Answer / sameer gadekar

If we use the voltage signal then at the certain distance the voltage level may drop due to the losses like resistance of cable capacitance inductance etc etc
These losses are not present in the current signal.
Secondly if the sensor is not working or cable is ok or not this can not be detected with 0-10v, or 0-20 ma so that 4-20ma signal is used in hart protocol.

Answer / a

4 to 20 ma is standard signal which is defind by instrument manufacturer to make a standard out put in which 4 ma act as zero and 20 ma act as maximaum output signal again the current signal is good compared to voltage signal due to minimum loss capability.

why do we use 4to20mA not a 0to20mA?

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