Chapter 3: Certify Twisted Pair Cabling
Twisted Pair Autotest Results
109
The tester uses the propagation delay for each pair and the
NVP for the cable type to calculate the length of each pair.
The tester compares the length of the shortest pair to the limit,
and gives the test a PASS result if the pair is not too long. The
lengths of the other pairs are gray on the screen.
The tester gives a PASS result if the shortest length and the
longest delay skew do not exceed their limits.
Loop Resistance
Loop Resistance results show the DC loop resistance for each wire
pair. The remote puts a short at the end of each pair to make the
loops. A pair’s resistance depends on the quality of the contacts in
the connector, the length of the pair, and its wire gauge. Figure
43 shows the loop resistance results screen.
Resistance problems always affect other tests. For example:
A link that is too long has too much resistance and will fail the
length test.
High-resistance connections reflect signals, which causes the
return loss test to fail. Use the tester’s HDTDR analyzer to see
the distance to the bad connection.
A difference in the resistances of the wires in a pair causes the
impedances of the wires to be unbalanced, which can cause
TCL tests to fail.
Note
You can also measure resistance continuously. See
“Continuous Tests” on page 111.
To Next Page
Loading...
