why we use 4-20 mA to do calibration of the instruments.why
we cant use 0-20 mA?

Answer Posted / ramu

For electronic Instruments operates with 24V(DC),will give
output 4-20MA and pnuematic Instruments operates with 20PSI
will output 3-15PSI.These instruments circuits are arranged
in such a manner that the out put should be as mentioned
above because you will get LENIERITY only in these
ranges.If you take 5-22 MA, you will not get lenier output
( 0%-4MA,25%-8MA,50%-12MA,75%-16MA and100%-20MA)

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