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UK 04/2006
Electronics Packaging www.schroff.biz
Systems and devices which are used in Europe must adhere to the
EMC standard regarding interference emission and interference
immunity.
In case that the pre-specified limit values are exceeded, a remedy
may be provided by a shielded case. In this case, various
measures are available for reducing interference emission or for
improving interference immunity.
However, attention must also be paid to the special insertion of the
cables and lines into the case. Otherwise, the suppression
characteristics of the case cannot be guaranteed.
When testing a device or system with regard to electromagnetic
compatibility, the link between the various standards must be
taken into consideration. The basis of the EMC measurement is
the product standard. If this does not exist, then the valid generic
standard must be applied.
During the execution of EMC measurement, the basic standard, to
which reference is made in the individual product and generic
standards, must also be taken into consideration.
Shielded case
Basically, no EMC standards apply to "empty" electronic
construction systems, because only if corresponding electrical
devices have been installed can the overall system emit
electromagnetic interference or be influenced by external
influences.
Schroff construction systems are manufactured entirely from
metal, and therefore have good EMC characteristics in theory. In
the case of EMC shielded construction systems, the conductivity of
the case surfaces is additionally ensured via a galvanic coating.
The individual components are contacted via a EMC gasket such
as, for example, stainless steel springs, and via the large-surface
conductive connection of the individual components.
When designing shielded cases, special requirements are
additionally made on cable ducting and ventilation. An overall
shielded system can only be assessed if these two parameters are
taken into consideration.
Shielding and measurement process
Shielding specifies the dimension by which the intensity of
electromagnetic radiation is reduced on passage through a case.
This is specified in the logarithmic dimension dB. Shielding
measurements for Schroff construction systems are carried out by
an independent institute.
Shielding is measured in accordance with the VG 95373, part 15
(German defence standard) measurement process. This
measurement process is currently being transformed into a
civilian standard.
An additional measurement process in accordance with
MIL-STD 285 (American military standard) also exists. This
measurement process was principally developed for measuring
material shielding, therefore it is only suitable to a limited degree
for measuring electronic construction systems such as cabinets,
cases and subracks.
Shielded products (EMC)
Schroff system solutions
All electrical and electronic devices or systems
marketed in the EU after 01.01.1996 must
display the CE symbol.
However, the CE symbol is not a form of special
EMC certification. It encompasses different
standards for various products.
With the CE symbol, the manufacturer or importer confirms the
conformity of his products to the EU standard.
However, responsibility for the declaration of conformity is borne
by the manufacturer or importer, unlike, for example, in the case
of the TÜV or GS symbol, in which conformity is tested by a
responsible body. The owner must therefore ensure that his
device displays the CE symbol, and is only allowed to use this
device in the specified environment, e.g. in industrial or
domestic applications.
Important
The affixation of the CE symbol is the personal responsibility of
each manufacturer. It is not assigned by an official body.
The CE symbol only provides the consumer with indirect
protection; it is predominantly affixed to the product for the official
body which monitors the market.
Liability and responsibility
In the field of electromagnetic compatibility, the manufacturer
certifies that his product is in accordance with the European
EMC standard via the affixation of the CE symbol.
The guidelines are monitored by the Federal Office of Postal and
Telecommunication Services (BAPT). Adherence to the protection
requirements is checked via random sampling.
In the event of non-adherence, the product may be withdrawn from
the market and a high fine imposed. In addition to the EMC
standard, the product liability legislation also applies in this case.
The CE symbol
30402051
Appendix – Standards
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