Honeywell Sensepoint XRL Instruction Manual page 16

Installation
16
voltage is maintained at the Sensepoint XRL, taking into account
voltage drops due to cable resistance.
V+ detector
XRL V detector
V− detector
The maximum loop resistance (R
as follows:
R = (V
loop max controller
I = W
detector max detector max
Example
The controller is supplying a nominal 24 V DC (V
minimum allowable voltage of Sensepoint XRL is 11 V DC (V
Therefore the maximum allowable voltage drop across the cable
between the controller and detector is V
Power consumption of the detector is maximum 2.6 W (W
The maximum current required to drive the XRL at the minimum voltage
is 2.6 W ÷ 11 V DC = 236.4 mA (I
loop resistance (R
loop max
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)
2 †
0.5 mm (20 AWG )
2 †
1.0 mm (17 AWG )
2 †
1.5 mm (16 AWG )
2 †
2.0 mm (14 AWG )
2 †
2.5 mm (13 AWG )
†
nearest equivalent
Field Cable (L)
) in the field cable is calculated
loop max
− V ) ÷ I
detector min detector max
÷ V
detector min
controller
). So the maximum field cable
detector max
) is 13 V DC ÷ 0.2364 = 55 Ω. Therefore, the
Typical cable resistance
36.8 Ω/km
19.5 Ω/km
12.7 Ω/km
10.1 Ω/km
8.0 Ω/km
V+ controller
V controller Controller
V− controller
), and the
controller
detector min
− V = 13 V DC.
detector min
).
detector max
Maximum cable length (L)
747 m
1410 m
2165 m
2722 m
3437 m
).