Answer Posted / dinesh priyadarshi
1)1-5Vdc have voltage drop at longer distance. It is only
loop voltage for 4-20mA signal
2)4-20mA gives linear output
3)All the eletronics circuit have a leakage current range
between 0-3mA. so for perfact meausre of curent we start
from 4 mA
4)If we see the span of 4-20mA is 16 mA. We are using
digital eletronics, so we have achieve good resolution with
16 bit resoution with successive approxiation DAC. We can
say i the step of 65,353 in terms or digital count for
processor.
5)4 mA is also called live zero. If cable may cut or damage
transmitter shows you 0 mA. So we cannot differentiate
between our signal so we used 4mA as live starting signal.
So if cable cut or damage we get 0 mA.
6)We use 20mA as maximum current because between 4 to 20 mA
we have get linear output.
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