sebaKMT Easyflex Com, Инструкция по эксплуатации

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32 MAN_Easyflex_com_eng_01.doc
(5) A humidity-induced fault is brought about by water penetrating into a
defective line. At the beginning of a wet section a negative reflection
similar to a short-circuit can be observed, followed at the end of the
wet section by a small positive fault reflection typical of an open cable
end. In some cases, e.g. if the moisture gradually increases or
decreases with distance, these points of reflection spread into a
constant up and down in the horizontal traceform. In an old cable
which is wet along its entire length it may be difficult to detect a
moisture-induced fault because the beginning and the end of the zone
of moisture exposure are not clearly marked. It is only in rare cases
that the fault reflection becomes apparent as clearly as for a short-
circuit or broken line. Moisture in a cable filled with petrolatum may
possibly result in very small fault reflections as the volume of moisture
is only limited.
3.8.1.3 Further Fields of Application
(1) T-joints (Tapped joints) occur when a conductor pair leading to an
extension is tapped off a pair in the main line. Halving the
characteristic impedance at the tap or bridge will result in a fault
similar to a short circuit (negative reflection). The trace on display is
difficult to assess if a pair of conductors is tapped at many points
unless precise information about the structure of the cable network is
available.
(2) Some telephone lines are coil-loaded in order to increase the
inductance of the line and thereby improve the transfer characteristic
of a trunk line. The
Easyflex Com
will interpret the coils used for the
inductive loading of the system as open ends. Connect the instrument
to some point behind the coil if you want to locate a fault which is
situated beyond the bounds of a coil-loaded section.