3M CablePipe Locating Techniques Manual

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4.2 The Dyna-Coupler can identify one of several
CATV cables which fan out from a common
point, as in a header pedestal. Even though signal
is coupled onto each cable, the cable with the
Dyna-Coupler is clearly identifiable because it
has the strongest signal. If the header is not
grounded in the pedestal, do so using the ground
rod and the ground extension cable. This helps
shorten the ground return path and increases
signal. 4. Applying Signal to CATV Cables: Dyna-Coupler Method
4.1 The Dyna-Coupler is the easiest method to apply signal to a CATV cable. It is not necessary to
disconnect the cable. Open the Dyna-Coupler jaws and place them around the desired cable. Make
sure that the jaws close completely. The Dyna-Coupler couples the Transmitter signal onto the
cable. The cable and its shield grounds form a complete circuit path for the signal to follow. When
the Dyna-Coupler is applied to the cable anywhere between earth grounds, signal is on the section
between the grounds. Be aware that the shield may be grounded at the subscriberÕs premises and
also at a bridging amplifier on an aerial feeder line several blocks away. Everything between these
grounds will carry signal. A removable ground (use the ground rod and ground extension cable)
placed at a surface access point limits signal to that part of the cable between the grounds and
keeps signal from going where it is not needed. Remove the ground when the job is finished.
Note: Always use high output level with the coupler. 
						

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5. Locating Cable Slack Loops
5.1 To identify the presence of a slack loop in the cable path, first locate and mark the cable path.
Retrace the path in the following manner:
Find the strongest response over the marked cable path and press the gain adjust key.
Hold the Receiver so the handle is perpendicular to (across) the cable path, and retrace
the cable path. When the Receiver passes over a slack loop, the tone increases and the bar
graph closes. Mark each response.
6. Locating Cables from Pedestals
6.1 To locate a single CATV cable path from a pedestal, follow these steps:
6.2 At the pedestal, apply tracing tone on the target cable using the Dyna-Coupler method.  If the
header in the pedestal is not grounded, use the ground rod and ground extension cable to ground
it.
6.3 Walk 10 to 25 feet away from the
pedestal holding the Receiver so that the
display end of the handle points directly
away from the pedestal. Start walking in
a circle around the pedestal with the
Receiver always pointing outward.
6.4 The Receiver remains relatively quiet
until it crosses a cable. Stop when there
is a response. Find the point of strongest
response and press the gain adjust key.
Check the numeric display for relative
signal strength. Remember the number
and continue walking the circle. As you
walk away from the cable, the signal
drops. Press the gain adjust key and
continue. When another response is
encountered, find the point of strongest
signal response. If the greatest signal
strength is more than 25 points higher
than the others (if any found), then that
is the target cable. If the signal levels are
closer, then measure the depth of each
cable found and note the bar graph in the
depth mode (this is a relative
measurement of the current flowing in
the cable). The cable that shows at least
two more segments on the bar graph
than the other cables is the target cable. 
						

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Section 5  Pipe Locating Techniques
1. Introduction
1.1 Read Section One of this manual to learn more general information about each of the following
signal application methods. The following paragraphs provide specific instruction on applying
signals for pipe locating.
2. Applying Signal to Pipe: Induction Method
2.1 The Induction method broadcasts signal into an area.  No access to the cable is necessary.  Use
this only when there are no other buried conductors present, or when locating all conductive
buried services in a general area.  Perform the following steps to use the Induction method.
2.2 Place the Transmitter on the ground over the cable to be located. The Transmitter hinge should be
in line with the cable path, as shown above.  Be certain that the Transmitter is directly over the
cable to be located.
2.3 Turn the Transmitter on and choose 33 kHz signal or higher.
2.4 Use the Receiver to test the signal level by placing the Receiver 50 feet away from the Transmitter
on the ground near the cable.  Move the Transmitter back and forth across the path.  Listen for
strongest signal from the Receiver.  If the Receiver has trouble picking up the cable path, return to
the Transmitter and switch to a higher frequency. If the highest Transmitter frequency will not
give satisfactory Receiver response, then boost the Transmitter output as instructed in the unitÕs
Operators Instructions. You can also increase the response by placing the Transmitter on the
located position over the cable (50 feet away from the Transmitter Õs previous position). 
						

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3.2 A far-end access point may not be available to apply a far-end ground. If this is the case, you can
still use the direct-connect method. The red lead connected to the pipe sends signal current in both
directions from the application point. The signal continuously Ôleaks offÕ the pipe and returns to
the Transmitter ground rod connected to the black lead. The rate at which the current leaks away
from the pipe determines how far down the pipe the signal can be detected. Two factors that
control this distance are the pipe size (diameter) and the frequency of the Transmitter. A general
rule of thumb to maximize the detection distance is Ôbig pipe - low frequencyÕ or Ôsmall pipe -
high frequency.Õ Select the lowest frequency which provides adequate signal for the receiver.
Setting the transmitter output level to high output increases the detection distance but only if the
frequency is correct. Ground rod placement should be as far away from the trace path as possible
and at a right angle to the path. 3. Applying Signal to Pipe: Direct-Connect Method
3.1 You can use the Direct-connect method to apply tracing signal to a coated metallic pipe at an
access point such as a valve, meter, or the metal pipe itself. The red lead is connected to the pipe
and signal current travels down the pipe. The return path to the Transmitter is through a far-end
earth ground such as a screwdriver stuck in the ground or by system grounding at buildings. The
circuit is completed by connecting the black lead to the ground rod. Ground rod placement should
be as far away from the trace path as possible and at a right angle to the path. With an arrangement
like this, use a low Transmitter frequency. Sometimes a pipe system is sectionalized by using
nonconducting gaskets at selected pipe joints. These insulated pipe joints stop the signal current.
After application of the far-end ground, use the ohms mode on the Transmitter to check if the
circuit is complete. 
						

