Rockwell-automation 1788-EN2PAR EtherNet/IP and ControlNet to PROFIBUS Instrukcja Użytkownika Pobierz pdf (Strona 19)

Rockwell Automation Publication 1788-UM058B-EN-P - September 2014 19

Installation Chapter 1

See Grounding/Earthing on page 19 for more details for shield connections.

PROFIBUS PA Physical

Network Design Guidelines

This section provides more guidelines for the design of your PA network.

Power Supply

Verify that the power supply is not over-specified for the application; otherwise,

the Switch mode generates noise when sufficient current is not being drawn.

Table 1

shows an example of current consumption for a typical application.

Table 1 - Current Consumption Example

The minimum allowed input voltage is 24V DC, and the maximum is 32V DC.

You must calculate the correct cable length and distance from the power supply

for your installation. If the cable is too long, it can cause voltage drops in the

supply rail when sufficient current is being drawn. See Cable Lengths

on page 20

to help you determine the proper cable length for your installation.

Grounding/Earthing

Per section 12.8.7 of IEC61158-2 (Physical Layer Specification), PA signal wires

(PA+ or PA-) must not be connected to ground/earth at any stage of the

network. The shield must be grounded/earthed at only one place.

To ground the shield, connect it to the PROFIBUS PA connector as shown in

Shielding

on page 18, and connect ground/earth to the shield of the power

connector as shown in Power Connection

on page 15.

IMPORTANT

If the shield is not correctly connected, noise from the environment on the PA

bus can cause the PA data to be corrupted. Corrupted data can result in a low

success rate and device connections being lost. Section 12.8.5 of IEC61158-2

(Physical Layer Specification), indicates that 90% of the full length of the cable

must be shielded.

Linking device current consumption at 24V = 260 mA

PA bus current consumption for a specific application at 24V = 150 mA

Total = 410 mA

IMPORTANT

Do not use a 24V DC, 10 A power supply. We recommend using a 24V DC, 1 A

power supply.

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Rockwell-automation 1788-EN2PAR EtherNet/IP and ControlNet to PROFIBUS Instrukcja Użytkownika Strona 19