Cable fault locator
TDR-TA3.3T
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9
4 The TDR-TA3.3T structure and functioning
4.1 Operating principle
The device operating principle implements the method of pulse-refletometry that is
based on the phenomenon of partial reflection of electromagnetic waves in places of
change of circuit wave impedance. When measured by the impulse method, the
rectangular probe pulse is being sent to the line. The pulse partially reflects from the
irregularities and returns. The probe and reflected pulses are being observed on the
screen scalable in distance and amplitude. The shape of pulses allows the user to
evaluate the line irregularity type (see Picture 2). The reflected pulses return to the device
in some time from the moment of sending the probe pulse. Knowing the electromagnetic
wave propagation speed along the line and the reflected signal delay time, the user can
calculate the distance to the irregularity of the wave impedance.
3
3
2
2
t
CS
С
t
where X
– the distance to irregularity, m;
v
– electromagnetic wave propagation velocity inside the line, m/µs;
t
3
–
reflected signal delay time,
µs
v = s/CS
s
– speed of light, equal to 300 m/µs;
CS
– coefficient of shortening.
Impedance irregularities are the result of violations of manufacturing technology of
cables as well as a consequence of mechanical and electrical hazards during the
construction and operation of the cable lines. Irregularity of the line impedance appears in
the connection points of some devices and the line (couple, split, joint, Pupin coil, etc.) or
in hazard points (break, short circuit, cable core wetting, ground leakage, leakage over the
