Endress+Hauser PROline promag 53 II3G Mise En Service page 39

PROline Promag 53 FOUNDATION Fieldbus
Endress+Hauser
In order that the available supply current I
the fieldbus line R must first be calculated:
cable
R = R x L
cable WK
44 Ω /km x 0.615 km
=
27 Ω
=
Calculation of the maximum available supply current I
When calculating the maximum available supply current it must be ensured that a min-
imum supply voltage of 9 V is applied at the field devices:
I = (U - 9 V) / (R
Seff. S
(19 V - 9 V) / (2 Ω + 27 Ω )
=
= 344.8 mA
Observing the conditions stated, a supply current of I
field devices on the bus segment. Since the actual current consumption of the segment
is only 54 mA, from the point of view of the functional considerations proper functioning
of the segment is ensured.
For reasons of safety the actual voltage U
culated as follows:
U = U - I
FG eff. S SEG
19 V - 54 mA x (2 Ω + 27 Ω )
=
= 19 V - 1.56 V
= 17.4 V
Checking the conditions
Consideration
≥ I
I
seff SEG
344.8 mA ≥ 54 mA
≥ 9 V
U
FG eff.
17.4 V ≥ 9 V
Final consideration
From a purely functional point of view the bus segment shown in the example can be
operated based on the positive results. Further optimization of the network with a view
to connecting a greater number of field devices or realizing a longer line length can be
achieved by selecting the right fieldbus power supply and cable type.
can be calculated the resistance value for
Seff.
SEG
+ R )
Q cable
FG eff.
x (R + R )
Q cable
Condition met?
Yes

Yes

of the fieldbus power supply:
Seff.
= 344.8 mA is available for the
Seff.
of the furthest field device can be cal-

17