Endress+Hauser PROline promag 53 - 4.6 Post-connection Check

Proline Promag 53 FOUNDATION Fieldbus
Endress+Hauser 29
0
<
In the example the calculation formula results in the following segment current con-
sumption I
SEG
, where I
FDE
= 0, I
startup
= 0, since the field devices used do not consume
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
MOD
for the installed bus power supply
KLD2-PR-Ex1.IEC1 by Pepperl+Fuchs need not be considered since the value of the
supply current I
S
already includes this.
I
SEG
= Σ I
B
= 79.5 mA
Checking the conditions:
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. 11) are connected at the end of the fieldbus line.
Fig. 11: Replacement circuit diagram
The resistance value R
cable
must first be calculated in order to calculate the voltage
drop caused by the fieldbus cable:
R
cable
= R
WK
x L
SEG
= 44 Ω/km x 0.66 km
= 29
Ω
Ohm's law is used to calculate the actual voltage U
FG eff.
at the last instrument:
U
FG eff.
=U
S
- (I
SEG
x R
cable
)
= 12.8 V - (79.5 mA x 29 Ω)
= 12.8 V - 2.3 V
= 10.5 V
Consideration Condition met?
I
SEG
≤ I
S
79.5 mA ≤ 100 mA
✓ Yes
KLD2-PR-Ex1.IEC1 (Pepperl+Fuchs)
I
SEG
U = 9 V
Min
FD
R
cable
U = 12.8 V
S
F-5xxxxxZZ-04-xx-xx-en-005