Endress+Hauser PROline prosonic flow 93 II2 GD Mode D'emploi page 63

PROline Prosonic Flow 93 FOUNDATION Fieldbus
Endress+Hauser
Bus cable type 3076 from Belden (shielded bus cable):
• Nominal values:
24 Ω/km (loop resistance)
R' =
C' = 82 nF/km (capacitance per unit length between the two wires)
623 µH/km (inductance per unit length of the two wires)
L' =
C' = 147 nF/km (capacitance per unit length wire against shielding)
LS
Bus termination:
• Nominal values:
U = 30 V
i
P = 1.2 W
i
C = negligible
i
The effective capacitance of the bus line is derived first from the capacitance per unit
length C', which is effectively the capacitance between the two wires. In the case of the
shielded wires the order of capacitance "wire against shielding" and "shielding against
wire" must be observed. The total capacitance of the bus line is thus calculated as fol-
lows:
C' = (C' + 0.5 x C'
eff/cable
The total length of the bus line L
length of all spurs. Using the system structure illustrated in Fig. 9 the following data rel-
evant to safety emerges for the bus line:
+ Σ L
L = L
SEG main
= 580 m + 35 m
= 615 m
C' = (C' + 0.5 x C'
eff./cable
= (82 nF/km + 0.5 x 147 nF/km) x 0.615 km
= 95.6 nF
L' = L' x L
eff./cable SEG
623 µH/km x 0.615 km
=
383.1 µH
=
) x L
LS SEG
is made up of the length of the main cable and the
SEG
spurs
) x L
LS SEG
<
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