why do we use 4-20 ma current why cant o-20ma

Answer Posted / s.chandra mowli

for example take a temperature process
0 degree it must indicate -0 ma
suppose if there is any fault in the circuit then for any slight increase in temperature it indicates only zero
in order to differentiate the malfunction of instrument
we use live zero and dead zero
the instrument is biased to 4 ma to indicate the proper function of the the instrument that is Live zero
if it indicates 0 then is a malfunction in instrument that is Dead Zero

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