Air Quality Sensor

[epierre]

@alex said:

Ok! Thanks.
And what about the ceramic sensors (like MQ serie). How long can we trust them?

a bit longer but they vary in time as Davide made the remark, so calibration is not one time in its life...

[alex]

Hello

@epierre : after received the PPD42NS, compared to the DSM501A, which one is the best do you think?

Other things, I planned to purchase soon the sensors that I need for my air station.
You made a list on the #1 post, and it's very useful thanks, but now I have to choose between them for each gas targeted (maybe some sensors are still missing on the list below)

Which one appears for you, the better for each gas, with a reasonable price?

O3		    MQ131   MICS-2610    Mics-2614
NO2 	      MiCS-2710    MiCS-2714
NO            ? 
PM10 PM2.5    PPD42NS    SamYoung DSM501
Benzene	   MQ135			
CO  	      MQ307A   MQ309A   AQ-7   MiCS-5525   TGS2442
So2 	      MQ136
COV       	MQ135  TGS2602
CO2 	      MQ135

[epierre]

@alex said:

@epierre : after received the PPD42NS, compared to the DSM501A, which one is the best do you think?

I currently have only the DSL501A working, many issues with the dead Shinyei (still in dispute escalade) and getting one from another seller takes so much time...

Which one appears for you, the better for each gas, with a reasonable price?
O3 MQ131 MICS-2610 Mics-2614
NO2 MiCS-2710 MiCS-2714
NO ?
PM10 PM2.5 PPD42NS SamYoung DSM501
Benzene MQ135
CO MQ307A MQ309A AQ-7 MiCS-5525 TGS2442
So2 MQ136
COV MQ135 TGS2602
CO2 MQ135

The price is low, but so is the result. Only the CO-MH-Z14 is calibrated. For all the others, there is the calibration issue.

See the sketch for a lit of known/tested sensors (some I don't have but a frien asked me for the curves so I added it to the Mega sketch)
https://github.com/empierre/arduino/blob/master/AirQuality-Multiple_Gas_Sensor1_4.ino

• The MiCS are problematic to find in Europe (!) so I have only one that I have not yet tested.
• The Figaro have been tested, but it is hard to know how to really test them on some gases...
• The MQxx:
  • MQ2: good result on smoke
  • MQ135 good result on CO2
    The others I'm not yet able to give any opinion.

[promy]

Great project!
I hooked up an MQ135 (sensor on a little pcb with (i think) smd resistor 102 (=1K ohm) between gnd and B )
The readings are however all over the place (135ppm to 1332ppm), so i think i need to calibrate. The raw reading is alwas in the range 71-80 (inside).

I know i have to get it outside and the reading should be 392 or 399 ppm but i am unsure what var i should change?
The sketch says mq135_ro (this has to be tuned 10K Ohm) but that does not seem to be used in the calculations?

I tried the sensor outside, but I am getting some different readings: the measured value changes from 59 to 82. The mq135_ro (i suppose that's the suggested ro) from 3081.00 to 81416 (does not go linear with the measured value?
The sensor was heated for more than 24h and then moved outside (started measuring after 5min, in windy conditions)

[jeylites]

I'm using the standard Smoke sketch from Mysensor library and it seem to be crashing MySensor plugin on Vera edge. Below is a snapshot of the problem. Any ideas?

[korttoma]

I take it that you are talking about the Air_Quality sketch right? The problem is that you do not have the device files for this kind of sensor in your Vera MySensor plugin. There is another thread that contains the files, I'll see if I can find it.

Edit: Found the thread -> http://forum.mysensors.org/topic/661/assistance-needed-completing-gas-air-quality-sensor

[jeylites]

@korttoma

I'm going to try experiment tomorrow... Thank you!

[jroseastro]

@epierre thank you for sharing this code - your work is stellar. I'm working with a team of three other people to build a payload for a near space weather balloon launch in a couple of weeks.

We're using the MQ131 Ozone Gas Sensor and your code has been quite useful to us. One question though, when our data logger reads the sensor we're getting a single number value. We're not exactly sure what that number means. Could you help explain what we're seeing? Are we getting a ppb number? ppm? Or something else altogether?

[epierre]

@jroseastro hello, first of all the MQ series are not so precise as that, use it for a test run, but for serious purpose please consider something better and with calibration.

Ozone is quite chalenging, if you go very high, since the MQ nead heating to work, it will drain fast your batteries.

For any sensor always refer to the datasheet.

MQ131 is given from 5 to 100 ppb (reason you get only a single value) if you use the provided calibration sheet. So the result is the one from the curve. We've had a discussion not yet settled with @hek about units and this is why I've not put it, but maybe I should uniformize everything in ppm since this is the most prevalent value used.

Also the datasheet says you need 6V to heat it, so you cannot heat it from the arduino except with a step up (not that good) or an external power source (best) with a voltage regulator.

