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 signaled by extending the range of the 4-20mA signal. When the loop 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.
Divize can supply a version of the A2007E current source capable of simulating both the upper and lower current signal. This current source has a range of 3,4 to 21,5 mA. This unit is specially designed for testing PLC and DCS systems according the Namur NE43 recommendation. By turning the potentiometer to the mechanical limit the signal will become so high/low to generate a fault, then the reaction of the PLC or DCS system can be checked. The current source uses a 10 turn potentiometer so the signal can be set very accurately.