158802.02 VDV II Pro 6
LENGTH MEASUREMENT
Cable length can be measured using the built
-
in Time Domain Reflectometer (TDR) with
either an open circuit
or short circuit or a Remote Unit or Identifier at the far end. Any
TDR can only be used to measure the length of cables with uni
form Characteristic
Impedance. The TDR may not give reliable results on cables that are not correctly
twisted or using crocodil
e clips to connect to the cable.
Length can be shown in units of either meters or feet.
To set the length measurement units:
• Press the TOOLS button repeatedly until either the
or
symbol flashes.
• Press or
o The length units change between meters and feet.
• Press the TOOLS button repeatedly until the Setting Indicator disappears.
Accurate length measurement relies on correct setting of the Nominal Velocity of
Propagation (NVP) for the cable to be tested
. This can be determined either from the
cable manufacturer’s data or by testing a known length of cable of the same type as the
cable to be tested.
• Connect a known length (>15m / 50ft) of cable to
the tester (if available).
• Press the TOOLS button repeatedly until the NVP
setting flashes.
• Press or until either the required NVP or the
known cable length is displayed.
• Press the TOOLS button repeatedly until the
Setting Indicator disappears.
To measure the cable length:
• Connect the cable to the tester.
o The display shows the cable length.
• Press the port selection button of the currently
selected port.
o The display changes to show the overall
cable length or the length of an individual
pair inside the cable.
• Repeat to show the length of each pair or the
overall length in turn.
o By investigating the individual pair lengths,
cable faults and distance to fault can be
found.
o The individual pairs are often different
lengths and may be longer than the overall
cable because of the internal twisted
construction.
Length
Pair 1-2
Pair 3-6
Length
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