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990DSL
Users Guide
TDR Test Operating Tips
The operating tips in this section are provided to help you in the "real world"
of TDR testing.
Determining the VOP
When you select a
CopperPro automatically uses a standard median VOP value. Several factors,
however, can make this value erroneous and cause the tester to incorrectly
determine the location of a fault:
•
Multiple gauges in the cable makeup
•
Cable dielectric differences between manufacturers
•
Dielectric variation with temperature (1% per 10°C)
•
Water in the cable
•
Age of the cable.
The following procedure outlines a reliable method for calibrating the VOP
factor to a particular cable type:
1.
Locate a known good pair in the same binder group as the test pair.
2.
Find the pair's exact length. There are several ways to do this:
•
Run an Ohms-to-Distance test with the far end shorted and with the
gauge configuration known.
•
Run an Opens test, using the proper cable type.
•
"Wheel off" the length with a measuring wheel (taking slack loops or
"snaking" into account).
6-18
and
Cable Type
Gauge
in the setup for the test, the
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