Section 6: Data Comms Connections; Rs485 Connection; Irig-B Connections - Siemens 7SR242 Duobias Technical Manual

Section 6: Data Comms Connections

6.1

RS485 Connection

The RS485 communication port terminals are located on the rear of the relay and can be connected using a
suitable RS485 120 screened twisted pair cable.
The RS485 electrical connection can be used in a single or multi-drop configuration. When used with Reydisp 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.
Each relay has an internal terminating resistor – this can be connected in circuit where necessary.
6.2

IRIG-B Connections

A BNC plug is provided to connect a co-axial cable carrying IRIG-B time synchronisation signals. The length of
the stub should be minimised by connecting the tee-connector directly to the rear of the relay. A suitable co-axial
cable would be type RG 58 50ohms.
©2015 Siemens Protection Devices Limited
Figure 6.1-1 RS485 Data Comms Connections
Chapter 5) 7SR242 Duobias Installation Guide
Chapter 5 Page 19 of 24