专注福禄克测试仪销售与技术

你是否在使用福禄克DTX-1800或者DTX-1500的时候长度会超出标准极限值？
Example1: (The display here is from?DTX Version 2.74, have you updated your DTX CableAnalyzer?)

这个结果是对的吗？这长度已经超出了90M。

从ANSI/TIA-1152工业标准，我们发现：

4.2.3.1无论速度和电磁速度。

4.2.3.1 Physical length vs.?electrical length
The pass or fail criteria is based on the maximum length allowed for the channel or permanent link as specified in ANSI/TIA-568-C.2 plus the nominal velocity of propagation (NVP) uncertainty of 10 %.

通过和失败的判断标准是依据ANSI/TIA-568-C.2 通道和永久的标准加上NVP速度的10%不确定性。

This means that although the limit is 90.0 m (295 ft), the tester will not fail the length parameter until the shortest pair of the four pairs has exceeded 90 m + 10 % (99 m) or 295 ft + 10% (325 ft). In the example above, the shortest pair was 92.5 meters, less than the 90 m + 10 % permitted by this standard.

这就意味着尽管极限标准是90M，但是DTX-1800或者DTX-1500显示92.5M，小于90M+10%的允许量。

Many customers do not like/agree with this feature. However, your DTX-1800或者DTX-1500 CableAnalyzer is standards based. Whilst Fluke Networks may not necessarily agree with the 10 % fudge rule, the industry agreed to this. We implement the standard as is. THIS IS NOT AN EXCUSE TO GO BEYOND 90 m!!!!!!!!!!! If the cable is marginally compliant, insertion loss will fail before length fails.

许多客户也许觉得不同意但是福禄克DTX-1800或者DTX-1500是根据标准来的。福禄克网络的设备也许没有必要咨询10%长度原则，但是工业标准支持，所以，我们根据标准制定了。

This rule applies to channel limits as well where the length limit is 100 m (328 ft). However, because of clause?4.2.3.1 in the standard, the length test will not fail until the shortest pair of the four pairs measured exceeds 100 m + 10 % (110 m) or 328 ft + 10% (361 ft).

It is important to understand that we used the shortest pair to report the length of the link. Again, this is detailed in clause 4.2.3.1 of ANSI/TIA-1152.

When physical length is determined from electrical length, the physical length of the link calculated using the pair with the shortest electrical delay shall be reported and used for making the pass or fail decision.

Example 2: (The display here is from DTX Version 2.74, have you updated your DTX CableAnalyzer?)

Here we see that the shortest pair is 7,8 with a length of 97.9 m and hence a PASS since it does not exceed the 90 m limit by more than 10%. The other two pairs did exceed 90 m plus 10% and are marked I for Information Only but are not used for evaluating the link.
我们通过上图可以看到DTX-1500显示的7.8线对是97.9M，结果显示是通道。因为它没有超过90M的百分百之十。其他两对线路已经超过了10%并且标记了I对于参考，但是我们没有评价没有用作评价对这条链路。

Example 3: If the pair with the shortest length exceeds 90 m plus 10%, then length is reported as FAIL (shown below).

如果所有的都显示超过90M+10%，那么它就会显示失败了。

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