- 9 -
The
two
weaker
indications
on
both
sides
of
the
actual
marker
occur
because
the
locator
is
extremely
sensitive
to
the
magnetic
field
components
parallel
to
its
long
axis.
At
point
B
and
C
,
the
field
is
perpendicular
to
the
locator
so
no
peak
audio
or
digital
indications
are
produced.
When
Placing
Stakes,
Correct
Orientation
is
Important
For
checking
purposes,
the
orientation
of
the
pin
relative
to
the
locator
is
shown
in
Figure
11.
Check
the
pin
with
one
orientation.
Then
rotate
the
pin
180°.
The
orientation
that
gives
the
largest
reading
is
the
one
that
should
be
used.
This
reading
will
be
positive
in
the
Northern
Hemisphere
and
negative
in
the
Southern
Hemisphere
(Australia,
New
Zealand,
etc.)
An
iron
pin
has
two
types
of
magnetization.
One
is
the
magnetization
induced
by
the
Earth’s
magnetic
field.
The
induced
magnetization
is
always
downward
in
the
Northern
Magnetic
Hemisphere
and
produces
a
positive
output
no
matter
which
end
of
the
stake
is
driven
into
the
ground.
The
other
type
of
field
is
the
permanent
magnetization
that
is
fixed
to
the
pin.
For
maximum
detection,
the
stake
should
be
driven
into
the
ground
so
that
the
permanent
magnetization
is
in
the
same
direction
as
the
induced
magnetization.
Locating
Manholes,
Septic
Tanks
and
Well
Casings
The
magnetic
field
is
strongest
at
the
edge
of
a
shallow
manhole
cover.
You
can
easily
trace
the
edges
of
covers
near
the
surface.
The
locating
depth
for
manhole
covers
ranges
up
to
8
feet.
The
great
length
of
a
well
casing
provides
a
strong
field
at
the
surface
that
makes
it
easy
to
locate
casings
buried
up
to
15
feet
deep.
Figure
12:
Locating
Manhole
Covers
Figure
13:
Locating
Water
Well
Casings
Figure
11:
Checking
a
Stake’s
Orientation
