iv) As with the peak method, the signal on the line will
gradually diminish as you continue to trace. Notice that
as you trace further away from the transmitter, the null
becomes wider and less sharp. To sharpen the null,
continue to advance the SIGNAL LEVEL control. If this
control has been set all the way clockwise and you
wish to sharpen the null more, press the SENSITIVITY
button so that the HI light glows, and continue tracing
as before.
v) If the null suddenly disappears, this could indicate that
the line has ended or turned. To determine if the line
has turned, you may follow the procedure described in
section (a)(vii) above, using nulls instead of peaks over
the line.
vi) Please note that the null method will not indicate the
direction of the line at a single point. As long as the
receiver is held flat to the surface, it will indicate a null
over the line regardless of how the box is rotated.
vii) If you have traced beyond a detectible range, you may
continue your trace by re-energizing the line at a point
closer to where you are locating.
c) Determining Depth of a Line
Using the null detection method described above, the
operator can make a surface measurement and determine
the depth of an energized line. The procedure requires
two null points to be marked.
i) Locate the point at which you want to measure the
depth of the line.
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