NAMUR NE 43 is a recommendation that seeks to promote the standardization of the signal level for failure information. The objective of NAMUR NE 43 is to set the foundation for proactively employing transmitter failure signals in process instrumentation and control. Using these failure signals, instrument faults are separated from process measurements. Because the faults get detected earlier, instrumentation and control engineers can design a system that keeps the instruments in operation thus enhancing productivity.
NAMUR NE 43 utilizes the 3.8 to 20.5 mA signal range for measurement information, with the signals ≥ 21 mA or ≤ 3.6 mA being used to indicate diagnostic failures. Using this information, it is much easier to detect say a fail high condition on a level transmitter i.e. finding out whether you have a full tank or a failed instrument.

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