People have asked me about setting fault alarms in level transmitter analog signals at 2mA or 3mA levels. What they typically don’t understand is that a two-wire transmitter uses the electrical current below 3.6 mA for its own power and operation. So, a 2.0 mA or 3.0 mA fault indication just isn’t possible. At these low currents, there wouldn’t be enough power to generate the fault indication signal and to keep the transmitter functioning properly.
NAMUR, an international association of process instrumentation user companies, made a recommendation, known as NE 43, to promote a standardization of the signal level for failure information. You’ll see Compliant to NAMUR NE 43 on the specs of most digital transmitters available today.
The goal of NE 43 is to set a basis for proactively using transmitter failure signals in process control strategies. Using these failure signals (A), instrument faults are separated from process measurements (M). And since the faults get signaled at an early stage, the team can design maintenance strategies that keep the instruments in operation and increase productivity.
NAMUR NE 43 uses the 3.8 to 20.5 mA signal range for measurement information, with ≥21 mA or ≤3.6 mA to indicate diagnostic failures. With that information, it’s easier to detect a fail high condition on a level transmitter, for example, that clearly tells you whether you have a full tank or a failed instrument.
Lesman Tech Tips 
#1 by Nick on March 9, 2016 - 2:01 am
If my transmitter has adjustable saturation levels ie 3.6 for low end and 21 for high end of scale does that make Tx Namur 43 compliant
#2 by danstips on April 20, 2016 - 2:34 pm
I don’t know what “adjustable saturation level” is. I interpret the NE-43 diagram as 21mA upscale burnout, 3.6mA downscale burnout. There can only be one burn-out selection, but those values are NAMUR burn-out values.
#3 by Nick on April 20, 2016 - 3:34 pm
Thanks dan for the info makes sense to me what I really meant to say was if your burnout level is adjusted to those settings 21ma upscale and 3.6ma downscale then the device becomes compliment to Namur 43 standard
Is that a true statement?
#4 by Naganaresh on August 22, 2013 - 3:52 pm
I need one confirmation, as per my understanding Namur 43 settings are made to increase the productivity of process plants, means reduce the shutdowns due to false Instrument faults. In our plant we are using Namur analog transmitters, which will saturate the output to 20.5mA and 3.8mA. Means if process overflow occurs, then values will saturate to either 20.5mA and 3.8mA depends on situation.
My question is when i need to decect the faulty signal in my software to generate trip signal
1. Only when Instrument failure??
or
2. even if process parameter value is overflow????
Your reply is highly appreciated……….
#5 by Naga on November 7, 2013 - 11:50 am
Thank you very much Mr. JPW for your information……….
One more doubt i am having,…….
for High PV means over range, should i generate trip signal or not????
means for example, if there is only Low Low trip for transmitter,if in such case if PV value goes High beyond the range and saturates upto 20.5mA(103.1%)…..in this case, should i generate trip or not????
#6 by Naganaresh on April 25, 2013 - 2:56 pm
Thank you very much for your information about Namur 43
I am having doubt, if the current is in between 20.5 and 21 then how can i consider, transmitter is failed or not failed????
#7 by danstips on June 14, 2013 - 3:11 pm
Hard to say. Would differ with each application.
#8 by JPW on November 5, 2013 - 10:42 pm
You will not get a current between 20.5 to 21mA. The high current saturation point is 20.5, therefore the transmitter will not output more than this, unless the transmitter has a fault, in which case the tx will output 21 or above.
It would be a poorly implemented measurement system if the actual measured process variable could reach a point where the tx would need to output more than 20.5mA.
That is why there is a window between saturation and fault status current values: to allow for tolerances/drift of components, both in the transmitter, and the SIS system that is configured to differentiate between a high PV, or a fault condition.
#9 by Rick Frauton on August 14, 2012 - 2:31 pm
Excellent article and exactly the information I was searching for. Thanks Dan!
#10 by danstips on July 25, 2012 - 8:44 am
This article has been the #1 post on Dan’s blog since it went live.
To our readers, I ask: What is it that you’re looking to learn when you read this? What’s your application or problem that drew you here? Are there other topics like it that Dan can explain for you?
Thanks in advance for the insight!
#11 by John Albers on July 24, 2013 - 2:27 pm
We are trying to use the Namur parameters to indicate a failed transmitter. I am trying to determine where to set the parameters on the controller that the transmitter is talking to. We had these set up on a couple of instruments but we are getting intermittant device failure alarms.
So the controller is set to say the signal is bad if it gets below 3.8 mA or above 20.5 mA. Should the controllers window be larger than the transmitters window since the transmitter is setting the signal?
#12 by Joe T Dobbelaere on February 19, 2012 - 6:40 pm
Nice job Dan! It’s this type of inforamation that goes a long way with our customers…keep up the good work! Joe T Dobbelaere