Endress+Hauser Proline t-mass 65 PROFIBUS DA, Operating Instructions Manual

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Proline t-mass 65 PROFIBUS DP/PA Electrical connection
Hauser 29
Spurs
Note the following points:
• Length of spurs < 6.6 m (21.7 ft) (at max. 1.5 MBit/s)
• No spurs should be used for transmission rates >1.5 MBit/s. The line between the connec-
tor and the bus driver is described as a spur. Experience has shown that you should proceed
with caution when configuring spurs. For this reason, you cannot presume that the sum of
all spurs at 1.5 MBit/s may be 6.6 m (21.7 ft). This is affected greatly by the arrangement
of the field devices. Therefore, we recommend you do not use any spurs, if possible, at
transmission rates >1.5 MBit/s.
• If you cannot avoid using spurs, then they may not include any bus terminators.
Bus termination
It is important to terminate the RS485 line correctly at the start and end of the bus segment
since impedance mismatch results in reflections on the line which can cause faulty data
transfer
→
46.
Further information
General information and further notes regarding the wiring can be found in BA00034S/04:
"Guidelines for planning and commissioning, PROFIBUS DP/PA, field communication".
5.1.2 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 con-
nected to the protective ground, the shield of the bus cable is grounded many times. Ensure
that the stripped and twisted lengths of cable shield to the ground terminal are as short as
possible.
This approach, which provides the best electromagnetic compatibility and personnel 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) equal-
izing 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, it is therefore recommended - in the case
of systems without potential equalization - to connect the cable shield directly to the build-
ing ground (or protective ground) at one end only and to use capacitive coupling to connect
all other grounding points.
"
Caution!
The statutory EMC requirements are
only met if the cable shield is grounded at both ends!
5.2 Connecting the remote version
!
Note!
A cable is not supplied for the remote version.