1,why we use 4-20 ma output of all instrument qhy not use 0-
20,
2,what is the different between PLC & DCS.
3,how can we meaure maximum span of new flowmeter if not
given any information.

Answer Posted / samir

4-20 ma is used to instrument because if there is an
instrument faulty of it not getting the power or damage then
it gives 0 ma signal so we can found that the instrument is
faulty so we can easily check the instrument.
if we use 0- 20 ma we can not identify from the signal that
the instruments is faulty or actual the low signal from the
instrument during the measurement.

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