Fibre Optic Interface - Siemens 7SR224 Technical Manual

2.1.5

Fibre Optic Interface

When connecting via the optional fibre optic interface the selection of fibre-optic cable is important. Fibres must
TM
be terminated with ST (BFOC/2.5) connectors.
The recommended type is 62.5/125µm glass fibre. Communication distances over 1 km are achievable using this
type of fibre.
A budget loss calculation should be made for all installations. The following table gives the Launch power and
receiver sensitivity of each of the fibre optic communication ports on the Argus relay when used with specific fibre
optic types.
Fibre Type
62.5/125µm
1mm Polymer
200µm PCS
The main factors limiting transmission distances with fibre-optics are: -
Transmitter launch power.
Attenuation, based on light frequency, fibre material and fibre diameter. (Consult fibre manufacturers'
data for actual values of fibre attenuation).
Number of intermediate connectors and splices. Fibre cables are supplied on reels of finite length which
may necessitate additional jointing. Typical losses at connectors are 0.5-1.0dB each. This allows for
normal age related deterioration. Typical losses at splices are <0.3dB. (Consult fibre manufacturers' data
for actual values).
Receiver sensitivity. The light power at the receiver must be above the sensitivity of the receiver in order
that effective communication can occur.
A 3dB safety margin is usually allowed after the budget calculation is performed.
Following installation the actual losses should be measured for each fibre using a calibrated light source and
meter and the measured values compared to the calculated estimate before the relay is applied.
The following table can be used to record budget calculations:
A Launch power
B Fibre Type
C Loss (dB/km)
D Length
E Total fibre loss (CxD)
F No. of Splices
G Loss at each splice
H Total loss at splices (FxG)
I No. of connectors
©2010 Siemens Protection Devices Limited
Tx Launch Power (dB)
Min Max
-11.7 -15.7
-6.4 -10.4
-2.8 -6.8
7SR224 Argus Data Comms
RX Receive Sensitivity (dB)
Min Max
-24 -9.2
-24 -9.2
-24 -9.2
Chapter 4 Page 8 of 76
dB
dB/km
km
dB
dB
dB