Namur interface IC - Page 1
Forum section: electronics / projects

author: Cicada
author_rank: Regular Contributor
timestamp: November 02, 2018, 08:36:36 am
content: HelloI need to do a design where I have inputs from inductive proximity sensors such as this sensor.https://docs-emea.rs-online.com/webdocs/1308/0900766b813082ab.pdfThe sensor's output is based on the namur standard.http://www.prelectronics.com/support/pr-knowledge-library/faqs/q11-what-is-a-namur-sensorWhen metal is close to the sensor the current flowing through the sensor is below 1.2mA and when its not detecting metal the current is bigger than 2.1 mA. This current flowing through the sensor also powers the circuitry inside.The circuit used to power the sensor, measure the low and high current to produce a digital output and possibly provide isolation is called a "Switch Amplifier""Switch Amplifier" This link describes what a "Switch Amplifier" does as follows:https://www.controlcomponentsinc.com/switch-amplifiers#1Switch isolators supply power to the proximity sensor in a hazardous area, receive a proportional current, convert input signals to digital output signals and transfer switching signals to a control device such as DCS or PLC.I am looking for a board level (PCB) module or IC solution. i would prefer it if this Module / IC can run of 5V.I know it is possible to design your own circuit that does what the "Switch Amplifier" does but I want to know if there is a complete solution.Thank you

author: Sudo_apt-get_install_yum
author_rank: Regular Contributor
timestamp: November 02, 2018, 08:57:58 am
content: I’ve just looked at this quickly but if I understand this correctly, the current flows/ signal is high when there is nothing in front and current stops flowing/ signal is decreasing proportional to the distance of the object.Is this a kind of an inverted 4-20mA standard?If you want to use this at 5v you’ll have to step up the voltage to the 8v that the sensor needs, you could use a charge pump to get the required voltage.You could just use an OP-amp to convert the current to a voltage and then use a comparator set to whatever voltage you want to get your digital signal out. If you want isolation you could use an octocopter.Here is a link to a complete solution:https://www.controlcomponentsinc.com/switch-amplifiers

author: Cicada
author_rank: Regular Contributor
timestamp: November 02, 2018, 09:10:04 am
content: HiI am not sure how the 4-20mA and Namur standards are related. This gives some indication.https://blog.lesman.com/2012/02/17/what-does-namur-ne-43-do-for-me/

author: Sudo_apt-get_install_yum
author_rank: Regular Contributor
timestamp: November 02, 2018, 09:32:33 am
content: Quote from: Cicada on November 02, 2018, 09:10:04 amIts seems like the Namur NE43 and "4-20mA" are the same standards, according to the link it operates identical to the "4-20mA standard". I’ve never heard the term "Namur NE43" neither have my coworkers.Anyway the info above applies to this "Standard" as well.Also just google 4-20mA receiver and you’ll get hundreds of results.

author: senso
author_rank: Frequent Contributor
timestamp: November 02, 2018, 10:15:40 am
content: Do you really need that sensor?Its ATEX rated, to be used in explosive atmosphere, thats why its a bit strange on how it operates, its due to the ATEX rating, if there is no need for such rating, use a conventional inductive sensor that will cost 1/10 or less of that one.

author: Cicada
author_rank: Regular Contributor
timestamp: November 02, 2018, 10:48:02 am
content: Quote from: senso on November 02, 2018, 10:15:40 amYes you are right. The environment where this is going to be used does not require intrinsically safe electronics. The problem is that I am designing new boards for an existing systems where many of these sensors are already installed. We did not plan to replace the existing sensors. There will also be new sensors installed.So I guess it would be better to just completely get rid of the existing sensors.

author: Wolfram
author_rank: Frequent Contributor
timestamp: November 02, 2018, 12:41:48 pm
content: If I understand the problem correctly, you need to generate a digital signal that indicates whether the current is below 1.2 mA or above 2.1 mA. This could easily be accomplished using a resistor to turn the current into a voltage, and a voltage comparator with the right threshold and hysteresis. I don't think a dedicated sensor interface chip could simplify this. If you need isolation, add a digital isolator or an optocoupler. Don't forget proper input protection if the circuit is for an industrial environment.