Cable testers Testing Cabling

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3.1.3.2 Cable testers

A wide variety of cable testers are available. Typically, you get what you pay for. Some check little more than continuity and the cables pin-out that the individual wires are connected to the appropriate pins. Others are extremely sophisticated and fully characterize the electrical properties of your cabling. These can easily cost thousands of dollars. Better testers typically consist of a pair of units— the actual tester and a termination device that creates a signal loop. These devices commonly check the following: Wire-map or pin-outs This checks to see if the corresponding pins on each end of a cable are correctly paired. Failure indicates an improperly terminated cable, such as crossed wires or faulty connections. Near End Cross-Talk NEXT This is a measure of how much a signal on one wire interferes with other signals on adjacent wires. High values can indicate improper termination or the wrong type of cable or connectors. Attenuation This measures how much of the original signal is lost over the length of the cable. As this is frequency dependent, this should be done at a number of different frequencies over the range used. It will determine the maximum data rates the cable can support. Problem causes include the wrong cable type, faulty connectors, and excessive lengths. Impedance This is the opposition to changes in current and arises from the resistance and the inductance of the cable. Impedance measurements may be useful for finding an impedance mismatch that may cause reflected signals at the point where cables are joined. It can also be useful in ascertaining whether or not you are using the right type of cable. Attenuation to Cross-talk Ratio ARC This is a comparison of signal strength to noise. Values that are too low indicate excessive cable length or poor connections. Capacitance This is the electrical field energy that can be stored in the cable. Anomalous values can indicate problems with the cable such as shorts or broken wires. Length By timing the return of a signal injected onto the cable, the length of a cable can be discovered. This can reveal how much cable is hidden in the walls, allowing you to verify that cable lengths are not exceeding the maximum allowed by the applicable standards. 40 The documentation with your cable tester will provide more details in understanding and using these tests. The better cable testers may be preprogrammed with appropriate values for different types of cable, allowing you to quickly identify parameters that are out of specification. A good tester should also allow you to print or upload measurements into a database. This allows you to easily compare results over time to identify changes.

3.1.3.3 Other cable tests