Siemens S5-135U/155U - Manual (Page 54)

3-28
System Manual
C79000-G8576-C199-06
3.5 Interference-Free Installation of Centralized and Distributed
Interface Circuits
Subjects described in the following sections are the shielding and grounding
concept with centralized and distributed interface circuits.
Information on component selection, the mechanical arrangement and wiring
can be found in the appropriate reference manuals for the interface modules.
Note
If you use components which are not approved for the installation of a
centralized or distributed interface circuit, interference rejection may be
impaired.
3.5.1 Interference-Free Installation of Centralized Interface Circuits
When you connect the central controller and expansion unit centrally via
suitable interface modules, no particular shielding and grounding measures
are required. Ensure, however, that
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all subracks are interconnected at a low resistance;
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the subracks in a grounded arrangement have star-configuration
grounding;
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the contact springs of the modules are clean and not bent, which could
affect the path to ground for interference currents.
3.5.2 Interference-Free Installation of Distributed Interface Circuits
If you interconnect the central controller and expansion unit in a distributed
arrangement using suitable interface modules, no particular shielding and
grounding measures are usually required. Only in industrial environments
with an extremely high level of interference is there a need for special
shielding and grounding.
In these cases, please observe the following points:
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Cable shields should be connected to the shield bar in the cabinet,
immediately after the cable inlet;
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insulation is fully stripped from the cable for the purpose;
- braided shields are secured to the shield bar with as large an area as
possible (e.g. with metal ties which enclose the shield over a large
area).
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Shield bars should be connected to the frame or cabinet panel over a large
area.
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Cable shields should be connected to the cabinet conductor.
Installation Guidelines