Rockwell Automation 1786-series ControlNet Fiber Media Planning and Installation Guide - Manual (Page 37)

Rockwell Automation Publication CNET-IN001C-EN-P - October 2011 37
Topology and Signal Considerations Chapter 2
Step 3: Subtract loss for cable lengths
Select fiber cable and identify loss = length of cable x (loss due to
fiber cable/km)
Measured @ .1 dB
Step 4: Compare losses
Compare the sum of losses in steps 2 and 3, with total power budget
in step 1.
4.2 dB - 3 dB - .1 dB = 1.1 dB
If the sum of steps 2 and 3 are equal to or less than step 1 (which applies
for our example), then you are within the power budget.
If steps 2 and 3 are greater than step 1, then you will need to reconfigure
the topology, shorten cable lengths, or re-calculate the loss budget.
Attenuation Levels for Medium-distance Fiber Segments
The power loss budget for the medium-distance fiber repeater
(catalog number 1786-RPFM) is 13.3 dB. The maximum amount of attenuation
between the two fiber repeaters shall not exceed 13.3 dB. This power
loss budget includes the entire bulkhead/fusion splice.
This power loss budget is valid throughout the operating temperature range
(0…60° C) of the 1786-RPFM module.
IMPORTANT Due to possible fiber connector degradation, it is recommended that an
allowance of 0.5 …1.0 dB per short-distance fiber cable segment be
added to the total attenuation. In the above example, the maximum cable
length would be 20…70 meters.
There is no minimum length of cable for the short-, medium-, or long-
distance fiber repeaters.
IMPORTANT Due to possible fiber connector degradation, it is recommended that an
allowance of 1.0 dB per 62.5/125 multi-mode cable segment be added to
the total attenuation.
There is no minimum length of cable for the short-, medium- or long-
distance fiber repeaters.