Standards
NAMUR NE 43
Definition
A recommendation defining how a transmitter signals a fault: by driving its output outside the measurement range, below 3.6 mA or above 21 mA.
This turns a sensor diagnostic into something a controller can act on. A radar transmitter that has lost echo can report 3.5 mA rather than a plausible level of zero.
The fail direction is configurable and should be chosen deliberately, because failing low and failing high have very different consequences on a wet well.
See also
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