EXFO CableSHARK P3 VF/DSL Cable Qualifier User Manual
Page 21
CableSHARK P3 User Guide
9
Section 3 Time Domain Reflectometry Overview
Time Domain Reflectometry (TDR) is a cable testing technique that is used to detect faults along power
transmission lines. Using this technique, voltage pulses are sent out over the line and voltage reflections
caused by cable abnormalities are monitored. Reflection times are measured from the reflection location on
the cable to the TDR device, which is attached to one end of the cable.
TDR technology can be compared to sonar. In sonar, a ship sends out an energy pulse through the water. If
an object, such a submarine, fish, ship, or underwater mountain is in close proximity, part or all of the pulse
is reflected back. The distance to the object can be calculated from a measurement of the time that it takes
for sound to travel through water.
In TDR, a pulse of energy is transmitted down a length of cable. When the energy pulse encounters the end
of the cable or a possible problem area (like a bridge tap or an open circuit), part or all of the energy is
reflected back to the TDR device. The TDR device measures the time it takes for the energy pulse to travel
down the cable and to be reflected. A calculation is made using the total pulse travel time and the Velocity
of Propagation (VOP) of the cable to determine the distance from the TDR equipment to the cable problem.
The VOP varies and depends on the cable size, material, etc.
1000 ft / 305 m
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CABLE
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13:16:20
Copyright Consultronics Limited 2000 - 2006
Software Version 3.86
AUTO
TESTS
AUTO
SETUP
CableSHARK P3
VF/DSL Cable Qualifier
Figure 3A - CableSHARK using TDR on a 1000 ft (305 m) cable
1000 ft / 305 m
+ -
F1
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W
X
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0
Q
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#
RUN
STOP
E
F
CABLE
TESTS
13:16:20
Copyright Consultronics Limited 2000 - 2006
Software Version 3.86
AUTO
TESTS
AUTO
SETUP
CableSHARK P3
VF/DSL Cable Qualifier