UNIPOINT OPERATING MANUAL
2306M5001 MAN0638 ISSUE 7 01/2011
9
4.3 Maximum Cable Lengths
4.3.1 mA Detectors
To calculate the maximum cable run length from power source to the detector refer to the
following example diagram and formula.
Rloop = (Vcontroller - 1.5V - Vdetector min) / Idetector
Maximum cable run length = Rloop / cable per metre resistance where:
Rloop =
maximum working cable loop resistance
Vcontroller =
maximum available supply voltage at controller
Vdetector min =
minimum voltage at which the connected sensor can operate
(sensor dependent, see individual sensor technical manual/
data
sheets)
Idetector =
sensor maximum drawn current. 30mA for 2 wire mA detectors.
See individual detector technical manual/data sheets for max power
consumption of 3 wire detectors.
4.3.2 mV Detectors
To calculate the maximum cable run length to the detector refer to the following typical
example cable resistances. Max cable loop resistance = 28 ohms.
Solid Copper Conductor
Cross Sectional Area
Maximum resistance at 20ºC
(mm2)
AWG
(ohm/bucle/km)
0.50
21
72
0.75
19
50
1.00
18
36
1.50
16
24
Stranded Copper Conductor
Cross Sectional Area
Maximum resistance at 20ºC
(mm2)
AWG
(ohm/bucle/km)
0.50
21
73.6
0.75
19
49
1.00
18
35.2
1.50
16
23.4