why do we use 4-20mA as o/p and why don't use 0-20mA or 5-
21mA?

Answer Posted / ahmed eid

Ohm's law voltage = current * resistance
of the standerd voltage in the dcs from 1 to 5 voltge
and the standerd resistance of loop 250 oums
so
V=I*R
the first in the low signal 1 volt
1(v)=I*250(r) =.004 A
.004*1000 = 4 MA
the sacand in the high signal 5 volt
5(v)=I*250(r) = 020 A
.020*250 = 20 MA


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