Answer / anshul jaiswal

if we use 0-20 mA scale for 0-100%,then 0% will be read in two cases;1)when instrument has any kind of damage problem(not responding case)& 2)for the ground level reading.so we use 4-20mA which shows 4mA for 0%(ground level) & 20mA for 100%(full value) and 0mA shows that instrument has any damage problem.And guyz,in the range of 4-20mA the calibration shows linear characterstic too.

Answer / ramali

current output is 4-20 mA.
Let take a transmitter operating range is 0-100%
in this case, 0% is only 4 mA,100%is 20 mA.
Because the transmitter have no power,then its output is
0mA.That means zero , live zero.
zero means there is no process is done.
live zero is transmitter have no power,etc.,

Answer / p.v.srikumar

because if use 0 -20 mA as 0-100% there is any signal cable
damage or cable open it will show only 0%. if use 4-20mA as
0-100% it will show bad process value(live zero).

Answer / yakin patel

Upper all answer is right but its 4ma not 3,2,1 bcz it is calculting prove. Has calcultion

Answer / girish

this answer which are not exact answer
1. signal is linear
2.no noise
3.current signal will not drop

in instrumentation why we are using 4-20mA , why not voltage ? if somebody design a instrument which works on voltage then can we use that instrument?

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