你是否在使用福祿克DTX-1800或者DTX-1500的時候長度會超出標準極限值？
Example1: (The display here is from?DTX Version 2.74, have you updated your DTX CableAnalyzer?)
這個結果是對的嗎？這長度已經(jīng)超出了90M。
從ANSI/TIA-1152工業(yè)標準，我們發(fā)現(xiàn)：
4.2.3.1無論速度和電磁速度。
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 %.
通過和失敗的判斷標準是依據(jù)ANSI/TIA-568-C.2 通道和永久的標準加上NVP速度的10%不確定性。
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.
這就意味著盡管極限標準是90M，但是DTX-1800或者DTX-1500顯示92.5M，小于90M+10%的允許量。
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.
許多客戶也許覺得不同意但是福祿克DTX-1800或者DTX-1500是根據(jù)標準來的。福祿克網(wǎng)絡的設備也許沒有必要咨詢10%長度原則，但是工業(yè)標準支持，所以，我們根據(jù)標準制定了。
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.
我們通過上圖可以看到DTX-1500顯示的7.8線對是97.9M，結果顯示是通道。因為它沒有超過90M的百分百之十。其他兩對線路已經(jīng)超過了10%并且標記了I對于參考，但是我們沒有評價沒有用作評價對這條鏈路。
Example 3: If the pair with the shortest length exceeds 90 m plus 10%, then length is reported as FAIL (shown below).
如果所有的都顯示超過90M+10%，那么它就會顯示失敗了。
