VEGA VEGASON 54P…56P Profibus PA - Manual (Page 28)

28 VEGASON 54P … 56P
Electrical connection
In the so-called Fieldbus Intrinsically Safe
Concept (FISCO), the general conditions for
an Ex safe bus configuration have been laid
down. Therein, the electrical data of the
participants and the bus cable have been
determined, so that the linking of these com-
ponents always meets Ex requirements. This
makes the otherwise time-consuming Ex
calculation unnecessary. You can build your
Ex bus according to the IEC standard
1158-2.
The Ex segment coupler delivers a controlled
power supply to the PA bus. It acts as
source in the PA branch. All other compo-
nents (field instruments and bus terminators)
are only consumers. A field instrument must
consume at least 10 mA. Ideally, an individual
sensor should not consume more than
10 mA, so that the number of instruments can
be as large as possible.
VEGA PA sensors, whether Ex or non Ex,
consume a constant current of 10 mA. Ac-
cording to the Profibus specification, this is
the minimum participant current. With VEGA
sensors it is therefore possible to connect 10
sensors (also in Ex environment) even with a
limited energy supply from the Ex segment
couplers.
Watch out for potential losses
Due to potential transfer, earthing on both
sides without a potential equalisation system
is not allowed in Ex applications. If an instru-
ment is used in hazardous areas, the re-
quired regulations, conformity and type
approval certificates for systems in Ex areas
must be noted (e.g. DIN 0165). Please also
note the approval documents with the safety
data sheet attached to the Ex sensors.
Electrical data of the cables
R
DC
No. of A in Z
31.25kHz
C in Damping Screen
cores mm 2 nF/km
SINEC 6XV1 44
Ω
/km 2 0.75 100
Ω
< 90 < 3 dB/km Cu braiding
830-SEH10 +/- 20
Ω
39 kHz
(Siemens)
SINEC L26XV1 44
Ω
/km 2 0.75 100
Ω
< 90 < 3 dB/km Cu braiding
830-SFH10 +/- 20
Ω
39 kHz
(Siemens)
3079A 105
Ω
/km 2 0.32 150
Ω
29.5 < 3 dB/km Foil
(Belden) 39 kHz