Installation
XCL
Field Cable (L)
V detector
V+ detector
V− detector
V+ controller
V− controller
V controller
Controller
The maximum loop resistance (R
loop max
) in the field cable is calculated
as follows:
R
loop max
= (V
controller
− V
detector min
) ÷ I
detector max
I
detector max
= W
detector max
÷ V
detector min
Example
The controller is supplying a nominal 24 V DC (V
controller
), and the
minimum allowable voltage of XCL is 11 V DC (V
detector min
). Therefore
the maximum allowable voltage drop across the cable between the
controller and detector is V
controller
− V
detector min
= 13 V DC. Power
consumption of the detector is maximum 2.3 W (W
detector max
). The
maximum current required to drive the XCL at the minimum voltage is
2.3 W ÷ 11 V DC = 209.1 mA (I
detector max
). So the maximum field cable
loop resistance (R
loop max
) is 13 V DC ÷ 0.2091 = 62
Ω
. Therefore, the
maximum cable length for any given cable type can be found by
dividing the maximum allowable cable resistance per core by the cable
resistance provided by the cable manufacturer.
The following table shows the typical maximum cable distances for our
example.
Cable size
(cross sectional areal)
Typical cable resistance
Maximum cable length (L)
0.5 mm
2
(20 AWG )
36.8
Ω
/km
842 m
1.0 mm
2
(17 AWG )
19.5
Ω
/km
1589 m
1.5 mm
2
(16 AWG )
12.7
Ω
/km
2440 m
2.0 mm
2
(14 AWG )
10.1
Ω
/km
3069 m
2.5 mm
2
(13 AWG )
8.0
Ω
/km
3875 m
nearest equivalent
15
