Siemens Argus 7SR21 - Serial Fibre Optic Interface (COM3 & COM4)

7SR220 Technical Manual
Chapter 4 - Page 10 of 96 © 2017 Siemens Protection Devices Limited
To Control
System
Rear terminals
14
16
18
RS485 Screened
twisted pair
14
16
18
RS485 Screened
twisted pair
Rear terminals
14
16
18
20
Ext Wire loop
(terminating
resistance) added
where permanent
drive from master
station available
To Control
System
Bus Termination Polarity
5V
B
A
Sc
Fig. 2-2 Communication to Multiple Devices using RS485 (Standard Port)
2.4 Serial Fibre Optic Interface (COM3 & COM4)
When connecting via the optional fibre optic interface the selection of fibre-optic cable is important. Fibres must 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 Relay when used with specific fibre optic types.
Fibre Type
62.5/125µm
Tx Launch Power (dB) RX Receive Sensitivity (dB)
Min
-11.7
Max
-15.7
Min
-24
Max
-9.2
1mm Polymer
-6.4 -10.4 -24 -9.2
200µm PCS
-2.8 -6.8 -24 -9.2
Factors to be considered when calculating fibre-optic transmission distances:
• 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).
RS485 RS485 RS485
RS
485
Twisted
pair
Cable
A 14 Sc 16 B 18 Term. 20 A 14 Sc 16 B 18 Term. 20 A 14 Sc 16 B 18 Term. 20