Fluke 990DSL, Руководство пользователя

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POTS Testing and Fault Location
The POTS Toolbox
4
4-33
RFL Test: K-Test Option
The “K-Test” is a variation of RFL that can be used whenever a double-sided
fault is present,
and there are no good conductors in the cable to use for either
the “Good Wire” or “Good Pair” strapping function.
Oftentimes, one fault will be ten or more times greater than the other in a
double-sided fault scenario. In cases like this, the Fault Resistance Pass
Threshold (in RFL Setups) can simply be lowered to eliminate the larger value
fault, and you can run the simpler single-sided RFL test and still maintain a
fair degree of accuracy. In other cases, use the K-Test option.
K-Test Pair Requirements
•
Both resistance faults must be to the same fault potential , and occur at the
same physical place on the cable.
•
The larger fault resistance must be greater than twice the smaller value.
•
The larger fault resistance must be at least one hundred times greater than
the pair’s loop resistance.
Running the K-Test
After performing an initial RFL test on a pair having a double-sided fault, and
whose values meet the K-Test requirements (as in Fig. 4-13), do the following:
1. Press
C
(
K-Test-2W).
The tester then runs the first part of the test, performing a nulling
bridge operation on the pair
with the far end open .
Note
If one fault resistance is not greater than twice the other, an error
message is displayed at this point, and the K-Test cannot be run.
2. If the fault ratio requirement is met, the tester prompts you to connect
a far-end T-R short. The unit may be powered down at this time, as
with other RFL options, and the test resumed (
Continue Prev. Test)
after the short is connected.