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I
= 10 mA
I
B1
B2
Fig. 88 - Example of current consumption calculation in a PA segment
12.5.5 Voltage at the end of the segment
The resistance of the cable causes a lower voltage at the end of the cable. At least 9V should be available for
the last device at the end of the cable. The following calculation is a 'worst case' scenario where all devices are
connected at the end of the cable:
U
= U
– (I
* R
* L
B
S
SEG
CABLE
U
= Bus voltage at the last device (V)
B
U
= Voltage of the segment coupler (V)
S
I
= Total current In a segment (A)
SEG
R
= Resistance per unit length of the cable (Ω/km)
CABLE
L
= Length of all cables in the segment, including stubs (km)
SEG
U
= Minimal specified operating voltage of the last device (V)
min
Trunk line = 1450 m
20 m
Fig. 89 - Example of voltage calculation at the end of the cable
In this example the voltage at the end of the cable is 24 V - (0.05A * 44 * 1.5) = 20.7 V
ComBricks User Manual v6.4.0 | January 18| © PROCENTEC
I
= 500 mA
S
I
= 10 mA
B0
= 12 mA
I
= 18 mA
B3
I
= 10 mA
FDE
)
(where U
> U
SEG
B
min
U
= 24 V
S
20 m
10 m
I
< I
SEG
S
I
= 60mA
SEG
)
U
> U
B
MIN
I
= 50 mA
SEG
L
= 1500 m
SEG
134/219
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