Profibus Cable Connector; Shielding Precautions - Omron PROFIBUS DP GATEWAY Operation Manual

Setting up a PROFIBUS Network
2-5-3

PROFIBUS Cable Connector

Bus Cable Connector
To next
station
From
previous
station
2-5-4

Shielding Precautions

Cable Shield Connection
Inside cabinet
Ground Rail
Outside cabinet
34
The plug connector to be used on the PRT1-SCU11 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 PRT1-SCU11 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 color should be connected to which of the two data
terminals on each PROFIBUS device; the sole requirement is to ensure that
the same core color 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 color
codes: PROFIBUS cables in general will use the colors 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.
When entering the control cabinet in which the PRT1-SCU11 Unit is installed,
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 con-
tinue in the cabinet right up to the PROFIBUS device.
Ensure that the Unit 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.
• Other test methods.
• Example of an equipment report in the PROFIBUS guideline.
Section 2-5