Operation - Megger TDR2000 Manual De Instrucciones

Ensure the test leads are firmly fitted into the sockets of the
instrument. Ensure the cable(s) under test is (are) de-energised
before connecting the test leads. If working on live power
cables, a blocking filter(s) must be used to isolate the
instrument from the live line(s).
Switch the instrument on and the instrument will display the
start screen for a couple of seconds. The TDR will then display
a trace. The instrument will have powered up, set to the last
used mode, range and velocity factor. If the settings are
different for the cable under test (C.U.T) then first use the mode
key to cycle through the available modes and select the
required one. Next, use the VF bi-directional key to set the
velocity factor for the C.U.T. (If this is unknown then follow the
steps detailed in the Velocity Factor section.) Finally, cycle
through the available ranges until you select a range long
enough to see the whole cable length of the C.U.T.
With the gain set at the lowest level required to easily identify
the cable feature, e.g. an open or closed circuit, move the
cursor to the very beginning of the reflection. To locate the start
of the reflection more accurately, press the DISPLAY key to
zoom in around the current cursor position. The cursor is now
fixed and using the cursor left and cursor right keys, the trace
will move relative to that point. The current zoom location with
respect to the whole trace range is shown at the top of the
display. The distance is then directly read from the display. The
distance calculation is performed using the current velocity
factor. If this velocity factor is not correct, the displayed
distance will be incorrect.
To enable partial cable faults to be identified, i.e. those faults
that only reflect part of the signal back to the instrument, the
8

Operation

gain of the instrument can be adjusted. With the gain at the
minimum required to see the end of the cable on the trace, if a
minor fault is suspected then increase the gain until the fault is
more visible.
Below are shown two typical trace displays. The top one is an
open circuit cable, the open circuit at 1200m away, the second
is a short circuit at 1200m away and the instrument is
displaying the low battery warning.