Thank you for purchasing this quality AVO product. Before
using your new instrument please take the time to read this
user guide, ultimately this will save you time, advise you of any
precautions you need to take and could prevent damage to
yourself and the instrument.
Your TDR2000 is a very advanced instrument capable of
identifying a wide range of cable faults. The instrument uses a
technique called Time Domain Reflectometry (TDR) which in
many ways is similar to radar. Narrow pulses of electrical
energy are transmitted along a pair of conductors in a cable.
The pulse travels through the cable at a velocity determined by
the insulation between the conductors and the resistance to the
flow of the pulse is characterised as impedance for the cable.
Changes in cable impedance will cause a proportion of the
pulse to be reflected. The pulse velocity is normally described
as a fraction of the speed of light and is called the Velocity
Factor. By measuring the time between the transmitted pulse
and the reception of the reflected pulse, and multiplying this by
the speed of light and the velocity factor, the actual distance to
the reflection point can be given.
Faulty cables, poor joints or discontinuities will all cause a
change in impedance. Impedance’s higher than the cable’s
cause a normal reflection. Impedance’s lower than the cable’s
cause an inverse reflection. Matched terminations absorb all the
pulse hence no reflection will occur, the cable appearing
endless. Open or Short circuits will reflect all the pulse energy
and the TDR will not ‘see’ the cable beyond that fault.
As a pulse is transmitted down a cable, the size and shape of
that pulse is gradually attenuated by losses in the cable: the
pulse gets smaller in height and more spread out. The level of
attenuation is determined by the cable type, the condition of the
cable and any connections along its length. The limit of how far
you can see is determined by the point beyond which you will
not discern a reflection. To maximise the instruments range, the
TDR2000 has an adjustable gain setting on its input that can
apply up to 90dB of gain to the reflected signal to allow you to
discern a reflection from farther away. By combining this
variable gain with increasing pulse widths, the TDR2000 can
discern faults up to 16Km away.
The MEGGER TDR2000 can be used on any cable consisting
of at least two insulated metallic elements, one of which may be
the armouring or screen of the cable. The balancing circuit,
which is described in the Operating Instructions, can balance
for any cable with a characteristic impedance of 0-120
Ω
. Dual
inputs and the large graphic display allow a wide range of
comparative tests to be performed between cable pairs or
stored results. The instrument has 15 trace memories, enabling
previous test results to be displayed and compared with “live”
results. This allows the gradual ageing of a cable to be
monitored or characteristic changes to be detected between
periodic tests, for example if the cable has suffered water
ingress or has been tapped and split.
Introduction
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