VEGA VEGALOG 571 EP (Ex) - Manual (Page 15)

According to the Profibus specification, the screening should
be carried out on two ends. To avoid potential equalization
currents, a potential equalisation system must be available
apart from the screening.
For grounding on both sides in non-Ex area, the cable screen
can be also connected on one ground side capacitively to
ground potential. Make sure that a low impedance ground
connection (fundamental, plate or mains earth) is used.
When used in Ex areas, a PA bus including all connected
instruments must be setup in flame proofing intrinsic safety "i".
With four-wire instruments requiring a separate power supply,
at least the PA connection must be in intrinsica safety. VEGA
sensors for PA Ex environment are generally ia two-wire
instruments.
The connection cables must correspond to the Profibus
specification and the FISCO model. The sensor cable must
correspond to the values of the reference cable according to
IEC
61158-2.
The following three factors must be taken into account for
calculating the max. line length:
l
Transmission speed
l
Bus structure (cable sections, branch cable)
l
Current consumption of all sensors [mA]
Transmission speed
Up to 31.25 bits/s
l
Max. 1900 m Profibus PA
l
Max. 1000 m Profibus PA in Ex area
Bus structure (cable sections, branch cable)
Each branch >1.2 m is a branch cable, max. number of branch
cables = 24.
Max. lengths of the branch cables:
l
1 … 12 branch cable = 120 m each (Ex: 30 m)
l
13 … 18 branch cable = 60 m each (Ex: 30 m)
l
19 … 24 branch cable = 30 m each (Ex: 30 m)
Length of all cable sections + length of all branch cables =
cable length.
The total length of the cable must not exceed 1900 m (1000 m
with Ex).
Screening
Profibus PA in Ex area
Connection cable and lengths
VEGALOG 571 EP (Ex) - Input card Profibus PA 15
Connecting to power supply
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EN
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