Transmitter- current 4 to 20 mA. Why?

[nm2007k]

Why the standard for a transmitter current (example : in a differential pressure transmitter) is set as 4 to 20 mA?

 

[ckshivaram]

refer these links
Current loop - Wikipedia, the free encyclopedia
https://www.dataforth.com/catalog/pdf/an104.pdf

---------- Post added at 18:48 ---------- Previous post was at 18:46 ----------

**broken link removed**

check this discussion too,

Why 4-20 ma is used in Analog Signals?

 

[FvM]

Of course there are various previous Edaboard threads, e.g. https://www.edaboard.com/threads/166649/