Author Topic: Cable Testers  (Read 608 times)

La.kl

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Cable Testers
« on: April 30, 2013, 04:56:12 AM »
The most frequent hardware-related cause of network problems involves bad
cabling and connectors. Several specialized, handheld devices designed for
testing the various types of data communication cabling are available. These
Unlike voltage checks, resistance checks are always made with power removed from
the system.
. . . . . . . . . . . . . . . . . . . . . . . . . . . .H.ar.dw. a.re. T.ro.ub. le. s.ho.o.tin.g. T.ec.hn. iq. u.es. 185
devices range from inexpensive continuity testers, to moderately priced data
cabling testers, to somewhat expensive time domain reflectometers (TDR).
Although inexpensive continuity testers can be used to check for broken
cables, data cabling testers are designed to perform a number of different
types of tests on twisted-pair and coaxial cables. These wiring testers normally
consist of two units—a master test unit and a separate load unit, as illustrated
in Figure 3.4.
The master unit is attached to one end of the cable and the load unit is
attached to the other. The master unit sends patterns of test signals through
the cable and reads them back from the load unit. Many of these testers feature
both RJ-45 and BNC connectors for testing different types of cabling.
When testing twisted-pair cabling, these devices can normally detect such
problems as broken wires, crossed-over wiring, shorted connections, and
improperly paired connections.
Cable
Tester
Master
Unit
Coax
Port
UTP
Port
UTP
Port
Data
Cable
Remote
Module
Figure 3.4 Cable tester.
TDRs are sophisticated testers that can be used to pinpoint the distance to a
break in a cable. These devices send signals along the cable and wait for them
to be reflected. The time between sending the signal and receiving it back is
converted into a distance measurement. The TDR function is normally
packaged along with the other cable testing functions just described. TDRs
used to test fiber-optic cables are known as optical time domain reflectometers
(OTDRs).