What does a NAMUR sensor mean and how do you operate a NAMUR sensor at 8V when the available power at plant is 24VDC?


#1

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.


#2

Thanks for sharing this useful information here. Hope it will be helpful for my future projects.
I want to know about the compatibility of these sensors? Are they compatible with all boards?
Or they need any extra board? Also what is their interfacing mode?
Can you please tell more I/O and I-V specification of these sensors?


#3

Yes. These senseors required seperate Input modues. Conventional Input modules ( 4 - 20 ma )detects overflow and undeflow when input signal detects outside range. Namur does have overflow and underflow, it goes to signal bad when outside the signal range.