Episode 6 of the Telcom Corner Café Podcast discusses Inspection.
Inspection remains both a hot topic and a very controversial topic in our industry. What are you cleaning, what materials are you using to achieve the desired effect, what’s your definition of acceptable verses the lead tech, project manager or the expectations of the customer that you are doing the work for, and surprisingly there is both a very significantly different view and expectations, as well as very little commonality between people, regarding the parameters of what’s acceptable or what’s unacceptable.
Let’s begin with, what are you inspecting? Are you inspecting multimode connectors or single mode connectors. Why is this even a question? There are 3 widely unknown, or not even considered practices that are at the center of inconsistencies regarding inspection practices, expectations and results desired.
#1. What you use to clean with, will have a significant effect on what see, how clean it actually is, what will or will not be left behind, and the effects that it will or will not have on the network.
For instance, isopropyl alcohol is no longer recommended to clean connector end-faces with due to the potential for residue that it could leave behind, which if happens will cause highly reflective (for more on reflectivity, cleaning materials and connectors, check put episodes 3, 4 and 5 of this podcast)
#2. Scope power. I have been a part of, have walked by, and been within ear shots of many discussions and heated debates that this is a non-issue. Unfortunately, that is 100% incorrect. Scope power matters a lot. Why, because to much magnification allows the inspecting individual to see to much. That must sound odd to have heard me say see too much, wouldn’t one want to see everything, kind of. I am going to use an equally odd comparison to significantly move the needle on this particular topic.
If you have ever heard the term overkill, you have just successfully connected why too much magnification is not good, and why one does not want to see everything or to much. It’s over the top, or if preferred excessive, unneeded, unnecessary and will cause far more problems than it will ever prevent or solve.
What do I mean by this. Drifting all the way back to the 80’s for a moment, the reason that 200x or lower magnification scopes were specified for multimode connector inspection, was the determination from years of research by Bell Labs that is was the maximum amount of magnification necessary to adequately inspect the end-face of multimode connectors base on inspection criteria, meaning is it a good or bad polish, where is the damage located? What kind of damage is there and risks or impacts that is poses or could cause.
There cannot be any damage in the core or in the inner cladding region right next to the core, as it may spread into the core due coupling and decoupling of the connectors involved.
Scratches, pits, and over-polishing have long been considered non-issues in multimode connector inspection, because multimode systems remain to date unconcerned about and unaffected by reflectivity issues (which was a big discussion in episodes 3, 4 & 5) Therefore, magnification greater than 200 X significantly enhances the potential for obsessiveness, that quickly creates problem’s because one goes to far, too fast, and before they realize it, a problem that was not going to be an issue previously, is now indeed a problem, whereas if it had been left alone, it would not have caused any network impacts.
However, this is not the case in the single mode environment. It’s an entirely different process when working with single mode. Instead of having the benefit of looking at core sizes of 62.5um or 50 um that are either 40% or 50% of the entire 125um surface of the glass within the ferrule end-face of the connector one is inspecting, in single mode one get’s to look at a 8.3um core inside of 125um cladding that is in the center of the connector ferrule that one is inspecting, which is also both highly affected by and sensitive to reflectivity, that multimode is not.
Coming back to scop power, single mode is the home for, as well as the recommendation for, the use of 400x scopes per Bell Lab s. The individual inspecting will need that 400x power magnification to properly evaluate the sizes of, and conditions of what they are inspection, a 200x or less magnification doesn’t provide that depth of view for the level of proper inspection for single mode component inspection.
#3. Before I get to that, there is certainly room to make the points of what about laser eye filtration, the ergonomic design and fatigue of the scope to be used, and if one is goin to use a hand-held scope or video inspection device. These are very valid points.
However, point #3 in our discussion today centers on, is the person conducting the inspection using an oblique view or Coaxial view designed inspection device? Are they even aware these differences even exist?
What is this, why does it matter and why should it even be a consideration or considered in the first place? Because the resulting view, will be completely different and could cause and result is a lot of unnecessary rework, network downtime, perfectly good connectors being cut off, and thrown away do to not being aware of the different views that oblique and Coaxial designs provide for inspecting connectors. In the case of the Coaxial design, it’s a straight on or if preferred a dead-on view, such as 2 people looking straight at each other.
So, when one is viewing the connector, that technician will see 2 concentric circles. A smaller one inside of a larger one if you will. The Smaller circle which is the core of the glass is very rarely any color other than black. The larger of the 2 circles, which is the cladding region of the glass and will be gray in color, the remaining white bright area is the connectors ferrule within the view of what one is inspecting.
In the case of the Oblique view design, the views of the connector ferrule and cladding region area’s will remain the same as the Coaxial view. The difference is the view of the smaller inter circle or core area.
Unlike to coaxial design that provides a straight on view, the Oblique design casts the light down the long access of the scope hitting a prism that casts a Silhouette over what one is inspecting. This creates a different resulting view of what you will see when using an Oblique view designed inspection device.
The core region view will not be visible unless ambient light is present in some amount to light it up, at which point the core region will light up white to define it. However, if there is no ambient light present, an Oblique view device will only show one concentric circle of 125um’s, which can lead to the determination that the connector is broken, and needs to be replaced, when in fact, there is actually nothing wrong with the connector under inspection.
