AEA Technology, Inc. E20/20, Руководство по эксплуатации

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Measuring cable on a reel or in a box (spooled cable). One factor that can lead to
a higher than normal loop resistance reading and display an erratic trace close to
the TDR is measuring the cable while it is spooled or coiled up, even loosely. In
that form the TDR signals create minor interference with each other. Figure 3-40
is an example of both issues. The loop resistance is too high and the first 75ft
(22.8m) of cable display an erratic trace. Removing the cable from the spool or
coil will correct this. Figure 3-41 shows a 1,000ft (305m) cable with 375ft
(114.3m) removed from the box and laid straight. Note the smoother trace near
the TDR and reduced loop resistance over that section as compared with the
641ft (195.4m) section still coiled in the box.
Figure 3-41
Intermittent Fault – Figure 3-42. Intermittent faults, open or short, will cause the
TDR’s trace to become erratic. Each updated trace will show a different pattern
or return to normal then become erratic again when the fault returns. The best
tracing method is to have one person monitor the TDR for change and the other
person hand-over-hand along the cable, particularly at connection points, wiggle
and bend the cable slightly until the intermittent is located.
Figure 3-42
Series Resistive Fault – Figure 3-43. This fault is the results of corroded or dirty
connection on one or both wires in a pair. The example shows a rather dramatic
jump in impedance as the faults resistance is added to the pair’s impedance.
This jump will never return to normal impedance. Placing the cursor on either
side of the fault will show it to be about 30 Ohms. Minor resistive faults (1-2
Ohms) will be much less dramatic, but still contribute to attenuation and signal