White’s Electronics TDI - Manual (Page 31)

PulseScan TDI Owner’s Guide
Delay affects the signal, you can try the same tests with the Ground Balance
on and the Conductivity Toggle to all. At this time you can observe whether the
target produces a high tone or a low tone. You can then choose either the low
or high settings to observe how the Conductivity Toggle setting can eliminate or
accept a target.
The important thing is that you do have control over the Pulse Delay, and
therefore over the optimization of the sensitivity of the detector to certain desired
targets. The rule of thumb would be to set the Pulse Delay at 10 uS when
prospecting for small to moderate gold nuggets, and set it closer to 25 uS when
hunting on beaches for coins or relic hunting for iron and more conductive metals
such as brass.
Since the Pulse Delay setting does affect the Ground Balance process, you will
find that you have to ground balance after changing the level of pulse delay. In
addition, the level of pulse delay will have an affect on the ability to ground bal-
ance.
This was found out during our initial testing of the Pulsescan TDI on an extremely
black sand salt water beach. The Pulse Delay was initially set at 10 uS. At once,
we found that we had trouble achieving a clear ground balance point as the
extreme negative black sand and salt were too reactive. The audio was too
noisy to operate. Lowering the GAIN helped a little, but increasing the Pulse
Delay closer to mid-range (around 17.5 uS) rendered the threshold smooth, and
we achieved a clear ground balance point. Even though a Pulse Rate of 10 uS
would have been ideal for detecting for low conductive metals like gold, in this
instance, the higher pulse rate allowed for balancing the extreme black sand
which was our first concern. Even at the higher pulse rate, our first target was a
nickel coin over 12 inches, which has low conductivity just like gold.