why we r using 4-20ma instead of 0-20ma in instrumentation

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why we r using 4-20ma instead of 0-20ma in instrumentation..

Answer / nithi

This is to discriminate the wire-break of sensor and the
zero value of measured parameter.
ex:If pressure transducer measures 0 bar pressure,it will
send 4mA signal to the monitoring unit(EX:PLC).in case ,if
there is any break(dis-continuity) in wire then PLC senses
the 0 mA and gives alarm or shutdown depends on the
important of that parameter.

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why we r using 4-20ma instead of 0-20ma in instrumentation..

Answer / ind/elec

4-20 ma is used as opposed to 0-20 ma as at 0 ma this could
because of a break in cable or loss of supply and so
control would be ineffective.

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