Atest Gaz PW-033-A, User Manual

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4 Power supply of the gas detector
As a standard, in gas detectors with digital data transmission, it is assumed that the voltage cannot drop
below 12 V (see the documentation of the detector). The power consumption of the detector is constant
within the range of acceptable voltages. With the decrease of supply voltage, the current consumption from
the power supply increases.
For example, if the sensor consumes 1 W:
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when powered by 24 V, the supply current will be 1 W / 24 V = 40 mA
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when powered by 15 V, the supply current will be 1 W / 15 V = 67 mA
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when powered by 10 V, the supply current will be 1 W / 10 V = 100 mA
5 Example – a system with a single sensor
Task: Select the sensor power cable under the following conditions:
Data:
• power consumption of the sensor: 2 W
• min. power supply voltage: 24 V
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min. UPS supply voltage 21V
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min. permissible sensor supply voltage: 12 V
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distance between the control unit and the sensor: 800 m
Calculations:
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max. current consumption of the sensor: 2 W / 12 V = 0.167 A
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permissible voltage drop on the line: 21 V – 12 V = 9 V
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maximum allowable line resistance: 9 V / 0.167 A = 54 Ω
Cable selection:
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cable with the cross-section of 0.5 mm 2 : R(2x800 m) = 36 / 1000 * 1600 = 57.6 Ω > 54 Ω
The cable has a resistance greater than the maximum permissible line resistance, so it does not
meet the requirements and cannot be used in the system.
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cable with the cross-section of 1.0 mm 2 : R(2x800 m) = 18 / 1000 * 1600 = 28.8 Ω < 54 Ω
The resistance of the cable is less than the maximum acceptable line resistance – the requirements
are satisfied so the cable can be applied to the above system.
The design line can not be longer than 1200 m.
Atest-Gaz A. M. Pachole sp. j.
ul. Spokojna 3, 44-109 Gliwice, Poland
VAT No.: PL 9691433231
tel.: +48 32 238 87 94
fax: +48 32 234 92 71
e-mail: contact@atestgaz.pl
p. 2/2 Appendix: PU-Z-003-ENG R03
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