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 / narendra mishra

suppose 0 to 20ma is used where 0 for
min.process value and 20 for max.then if
feed back cable get shorten or erthed or
broken it wil show min process value.where
in case of 4 to 20ma it will show "bad".

Plc are used to handle specific area where
DI DO signals are required like burner
managment system.plc response time is in
milisec. And that of dcs is in microsec.

Max span can be found by taking it online
and interfacing it with HART.

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