ACCESSORIES

Some regularly used industry terms:

Ducting & Trunking

Cable Duct: A pipe, either earthenware or concrete, through which prestressing wires or electric cable are pulled. 

Trunking: In telecommunications it refers to the grouping of connection switches and circuits within a telephone exchange. Trunking is a process that enables the service provider to use fewer circuits because users are sharing connections.

Tools

Copper Cabling Testers & Certification: In copper twisted pair wire networks, copper cable certification is achieved through a thorough series of tests in accordance with Telecommunications Industry Association (TIA) or International Organization for Standardization (ISO) standards. These tests are done using a certification-testing tool, which provide “Pass” or “Fail” information. While certification can be performed by the owner of the network, certification is primarily done by contractors. It is this certification that allows the contractors to warranty their work.

Fibre Optic Network Testing

Fibre Optic testing includes three basic tests: 
- Visual inspection for continuity or connector checking
- Loss testing
- Network Testing

Visual Inspection

Continuity checking makes certain the fibres are not broken It involves tracing a path of a fibre from one end to another through connections by using a visible light "Fibre optic tracer" or "pocket visual fault locator". It resembles a flashlight with a light bulb or LED source that mates to a Fibre optic connector. Attach a cable to the visual tracer and look at the other end to see the light transmitted through the core of the Fibre. If there is no light at the end, go back to intermediate connections to find the bad section of the cable.

 

A higher powered version of the tracer uses a laser. The red laser light is powerful enough to show breaks in fibres or high loss connectors. One can see the loss of the bright red light even through many yellow or orange simplex cable jackets, but not through black or grey jackets.

 

Optical Power - Power or Loss? ("Absolute" vs. "Relative")

The power output of a transmitter or the input to a receiver are "absolute" optical power measurements, meaning you measure the actual value of the power. Loss is a "relative" power measurement, the difference between the power coupled into a component like a cable or a connector and the power that is transmitted through it. This difference is what we call optical loss and defines the performance of a cable, connector, splice, etc.

 

OTDR Testing
OTDRs are always used on OSP cables to verify the loss of each splice. They are also used as troubleshooting tools.

How OTDRs Work
Unlike sources and power meters which measure the loss of the Fibre optic cable plant directly, the OTDR works indirectly. The source and meter duplicate the transmitter and receiver of the Fibre optic transmission link, so the measurement correlates well with actual system loss.


The OTDR, however, uses backscattered light of the Fibre to imply loss. The OTDR works like RADAR, sending a high power laser light pulse down the Fibre and looking for return signals from backscattered light in the Fibre itself or reflected light from connector or splice interfaces. 
At any point in time, the light the OTDR sees is the light scattered from the pulse passing through a region of the Fibre. Only a small amount of light is scattered back toward the OTDR, but with sensitive receivers and signal averaging, it is possible to make measurements over relatively long distances. Since it is possible to calibrate the speed of the pulse as it passes down the Fibre, the OTDR can measure time, calculate the pulse position in the Fibre and correlate what it sees in backscattered light with an actual location in the Fibre. Thus it can create a display of the amount of backscattered light at any point in the Fibre.


Since the pulse is attenuated in the Fibre as it passes along the Fibre and suffers loss in connectors and splices, the amount of power in the test pulse decreases as it passes along the Fibre in the cable plant under test. Thus the portion of the light being backscattered will be reduced accordingly, producing a picture of the actual loss occurring in the Fibre. Some calculations are necessary to convert this information into a display, since the process occurs twice, once going out from the OTDR and once on the return path from the scattering at the test pulse.

 

OTDRs can also detect problems in the cable caused during installation. If a Fibre is broken, it will show up as the end of the Fibre much shorter than the cable or a high loss splice at the wrong place. If excessive stress is placed on the cable due to kinking or too tight a bend radius, it will look like a splice at the wrong location.