KROHNE H250 M9 PROFIBUS PA EN - Manual (Page 9)

9 Supplement to Installation and Operating Instructions H 250/ESK3-PA
3 Connecting the device to the PROFIBUS-PA
3.1 Interconnecting devices in the hazardous area
We recommend the set-up of a PROFIBUS-PA network in the hazardous area conforming to
PTB’s FISCO model (discussed in the KROHNE brochure “PROFIBUS-PA Networks”). For this
purpose, all the electrical components to be connected (including the bus termination) must
be approved in conformance with the FISCO model.
3.2 Bus cable
The statements of FISCO model only apply if the bus cable in use complies with 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 system electromagnetic compatibility it is very important that the system com-
ponents, especially the bus cables connecting the components, are shielded and that these
shields provide an electrical shield which is as complete as possible.
This means for use in non-hazardous-systems that the cable shield must be grounded as
often as possible.
In hazardous systems, adequate equipotential bonding should be provided in the hazardous
and non-hazardous areas throughout the whole field bus installation. Additional instructions
regarding this subject can be found in the additional “Ex” documentation.
The use of twisted and shielded cables is urgently recommended, since otherwise the
requirements for industrial flowmeters relating to “EMC” cannot be assured.
3.4 PROFIBUS-PA connection
Connection of the bus cable as shown on the right:
Connect the cable conductor to D and D
Gnd
;
(polarity reversal has no effect )
The cable shield should be connected at minimal length to
the functional ground FE.
The potential equalizer must be connected to the device;
(if necessary using the external ground U-clamp terminal of
display component M9)
bus
connection
D D
FE