White’s Electronics TDI SL 7.5 User Manual
TDI
SL
White’s Electronics, Inc.
Sweet Home, Oregon USA
Building the World’s Finest
metal detectors for over 60 years.
TDI SL
Owner’s Manual
CONTENTS
Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Batteries and Charger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
QuickStart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Principles of Pulse Induction . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Controls
Threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Power/gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Pulse Delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Target Conductivity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Ground Balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
TDI In Depth
Ground Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Audio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Pulse Delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Dual-field coil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Dealing with Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Code of Ethics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Back Cover
Page 2
TDI SL
Search coil
Lower rod
Arm cup
Battery door
Clevis
Rubber
washers (2),
fiber bolt
Cam lock
Owner’s Manual
Assembly
1. Remove all parts from the shipping carton and check assem-
bly diagram to ensure all parts are present.
2. Install black rubber washers on fiber clevis/lower rod, insert
clevis lower rod onto loop ears. Use only nonmetallic washers, fiber bolt, and fiber thumb nut to secure loop/search coil
to clevis/lower fiber rod.
3. Unlock “S” rod cam-lock and insert clevis/lower rod into
4. Wind the loop cable around the rod assembly, first revolu-
5. Grip the instrument by the handle, with your arm in the
curved “S” rod so that stainless steel spring clip buttons line
up and lock into one of the adjustment holes in the curved
“S” rod. Turn cam-lock to secure. The second or third
adjustment holes are suitable for average sized adults.
tion over the top of the rod, all the way to the top of the
curved “S” rod, about five revolutions. Use the black cable
retainers, one near the loop, and one near the top of the
curved “S” rod, to hold the loop cable in place. Plug the
cable into the jack on the front of the control box.
elbow cup with strap and sweep the loop/search coil over
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TDI SL
the floor. If the instrument fit feels uncomfortable, readjust
clevis/lower rod length with spring clip button and camlock so that search coil can be held near the floor without
stooping over.
6. Remove the protective paper from the two black arm cup
foam pads. Carefully align pads on the inside of the elbow
cup, one on each side of the center rod, and press firmly into
place.
7. Adjust the elbow cup strap so that it is loose enough for you
to slide your arm in and out without loosening each time
you want to set the detector down. The elbow cup strap provides extra leverage and control. However, some prefer not
to use it.
8. Install the battery pack; see the next section for information
on batteries and charging.
Owner’s Manual
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TDI SL
Owner’s Manual
Batteries and Charger
The TDI-SL includes a rechargeable NiMH battery pack as
the primary power source, and a standard alkaline battery pack
as a backup. Fully charged, they supply a nominal 12 volts (the
NiMH may be slightly less) and will power the TDI-SL for
about 4-5 hours. The TDI will operate until the batteries drop to
about 8.5 volts, at which point the low battery LED will turn on.
A drop-in charging cradle (Part Number 509-0036) is used
for recharging the NiMH battery. With the wall transformer
connected to the cradle and plugged into a wall socket, simply
drop the NiMH pack into the cradle. An LED indicates the status of the charge cycle; when the LED turns off, the charge
cycle is complete and the charger will automatically switch to a
trickle mode. A typical recharge time of a depleted NiMH pack
is 1-2 hours. It is normal for NiMH batteries in storage to
slowly lose their charge over time; be sure to top off them off
before going out.
The alkaline pack is designed so that it cannot be used with
the charger, and trying to recharge alkaline batteries can cause
them to burst and leak. Individual NiMH batteries can be used
in the alkaline tray; it is recommended that the batteries be
removed and charged using the manufacturer’s charging system.
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TDI SL
Owner’s Manual
QuickStart
1. Set the Conductivity switch to ALL.
2. Set the Frequency offset to the midpoint.
3. Set the Ground Balance to ~8.
4. Turn on the power and adjust the Gain to “2.”
5. Adjust the Threshold to achieve a faint background hum.
6. With the coil on the ground (no motion) increase the Gain
until the audio begins to chatter. Back off slightly for a reasonably smooth threshold.
7. Optional: adjust the Frequency offset to minimize the
amount of chatter.
8. Using a spot free of targets, bob the coil up & down and
adjust the Ground Balance control to minimize the audio
response.
9. For most nugget hunting, set the Conductivity switch to
LOW.
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TDI SL
Exponential decay
Pulse Rate
TX
RX
No target
High-conductive
target, long decay
Low-conductive
target, fast decay
Raw Response
Owner’s Manual
Principles of Pulse Induction
Pulse induction (PI) detectors are very different from traditional induction-balance (VLF) designs. Instead of transmitting
a continuous-wave magnetic field, the PI detector periodically
transmits brief impulses of magnetic energy. The PI receiver
then looks at the impulse decay for target (and ground) information.
The use of high-powered impulses results in better ground
penetration than VLF, especially in highly mineralized soil.
This makes the PI detector the best choice for certain kinds of
hunting in bad ground where many VLFs simply won’t work.
There is no traditional discriminator in PI detectors,
although there is some ability to discern certain types of metals.
The decay response varies with target conductivity (plus other
characteristics) so that low conductive targets have a fast decay
and high conductive targets have a slow decay:
The Pulse Delay control, which determines the point where
the decay is sampled, can be used to eliminate low conductive
targets such as thin foil. Further increasing the delay can knock
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TDI SL
No target
Differential Response
High-conductive target
Low-conductive target
Ground balance point
Owner’s Manual
out other minor trash targets at the expense of eliminating
potentially good targets such as jewelry, but this method is very
limited in the range of trash targets that are rejected.
Furthermore, the ground balancing method used by TDI has
a side affect with target responses. Target conductivities below
the ground balance point produce a positive response for which
TDI assigns a high tone. These targets are generally low conductive such as small nuggets, jewelry, and small iron. Target
conductivities above the ground balance point produce a negative response for which TDI assigns a low tone. These targets
are generally high conductive such as silver coins, relics, and
large iron.
The Target Conductivity switch can be used to eliminate either
class of targets, or to accept them all. Care should be used with
this feature as it is not always obvious as to how a target might
respond. Testing with known targets is the best way to learn the
responses, both with delay settings and conductivity mode.
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