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Id.-Nr.: 1556.212.1-07
Appendix: EMC-resistant wiring
17
Appendix: EMC-resistant wiring
The interference immunity of an electrical system is crucially dependent on EMC-re-
sistant wiring and shielding. Experience in service shows that inadequate wiring and
shielding of plant components are the most frequent causes of faults and plant fail-
ures.
Faults caused by EMC are much more unpleasant than "conventional" failures:
•
Due to the type of symptom which occurs, they mostly cannot be recognized as
such and often resembles a fault in a module that is actually working correctly.
•
They mostly occur intermittently and are difficult to reproduce.
The troubleshooting is correspondingly complex and expensive.
Thus, pay attention from the outset to careful wiring and shielding in accor-
dance with the guidelines described below.
17.1
Basic structure of EMC measures
The EMC concept of the entire MotionOne 3 system is designed in such a way that
each module can independently withstand the influences that occur in an electromag-
netically affected industrial environment.
electromagnetically affected industrial environment. A closed shield casing is as-
sumed. This shield cover is respectively expanded by shielded interfaces or, if un-
shielded interfaces are used, the open shield cover is “closed” again via a filter (see
graphic).
Fig. 17.22:
Shielding principle
17.2
Which EMC measures must be taken?
EMC measures are concentrated in the areas:
•
Shielding
•
Potential equalization between plant components
It is important to carry out the practical measures described in the following sections
correctly. The most frequent causes of failures are poor contact of the ground and
shield connections. This is the reason why attention must be paid to all of the follow-
ing generally accepted points:
Contacting of ground and shield connections
•
Low impedance connection of the part. That means it conducts well even for high
frequencies and is it achieved by:
–
large connection areas
–
shortest possible grounding conductors
–
use of wide grounding ribbons instead of wires, if possible.
•
Surface contact with bare metal must be available.
•
Contact surfaces must be protected against corrosion.
•
Use toothed washers on all connection points if possible for connecting painted
parts or parts with rough surfaces.
