NAMUR-compliant transmitters are designed to limit their output signals between 3.8 mA and
less than 21 mA when functioning properly. Signals lying outside this range indicate some form of
failure has occurred within the transmitter or the circuit wiring.
The 8.2 V sensor is for proximity switches as per NAMUR NA 01 (1967) “Noncontacting Initiators and amplifiers” now known as IEC 60947-5-6
- mA is for transmitters as per NAMUR NE 43
Do not confuse the two standards
Lots of companies make signal conditioners and barriers to convert the 8.2 V NAMUR signal to 24 VDC signal or relay contact
NAMUR sensors are designed to be intrinsically safe. In order to achieve this they should be powered by a 8 V DC supply, and their on/off state will be determined by a 1/3 mA current signal.
In order to provide these requirements a IS interface should be used to connect the sensor to the control system.
This can be done by:
Using a zener barrier, which will require an intermediate relay a a low impedance earth connection.
Using a IS galvánic isolator, which offers galvánic isolation, either relay or electronics outputs and wiring diagnostics.
Using a I/O card compatible with NAMUR sensors. These can be IS or non IS.
Although the main use of NAMUR sensors is as proximity switches in hazardous areas, they are also used in non hazardous areas since the wiring is simpler when compared with a typical 3 wire PNP or NPN proximity sensor.
NAMUR sensors not used in hazardous areas may be powered with 24 V DC, but in that case they should never be used in a hazardous application again.