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A. Direct-Connect Method on Tracer Wires
3.3 To locate tracer wires buried with nonmetallic pipe, connect the TransmitterÕs red lead to the
tracer wire at an access point. The black lead is connected to the ground rod.  For best results,
ground the tracer wire at the far-end. If you cannot access or locate the far-end, use a high
Transmitter frequency. Otherwise, use a low Transmitter frequency.  If you use a high frequency,
be aware that in some installations a tracer wire for a service line may not be electrically
connected to the tracer wire for the mainline.  The purpose is to reduce confusion by not allowing
tracing signal applied to the main from appearing on the service line.  The unconnected end of the
service tracer wire may have been placed in the trench and covered or it may have been twisted
around the tracer wire for the main.  If the twist method was used and the Transmitter frequency is
high, signal may appear on both the main and service tracer wires.  High frequency signal couples
from one tracer wire to the other through the twist, even though there is no metallic connection.
4. Apply Signal to Pipe: Dyna-Coupler Method
4.1 The Dyna-Coupler method works well on buried
metallic pipe. When the Dyna-Coupler is clamped
around a pipe, you can detect signal on either side. 
						

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4.2 You can control the direction of the signal on
the pipe by using the ground rod and ground
extension cable to apply ground to that part of
the pipe where signal is not needed, as shown.
The external ground keeps the signal off the
pipe on that side of the Dyna-Coupler. Since
the signal is being sent to only one part of the
pipe, the signal magnitude is greater on that
part.
4.3 When you use the Dyna-Coupler to
apply signal to a metallic service line
at a gas meter, always ground the
valve. This provides good return for
signal.  Otherwise, the insulating
coupling above the valve isolates the
returning signal from ground and may
make locating the service line difficult.
5. Locating Non metallic Pipe
5.1 One end of the pipe must be accessible.  Push a metal fish tape, snake, or heavy gauge wire into
the pipe.  Use a direct-connect hookup to the tape, snake or wire and choose 33 kHz signal or
higher to locate. 
						

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6. Locating Pipe with Impressed Cathodic Protection
6.1An impressed current cathodic protection system uses an AC powered rectifier as a source of DC
current. The current flows from buried anodes to the pipeline to protect it from corrosion.
6.2To trace the path of the pipe, use the second harmonic of the 50 or 60 Hz passive power frequency
(100 or 120 Hz) in Peak mode. This frequency is especially sensitive to rectified AC signals.
6.3You can also locate the anodes and find a broken anode lead using this frequency. As you trace the
path of the anode lead past a buried anode, the signal strength will drop (numeric indicator
decreases). At a broken lead wire, the signal diminishes suddenly to nothing.
Broken Anode  Lead AnodePositive Supply
Negative Return
Rectifier
Pipeline 
						

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Section 6  Locating Faults
1. Introduction
1.1 Sheathed cables with a metallic shield (CATV and some telephone cables) can experience damage
to the sheath which exposes the shield to contact with the earth. These damaged spots on cables
are called sheath faults because the damaged sheath allows water to enter the cable creating a fault
which may degrade service. Buried power distribution cables have no shield but damage to the
insulation can expose the conductor to earth creating a fault condition.
Transmitter Connection for Faults 
						

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2. Locating Sheath Faults
2.1 To locate a sheath earth return fault, the Transmitter sends a current down the shield to the
damaged sheath (the fault) and back to the ground rod through the earth.  The operator uses the
earth contact frame to find the point where the current stops traveling through the shield and starts
traveling through the earth.  At the same time, tracing tone may be applied to the faulted section to
help find the buried cable. This is especially useful if the cable passes under concrete or asphalt.
Perform the following steps to locate a sheath fault:
Make sure both the near-end and far-end shield bonds (shield grounds) are removed from
the test section.
Attach the Transmitter to the cable as shown above.  Select the fault mode.
Always measure the resistance between shield and ground to verify the fault exists.  Use
the Transmitter ohms mode.  To determine if a sheath fault exists, use the following
criterion:
Resistance greater than 1.0 megohms: no significant fault exists in the cable sheath.
Resistance between 1.0 megohms and 50,000 ohms: a high resistance fault exists that
may or may not cause problems yet but gets worse with time.
Resistance less than 50,000 ohms: a heavy fault exists between the shield and ground.
Failure to disconnect the shield bonds at either the near-end or the far-end produces a
heavy fault reading.
Connect the Earth Contact Frame to the Receiver using the frame cable.
Turn the Receiver on and place the Receiver in fault mode.
Hold the Receiver in one hand and the earth contact frame in the other with the green-
banded leg toward the fault. Near the location of the ground rod, insert the frame probes
fully into the ground in line with the cable path while facing the section under test. The
Receiver bar graph is visible on the right side (green).  This indicates that the fault is
ahead of the operator in the direction of the green-banded leg.
Continue along the cable path, reinserting the frame probes every few steps while
watching the Receiver bar graph.
Note: A high resistance of distant earth fault may cause the bar graph to become very small or even
invisible. However, it increases as the operator gets closer to the fault. This is because the
signal is highest at the ground rod and at the fault, but drops off between.  If the bar graph
shows random changes in magnitude or erratic reversals over the entire test section, no fault is
on the section.
When the bar graph is visible on the left side (red), the fault has been passed and is now
behind the operator.
Move back, inserting the frame every few inches, until the bar graph returns to the green
side. The fault is located beneath the center of the frame when the bar graph changes
from one side to the other.