Profibus Cable Connector; Shielding Precautions - Omron GRT1 - 27-11-2006 Operation Manual

Setting up a PROFIBUS Network
2-4-3

PROFIBUS Cable Connector

Bus Cable Connector
To next
station
From
previous
station
2-4-4

Shielding Precautions

Cable Shield Connection
Inside cabinet
Ground Rail
Outside cabinet
The plug connector to be used on the CS/CJ-series PROFIBUS DP Master
Unit is a 9-pin male sub-D type, preferably encased in metal and having a
facility to connect the shield of the cable to the case or to pin 1. The cable
should be connected to the receive / transmit lines, pin 3 (B-line) and pin 8 (A-
line).
The use of special PROFIBUS DP cable connectors, which are available from
several manufacturers, is highly recommended. Various models are widely
available, with or without the bus termination and inductors built-in. If provided
in the connector, the Bus termination can often be enabled or disabled
through a switch on the connector.
The special PROFIBUS DP cable connectors often provide a convenient way
of connecting the cables. The figure on the left, provides an example of such
a bus cable connector.
A standard 9-pin sub-D plug can only be used if the PROFIBUS DP Master
Unit is not at the start or the end of a bus segment, or on a stub line at a baud
rate of 500 kbit/s or less.
The two PROFIBUS data lines are designated A and B. There are no regula-
tions on which cable core colour should be connected to which of the two data
terminals on each PROFIBUS device; the sole requirement is to ensure that
the same core colour is connected to the same terminal (A or B) for all
devices throughout the entire system (across all devices and bus segments).
The PROFIBUS Organization recommends the following rule for data line
colour codes: PROFIBUS cables in general will use the colours red and green
for the data lines, with the following assignment:
• Data cable wire A - green
• Data cable wire B - red
This rule applies to both the incoming and the outgoing data lines.
To ensure electro-magnetic compatibility (EMC), the shield of the cable
should be connected to the metal case of the plug connector.
If the Unit is installed in a control cabinet, the bus cable shield should be
brought into physical contact with a grounding rail using a grounding clamp or
similar device. The cable shield should continue in the cabinet right up to the
PROFIBUS device.
Ensure that the PLC and the control cabinet in which it is mounted have the
same ground potential by providing a large-area metallic contact to ground,
e.g. galvanized steel to ensure a good electrical connection. Grounding rails
should not be attached to painted surfaces.
For further information regarding PROFIBUS network installation, please refer
to "Installation Guideline for PROFIBUS DP/FMS" (PNO Order No. 2.112),
which is available at every regional PROFIBUS Organization. The information
covers:
• Commissioning of PROFIBUS equipment.
• Testing the PROFIBUS cable and bus connectors.
• Determining loop resistance.
• Testing for correct bus termination.
• Determining the segment length and cable route.
Section 2-4
27