White’s Electronics TDI SL 7.5 and 12 - Manual (Page 15)

Page 15
TDI SL
Owner’s Manual
With Ground Balance = On and Conductivity Mode = All , all tar-
gets will give an audio response, either a high or low tone. New
users are encouraged to use this setup and practice with various
targets to learn their audio responses. A US nickel or small gold
nugget works well for a low conductive target, and a US quarter
makes a good high conductive target. TDI is a motion detector,
so target responses depend on the motion of the coil. If you hold
the coil steady over a target, the audio response will fade back
to the threshold tone.
In some cases there is not enough mineralization to require
ground balancing (e.g. non-mineralized beaches), and
Ground
Balance
may be turned off. In this mode the audio response is
high for all targets.
In cases where you have determined that you definitely
need only one of the conductivity modes and not the other, you
will often find that switching to that mode reduces the amount
of audio noise (chatter) and allows you to run a higher gain. To
better illustrate this, let’s use a strictly inaccurate but useful dia-
gram. The following is a representation of the audio response,
including a low conductor response, a high conductor response,
and random noise:
The ideal no-noise response is what you would get if you dis-
connect the search coil. With
Target Conductivity
=
All
, any-
thing above the ideal response will have a high tone and
anything below the ideal response will have a low tone. If there
is a lot of EMI or the
Gain is set aggressively high this can result
in a lot of audio chatter.
Low-conductor
response
High-conductor
response
Noise
Ideal no-noise
response
Target Conductivity = ALL