IFC Networking—Metasys Intelligent Fire Network
23
Fiber Optic Cable Circuits
Fiber optic cable is the second media option on the FN. The attenuation of
fiber optic cabling between two nodes/repeaters (by default, fiber optic
circuits are point-to-point) must not exceed a 10 dB limit. If the distance
required for a circuit segment, using a fiber optic cable produces an
attenuation of the data signal that is greater than permitted, a Repeater
module (model RPT-F) must be inserted into the circuit at intervals less
than, or equal to, the 10 dB length restriction.
Note: When using fiber optic cable, each point to point segment between
network nodes requires two fibers, one for each direction.
To calculate the total dB loss:
1. Find the rated dB loss per foot within the cable manufacturer’s
specifications.
2. Determine the total attenuation between the two nodes/repeaters due
to the cable. Total Loss = (loss/ft) x (length in feet).
3. Add 0.5 to 1.5 dB loss per connector or splice used in the segment.
Attenuation of fiber segment can be estimated by taking distance
between two nodes and dividing it by attenuation per unit length
(dB/km) specified by fiber manufacturer. Since fiber optic cable is
normally sold in spools of up to 1 or 2 km, it is sometimes necessary
to connect several sections of fiber cable.
The following connections can cause 0.5 to 1.5 dB loss:
•
each coupler connecting two fiber optic sections
•
connections on each end of the cable (to and from MIB-F)
The loss can vary from 0.5 to 1.5 dB depending on the connector type.
See the information that comes with the connector for the exact loss.
These losses have to be subtracted from the 10 dB total prior to
dividing by attenuation per unit length.
A
t
+A
r
+[(n-1)
⋅
A
a
]+[1
⋅
a]<10 dB
Where:
A
a
- attenuation of the coupler
A
r
- attenuation of connector between fiber and receiver
A
t
- attenuation of connector between fiber and transmitter
n -
number of fiber optic cable sections
a
- attenuation per unit length
1
- distance between transmitter and receiver
Summary of Contents for FIRE-MON-17
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