2
0
1
8
-1
2
60
Installation
3.15
Potential Equalization and Shielding
3.15.1
Sources of Noise
Electromagnetic fields can interfere with the communication path.
Figure 3.29
Interfering signals caused by induction in parallel conductors
Twisted-pair cables significantly reduce the influence of these interference fields, particularly
when compared to cables with parallel cores. The direction of the recorded interference field in
a twisted-pair cable reverses over short intervals. This means that the induced noise is
practically canceled out, while in parallel cores the noise is active across the entire area.
Figure 3.30
Reduced admission of interfering signals in twisted-pair cable
A shielding keeps interfering noise away from the communication path.
Figure 3.31
Shielding prevents the entry of interference fields
EMC filters are used in many devices to divert any noise to ground. High-frequency noise
occurring in the same way on both lines is dissipated symmetrically through the capacitor
impedances and does not appear as a differential signal.
Figure 3.32
EMC filters in signal paths
Note!
The following subchapters cannot provide the reader with a complete picture of all
requirements in terms of grounding, shielding, and lightning protection. More information on
this topic can be found in the technical literature and the applicable standards.
