Why we use 4 - 20 ma?

Answer Posted / sam daniel, marthandam, kanyak

To operate a Digital signal we need 1-5Vdc. For Analog
Instruments we are using 250 ohms as load resistance. When
we converting this signal into current By Ohm's
Law V=IR
I=V/R
Put, V=1V Then I=1/250=4mA
Put, V=2V Then I=2/250=8mA
Put, V=3V Then I=3/250=12mA
Put, V=4V Then I=4/250=16mA
Put, V=5V Then I=5/250=20mA

*Also, since this is linear region
*Not possible to cause spark
*Since it is a current signal we can transmit it into long
distance.
*Suppose if the instrument is dead we can identify it.

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