Chapter 7
– Tips and Tricks
Electromagnetic
shielding
Bus and power
cables
Unused
leads
Plug housing
Mounting plate
Use always screened cables for the interface cable and the
supply cable. Thereby you reduce the interference probability
by a ratio of 100 compared to unshielded cables and even up
to a ratio of 1000 if you also avoid loops.
The density of the shield netting should be at least 85%. To
avoid that the injected interference current on the shielded
cable becomes a source of interference itself, a connection
with low impedance to the grounding point is very important.
Connect the shield always on both sides to EMC grounding
(in general PE).
Place the bus cables at least 20 cm away from the power
cables, if possible in separate cable ducts.
Connect all unused leads of a cable always on both sides to
PE.
Use metallic or metallized plug housing. The shielding of the
cable should always be connected to the plug housing.
Always mount all electronic devices on a galvanized
mounting plate in the control cabinet. This mounting plate
functions as EMC earth (neutral point) and is significant for
the interference suppression. That is the only way the
interference energy can flow back to the source of
interference. Avoid
coated surfaces such as Eloxal, yellow chromated.
A sufficient discharge of the HF fields through the PE net is
not possible due to the high cable impedance. Therefore the
PE net cannot be compared with EMC earth, event though
they are directly electrically connected.
Assembly and commissioning instructions DATAEAGLE 3000
8-2
