20
9
Step 2. Determine the Direction of the Line
Move about 5 feet away from the Peak Spot and switch
to the Crossing screen by clicking once to the right.
Increase the sensitivity until you have the strongest
signal. Now walk in a 5 to 10 foot diameter circle, with
the Peak Spot as the center of the circle, while you
listen and watch the screen carefully. You will encounter
a spot where the clicking slows down almost to a stop,
the red LED at the lower right of the screen comes on,
and the handle vibrates. At the same time you will see
an image of the line appear on the screen, as seen
here. Note that the way the pipe lies on the screen is
the way the pipe lies in the ground beneath you. You
may need to raise or lower the sensitivity to “fine tune”
the image. This is a “Crossing Null”. Mark this spot
and continue your trip around the circle. You will find
another “Crossing Null” on the opposite side of the circle
from the first one. Mark this spot also.
A line drawn between these points will pass
directly over the center of the transmitter, and
is parallel to the transmitter. It also describes
the lay of the line the transmitter is in. This is
very valuable information, and sets the stage
for determining the precise location and depth
of the transmitter. Many people skip this step,
thinking it unnecessary, but it is the key to
successful locating. See “Getting to Know Your
Tools” for more information.
Crossing null image
Walk in the direction that the clicks get faster
and the number in the center of the screen
reaches its highest value. When you have
reached a point where the clicking is fairly
rapid and everywhere else you move makes
the clicking slow down and the number in the
screen get lower, you have found the “Peak
Spot”. Now repeat this procedure starting from
a different place until you consistently come
back to the same spot. Mark it with a rock or
other marker.
X
X
Or does it ?
Go back to where the receiver is directly over the transmitter, and the sonde
image is showing clearly in the screen. Now move the receiver to the right a
foot, keeping it parallel to the transmitter. Move it another foot away. Now go
back to the original point and move it to the left the same way. Surprised?
The sonde signal can show on the screen for many feet on either side of its
actual location. The only way you can be sure which of these spots is the actual
location is to have first found the crossing nulls with the Crossing screen. The
exact location of the sonde is along the line through the crossing nulls.
Step 4: The Depth Screen
Now that you know for sure where to stand so that the
sonde is directly below the receiver, it’s time to deter-
mine its depth. Holding the receiver at chest height,
click the rocker switch once more to the right with your
thumb to get to the Depth screen. Hold the receiver
still in this position; in just a second or two, the depth
(i.e., the distance between the bottom of the receiver
and the transmitter) will be displayed, and the red LED
will light.
What if you had settled on one of the “ghost” sonde locations we discovered a
minute ago, and tried to determine depth on it? Try it and see. The depth will
appear to be considerably deeper than actual as you move to the right or left of
the true sonde location. And, of course, it won’t be down there when you dig.
That’s why it’s so important to establish your crossing nulls on the Crossing
screen before you proceed to the Sonde screen.
With what you have learned here, you should be able to go out and be suc-
cessful at locating a transmitter you have sent underground without knowing in
advance where it is. Be sure to read “At the Jobsite” for practical considerations
when doing actual field locating. Good luck!
The appearance of the sonde in this screen is a reliable
indication that you are directly over the sonde IF you have
gotten to that point by following the line described by the
crossing nulls using the Crossing screen. If you have skipped
that step and just looked for the sonde image, you can be way
off, and be very disappointed. Let’s demonstrate why.
When the pointer is at “FAR”, the receiver is at its most sensitive. Use
this setting when you start your locate, because you are relatively “far”
from the transmitter. As you get closer and the signal gets stronger,
the receiver automatically reduces its sensitivity (moving toward
“NEAR”) while the signal strength numbers in the middle of the Peak
screen start over at a smaller value, getting higher as you again
move closer to the transmitter.
When the pointer reaches “NEAR”, it means the receiver is at its least
sensitive because it is picking up a strong signal. In all cases, your objective is to find
the path that causes the numbers to increase within the current sensitivity setting,
while also causing the sensitivity setting to move toward NEAR as you locate.
This step is very
important - don’t
skip it!
