White’s Electronics TDI - Manual (Page 30)

0 PulseScan TDI Owner’s Guide
MORE ON PULSE DELAY
Sampling as close as possible to the end of the transmitted pulse gives the
highest sensitivity to all metal targets regardless of their content or conductivity.
The best signal from all targets is obtained when using a short (10 uS) delay.
However, increasing the Pulse Delay beyond 10 uS toward 25 uS will minimize
or eliminate the signal from low-conductive targets, so that high-conductors
stand out more even though they are giving out less of a signal because they are
sampled further down the decay curve. For maximum sensitivity to all targets, you
would want to set the Pulse Delay as close to 10 uS as possible. Thus, when
positioning the Conductivity Toggle at “ALL”, you will hear the familiar high tone if
the target is seen as low conductive, and the corresponding low tone if it is seen
as high conductive.
As you would expect, a nickel would fall into the same category as gold and will
be heard at 10 uS as a high tone, but larger silver and clad coins will produce
the low tone. With alloyed gold, the conductivity can vary, so the optimum pulse
delay can vary as well. Generally speaking, alloyed gold will be seen as low
conductive, so will be seen best at a lower pulse delay (10 uS ). 10k or 14k
rings will usually react as low conductive, whereas a purer gold ring, ( 22 k), may
react as high conductive . This can also be the case with very pure or large gold
coins and gold nuggets. A solid US $5, $10 or $20 gold coin will usually read as
high conductive, whereas, a $2 1/2 gold coin will read low conductive. Pure gold
Bullion (24k) like a one ounce Canadian Maple Leaf will read as high conductive
as well. This can be the case with a very large gold nugget or a very pure or high
gold content nugget, Fortunately, most gold nuggets are of mixed alloy and fall
into the low conductive category. Most U.S. gold nuggets readi as low conduc-
tive, thus producing the familiar high tone. However, most Alaska and Austrlian
gold which is over 90% gold will read as high conductive with a low sound.
The size and shape (surface area) of the target, not just the type or conductivity
of the metal, continues to have a bearing on the optimum setting for the Pulse
Delay. It would be a good idea to experiment with different targets at different
Pulse Delay settings. This is best done with the Ground Balance switched to
off, so that all targets sound the same, and the sensitivity to the target can be
observed. In this way, you can observe what happens to certain targets as the
Pulse Delay is advanced up from 10 uS. Setting pulse delays can be an impor-
tant part of operating the Pulsescan TDI. After you have seen how the Pulse