EN
14392029.02 08/2020 EN/DE
Operating instructions magnetostrictive level transmitter, models FLM-xAI, BLM-TAI (Ex)
20
5.2.2 Cable length
The maximum cable length is dependent upon the overall resistance, which is composed
of the wiring resistance and the load of connected instruments (see chapter 5.2.1
“Connection diagram (Ex)”).
The cable (length and cross-section) must be selected such that, in the event of the
highest current supply (21.5 mA), the voltage does not drop below the probe-specific
minimum supply voltage (8 V).
Make sure that, when used in hazardous areas, the permissible external capacitance C
0
and inductance L
0
of the associated equipment are not exceeded (see chapter 6 “Safety-
related characteristic values”).
Maximum overall resistance with different supply voltages and also cable resistances at
different cross-sections:
Supply
voltage in V
Max. overall
resistance in Ω
Cable cross-
section in mm²
Cable resistance per m
of copper cable in Ω/m
12 (-5 %)
158
0.5
0.0356
1.0
0.0178
1.5
0.0119
24 (-5 %)
688
0.5
0.0356
1.0
0.0178
1.5
0.0119
The maximum cable length is calculated as follows:
L = Cable length in m
U = Supply voltage V (with negative tolerance value -5 %)
U
min
= Minimum supply voltage V = 8 V
I
max
= highest current supply A = 0.0215 A
R
B
= Load
R
Q
= Cable resistance of copper cable (per m) in Ω/m with cable cross-section Q in mm²
5. Commissioning, operation
