Fluke Networks TS100 Mode D'emploi page 17

start, the impedance changes, and the end of the cable.
The size and shape of the flat and bumpy sections
depend on the distance to the impedance changes and
the magnitude of the impedance changes.
For example, two runs of 12/2 AC wire joined with a
splice will have a TDR waveform with 2 flat sections
separated by a bump. The two flat sections represent
the lengths of the two sections of wire. The small bump
in the middle represents the small impedance change
at the splice point. The large bump at the end
represents the large impedance change at the end of
the wire run (see Figure 4).
TDR technology examines this TDR waveform (see
Figure 4), looking at the sizes of the flat sections and
the bumps. The software decides which of the
elements of the waveform is most representative of the
common problems encountered in the wiring
industries and reports the distance to that element.In
the case of the waveform in Figure 4, the TS100 will
report the distance to the end of the wire run and will
ignore the small bump in the middle because it is too
small to be considered a problem.
Time Domain Reflectometry (TDR) Technology
If more than one problem exists on the cable, the
software in the TS100 Cable Fault Finder only reports
the nearest problem.
The actual result of the measurement is the TIME to the
fault. The software in the tester converts the measured
time to a length by multiplying the time by the speed
of the electrical signal in that particular cable. That
speed is represented as a percentage of the speed of
light and is called the Velocity of Propagation (VOP).
The actual formula used is as follows:
Length= Time in billionths of a second
The time is divided by two because the signal traveled
the length of the cable twice. Once when it left the
tester and went to the failure point, and again when it
reflected back to the tester to be detected. The speed
of light expressed in billionths of a second per foot is
0.9835 (about a billion feet per second) (0.2998 [about
300 million meters per second]).
Figure 4. TDR Waveform
VOP
X
2 0.9835
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