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The only way to be sure of the depth of a utility is to exposes the utility.
At any given time, the depth readout may be inaccurate.
The PATHFINDER PLS Receiver can perform digital depth measurement. The depth is dis-
played at the top of the LCD display in centimeters or feet and inches. Push button depth is
useful in quickly estimating the depth of the conductor during path locating.
Begin this measurement by locating the path of the cable or pipe. Stay at least 15 feet (4.6
meters) away from the Transmitter. Pin-point this location as accurately as possible (see Peak
Mode Locating page 19, Null Mode Locating page 20 and Absolute Signal Strength page 21).
Place the Receiver vertically over the conductor and rest the foot of the locator on the ground.
While holding the Receiver vertical, press and release the DEPTH button. The Receiver will
briefly indicate a measurement is being performed and then display the depth at the top of the
LCD display.
Caution must be exercised when using the push button depth feature, as tilted magnetic fields
and adjacent conductors can significantly influence this measurement. The operator should
periodically check for adjacent conductors and tilted magnetic fields when taking push button
depth readings. For information on identifying tilted magnetic fields, refer to Tilted Magnetic
Field Identification and Depth Measurement 45º Method.
Depth is determined by reading the electromagnetic field radiating from the conductor. The
field must be even and circular for the most accurate reading. Interference of this field may be
caused by bends in the cable, faults on the target conductor and signals radiating from adja-
cent non-target conductors. Interference will warp the field and skew the depth reading. The
only way to be sure of the depth of a utility is to expose the utility. At any given time, the depth
readout may be inaccurate.
The following are methods and procedures that will aid in increasing the reliability and testing
the accuracy of the depth reading:
•
Take depth readings at least 5 yards from cable bends or depth changes. Follow the
cable both forward 5 yards and backward 5 yards, ensuring the line is straight and
there is a consistent signal strength reading.
•
Check for non-target conductors within 5 yards of the target cable. Sweep the
area looking for coupled signals into both the tracks and adjacent cables. Adjacent
conductors carrying the locate signal can result in a 50% error rate of the depth
reading.
•
Test for interference in the magnetic field by comparing the PEAK location to the Null
location. The determined cable position by these methods should be within 3 inches of
each other. A greater disparity will indicate interference resulting in inaccurate depth.
•
Place the receiver vertically over the conductor and perpendicular to the conductor.
Rest the foot of the locator on the ground. Take several depth readings moving slightly
across the perpendicular plane to the conductor looking for the lowest depth reading.
•
Once the lowest depth reading is found, take several readings. Each reading should be
within one inch of the other reading. Wider variation will indicate interference resulting
in inaccurate depth.
•
Lift the receiver up 12 inches and take a depth reading. The reading should reflect the
change in distance accordingly. If not, interference is present resulting in inaccurate
depth.
•
Verify the depth reading using the triangulation method as described below:
·
Mark the path on the ground as precisely as possible using the Null method.
·
Place the Receiver on the ground with the LCD meter facing up. Position the unit
so that the Bubble Level on top of the meter is centered (45º).
·
Pull the Receiver away from the cable path (at 90º to the cable path) keeping the
Bubble Level centered.
·
When the receiver indicates a Null reading, mark the location of the receiver’s foot.
·
The distance between the Receiver and the cable path is the depth of the pipe or
cable. A false depth reading may be caused by nearby buried metallic objects, such
as a second cable, pipe, sewer, fence or railroad track.
·
Confirm the depth measurement by repeating the above steps on the opposite side
of the pipe or cable.
·
A variance greater than 5 inches in depth measurement may indicate interference
from adjacent cables, pipes or other objects.
p
ush
b
utton
d
epth
D
E PTH
R
EA DI NG
EP TH
R
EA DI NG
(A + 12" )
L
IF T
12"
Buried cable or pipe
Earth
locate
Path
1st
Null
Null
centered
Bubble level
2nd
(end view)
Depth
Dept
h
45°
D
(A )
•
Peak & Null readings match
•
From the Peak/Null location take several
readings across cable.
•
Mark position indicated by lowest depth reading.
•
While stationary take multiple depth readings.
•
Reading should be consistent.
