Rockwell Automation 1788-EN2PAR EtherNet/IP and ControlNet to PROFIBUS PA Linking Device User Manual - Manual (Page 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.