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Why people are using mostly 4 - 20ma instead of 0 - 20 ma?

Mail ID: aakarthikeyan @ rediffmail. com
 
C

Curt Wuollet

It gives you a live zero so you can tell the
difference between zero (4ma) and an open
wire (0ma). Also it provides 4ma to run
loop powered transmitters.

Regards
cww
 
R

Robert Scott

The 4 ma. minimum current flow provides power for loop-powered sensors. If you allowed the current to go to 0, then loop-powered sensors would not be able to operate. Also, having a current that is supposed to be from 4 to 20 ma. means that a cut cable can be detected as a fault.

Robert Scott
Real-Time Specialties
 
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