MTL 9312-FB-ST-SS-SP, Инструкция по эксплуатации

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INM9312-FB-ST-SS-1 Oct 2008
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8.2.1 Proof of intrinsic safety in accordance with FISCO
A spur is intrinsically safe if:
♦
the field device is certified in accordance with FISCO.
♦
the conditions regarding cable values as per IEC 60079-27 are adhered to:
Rc 15 –150 ohm/km
Lc 0.4 – 1mH/km
Cc 45 – 200nF/km
Where these requirements are complied with, it is not necessary to consider the inductance and
capacitance of the spur cables.
8.2.2 Proof of intrinsic safety in accordance with the classic "entity concept":
A spur is intrinsically safe if the safe maximum values for the field device and spur connections are
met:
Spur of Field device
Fieldbus Barrier
U
o
≤
U
i
I
o
≤
I
i
P
o
≤
P
i
C
o
≥
C
i
+ C
cable
L
o
≥
L
i
+ L
cable
Where, C
cable
and L
cable
are the total capacitance and inductance, respectively, of the spur cable, which,
in turn, depends on the cable length.
8.3 Cable lengths for trunk and spurs
IEC 61158–2, Annex B states that the maximum length for all cables per segment, including all trunks
and spurs, must not exceed 1900 m. In addition, the maximum spur length depends on the total number
of field devices per segment, as follows:
In practice, the actual trunk and spur lengths may be shorter because of voltage drops.
For a typical installation, with up to two 9312–FB Fieldbus Barriers per segment, and all spurs connected,
the maximum spur length will be 90m. This applies for spurs connected to field devices that have either
FISCO or Entity certification.
Note: The maximum length of an Ex i spur according to IEC 60079-27 (FISCO) is 60 m. However,
from the viewpoint of the FISCO model, the Ex i spurs of a Fieldbus Barrier are considered as a new
segment (where the maximum segment length = 1000 m). The maximum spur length is therefore 120m,
limited by IEC 61158-2.
Number of all field devices on the segment,
including host(s)
1 ... 12 13 ... 14 15 ... 18 9 ... 24 25 ... 30
Max. spur cable length, 120 m 90 m 60 m 30 m 1 m
assuming1 field device per spur