Endress+Hauser PROline 93 II2G Serie Bedienungsanleitung Seite 68

30
In the example the calculation formula results in the following segment current con-
sumption I , where I
SEG FDE
additional current in the event of a fault and the startup current is less than the bus cur-
rent. In addition, the modulation current I
KLD2-PR-Ex1.IEC1 by Pepperl+Fuchs need not be considered since the value of the
supply current I already includes this.
S
Σ I
I =
SEG B
= 79.5 mA
Checking the conditions:
Consideration
≤ I
I
SEG S
79.5 mA ≤ 100 mA
Step 4 – Voltage at the last instrument
The cable resistance causes a segment voltage drop, which is largest at the instrument
farthest away from the bus power supply. For this reason it must be ensured that the min-
imum operating voltage of 9 V is available at this instrument.
To make the overall considerations easier it is assumed that all the field devices FD
(refer to Fig. 12) are connected at the end of the fieldbus line.
FD
Fig. 12: Replacement circuit diagram
The resistance value R
cable
drop caused by the fieldbus cable:
R = R x L
cable WK
44 Ω /km x 0.66 km
=
29 Ω
=
Ohm's law is used to calculate the actual voltage U
U = U - (I
FG eff. S SEG
12.8 V - (79.5 mA x 29 Ω )
=
= 12.8 V - 2.3 V
= 10.5 V
PROline Prosonic Flow 93 FOUNDATION Fieldbus
= 0, I = 0, since the field devices used do not consume
startup
for the installed bus power supply
MOD
Condition met?
Yes

KLD2-PR-Ex1.IEC1 (Pepperl+Fuchs)
R I
cable SEG
U = 12.8 V
U = 9 V
S
Min
must first be calculated in order to calculate the voltage
SEG
x R )
cable
at the last instrument:
FG eff.
Endress+Hauser