Versiv Series Cabling Certification Product Family
Technical Reference Handbook
106
Scalar Results
Scalar results are measurements that do not change with
frequency. These are the Length, Propagation Delay, Delay Skew
and Resistance results. These results do not have plot data.
Length, Propagation Delay, and Delay Skew
The length results show the length, propagation delay, and delay
skew of each cable pair. See Figure 42.
The length shown on the PERFORMANCE screen is the length of
the shortest pair. The tester uses the length of only the shortest
pair to get a PASS or FAIL result for the length test.
Note
If the length of the shortest pair does not exceed the
limit by 10 %, then the length test passes even if
other pairs exceed the limit. This is the 10 % rule for
length, as given in the ANSI/TIA-1152 standard. See
the Fluke Networks Knowledge base for details.
A 2 % to 5 % difference in measured lengths of wire pairs in a
cable is normal for these reasons:
Signals travel at slightly different speeds in each wire pair, but
the tester uses the same NVP to calculate the length of each
pair.
The twist rate varies slightly among wire pairs. If you untwist
and straighten all the pairs, they will have slightly different
lengths.
Differences between measured and actual lengths can be caused
by variations in the cable’s NVP value. NVP values can vary among
cable types, lots, and manufacturers. In most cases, these
differences are minor and may be ignored.
Propagation delay is the time taken for a test pulse to get to the
end of a wire pair. The delay is measured in nanoseconds. One
nanosecond is one-billionth of a second, or 0.000000001 second.
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