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.
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.