Never use bend insensitive multimode fiber for test reference cords. Your 850 nm reading will be pessimistic.
This article will describe the steps required to successfully certify a multimode ST to ST duplex fibre link in accordance with ISO/IEC 14763-3 using the DTX-MFM2 fiber adapters. This standard permits two methods, a 1 Jumper and 3 Jumper Reference Method. The 3 Jumper Reference Method often results in negative losses, which is why the 1 Jumper Reference Method should be carried out (shown below). Your cabling vendor may not permit the use of the 3 Jumper Reference Method.
Items required in addition to a DTX CableAnalyzer:
Cleaning is critical. It is the single most reason for ending up with negative loss values. You cannot clean without some means of visually inspecting the end face. This can be anything from a simple Fiber Viewer to a Video Scope such as the FiberInspector Mini shown above. If you have no inspection device, you cannot proceed. Let's define what is acceptable and not acceptable.
The Test Reference Cords (TRCs) are critical to a successful measurement. Your multimode TRCs loss MUST not exceed 0.10 dB at each end. The multimode TRCs shipped from Fluke Networks;
NFK1-DPLX-ST Duplex MM 62.5 µm TRC for ST Adapter, Set of 2
NFK2-DPLX-ST Duplex MM 50 µm TRC for ST Adapter, Set of 2
have a mated loss better than 0.10 dB at each hardened end face. And yes, you must inspect and clean these TRCs every time you use them - even new ones out of the bag. We'll show you how to check your TRCs for 0.10 dB loss later on in this article.
Where did Fluke Networks get that 0.10 dB requirement?
ISO/IEC 14763-3 requires that the TRC must not exceed 0.10 dB for multimode and 0.20 dB for singlemode at the connectors.
In this example, we're going to test a 100 m duplex 50/125 µm multimode fibre link with ST connectors at each end to ISO/IEC 14763-3.
Setting up the DTX CableAnalyzer
- With the fibre modules inserted into the DTX CableAnalyzer, power up the main and remote units.
Sources will need at least five minutes to stabilize, longer in colder or hotter environments.
- Replace the SC Adapters on the main and remote units with the optional ST Adapters.
- Rotate the dial on the DTX CableAnalyzer to SETUP.
- Select Fiber Loss and press ENTER.
- Change the Test Limit to ISO/IEC 14763-3.
- Change the Fiber Type to the cable you are testing.
This setting changes the Refractive Index (n) value. The DTX uses n to calculate the length of the fibre. You can manually enter the n values in Tab 3 of the Setup. If you cannot find your cable in the DTX Cable Library, look to the cable vendor's website for their datasheet. Since the ISO/IEC 14763-3 limit is calculated based on length, it is important to get this value right.
- The Number of Adapters is going to be 2.
This is always the number of adapters per fibre strand added after the reference has been set.
- Set the Connector Type to ST.
This will not affect the outcome of the result. It only affects the help screens.
- Set the Test Method to 1 Jumper.
- Clean AND inspect the TRCs.
- Connect the main and remote units together as shown below.
Mandrels must be used. Failure to do so can result in good fibre links failing. Red and grey mandrels are shipped with the fibre modules from Fluke Networks. The red is for 50/125 µm and the grey is for 62.5/125 µm TRCs.
- Rotate the dial to SPECIAL FUNCTIONS.
- With Set Reference selected, press ENTER then TEST.
- You will then be presented with the results of the Reference.
For 50/125 µm it should be better than -24.50 dBm where -23.50 dBm is better than -24.50 dBm.
For 62.5/125 µm it should be better than -20.00 dBm where -19.50 dBm is better than -20.00 dBm.
These values reflect the cleanliness of the Ports and TRCs. The fact that your reference values are better than the minimum stated above does not mean they are good/clean. In the next few steps, we'll see how good/clean your TRCs really are.
- Press F2 OK.
- You can enter the length of your TRCs here. It does not affect the outcome of the test, but will be displayed on the test report.
- Press F2 OK when done.
- Remove the ST connectors from the Input Ports and put the dust caps back on them.
Never disconnect from the Output Ports. Doing so invalidates the reference you just set.
- Insert one of the ST to ST TRC's into the Input Port on the main unit.
- Insert the other ST to ST TRC into the Input Port on the remote unit.
- You are now ready to test the fibre link, but before you do, IT IS CRITICAL to check out your TRCs. To do this, connect the main and remote units using a singlemode rated ST to ST adapter as shown below.
- Rotate the dial to AUTOTEST and press TEST.
- SAVE the test result so you have evidence of a good Set Reference.
- To view the result, press ENTER. IGNORE the test limit. We're looking to make sure the loss is no greater than 0.15 dB at 850 nm 1300 nm. (The extra 0.05 dB is to take into account the uncertainty of the adapter used above for the TRC verification)
This is the fibre connected to the Input Port of the main unit and it looks good.
- Press EXIT and with Loss (Main Remote) highlighted, press ENTER.
This is the fibre connected to the Output Port of the main unit and it too looks good.
If it was more than 0.15 dB then you would want to inspect, clean and redo the Set Reference again. The test limits in ISO/IEC 14763-3 are based on you having a 0.10 dB Test Reference Cord.
Important additional information
When you look to ISO/IEC 11801 you will see that the mated loss requirement is 0.75 dB. However, in ISO/IEC 14763-3 the limit for a mated Test Reference Cord to a random connector is 0.30 dB. If your Test Reference Cord is worse than 0.15 dB, you may have trouble meeting the 0.30 dB requirement.
Can't get anywhere near 0.15 dB? They look ok under the FiberInspector? Your patch cords may not be ISO/IEC 14763-3 TRC rated. Please check with the supplier. Most cords come with the test results in the bag.
If you are using the DTX where the temperature is not typical, run the TEST repeatedly with 1 minute intervals to see if the result changes. If it does, you will need to let the sources stabilize and repeat the Set Reference process again.
This procedure is likely to be new to the technician. Have them try this in the office before leaving for the installation.
- Disconnect the main and remote units.
Place dust caps on the remote TRCs if it is more than a short walk to the other end. According to the EPA, dust in an office can be anything from 2.5 µm to 10 µm so protecting the end faces is critical.
- Connect the TRCs to the link you're testing.
- Press TEST.
The 0.30 dB at the connectors is not an error. This is the maximum permitted loss between a Test Reference Cord and a random fibre connector in ISO/IEC 14763-3. Let's take a look at another link with a fibre connector in the middle of it.
You will note the adapter count has increased to three and that the middle connection is permitted to be 0.75 dB. That's because the mated connectors in the middle do not involve a Test Reference Cord. These are two random mated connectors.
Test Reference Cord + Random Connector ≤ 0.30 dB
Random Connector + Random Connector ≤ 0.75 dB dB
How often should I Set Reference?
The quick answer is; every time you begin to test a series of fibre links. It is critical to continually inspect the TRCs.