First off, what’s loopback OTDR testing?
The idea is straightforward: it entails utilizing a single OTDR, which stays at one web site, and testing two fibers on the identical time by utilizing a loopback fiber or loopback system on the different web site.
And naturally with regards to OTDR testing you could have the choice of uni-directional (uni-dir) or bi-directional (bi-dir) certification, and in an earlier weblog seems to be at the benefits of performing bi-dir take a look at. As a consequence of these benefits, the vast majority of fiber certification carried out utilizing a loopback OTDR methodology is bi-directional, in order that’s the case we’ll think about right here.
The take a look at course of is that this: as soon as the launch/obtain and loopback fibers are inspected and linked, the fiber pair is examined in a single route (from 1A as proven above). The launch and obtain fiber connections are then reversed and the fiber pair examined in the other way (from 2A).
You must guarantee that your OTDR helps loopback testing. And by that I imply that its take a look at purposes or algorithms can mechanically determine the loopback fiber and separate out the 2 fibers being examined. This provides you with a set of outcomes for every fiber within the pair; in any other case, there may be numerous post-processing work required with extra software program to do this work. Luckily, VIAVI OTDR do assist loopback take a look at in order that’s all carried out on the devices.
Human error is at all times a threat with loopback testing, and as a lot of the launch/obtain cables and fibers being examined are all the identical shade, it may be straightforward to make a mistake, An excellent tip is to make use of completely different colours in your launch/obtain fibers so that you don’t get muddled up and by chance take a look at the identical route twice, which might imply any bi-dir OTDR evaluation would even be void.
So what are the benefits of loopback testing?
First, there may be the take a look at gear saving, one instrument versus two … can’t argue with that one. Shopping for or renting one instrument is cheaper than two, or no less than it might appear that method, significantly in case you are speaking about certifying a smaller variety of fibers. (In future blogs we’ll have a look at the sort of time financial savings that may be achieved with a two-instrument method.)
Subsequent, testing two fibers directly cuts the variety of exams you need to carry out in half, so that you seem to have a direct 50% time saving. Nevertheless, whereas it’s true that the variety of exams is lowered, that’s simply the testing time. There are nonetheless the entire different actions and steps which should be carried out (and people are very handbook) so total you by no means acquire a full 50%.
So, what are the constraints?
You continue to want two technicians so that you don’t save on labor, though the far-end tech is barely performing finish face inspection and shifting a loopback fiber to the subsequent fiber pair being examined.
Plus, as talked about, the vast majority of loopback OTDR testing carried out is for bi-dir certification, so you continue to should carry out two exams per fiber pair that means there are nonetheless additional handbook steps to disconnect/reconnect the OTDR take a look at port and provoke the subsequent acquisition. Then swap to the subsequent fiber pair, affirm with the far-end tech (by telephone or radio) that they’re able to go and once more manually begin a take a look at. All of which creates pauses/delays between exams being initiated and wastes time. The beginning/cease nature creates an interrupted take a look at move and permits inefficiencies to creep in. This might not be a lot or important when coping with decrease volumes of fiber, nevertheless it definitely provides up whenever you begin to have a look at multi-fiber and high-fiber-count cables. We’ll have a look at this in additional element in a future weblog within the collection.
The usage of obtain fibers for bi-dir OTDR certification and what the trade requirements should say was additionally the subject of a earlier weblog.
Till lately, OTDR might assist with a part of the loopback take a look at by mechanically figuring out the 2 fibers within the take a look at outcome and separating them out into particular person outcomes information which might then be used for post-processing to carry out the bi-dir evaluation (loss averaging). VIAVI OTDR can now do the on-board bi-dir evaluation too, we consult with it as TrueBIDIR.
One other limitation is the size of the hyperlink that may be examined. Two fibers signifies that the utmost hyperlink size you may take a look at is halved, so loopback testing could not really be an choice if the full hyperlink size for 2 fibers (and launch/obtain fibers) exceeds the utmost vary of your OTDR.
Continuity testing additionally turns into a bit of extra concerned. You must make sure the loopback system and obtain fiber are linked accurately so you might be testing the suitable pair of fibers. A visible fault locator (VFL) can be utilized for continuity take a look at however they’ve a restricted energy output and due to this fact restricted vary (distance). Most techs go for a real-time OTDR take a look at to examine for the presence of the loopback and obtain fiber, however real-time OTDR outcomes are at all times and solely an OTDR hint (not a easy icon view). So that you want a bit of extra expertise to learn it and determine the loopback and obtain fiber after which depend on the colour coding of launch/obtain fibers to keep away from connection errors.
Nevertheless, the opposite choice of utilizing two devices could initially price extra, nevertheless it has benefits:
- Permits testing of longer hyperlinks
- Permits automated continuity take a look at
- Permits automation to be utilized for optimization of take a look at sequencing and outcomes processing (offered you could have a mechanism for exchanging knowledge, in real-time, between close to and much finish models. Ideally this might be through the fiber below take a look at, a VIAVI-patented functionality, to ensure the testers are impartial of web entry so that you don’t should depend on cloud purposes to switch knowledge, particularly with regards to bi-directional OTDR evaluation)
- Delivers higher ROI over time (or over quantity of fibers examined) and considerably higher workflow when integrated with a totally automated answer that features an optical swap for batch testing and bi-directional OTDR outcomes averaging/evaluation (VIAVI’s FiberComplete PRO)
In a future weblog I’ll have a look at how a two-instrument method may also help with workflow effectivity, significantly for prime fiber depend cables, plus how the bodily configuration and automation of the take a look at gear itself can have a big impact on take a look at move effectivity.
To study extra, check out our Bi-directional OTDR Testing web page.
Dou
glas Clague is at the moment options advertising supervisor for fiber optic subject options at VIAVI. Doug has over 20 years of expertise in take a look at and measurement with a major give attention to fiber optics and cable applied sciences, supporting the telecommunications trade. Previous to VIAVI, Doug held positions as manufacturing engineer, options engineer and enterprise growth supervisor. Doug has participated on quite a few trade panels round fiber and cable know-how traits. He attended Brunel College in London and graduated with an honors diploma in electrical and digital engineering.
