TDR Testing and Fault Location
TDR Test Operating Tips
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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 Cable Type and Gauge in the setup for the test, the
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).
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