Emerson Rosemount 975HR, Справочное руководство

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B.1.1 Calculation formula
Use the following formula to calculate minimum wire gauge per wire length between the
power supply (controller) and the detector, considering the number of detectors on the
same power line, where:
L = Actual wire length between the detector and the power supply.
N = Number of detectors per loop
R = Resistance of wire per 100 m (see Table B-2 )
V = Voltage drop on the wire
Calculate the voltage drop on the wire as follows:
20 + V = Minimum required voltage of the power supply.
0.2 A is the maximum power consumption of the detector.
For example:
If N = 1 (1 detector in loop), L = 1,000 m, wire size = 1.5 mm
2
(see Table B-1 , the resistance
per 100 m for 1.5 mm
2
is 1.4 Ω).
You calculate the voltage drop in the wire as follows:
The minimum voltage of the power supply should be 20 V + 5.6 V = 25.6 V.
Wiring instructions Reference Manual
June 2021 00809-0100-4976
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