Precision Level concept of cable Tester

Measurement Accuracy determines the required testing tools

When you need to perform a length test, you must select an appropriate measuring instrument or technique according to the precision requirements for length measurement results. For example, you need to measure the length of a small wire. According to the requirements, you know that the length of the wire is measured in millimeters. The error of this measurement, or the deviation between the actual length value and the measured value, must be less than 1mm. A ruler with a precise millimeter scale can complete the test within the required precision. On the other hand, if you want to use this wire, perform a more accurate length test, for example, you need to reach the level of five thousand to 1mm, we have to choose a measurement tool with a high accuracy-the micrometer to complete the test. This is the same as the test electrical signal.

On-site authentication of installed data links

ISO/IEC11801: 2002 and TIA/EIA-568-B standards have specific descriptions and provisions on methods for field-certified installed data links. These standards define cabling systems with different performance metrics. Components in a link are described as "classes", such as Category 5, Category 6, or category 7. The larger the number of categories, the higher the performance, of course, the more expensive the price ).

The on-site authentication process defines a series of test parameters and their passing/failure conditions to indicate whether the installed links meet certain or some level of link requirements. On-site authentication is mainly based on the analysis of signal-to-noise ratio. In other words, you need to measure the signal strength received at the end of the link, at the same time, you also need to measure the interference factors that affect the transmitted signal before the signal reaches the receiver's input end point: noise or interference. These disturbances must be avoided as much as possible and cannot exceed a certain level. The performance of a link depends on the maximum level of interference that may affect signal transmission. Second, you also need to measure within the frequency range required by the signal. Test the performance of the D-level link defined in the standard-consisting of five components-from 1 MHz to 100 MHz, and 6 class components of the E-level link) from 1 MHz to 250 MHz, class F links and seven components) require up to nhz. This frequency is also the highest bandwidth supported by the link.

As the link performance improves, the interference signals we need to measure become increasingly weak. Therefore, the accuracy requirements of the Tester Used for certification must be improved accordingly as the accuracy required for the measurement of weak signals can meet the requirements of high performance standards.

Link Measurement

These standards define both the link and component performance levels and the performance of the on-site certification tester. Level II accuracy is the minimum accuracy requirement for measuring Level D links composed of five components. The frequency range of the "Level II" Tester must match the frequency range of the required parameters for the five types of links, that is, from 1 MHz to 100 MHz. Level II accuracy was later revised to IIe level accuracy due to additional requirements of Category 5 cabling systems. With the introduction of six components and six/E-level links, Level III accuracy is defined.

Compared with level II or IIe, the requirements for Level III accuracy are improved in two aspects:

The amplitude of the interference signals to be measured, such as near-end crosstalk NEXT, remote crosstalk FEXT, and Return Loss) is lower, and the frequency range to be tested must be extended to 250 MHz. The ISO/IEC Standard defines seven components to form a F-level link. The interference signal to be measured is weaker than that of Class 6/Class E, and the testing frequency of Level F links is extended to 600 MHz. For these required parameters, adequate accuracy is required within the extended frequency range, and the standard plan defines Level IV accuracy. The technical requirements that are sufficient to authenticate the accuracy required for the F-level link are still under study. The results, that is, the requirements for Level IV accuracy, have been included in the IEC 61935-1 standard draft version 2nd. These indicators are expected to be approved later this year.

Comparison between Level III precision and Level IV precision

Table 1 lists the allowable values for the residual NEXT feature of the Class III and IV precision field testers. Residual NEXT refers to the crosstalk value of the tester itself measured when the tester input is not connected to any cable. It is part of the bottom line noise measurement for near-end crosstalk. Residual NEXT is one of the many factors that affect the accuracy of the tester. For baseline and permanent link indicators, the minimum difference between the residual NEXT of the IV-level precision tester at 100 MHz is 18 times less than that permitted by level III accuracy. The residual NEXT data expressed by μV microv or one thousandth of a volt) clearly shows this proportion. As mentioned above, the requirements for Level IV accuracy are equivalent to 18 times smaller than the weakest signal that can be tested by a level III accuracy tester.

Table 1 also raises another topic that has not been discussed so far. The standard defines the accuracy of both basic instruments (also known as baseline accuracy) and the accuracy of the instruments with an adapter for testing permanent links and channels. Some manufacturers only mention the baseline accuracy. In practice, this is a misleading concept, because the tester always works with the test adapter, whether it is a permanent link or a channel. The standard does plan to define baseline accuracy while setting strict performance requirements for the adapters required to test the actual link.

Conclusion

The minimum precision requirements defined in the standard within the specified frequency range are usually expressed in formulas, in dB. These formulas are written by experts. In fact, as described in this article, it is easier to compare the absolute values of some parameters at a fixed frequency point.

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