AEA Technology 20TDR, Основное руководство

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Section 2 Setup and Measuring Cables
General Information
The following pages provide some basic information concerning cable construction and how a
step TDR works. This information is designed to help users set up their TDRs and better
understand what a step TDR can show about a particular cable type. For more detailed
information please refer to the Operating Manual found on the CD included with the TDR or
available on our web site at
www.aeatechnology.com .
Step TDR Operation
TDR’s are divided into two basic types: Pulse and Step. A pulse TDR sends out just one pulse at
a time and waits until no more reflection can be received from that pulse to send another pulse.
This requires adjusting the pulse width and/or gain control on those TDR’s to clearly see longer
cables and faults further away.
Step TDR’s, like the TDR, transmit continuous wave sweeps on the cable and interpret the
reflections to provide more detailed information on the condition of the cable. A Step TDR can
not only provide accurate distance to the end of the cable or faults. It can also provide the cable’s
impedance over length, loop resistance and more detailed reflective information to determine fault
type and amplitude.
Figure 2-1
Figure 2-1 is a representation of the sweep sent by a Step TDR. The wave is uniform at any
range setting and the TDR calibrates to the range selected by the user and the cable’s velocity
factor used. The result is accurate measurements both in distance and fault amplitude. In a Step
TDR a 10 Ohm fault detected 10 feet (3 meters) from the TDR will still show up as a 10 Ohm fault
if the cable is reversed and it is now seen at 100 feet (33 meters) from the TDR.