L
L
L
L
IIIIN
N
N
NE
E
E
E
T
T
T
T
R
R
R
RA
A
A
AC
C
C
CIIIIN
N
N
NG
G
G
G
G
G
G
Geee
en
n
n
neee
errrraaa
allll O
O
O
Ovv
v
veee
errrrvv
v
viiiieee
ew
w
w
w o
o
o
offff LL
L
Liiiin
n
n
neee
e LL
L
Lo
o
o
occccaaa
attttiiiin
n
n
ng
g
g
g B
B
B
Baaa
assssiiiiccccssss
More often than not
underground pipelines and
cables are located and traced
by sensing invisible “fields”
around the line Such fields
are typically created by an
active transmitting device
which connects to an access
point on the target line and
causes electrical current to
flow in the line Wherever a
current flows in a line an
associated field is present as
well
The Triad
Receiver like
traditional locating receivers
that have been used for decades responds to the magnetic field associated
with an electric current that is travelling along the path of the line The
shape of this field is cylindrical with the center of the cylinder being the
current carrying line itself The receiver
determines the location of the actual line
based on measurements made by the
detection antennas
In the case of a pipeline or cable (or
other conductive line) the receiver
reports in an intuitive way the location
of the line relative to the “pointer” head
When the receiver is held such that the
virtual line on the screen is centered
under the crosshair the line will be
located directly under the pointer head
H
H
H
Ho
o
o
ow
w
w
w tttto
o
o
o T
T
T
Trrrraaa
acccceee
e A
A
A
A LL
L
Liiiin
n
n
neee
e W
W
W
Wiiiitttth
h
h
h tttth
h
h
heee
e
R
R
R
Reee
ecccceee
eiiiivv
v
veee
errrr
Typically there are three steps involved
in line tracing:
[[[[ ]]]]
Energize the line
[[[[ ]]]]
Search/Trace the line and
[[[[ ]]]]
Pinpoint
the line
[[[[ ]]]]
E
E
E
En
n
n
neee
errrrgg
g
giiiizzzzeee
e tttth
h
h
heee
e lllliiiin
n
n
neee
e
Before a line can be traced it must carry a current at the frequency of
interest A line that carries a tracing current is referred to as being
“energized” Following here are a few typical methods of introducing a
current into a line
