4 Wiring Instructions
4.1, Cable requirements:
Power lines and 4-20mA signal lines need to use shielded cables, and RS485 lines are recommended to
use twisted pairs. When using RS485 communication to connect with the controller (Under normal
conditions) , the RS485 signal transmission distance of our detector can reach more than 1000 meters.
When the signal interference is large or the transmission distance is longer, it is recommended to add an
RS485 repeater, a 120Ω/0.5W matching resistor should be connected in parallel between the A and B lines
of the farthest detector.
The power supply voltage of this series of detectors is 12~24VDC. Due to the voltage drop caused by the
impedance of the cable itself, it should be ensured that the minimum supply voltage of all detectors is
12VDC.
When the detector is powered by the controller, the power supply voltage of the controller of our
company is 24VDC. To ensure that the minimum input voltage of the detector is 12VDC, the circuit
voltage drop must be less than or equal to 12VDC, as shown in the figure below.
Maximum Loop Impedance: Rloop = (VController – VDetector(min)) / IDetector
Calculated
according to the above formula.
The maximum current of combustible gas detector is 250mA, and the maximum loop resistance is
48Ω;
The maximum current of the toxic gas detector is 100mA, and the maximum loop resistance is 120Ω.
The cable cross-sectional area and the farthest transmission distance are shown in the table below
(when connected to our controller). Make sure that the actual installed cable length is shorter than the
calculated maximum cable transmission distance.
4-20mA
Maximum Loop Resistance
V Controller=24VDC
V Controller=12VDC
Gas detector
Controller
0VDC
0VDC
1
2
3
3
2
1
RL
Cross-sectional area of cable core (mm )
0.75
1.00
1.50
2.50
Resistance (ohm/km copper wire)
24.7
18.5
12.3
7.4
The longest cable distance (m)
(loop length/2)
Combustible gas
1000
1250
2000
3200
Toxic gas
2400
3200
5000
8000
Note: The above transmission distance is calculated based on the cable core with a resistivity of
1.85×10ˉ Ω·mm . If a cable of the same wire diameter with a smaller resistivity than this is used, the
transmission distance can be longer; if a cable of the same wire diameter with a higher resistivity than this is
used, the transmission distance will be shortened. The loop length indicates the total length of the positive
and negative wires of the power supply, and the actual length of the cable is equal to half of the loop length.
7
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