Answer / jb

In long distance wire if some wire are broken then at the
receiver end there will be current value 0. If we take 0-20
standard in that case it will be difficult to know that the
current value is actually 0 or its 0 because of broken wire.
but in case of 4-20 it the the signal is in off state then
at the receiver end we will have current value 4 and in
case of broken wore we will have current value 0.

Answer / bhanu prabhath

yes, i agree with JB,s answar, to some exctent, some times transmitter 0 drifts due to calibration disterbance,if we use 0-20ma we cont find the -ve 0 drift of the transmitter in case of 4-20 the drift will be within the 0-4ma. also the 4-20ma is easy to equal division and calculate with any range .

Answer / parag pathak

Signal can be sent via voltage, but as signal will be drop
if it has to sent long distance,but current signal will not
not lost,so we are preffering current signal over voltage
signal. secondly we can use 0-20 mA instead of 4-20 mA, but
then we cannot know whether it is dead zero or 0 reading.
Now once any manufacturer make any standard it is accepted
throughout so that new Instrument will also be compatible
with that system.

Answer / charankumar

We are using 4 -20 ma because we will get linear current
with respect to 24 V,so i most of cases 4-20ma is used.
If u want to try plese plot a graph and check.

Answer / muthu

in communication, some loss occurs . if we sent 0-20 mA
signal through comunication, 0-4 mA vanishes due to loss.
so 4-20 mA current signal are preferred in standard.

Answer / anwar azim

Other communication methods suppose RS232 are having
constrains for long distance communication and require
repeater after some distance and are prone to external
disturbances.4-20mA is not prone to external disturbances
and the cabling can be done for long distances with out any
effect on signal.

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