Promag 53 PROFIBUS DP/PA Wiring
Endress+Hauser 49
Further information
General information and further notes regarding the wiring are contained in BA034S/04:
"Guidelines for planning and commissioning, PROFIBUS DP/PA, field communication."
4.1.3 Shielding and grounding
When planning the shielding and grounding for a fieldbus system, there are three important
points to consider:
• Electromagnetic compatibility (EMC)
• Explosion protection
• Safety of the personnel
To ensure the optimum electromagnetic compatibility of systems, it is important that the
system components and above all the cables, which connect the components, are shielded
and that no portion of the system is unshielded. Ideally, the cable shields are connected to
the normally metal housings of the connected field devices. Since these are generally
connected to the protective ground, the shield of the bus cable is grounded many times. Keep
the stripped and twisted lengths of cable shield to the terminals as short as possible.
This approach, which provides the best electromagnetic compatibility and personal safety,
can be used without restriction in systems with good potential matching.
In the case of systems without potential matching, a power supply frequency (50 Hz)
equalizing current can flow between two grounding points which, in unfavorable cases, e.g.
when it exceeds the permissible shield current, may destroy the cable.
To suppress the low frequency equalizing currents on systems without potential matching,
it is therefore recommended to connect the cable shield directly to the building ground (or
protective ground) at one end only and to use capacitive coupling to connect all other
grounding points.
"
Caution!
The legal EMC requirements are fulfilled only when the cable shield is grounded on both
sides!
To Next Page
Loading...
