D-BA-0000305.4.10
Installation
Operating instructions
OI-26
V05 / September 07, 2010
4.6 Shielding of signal cables
All cables except those used for the supply voltage must be shielded.
Cables are shielded to reduce the effects of magnetic, electrical and electro-
magnetic interference.
Operating principle
Interference currents on cable shields are directed to the ground via the housing.
To prevent these interference currents from becoming interference sources
themselves, an electrically well conductive (low-impedance) connection to the
ground is extremely important.
Suitable cables
Only cables with braided shields should be used. Cables with foil shields should be
avoided, as they can easily be damaged through mechanical stress, which would
reduce the shielding effect.
Grounding cable shields
Optimum interference suppression in the high frequency range can be achieved by
grounding the shield cable at both ends.
Single-sided ground connections only provide attenuation at low frequencies.
However, positive effects may result, if
•
no potential equalization cable can be used.
•
Analog signals are transmitted (in the range µA to mA).
•
Foil shields are used.
4.6.1 Connector wiring
For data cables with a serial coupling metallic or metallized connectors must be
used. The shield of the data cable must be directly connected to the connector
casing.
In case of potential differences between the grounding points an potential
equalization current can flow through the double-connected shield. In this case an
additional potential equalization must be provided.
