0602IB1503-03

Two-Wire RS 485 Isolated Repeater Module

Introduction

The IFM interface with part number STRV00210 is not isolated. A two-wire RS 485 isolated repeater module must be used to electrically isolate a 2-wire RS 485 Modbus network inside the electrical equipment from a two-wire RS 485 Modbus network outside the electrical equipment.

For information on installation, refer to S1A2181101, Two-Wire RS 485 Isolated Repeater - Instruction Sheet .

Hardware Compatibility

The two-wire RS 485 isolated repeater module is compatible with IFM interface with part number STRV00210 .

IFM interface with part number LV434000 does not require the use of a two-wire RS 485 isolated repeater module in a Modbus network.

Hardware Description

A

Modbus 4-pin connector

B

2 stacking accessories (supplied with the repeater)

C

Rotary switch (to set the transmission speed and format)

D

Modbus traffic LED

E

Status LED

F

Mechanical lock

G

Stacking accessory connection

Modbus Connection Linking Two Pieces of Electrical Equipment

When the Modbus network is not contained within the electrical equipment, the two-wire RS 485 isolated repeater module must be inserted between the Modbus network inside the electrical equipment and the Modbus network outside the electrical equipment.

The following figure shows a Modbus link connecting three pieces of electrical equipment S1 , S2 , and S3 via two-wire RS 485 isolated repeater modules. In this example, the Modbus 0 V terminal must be connected to the Modbus client at only one point of the Modbus line, and no other devices must have 0 V connected to ground.

A

Two-wire RS 485 isolated repeater module

B

IFM interfaces grouped in islands with the stacking accessory

C

Modbus line termination

D

IFM interfaces daisy-chained with the Modbus cable

The rules below must be followed:

  • Each isolated Modbus segment must include a polarization at one point, and a Modbus line termination at each end:

    • On the segment outside the electrical equipment, the line polarization and a termination are integrated in the Modbus client, and a Modbus line termination must be connected at the other end, that is, on the last two-wire RS 485 isolated repeater module (the one on electrical equipment S3 in this case).

    • On the segment inside the electrical equipment, the polarization and a Modbus line termination must be integrated in the two-wire RS 485 isolated repeater module.

      A Modbus line termination must be connected at the other end, that is, on the last IFM interface or other Modbus server (on the last IFM interface in pieces of electrical equipment S1 and S2 in this case).

  • Maximum length (Lmax) of the Modbus trunk cable (excluding tap links):

    • Lmax = 500 m (1,640 ft) at 38,400 Baud

    • Lmax = 1,000 m (3,281 ft) at 19,200 Baud

Case of Several Power Supply Segments In Several Pieces of Electrical Equipment

It is mandatory to install a two-wire RS 485 isolated repeater in each electrical equipment when the Modbus network is distributed in several pieces of electrical equipment.

The following figure shows an example of a centralized Modbus architecture installed in three pieces of electrical equipment:

A

Modbus cable coming from Modbus client

B

24 Vdc power supply

C

Modbus line termination

D

Functional ground terminal block

E

Two-wire RS 485 isolated repeater

F

IFM interface with part number STRV00210

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