94
SCAN-LAN Vt
Do not mix cables with different characteristic impedances. Locations of any
significant impedance changes can be found by performing the Length test
on a segment. Refer to the previous section on Length for more
information on finding characteristic impedance changes or anomalies.
Test Results
Possible Solutions
Impedance is out of
Check specifications of cable. Compare expected
specification
value with measured value. Make sure you are
using the correct cable test standard.
Impedance is failing, but the
Check for split pairs. Correct wiring as necessary.
cable is the correct type
8.2.7 R
ESISTANCE
Resistance is defined as an electrical element that impedes the flow of DC
current. It is measured in ohms. As a test, it is used to confirm there are no
poor connections that add to the resistance of the segment. Many times, if
the resistance is not within the specification, the problem may also show up
as excessive attenuation or as an impedance anomaly.
Although the SCAN-LAN Vt uses TDR to measure length, Resistance can
also be used as a method to measure the length of a cable if you know the
rated resistance (ohms per foot or meter) of the cable. Resistance of a cable
is usually rated on a per-1000-feet or per-1-km basis.
The table below discusses some common resistance problems and solutions.
Test Results
Possible Solutions
Resistance is
Compare measured value with expected value. Troubleshooting
out of
resistance should be done the same way as troubleshooting attenuation.
specification
See the section on Attenuation.
All termination points should be checked. Perform a Length test to
check for anomalies.
