20
ControlNet Fiber-optic Ring Repeater Modules
Rockwell Automation Publication 1786-IN003D-EN-P - April 2011
The sample formulas in the example illustrate how you can determine the total
loss for fiber-optic cables in your system configuration. The values we use in the
formulas are typical: yours may vary, depending on your application.
EXAMPLE
Determining total loss for fiber-optic cables
The total loss of the fiber-optic cable between two modules must
not exceed the optical power budget. The total loss is the sum of
each connector loss plus the loss of the fiber plus the loss
associated with the splices in the system, if any. The total loss
can be determined as follows:
Total loss = [(loss per connector) x (the number of connectors)] +
[(loss per km of fiber) x (km of fiber)] + [(other losses)]
For example, with 2 connectors, each having 0.3 dB of loss,
10 km of multimode fiber with a loss of 1 dB/km, and no splices,
the total loss is 10.6 dB. See the following formula:
Total loss = [(0.3 dB x 2) + (1 dB/km x 10 km)]
Total loss = 10.6 dB
This fiber-optic cable is acceptable for use between two
1786-RPFRL/B modules because the total loss is less than the
optical power budget of 15 dB. However, this cable could not be
used with the 1786-RPFRXL/B module because the total loss
exceeds the optical power budget of 10.5 dB.