Answer / avinash kumar

if we consider 0-20 or any other value then we can't
differentiate that this instrument has fault or this
instrument has in its minimum position.if it indicated 0
means, it has some fault, if it indicates 4 means it is in
on state having minimum position.so by this idea we can
differentiate b/w damage instrument and the minimum
position instrument.

Answer / abhishek k sharma

1:-4ma - 20ma are used to ged know about the live zero
positon.it means that if we use 0ma then we cannot get
excect error as postioner do not gos negative values.
2:- also we have less chances of noise in 4ma to 20ma range
which help us to carry out calibration.
3:- it do not produces spack if we joints its (+)/(-) so
can be used in hazard conditions.
4:-it is idealy accepted for calibration of instruments by
all.

Answer / sreekanth

There are some Transmitters which operate from 0 to 20 MA.
But 4-20 MA is standard.
As above one of our friend told, we cannot differentiate
whether the Instrument is fault or not when we get 0 MA.

Rather than that there is one more reason. MA will be
accurate from 3 MA. But getting exact ratio between 3 to 20
MA is bit difficult. so 4-20 MA is commonly used so that 0,
25, 50, 75, 100% can be converted in to 4- 20.

Answer / saba anjum

we can easily find that this signal is live zero or dead
zero.

Answer / shoeb

we cant find dead zero or true signel zero

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