Troubles on selecting NO2 gas sensor

Hi everyone, I am going to build an Arduino model to monitor the NO2 concentration in the air.

However, I face troubles on selecting the suitable. Below is my two choices:

MICS-2714 sensor

Datasheet of MICS-2714 sensor: https://www.sgxsensortech.com/content/uploads/2014/08/1107_Datasheet-MiCS-2714.pdf

MICS-6814 sensor

Datasheet of MICS-6814 sensor:


  1. Which sensor is the better choice for my project?

  2. As MICS-6814 sensor can detect NO2, NH3 and CO, can the reading of these detected gases be separated? Can i detect the concentration of NO2 individually by using MICS-6814 sensor?

  3. It these two sensor suitable for outdoor measurement?

  4. Is there any gas sensor better than MICS-2714 and MICS-6814?

Thank you very much for your guidance and support!

Which sensor is the better choice for my project?

The one that best matches your requirements, which you forgot to state.

There are many gas sensors. In general, the more you pay, the more accurate and selective it will be. One source of certified, industrial NO2 detectors.

The very cheap sensors detect several gases and with just one sensor, it is not possible to say which gas might be responsible for observed changes in the output.

jremington:
The very cheap sensors detect several gases and with just one sensor, it is not possible to say which gas might be responsible for observed changes in the output.

Thats a very interesting comment.

The MICS-4514 sensor has become a common sensor to use in The Things Network (TTN) type applications for monitoring air quality.

These sensors are not expensive, circa £15.

Do you know to what extent you can be confident that the results they are providing are reasonable for the gases they are supposed to detect. The sensors are advertised as detecting Co and NO2, so are you suggesting that you can only be sure the sensor is detecting 'something' ?

The MICS-4514 sensor has two independent elements that detect different gases, using different principles.

According to the data sheet, the reducing sensor strongly responds to the presence of ethanol, hydrogen, ammonia and CO, over the same range of concentrations. See graph below.

If you can think of a way to determine which of those four gases produced an observed change in the output of the reducing sensor, without using any additional information, people would be keenly interested.
red_sensor.png

For sure, in a home, high concentrations of CO are more likely than ethanol, hydrogen or ammonia gas, and our noses would tell us about ammonia long before the detector would. Humans can detect 2 ppm NH3 by smell.

red_sensor.png

jremington:
The MICS-4514 sensor has two independent elements that detect different gases, using different principles.

According to the data sheet, the reducing sensor strongly responds to the presence of ethanol, hydrogen, ammonia and CO, over the same range of concentrations. See graph below.

If you can think of a way to determine which of those four gases produced an observed change in the output of the reducing sensor, without using any additional information, people would be keenly interested.
red_sensor.png

For sure, in a home, high concentrations of CO are more likely than ethanol, hydrogen or ammonia gas, and our noses would tell us about ammonia long before the detector would.

How about the MICS-6814 sensor, which should consist of three independent element? According to the data sheet , the OX sensor response to the NO2, NO and Hydrogen.

In practice, if i put the Arduino model with this sensor in outdoor usage, may i determine that the detected ppm is belonged to NO2 and/or NO? Or only Hydrogen will dominate the detected ppm?

Thank you very much!!!

OX sensor.png

in outdoor usage

The MICS-6814 is intended for indoor usage and the data sheet gives information for that particular sensor only for NO, NO2 and H2, and at only one value (50%) of the relative humidity and at only one temperature, 25 C.

For an outside application, where the relative humidity could range from 0% to 100%, and the temperature could range from -40 to 40 C, you really need to know how those variables will affect the sensor. It probably won't work at all under some conditions. Ask the manufacturer, or determine the effects yourself.

You might also ask the manufacturer if there are other gases that produce a strong response. That factory nearby could be producing just about anything.

If you really want to monitor NO2 concentration, you need a certified, calibrated NO2 sensor.

jremington:
If you can think of a way to determine which of those four gases produced an observed change in the output of the reducing sensor, without using any additional information, people would be keenly interested.

Alas I cannot.

That MICS-4514 sensor, together with a particle sensor, is being pushed as a TTN 'pollution' monitor, for the community to use the results, outside schools, in town centres etc.

One point I have been making for a while to the proponents of this type of monitoring is that for the results to be accepted and trusted, you need some way of calibrating on an on-going basis how accurate the things are, but this tends to fall on deaf ears.

I had looked at the sensor datasheet, working out how to do an Arduino interface, I just had not picked up that the sensor could be reacting to a lot of stuff.

So useful for a home sensor maybe, but not for community or public use, as the results might indicate CO/NOX levels or they might not.

@srnet:

The MICS-4514 is also intended for indoor use, and it makes no sense to use it outdoors, at the very least for the reasons quoted above (RH, Temp). I have experimented with similar sensors and have seen that those factors have significant influences on the sensing element.

They are discussed here by the manufacturer: https://www.sgxsensortech.com/content/uploads/2014/08/AN2-–-Frequently-Asked-Questions-for-MiCS-Gas-Sensors.pdf

See also the sections on calibration, and how the sensor can be poisoned by other gases:

IS CALIBRATION NEEDED, AND HOW OFTEN? It depends on the application, and on the required precision. Several factors tend to reduce the measurement accuracy e.g. production dispersion on base resistance (Ro) and sensitivity (S), temperature, humidity, the presence of interfering gases, ageing of the sensor, and on-time. Calibration is needed when the required accuracy cannot be obtained due to one or more of the factors listed above. This is the case for most applications where an absolute gas measurement is needed.

If people in your own community are pushing it, do some tests of your own by placing one outdoors and simply monitoring the output. If there are large changes in output that correlate with temp or RH, that should help them think a bit more about it.