fafnir HART TORRIX, Техническая документация инструкция

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Page 11/37 Electrical connection
The following table shows the maximum total resistances at different supply voltages, and
cable resistances at various cross-sections:
Supply volt-
age [V]
Max. total re-
sistance
[Ω]
Cable cross-
section
[mm²]
Cable resistance
per m copper ca-
ble
[Ω/
m]
For connection
housing HPH Ex d
suitable (yes/no)
12 (-5%) 158 0.5 0.0356 no
1.0 0.0178 no
1.5 0.0119 no
24 (-5%) 688 0.5 0.0356 yes
1.0 0.0178 yes
1.5 0.0119 yes
The max. cable length is calculated as follows:
L = (((U – U
min
) / I
max
) – R
B
) / R
Q
L = Cable length [m]
U = Supply voltage [V] (with negative tolerance value -5%)
U
min
= Minimum supply voltage [V] = 8 V
I
max
= Maximum power consumption [A] = 0.0215 A
R
B
= Load
R
Q
= Cable resistance per m copper cable [
Ω
/m] at cable cross-section Q [mm²]
Example:
Supply voltage: 12 V (± 5%)
Supply voltage U = 11.4 V (12 V - 5%)
Minimum supply voltage U
min
= 8 V
Maximum power consumption I
max
= 0.0215 A
Load R
B
= 86.8
Ω
Cable resistance per m copper cable R
Q
= 0.0356
Ω
/m at cable cross-section Q = 0.5 mm²
L = (((11,4 – 8) / 0,0215) - 86,8) / 0,0356 = 2000 m
Thus a cable with forward and return line (2-wire) can be up to 1000 m long.