Connection to the Modbus-SL Network with IFM Interface

Introduction

Connect intelligent modular units to the Modbus network with the IFM Modbus-SL interface for one circuit breaker.

The 24 Vdc power supply terminal block delivered with the IFM interface is used to supply the IFM interface with power either in a daisy-chain or in a star connection.

In terms of power supply, the maximum number of IFM interfaces stacked to one IFE server is 11 in order to limit voltage drop.

In terms of Modbus communication, it depends on the performance requirement. As it takes approximately 500 ms at 19,200 Baud per device to refresh 100 registers, the more interfaces added the longer the minimum refreshment period. The minimum refreshment period depends on the number of IFM interfaces stacked to one IFE server. Multiply the time to refresh one device by the number of devices to find the minimum refreshment period expected in the application. For instance, an installation with eight IFM interfaces stacked to one IFE server at 19,200 Baud would take approximately 4 seconds to be read.

Connection of RJ45 Modbus Cable to the IFM Interface

The RJ45 Modbus cable connects to the Modbus-SL RJ45 port located on the top of the IFM interface.

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Pin Connection of the RJ45 Male/Male Modbus Cable

The RJ45 male/male Modbus cable (VW318306R••) uses an RJ45 connector whose pin connection is described in the following table.

RJ45 connector

Pin number

Pin

Wire color

Description

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4

D1

Red

RS 485 B/B’ or Rx+/Tx+ signal

5

D0

Black

RS 485 A/A’ or Rx-/Tx- signal

8

0 VL

Green

0 V for Modbus common and power supply

Composition of the RJ45 Male/Male Modbus Cable

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A   Outer sheath

B   Shielding braid

C   Twisted communication wires (red/black/green)

The 0 VL cable (Modbus common) must be distributed along the entire length of the network, right up to the Modbus master.

Connection of the IFM Interface to an Open-Style Connector

The IFM interface can be connected to another Modbus slave without Modbus RJ45 port (for example, a Smartlink device) by one of the following ways:

oWith a LV434211 RJ45 to open connector Modbus adapter:

1. Connect the wires to the open connector of the Modbus adapter.

2. Connect the RJ45 connector of the Modbus adapter to the Modbus port of the IFM interface.

oWith an RJ45 male/male Modbus cable (VW318306R••):

1. Cut off an end of the RJ45 cable.

2. Strip the cable sheath over a length less or equal to 50 mm (1.96 in).

3. Cut off the shielding braid close to the cable sheath end.

4. Connect the wires to terminals (for example, screw terminals or tap junctions):

Pin number 4 (D1): red wire

Pin number 5 (D0): black wire

Pin number 8 (0 VL): green wire

5. Unstrip the cable insulation close to the cable end.

6. Fix the cable to a grounding clamp.

7. Connect the RJ45 connector of the ULP cable to the Modbus port of the IFM interface.

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oWith a Modbus serial link cable (VW3A8306D30) with one RJ45 male connector and free wires at other end:

1. Identify the three wires to be connected to a connector:

Pin number 4 (D1): blue wire

Pin number 5 (D0): white-blue wire

Pin number 8 (0 VL): brown wire

2. Cut off the five other wires.

3. Connect the three wires to terminals (for example, screw terminals or tap junctions).

4. Connect the RJ45 connector of the Modbus serial link cable to the Modbus port of the IFM interface.

oWith a Modbus cable with free wires at both ends:

1. Identify the three wires to be connected to a connector:

Pin number 4 (D1)

Pin number 5 (D0)

Pin number 8 (0 VL)

2. Cut off the other wires.

3. At one cable end, connect the three wires to a Phoenix Contact RJ45 connector (VS-08-RJ45-5-Q/IP20 - 1656725).

4. Connect the Phoenix Contact RJ45 connector to the Modbus port of the IFM interface.

5. At the other cable end, connect the wires to terminals:

a. Screw terminals by using lugs then connect the lug with the shield to the ground.

b. Tap junctions by using a Phoenix Contact RJ45 connector (VS-08-RJ45-5-Q/IP20 - 1656725).

RJ45 to Open Connector Modbus Adapter

The RJ45 to open connector Modbus adapter can be used to connect an IFM interface to a Modbus device without RJ45 port.

Illustration

Description

Part number

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RJ45 to open connector Modbus adapter

LV434211

Modbus Line Termination

The Modbus cable communication pair has an impedance of 120 Ω or 150 Ω. The Modbus cable must therefore be terminated at each end by a Modbus line termination with an impedance of 120 Ω or 150 Ω.

The Modbus master is at one end of the Modbus cable and usually has a switchable termination impedance. At the other end of the Modbus cable, a Modbus line termination with an impedance of 120 Ω or 150 Ω must be connected.

Illustration

Description

Part number

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Modbus line termination (150 Ω)

VW3A8306R

Modbus line termination (120 Ω + 1 nF)

VW3A8306RC