[Science Popularization Post] Why is the signal range for instrument signals 4–20mA instead of 0–20mA? . .

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Why is the 4–20mA signal in instrument signals not 0–20mA? . . 1. Since the signal amplification circuit itself consumes power, if the output signal is set to 0 mA, a two-wire system cannot be implemented. . . Do you understand? . . . Moreover, converting the circuit to a three-wire or four-wire system to achieve intrinsically safe explosion protection is not only difficult and troublesome and costly, but incorrect wiring can also cause the meter to burn out! 2. The reason why the standard for two-wire circuits back then was set at 4–20 mA, rather than 6–20 mA, 8–24 mA, and so on, is that the power consumption of the signal amplification circuits at that time was around 3 mA; therefore, setting the lower limit of the current at 4 mA was sufficient to ensure that the circuits could operate without any issues ，。 . . Do you understand? 3. The 2-wire 4–20mA circuit features protection against reverse polarity of the power supply, as well as upper current limit protection; these are standard features in circuit design. In other words, in the event of errors in wiring, sensor overload, or other common faults, both the transmitter itself and the devices that receive the output signal are protected from damage, preventing any risk of damaging meters. . . Do you understand? 4. If you dare pretend to not understand, I’ll bite you till your teeth get worn down :P:lol