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Example;
The controller or power supply is supplying a nominal 24VDC (V controller), the detector
minimum allowable voltage is 12VDC (V detector min), therefore the maximum allowable
voltage drop between the controller and detector is 12VDC; this means a voltage drop of 6V
in each core (V+ core and V- core).
Minimum power consumption of the detector without any optional module is 1W. The current
required to drive the detector at the minimum voltage is
(I = P / V) : 1.0 / 12 = 85mA (I detector).
Maximum power consumption of the detector when optional relay modules installed and all
relays are active is 4.0W. The current required to drive the detector at the minimum voltage
is (I = P / V) : 4.0 / 12 = 335 mA (I detector).
So, the maximum field cable loop resistance (R loop) = 12 / 0.335 = 36 Ohms, or 18 Ohms per
core, (allowing for component variations, losses, etc.).
The following tables show the maximum cable distances between the controller and
transmitter assuming a voltage drop of 6V in each core and for different cable parameters.
The table values are examples only and actual cable parameters and source power supply
voltage for the application should be used to calculate the maximum cable distance allowed
at the installation site.
Typical cable data for detector with relay module given in Table 5:
Cable size
(cross sectional area)
0.5mm
2
1.0mm
2
1.5mm
2
2.0mm
2
2.5mm
2
The use of industrial grade, suitably shielded field cable is recommended. Depending on the
distance between signal received or control panel and detector 0.5 to 2.5 mm2 (20 to 13 AWG)
conductors can give better results. Ensure the cable gland is installed correctly and fully
tightened.
PRS-UM-SV-EN-Rev1.0-16.12.2022
Diagram 4: Field cabling
Cable type
nearest equivalent
20AWG
17AWG
16AWG
14AWG
13AWG
Table 2: Typical cable details and maximum distance for cabling
Cable resistance
Maximum Cable length (L)
Ω/km
36.8 Ω/km
19.5 Ω/km
12.7 Ω/km
10.1 Ω/km
8.0 Ω/km
Meters
~400
~700
~1100
~1400
~1800
Page 12 / 41
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