C-SCOPE VLF 1000 Operating Instructions Manual page 4

"6. RELEASE THE AUTO-TUNE BUTTON
I(you look at the meter pointer you will find that it is now
approximately halfway across the scale.
GROUND ELIMINATION
When using the detector in the normal mode, ordinary soil
has little effect when the ground control is as 5. However,
you may notice that some types of soil cause a change in
volume as the head is brought close to the ground. This
'ground effect' can be eliminated by adjusting the ground
control. If the volume increases as the head if brought
towards the ground proceed as follows
- Raise the head well clear of the ground.
- Press the auto-tune button and keep it pressed.
- Turn the ground control to 6.
- Release the button.
- Lower the head to the ground.
If the volume still increases when the head is lowered this
means that the ground control hasn't been tuned far enough
yet. So repeat the procedure but this time set ground to 7.
If the volume now decreases when the head is lowered,
ground has now been turned too far, so repeat with the
control tuned back to between 6 and 7. Vou will soon find
a position where there is no change in volume when the
head is lowered. The detector is then correctly set for
'ground elimination'.
If the volume falls when you lower the head with ground
at 5, carry out the same procedure but turning the ground
control the other way, to 4, etc.
Vou'll soon learn to make these adjustments quite quickly.
Occasionally, however, you'll find that it is not possible
to 'eliminate the ground' in this way. There are two
possible explanations:
1. The piece of ground to which you have been lowering
the head contains buried metal. Try again nearby and if you
now succeed go back to the first spot and treasure hunt l
2. Vou have struck a patch of 'difficult' ground. A
typical example is a beach saturated with salt water. In
such cases the normal mode cannot cope, but you can still
get ground elimination by turning the function switch to
D1 and repeating the (]round elimination procedure but
this time using the reject control instead of the ground
control which is now inoperative.
If you immerse the search head in salt water even D 1 cannot
cope. Vou must then use D2 (setting up as before) and put
up with a certain amount of ground effect. See below under
"Discrimination" for how to use the detector in these
circumstances.
DISCRIMINATION (D1, D2, D3 on the Function
Switch)
The VLF 1000 rejects unwanted objects by a reduction in
volume as the head passes over them. Various amounts of
rejection can be selected by the Function switch. The
reject control provides fine adjustment. The ground control
is inoperative when the Function switch is set to one of the
D positions.
As usual, the auto-tune button should be kept pressed when
setting up the detector for discrimination. Begin with these
settings:
- Reject to 5
- Sensitivity to Max
-TunetoO
- Volume to off.
Turn the Function Switch to D1. Press the auto-tune
button (and keep it pressed). Turn volume to maximum
(fully clockwise). Turn tune until sound is just audible.
Release the auto-tune button.
The detector is now set to give a small amount of discrim­
ination. If a small iron nail is now brought near the head
the sound will disappear. Some adjustment to the size of the
iron objects that will be rejected in this way is possible by
pushing the auto-tune button and turning the reject control.
A clockwise movement increases the rejection capacity.
Silver paper is not rejected on D1 but it is on D2 as are
larger iron objects. D3 rejects most kinds of 'junk' with
suitable adjustment of the reject control ring-pulls can now
be rejected. But some useful objects are also rejected, so
use D3 with great caution.
The more discrimination you use the worse will be the
ground effect. On dry sand this may not be a problem but
on other soils ground effect may give false indications of
objects. The volume will change as the head is brought near
the ground.
To minimise this problem proceed as follows:
- Use the smallest amount of discrimination which
wi II work on the site.
- Set the tuning with the head held at the normal
search height, e.g., an inch above the ground level.
- Keep the head exactly at the correct height.
If you still have problems, turn down the sensitivity. The
detector sti II operates even with sensitivity set to 0 and
ground effect is reduced. For information, detection range
is halved if this sensitivity control is rotated fully from
maximum sensitivity to minimum sensitivity. Accordingly,
only reduce sensitivity as far as is necessary to overcome
ground effect.
DISCRIMINATION IN THE FIELD
If the site is relatively jun k free, the detector can be used in
the Normal mode with the detector adjusted for 'ground
elimination'. When an object has been located then the
detection mode can be reset by depressing the push button
and changing modes to D 1. The object can then be re­
scanned. The mode can then be reset as before to D2 and
then rescanned, and also to D3. By using this mode the
target object can be analysed. The drawback to this method
is that sensitivity to cupro-nickel coins is less on D2, or on
D3 than on Normal or D1, so a ten pence coin could be
ignored on D2 or D3 although it could be detected on
Normal or D1. The golden rule here is dig the object
unless there is a clear rejection of the target object, i.e.,
a negative meter swing or decrease in volume. Used
correctly this metAod will give the most comprehensive
analysis of the nature of the target object. It is extremely
lIseful to bury a range of objects such as an iron nail, a
piece of silver paper, a pull-tab, a copper coin, a silver
coin, and a cupro-nickel fifty pence piece, and familiarise
yourself with the reactions in the various modes.
If iron is a problem on a site and the Normal mode is
giving too many signals
to
be analysed, the detector can be
used on D1 as the main operational mode, and when an
object is located, the modes changed to D2 and D3 in
turn and the target object rescanned.
If silver paper or pull-tabs are problems, and the Normal
mode is giving too many signals to be analysed, the detector
should still be operated on D1 as the main operational
mode, and as previously when an object is located, the
modes changed to D2 and D3 in turn.
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