1, the signal sending end is a current source, the output impedance is very high, the line resistance of long-term transmission will not affect the quality of the current signal, the receiving end is a low impedance load, strong anti-interference ability. If it is a voltage signal transmission, the line resistance voltage division will cause errors.
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2, the minimum value of 4mA is not only the power supply (static) current of the sensor, but also a sign to determine whether the line is broken, killing two birds with one stone.
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3, the maximum 20mA to meet the needs of measurement, but also in line with explosion-proof, power consumption, cost and other requirements.