White’s Electronics TDI SL 7.5 and 12 - Manual (Page 14)

Page 14
TDI SL
Owner’s Manual
TDI In Depth
Ground Balancing
One of the key features of TDI is its ability to balance out
ground mineralization while maintaining pulse induction
depths. This is achieved using a differential technique whereby
two decay samples are compared; the
Ground Balance
control is
adjusted until the two samples have the same response, thereby
canceling the ground signal.
Targets below the GB point produce an overall positive
response, and targets above the GB point produce an overall
negative response. Broadly, the two ranges of targets depend on
conductivity, which gives TDI some ability to discriminate. In
rare cases a target might fall so close to the GB point that it
gives either no response at all or a double-tone response.
Because ground balance is achieved using a subtraction
method, there is a slight loss of depth any time ground balance
is on. Some ground, notably neutral beach sand, is mild enough
that no ground balance is needed. In such cases,
Ground Bal-
ance
can be switched off and TDI will run in straight PI mode.
This will slightly improve depth, but loses the ability to distin-
guish between low and high conductivity targets.
Audio
TDI has the following audio tonal responses:
Low
Conductor
High
Conductor
On High ‐‐‐ Low
On All High Low
On Low High ‐‐‐
Off ‐‐‐ High High
Audio Tones
Ground
Balance
Conductivity
Mode