Answer / sam

Please let us know where you have seen this in a instrument
in the field. The normal standard signal is 4 to 20mA.

Answer / pannu

actually we use 4-20mA:-
1. it is a current signal so it does not have a signal drop
as in case of voltage there is a voltage drop depending upon
the wire resistance.
1. if the output of the instrument is 0% it gives out put as
4mA for 100% it gives 20mA.if line breaks no signal is
there we receive 0mA so that we can blow an alarm for no
signal.

Answer / george mathews

The answer in my knowledge is that if we use a 0 - 20 ma ,
in instrument then we cant distinguish if it is off/ close
stage or the wiring to the instrument is cut off some where
in the connection . Bcos in both the case we will get an
input as 0 ma. But when we us 4 -20 ma here we can say when
the instrument is close and when its wiring is cut off bcos
only then we can get 0ma and 4ma on different condition.

Answer / sreenivasulu

because of getting the accurate results we using 0-20ma in
instrumentation instead of voltage

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