Numbers that tell a story
A tester gives you a table: forty links, each with a length and a few numbers. Most say pass. Two do not, and one passes by only a hair.
Reading the table well means more than spotting the word fail. It means saying what is wrong, how serious it is and what to do next.
Key words
| Word | What it means |
|---|---|
| Margin | how far inside the limit a result is, in dB |
| Limit | the standard's pass mark for a test |
| Headroom | another word for margin: the spare room before a limit |
| Event | a point on an OTDR trace where light is lost or reflected |
| Test software | the program that reads results from a tester and makes reports |
| Report | a document that lists every result and its pass or fail |
| Conclusion | what the results show, in a few clear sentences |
| Permanent link | the fixed cable from the patch panel to the wall outlet |
| Manufacturer's guidelines | the maker's own accepted range of results |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can read copper and fibre test results, compare them with limits, find the fault, and write a conclusion.
Starter: testing
Have a go
Starter: testing
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Five steps to a conclusion
First gather the data: results, traces and pictures. Second, use test software to load them and make a report. Third, compare each result with its limit and with the maker's guidelines. Fourth, analyse: group the failures and look for a pattern. Fifth, write the conclusion.
A good conclusion is short, exact and fits what the customer needs.
A copper result table
| Link | Length | Margin | Wire map | Result |
|---|---|---|---|---|
| A-01 | 70 m | 4 dB | Pass | Pass |
| A-02 | 95 m | 6 dB | Pass | Fail: over 90 m |
| A-03 | 60 m | -2 dB | Pass | Fail: margin below zero |
| A-04 | 88 m | 1 dB | Pass | Pass, but only just |
| A-05 | 40 m | 0 dB | Open on pin 6 | Fail: open wire |
The cells students fill in are left blank in this preview.
Your turn: read the copper table
Have a go
Your turn: read the copper table
5 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.