What is NAMUR NE43?

The Namur NE43 is a recommendation which gives a guideline how a sensor fault can be indicated to a control system by means of the 4-20mA signal.

Definition Namur NE43

A sensor fault is signalled by extending the range of the 4-20mA signal. When the current is below 3,6 mA or above 21 mA this is interpreted as a sensor fault. In order to avoid false alarms, the signal shall be present for at least 4 seconds before it is interpreted as sensor fault.

Advantage of Namur NE43

A process control system such as a PLC or DCS system can identify faulty sensors, and production can be adjusted or stopped to avoid production loss or off-spec product. Also an maintenance technician can automatically be notified to repair or replace the broken transmitter.

Functionality testing

In order to test the reaction of a PLC or DCS system to a defect transmitter, a 4-20 mA signal source shall be used capable of simulating the Namur NE43 current levels.



This is similar to the Standard Analog Signal, NAMUR NE43 compliant transmitters/PLc analog output are designed to signals greater than 20 mA & less than the 4 MA to Base signal, allowing for a small amount of Signal Saturation. To be compliant to NAMUR NE43, the device are set in the factory to have an Analog -LL and Analog-UL of 3.8 mA and 20.5 mA respectively.

The analog Signal also has values designed to indicate a self-diagnosed hardware failure, loop open or Burnout. Once it’s determined, the analog output holds at ≤3.2 mA or ≥21.6 mA.

Does your system, sensor or transmitter comply with the Namur NE43 recommendation? In this caser analog signal fault can be represented by a current higher than 21 mA or lower than 3 mA. Is your software/system capable to handle all these situations, fault diagnostics and?

Also Read NAMUR NE


NAMUR NE 43.pdf (688.3 KB)