Cable Tester test Parameters Detailed: Cabling Test basics

At present, the most widely used network cabling system is the use of twisted-pair wiring system, where the mainstream choice is super 5 class or higher performance of the system.

For cabling systems, the most basic test for installers is the use of connectivity testers to authenticate link end-to-end connections. These testers provide complete wiring diagram testing, using TDR technology to measure length and other additional information. This type of instrument is very helpful for testing voice lines, fast checking data links, and high-speed growth of residential LAN wiring markets.

The test standard for cabling system acceptance requires measuring several important electrical parameters to facilitate the authentication wiring system to meet certain transmission performance requirements. Some tests are to be carried out all over the world. Each standard has a specific pass/fail limit that depends on the link's category and the link model definition.

For an installed link, three basic tests are required. The first one is wiring diagram test. Wiring diagram tests are used to verify the end-to-end connectivity of each pin in the cable link, while checking for crosstalk problems. Any faulty wiring forms, such as circuit breakers, short circuits, bridging, reverse, and string windings, should be able to be detected.

Another important parameter for determining the performance of cabling systems is attenuation. Any electronic signal from the signal source after the transmission process will have the loss of energy, this is no exception for LAN signal. Attenuation increases with increasing temperature and frequency. The high-frequency signal decays more severely than the low-frequency signal. This is why the link has the correct wiring diagram, which runs very well in the 10BASE-T network and does not work properly in the 100BASE-T network. For the 5 type cabling system, the performance of each manufacturer's product is very close to the attenuation aspect.

The most important parameter to judge the performance of twisted-pair cabling system is crosstalk, in which the near-end Crosstalk (NEXT) is first proposed (starting from TSB-67). Crosstalk is caused by a pair of lines of signals that generate radiation and sense to other adjacent pairs of lines. Crosstalk also varies with frequency, and 3-class lines can support 10BASE-T applications well, but they cannot be used in 100base-t networks.

The balance between the close Shang and the line pair can effectively reduce the string winding. The smaller offset can form an electromagnetic field in the opposite direction to effectively cancel each other's influence, thus reducing the line to outward radiation. The 5-type line is smaller than the 3-class line, and the alignment is more consistent than the 3 line, and better insulation is used, which further inhibits crosstalk and reduces attenuation. The Tia/eia-568-b standard requires that all UTP connections that are not Shang at the end of the socket cannot exceed 1.3 cm (0.5 in).

The standard also requires measuring the length of the link. Length measurements look simple, and are actually very knowledgeable. In the standard regulations, the length of the permanent link can not exceed 90 meters, the length of the channel can not exceed 100 meters. The exact length of the measurement is affected by several aspects, including the rated transmission speed (NVP) of the cable, the length of the strand length and sheath, and the pulse scattering along the length direction.

When using the field test instrument to measure the length, the time delay is usually measured, and the length value is calculated according to the set signal speed.

The rated transmission speed (NVP) represents the speed at which the signal is transmitted in the cable, as a percentage of the speed of light. NVP setting incorrectly is a common error. If the NVP is set to 75% and the actual NVP value of the cable is 65%, then the measurement has more than 10% errors before it starts. In addition, the NVP between each pair of lines may vary, and will vary with frequency. For Line 3 and mixed 5 lines, the NVP value between lines is the most likely to have a 12% difference.

In addition, the copper core in the UTP is in the Shang state, so its actual length is longer than the outermost sheath of the cable. For 305.1-meter-box cables, the core may be 310 meters.

Based on the above reasons, the length measured from the test instrument can only be a good approximation and not an exact value.

The attenuation crosstalk ratio (ACR) represents the ratio of the effective signal to the noise in the link. Simply, ACR is the ratio of attenuation to next, measured by the ratio of the signal from the distal attenuation to the crosstalk noise. For example, a lecturer is lecturing in front of the teacher. The goal of the instructor is to be able to hear his speech clearly. The instructor's volume is an important factor, but more important is the difference between the instructor's volume and background noise. If the lecturer is really quiet in the library to speak, even whispers can be heard. Imagine what it would be like if the same instructor spoke at the same volume in a lively football field. The lecturer will have to raise his volume so that his voice (the desired signal) differs from the cheers (background noise) of the crowd to be heard. This is ACR.

In fact, the development of application technology also needs to measure other performance parameters. The return loss, expressed in decibels (db), is the reflection of a part of the signal caused by the mismatch of characteristic impedance. Echo loss is an increasingly important parameter in trying to achieve better performance of UTP systems. Manufacturers of High-performance UTP will pay special attention to ensure consistency in the cable's characteristic impedance, and all components must have a good match. Therefore, in the development of 5 types of systems, the return loss is not a big problem, and in the Super 5 and 6 types of cabling system is very important.

The integrated near-end crosstalk (Psnext) is actually a computed value rather than a direct measurement result. Psnext is calculated by formula on the basis of the next influence of each pair of lines from the other three pairs. Psnext and Fext (described later) are very important parameters to ensure that the performance of cabling systems can support applications like Gigabit Ethernet for simultaneous transmission of four pairs of wires.

Remote Crosstalk (Fext) is similar to next, which is the crosstalk that the signal emits locally and is measured remotely.

Fext is not very valuable in itself. Because the fext is influenced by the length of the cable link, the signal intensity including crosstalk will be affected by the attenuation after the signal source is emitted. It is also the reason that measuring the equivalent distal crosstalk (elfext) is more meaningful. The effect of attenuation is considered in the elfext result, so this parameter is more practical. For the same reason, there are also synthetic equivalent distal crosstalk (pselfext).

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Test 6 wiring system requires the use of at least the third level of precision tester, the old Grade II precision instrument in the test capacity is not equipped with six types of wiring test requirements:

The precision required to test all new parameters

The test fext and the dynamic range of the echo loss in the 6 class system are required,

Bandwidth at a MHz

The current market on the entry level with 6 types of testing capabilities of the instrument is Fluke DSP-4000, a new generation can be tested to the next 7 types of cabling system tester is Fluke DTX-1800.