Addendum to Operating and Instruction Manual for “Modis” Converters
KROHNE Ltd
•
Rutherford Drive
•
Park Farm Industrial Estate
•
Wellingborough
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Northamptonshire
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NN8 6AE
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UK
Tel. +44 1933 408 500
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Fax +44 1933 408 501
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WWW.KROHNE.com
Page 14 of 18
3. Connection of Instruments on the PROFIBUS-PA system
3.1 Interconnection of devices in hazardous locations
We recommend that a PROFIBUS-PA network in the hazardous location be projected in
accordance with PTB’s FISCO model (see KROHNE brochure “PROFIBUS-PA networks”). In
that case, all connected electrical components (including the bus termination) must be
approved in conformity with the FISCO model.
3.2 Bus cable
The statements given in the FISCO model apply only provided the bus cable used meets the
following specifications: R´=15...150 Ohm/km; L´=0.4...1 mH/km; C´=80...200 nF/km.
3.3 Shielding and grounding
For optimum electromagnetic compatibility of systems it is extremely important that the
system components, and particularly the bus cables connecting the components, be shielded
and that such shields - if possible - form an unbroken cover, electrically speaking.
Hence it follows that, for use in non-hazardous duty systems , the cable shield should be
grounded as often as possible.
In “Ex“ systems with adequate equipotential bonding in the hazardous and non-hazardous
location along the entire Fieldbus installation, multiple grounding of the shield is also of
advantage.
Note: The use of twisted and shielded cables is strongly recommended, otherwise EMC
protection of the mass flow meter cannot be assured.
3.4 PROFIBUS-PA connection
Connect the bus cable as shown in
the figure.
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Connect the cable cores to
terminals D and D• .
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Polarity reversal will not have
any effect.
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The cable shield should be
connected with minimum length
to the FE functional ground.
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The equipotential bonding
conductor must be connected to
the device by connecting it to FE
functional ground
PROFIBUS-PA with current output:
