Answer / fidelis

This is for the purpose of identifying a fault either in
the instrument or in the control loop. If there is a fault
in an instrument, the reading on that instrument will be
zero as when the transmitter is not reading any data due to
maybe a broken loop, so one may not be able to tell what
the problem is. But with the 4-20mA standard, it will be
simple to tell if the transmiter is faulty or not. This
makes trouble-shooting easy.

Answer / pramod

Answer 1 is also a reason

Answer / pramod

if we are using a transmitter there is defenite distance is
specified for it. if we dont have at least 4mA the signals
will be loss for the max. defined distance.
The mA is chosen because it will not make more electrical
hazardness in the field instead of that if micro A is used
loss of signal may occure.
By taking base as 4mA by persentage means 20 mA set as max
value

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