
contribute to how well the GPZ 7000 is ground balanced and 'tracks' tothe changing ground conditions as you detect.

Cover as much different groundas possible when performing
initial ground balance, trying not
to overlap your sweep.
* Refer to KBA 24 'ZVT Technology'
for further information and tips
on ground balancing in saturable
soil conditions.

At completion, the Quick‑Trak trigger should be released and thedetector is ready for searching using normal detecting methods.

To ground balance well, the GPZ 7000 requires as much
DIFFERENT data about the local ground conditions as possible,especially variations in the soil mineralisation.

You can then easily check how well the detector is ground balanced
to the exact location by using the conventional method of raising andlowering the coil over one spot to ensure the detector is quiet.
Note– you must NOT perform this ground balancing coil up‑downchecking method after initially turning on the detector, but only after
searching for at least several minutes.

Therefore, ground balancing using the typical PI method of raisingand lowering the coil over only one spot of ground is the worst way
to ground balance the GPZ 7000. This is because this method merely
provides the detector with data from just one small area of the soil,
and not data from a larger area and wider variety of soil mineralisation.

Even though the ZVT signal processing continually updates theground balance settings during searching, occasionally, the soil
conditions may change abruptly and the detector will need re-groundbalancing (by pressing and holding the Quick‑Trak trigger and using
the above sweeping technique).

KNOWLEDGE BASE ARTICLE | KBA 26-1

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Correcting poor initial ground balance
If you happen to initially ground balance in an abnormal location (e.g.
too close to a metal target or over an unusual patch of soil), the initial
calibration may end up being inaccurate. This will cause extra audio
signals when detecting. This is because the slowly updating calibration
is taking a longer time to become more accurate to the typicalconditions (rather than the initial abnormal conditions).
Thus if you think the detector is producing an unexpected level of soil
signals, switch the detector off, then on again, and re‑ground balance.
Usually, this time, your detector will be correctly calibrated from the restart.
If your detector is still producing an unexpected levelof soil signals, select Quick Start on the Detect page,
and then select Reset Audio and Detector Settings
when prompted by the menu. Then re-ground balanceby following the Quick Start guide sequence steps.

How do you know if your GPZ 7000 is correctly
ground balanced?
If you have a loud audio response from the ground, pass the coil backand forth over the same spot for approximately 20 seconds. If the audio
signal disappears then this likely indicates ground noise. This will beespecially so if you are also pressing and holding the Quick-Trak trigger.

An advanced ground balancing method
for optimum performance
In order to artificially add extra data for improved ground balancecalibration, you can use a dust iron toroid, commonly referred to as anelectronics 'ferrite'. The electronics industry uses these magnetic cores
extensively in computers, televisions, and mobile phones.
Ground balancing using a ferrite means that less soil needs to becovered during the initial ground balance period because the ferrite
artificially adds very useful data to assist achieving an accurate groundbalance.
The easiest way to add this data during the initial ground balance, andand ideally, at all later ground balancings, is to place the ferrite on thesoil surface and swing the coil over it several times in wide sweeps
at the operating height of the coil, whilst ground balancing, so as toinclude data from both the soil and the ferrite.

IMPORTANT: Make sure that you pass the coil over the ferrite
almost immediately when you start the ground balancing
procedure.

If the GPZ 7000 produces more than a faint audio ‘murmur’ when thecoil is swept over the ferrite, at a height of a centimetre or two, then it
is NOT correctly ground balanced. If it does produce a significant audio
signal, re‑ground balance using the ferrite as above. If it then still
produces a significant audio signal from the ferrite, switch the detector
off, then on again, and re‑ground balance using the ferrite as describedabove.
Minelab Accessory Ferrite (Part No. 3011-0301) can beobtained, at no charge to GPZ 7000 owners, from yourlocal Minelab dealer. This is supplied with a referencecard giving the step-by-step ground balancing
procedure for you to follow:

Ground Balance with the Ferrite
1. Find an open area free from targets and place the ferrite on
the soil surface.
2. Turn GPZ 7000 ON.
3. Select Quick Start on the Detect page.
4. Select Reset Audio and Detection Settings.
5. Carry out Noise Cancel.
6. When ground balancing, press and hold the Quick‑Traktrigger, then start to sweep the coil at normal detecting
height in a figure 8 motion.
IMPORTANT: Make sure that you pass the coil over the ferrite
almost immediately when you start the ground balancing
procedure.
7. Continue to sweep the coil over as much ground as
possible, for 10–12 seconds, while passing the coil over theferrite every sweep, as shown.

NOTE: Oncethe audio tone
remains quietand constantwhen the coil isswept over theferrite, groundbalance iscomplete.

Ferrite

8. Release the Quick-Trak trigger button and start detecting.

FerriteFurther technical informationA ‘dust iron’ toroid suitable for the HF frequency band (e.g.1–30MHzwith an initial permeability of between 6 and 10) has been carefully
selected. It is recommended to use this specific Minelab accessory,only. Alternate ferrites may significantly degrade ground balance
quality.

Ground balancing with a ferrite: The sweep path crosses over the ferrite numerous
times whilst also covering as much different ground as possible.

KNOWLEDGE BASE ARTICLE | KBA 26-1

Be careful not to drop ferrites because they are brittle and breakfairly easily!

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