ABB AC 800M, User Manual

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Tips on the most frequently asked installation issues Section 4 Commissioning of PROFIBUS
112 3BDS009029R5001 B
What happens if the bus gets grounded on one side (or at one end)?
• A temporary short to ground may temporarily disrupt the bus, but any errors
will be detected and handled by the fieldbus protocol. A permanent short to
ground could disrupt the bus until the ground is removed (just as with present
analog or digital communications).
I don’t understand “termination”. What is it, why do I need it, and is
placement critical?
• Termination is the addition of the appropriate fieldbus “terminator” at (or near)
the end of each fieldbus segment. The “terminator” has the same characteristic
impedance as the bus, and is required to preserve the integrity of the signal. It is
especially important on long segments, and placement is critical— one should
be connected to the bus as close as possible to each end of the segment. Some
devices (especially I/O and/or fieldbus test/simulation PC cards) include the
option of using an internal terminator. It is important to know in this case
whether it is connected.
• My PROFIBUS is not running properly.
– Check the bus terminations
– Check the connectors
– Check the cabling (polarity, grounding, short-cuts, etc.)
– Check the correct settings for all slave addresses (for example with the
Web server of CI854)
– Check the PROFIBUS master settings
For more details about the Web server of CI854(A) and the PROFIBUS master
settings please read the specific product documentation.