White’s Electronics TDI SL 7.5 and 12 - Manual (Page 10)

Page 10
TDI SL
Owner’s Manual
that higher gain will always give better depth. In air tests this is
generally true, but ground results can depend on the amount and
type of mineralization.
With the coil on the ground, increase the gain until the
detector exhibits chatter, then back off slightly for a reasonably
steady threshold tone. Use the
Frequency
offset control to help
deal with EMI-related chatter, and proper ground balancing will
minimize chatter due to mineralization.
The
Gain
control is also used to turn the detector on and off.
Pulse Delay
TDI transmits a pulse and then,
after a short time delay, samples the
received signal.
Pulse Delay
allows this
time delay to be adjusted from 10
s
(microseconds) to 25 s.
In response to a transmitted
impulse, all targets exhibit a response
with an exponential decay. Regardless of conductivity, the
response is strongest at low sample delays and weaker at higher
delays. However, targets of low conductivity or that are thin
will decay faster than highly conductive or thick targets. See the
Principles of Pulse Induction section for more details.
Smaller gold nuggets fall in the former category, so nugget
hunters will want the
Pulse Delay
set as low as possible. Coin or
relic hunters may want to increase the delay to knock out thin
foil trash and still detect desirable targets. Most iron (especially
larger) responds with a long decay and is usually not very
responsive to the delay setting.
Conductive salts also respond with a fast decay and can be
detected at low delay settings. If beach hunting in wet salt sand,
you may need to turn the delay up to 15
s to eliminate the salt
response. Dry salt is usually not a problem, so as you move out
of the wet sand into dry sand remember to turn the delay back
down to better detect small jewelry items.