Section 6: Data Comms Connections; Standard Rs485 Connections; Irig-B Connections; Figure 6.1-1 Rs485 Data Comms Connections Between Relays - Siemens Argus 7SR21 Installation Manual

Section 6: Data Comms Connections

6.1

Standard RS485 Connections

The standard RS485 communication port is located on terminal block 2 at the rear of the relay and can be
connected using a suitable RS485 120Ω screened twisted pair cable.
The RS485 electrical connection can be used in a single or multi-drop configuration. The RS485 master must
support and use the Auto Device Enable (ADE) feature.
The last device in the connection must be terminated correctly in accordance with the master driving the
connection. A terminating resistor is fitted in each relay, when required this is connected in circuit using an
external wire loop between terminals 18 and 20 of the power supply module.
Up to 64 relays can be connected to the RS485 bus.
The RS485 data communications link with a particular relay will be broken if the relay element is withdrawn from
the case, all other relays will still communicate.
To
Control
System
Rear terminals
To
Control
System

Figure 6.1-1 RS485 Data Comms Connections Between Relays

6.2

IRIG-B Connections

A BNC plug is provided on the optional additional communication interface modules to connect a co-axial cable
carrying IRIG-B time synchronisation signals. Ensure that the stub length is minimised by connecting the tee-
connector directly to the rear of the relay. A suitable co-axial cable would be type RG 58 50ohms.
©2010 Siemens Protection Devices Limited
14
16
18
RS485 Screened
twisted pair
RS 485 Twisted pair screened Cable
RS485
7SR21 & 7SR22 Argus Installation Guide
14
16
18
RS485 Screened
twisted pair
RS485
Ext Wire loop to
Include line
terminating Res
14
16
18
20
Rear terminals
RS485
Chapter 5 Page 14 of 22