Megger TDR1000/2 Guide De L'utilisateur page 9

Operation
General Testing procedure
Ensure the correct test leads are firmly fitted into the
sockets of the instrument.
Switch on the instrument. The TDR1000/2 will display
the start screen for a couple of seconds, followed by
a trace. The instrument will be set to the range and
velocity factor last used. If these settings are different
for the cable under test (C.U.T) then use the RANGE
and VF keys to set the correct values. Refer also to
'Velocity factor' later in this text.
Connection to Cable Under Test
Connect the test lead to the cable under test.
Connection may be made to a live system with a
voltage to earth (ground) less than 300V with an
installation (over voltage) category of III or lower. This
means that the instrument may be connected to any
fixed wiring of a building installation, but not to
primary supply circuits such as overhead cables.
A Fused Lead Set must be used to connect to
energised live systems. Refer to the accessories
section for options.
When selecting 25 cable impedance, an internal
50Hz/60Hz filter is automatically switched in.
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Measuring distance to fault
Ensure that the whole length of the cable can be seen
on the display, and that the range selected is correct.
Find key
The Find key searches for the furthest major
change of impedance. This may be a fault or the end
of the cable if this is a short or open circuit.
When found the event is displayed and the cursor
placed on the leading edge. The gain, zoom and
cursor position may need to be adjusted for accurate
measurement. Note that Find does not adjust the
TxNull or Velocity Factor.
To enable 'difficult to see' faults to be identified, the
gain of the instrument can be adjusted. With the gain
at minimum small changes of cable impedance may
be overlooked. By increasing the gain the fault
becomes more obvious.
If no faults are obvious, adjust the gain until any major
reflections appear. Open and short circuits should
easily be identified. Partial faults can be less obvious.
If no significant reflections can be seen use the "TX
Null" to minimise the effect of the output pulse on any
potential "near end" faults (refer to section on TX
Null).