[epierre]

I'm now testing the MICS-6814 (3 sensors in one) given for :
Carbon monoxide CO 1 -1000ppm
**Nitrogen dioxide NO2 0.05 –10ppm **
Ethanol C2H5OH 10 –500ppm
Hydrogen H2 1 –1000ppm
Ammonia NH3 1 –500ppm
Methane CH4 >1000ppm
Propane C3H8 >1000ppm
Iso-butane C4H10 >1000ppm

Datasheet maionly speaks on CO, NO2 and NH3:
http://www.seeedstudio.com/wiki/images/1/10/MiCS-6814_Datasheet.pdf

Here is are scripts:
http://www.seeedstudio.com/wiki/Grove_-_Multichannel_Gas_Sensor

http://www.seeedstudio.com/wiki/images/1/10/MiCS-6814_Datasheet.pdf

Some readings:

The concentration of NH3 is 0.99 ppm
The concentration of CO is 1.20 ppm
The concentration of NO2 is 0.15 ppm
The concentration of C3H8 is 1000.04 ppm
The concentration of C4H10 is 999.98 ppm
The concentration of CH4 is 2991.14 ppm
The concentration of H2 is 1.09 ppm
The concentration of C2H5OH is 1.40 ppm

I guess I'll make a script soon...

[bhavika]

I think MQ131 need 24 hours preheating time.Because of preheating time it will be costly. and for MiCS 6814 how do you calculate or measured other values of gases?? Because sensor's data sheet it hard to understand

[epierre]

@bhavika said:

I think MQ131 need 24 hours preheating time.Because of preheating time it will be costly.

no MQ is expected to run on battery for they always need pre-heating before getting a value.

and for MiCS 6814 how do you calculate or measured other values of gases?? Because sensor's data sheet it hard to understand

So fat I only use the provided library. Sensors are said to be factory calibrated, maybe a reason they are so costly. I'm not running it constantly at this time, but I saw no change in the few time I ran it so I'm still expecting to see something.

[haro]

@epierre Hi...it is ameasing your work :D

I am wondering about Mq-135. We have troubles with reading differents gases.
From the datasheet we read the slopes
Gas X" X0" "Rs/R0 "Rs/R0 pendiente (log y- log y0)/(log x-log x0)"
Air 200 10 3.6 3.6 0.00000
co 200 10 1.3 2.9 -0.26783
nh4 200 10 0.79 2.7 -0.41024
c02 200 10 0.8 2.4 -0.36673
3/4/ 200 10 0.72 1.9 -0.32391
1/4/ 200 10 0.64 1.5 -0.28432
+- 200 10 0.59 1.4 -0.28845

the data are in the next worksheet https://docs.google.com/spreadsheets/d/18Z6XyxwXVsWdMIk9vbUuCucaLJDdmR0QUFSTYG79ftw/edit?usp=sharing

¿may you share with us your code for this sensor in order to see your slopes and Rs/R0 values ?
¿do you know the meaning of the name of gases with 3/4 or 1/4 or +-

thank you in advance

[epierre]

@haro

based on a datasheet, this one:
https://drive.google.com/file/d/0B8OvrwVDp8fCcWpHSjZNVzB1TjQ/view

I apply a power regression (tool: http://www.xuru.org/rt/PowR.as ) on the following points (I've not marked down values but theses are close match):

0.8 200 
1 100
2.3 10

Result: y = 103.6748512 x-2.81699418
Residual Sum of Squares: rss = 45.01031346

 ¿do you know the meaning of the name of gases with 3/4 or 1/4 or +-

looks like you had a chinese datasheet ;-) just remember those are correlated gases based on particle size for those captors, so it is not very accurate...

You can find many more sensors hare : https://github.com/empierre/arduino/blob/master/AirQuality-Multiple_Gas_Sensor1_4.ino or simply in https://github.com/empierre/arduino/blob/master/

[haro]

@epierre
Hi, May be I do not explain my point correctly (or maybe I misundertood ), let me try again.
We adopt a code, which is the next. The blue lines are the points (for each gas we need two points) that we need.
https://docs.google.com/document/d/1CevnhBLL9uoyZ31kkrMn-SXeOF_4e9YFGmchj46pGPY/edit?usp=sharing

Specifically we read from the datasheet the pairs of points for CO
point1 (lg200 , lg1.3)
Point2 (lg10, lg2.9)
then, we construct the data format:{ x, y, slope};
COCurve[3] = {1.0,0.462,-0.268};

We are wondering about the pair of points for the others gases or the { x, y, slope} data for them, could you share them?.

and the other hand, the name of gases with 3/4 or 1/4 or +- appears as well in your datasheet (figure 3)... do you know why?

thank you so much

[epierre]

I prefer the power regression than the curves.

From your datapoints :
1.3 200
2.9 10

I find:
y = 532.6744764 x-3.73371402
rss=0

I don't remember where I found the datasheet with the chinese names that I translated through google.

[haro]

@epierre Now I see your point of view and of course it is better way to reduce the error.

in the other hand, I found the datasheet in chinese an then a friend translate it.
the meaning of the name of gases is for 3/4 (Alcohol), 1/4 (Tolueno) or +- (acetona)

Thank you so much.

[Yuki M]

Hi,

I've started working with an MQ135 sensor, attached to a board like the disucssion you had from a year ago. I measured some of the resistances between the Aouts and the sensor pins and seems similar with the 1kohm resistance between AO and Gnd, and the pot not changing the output.

I was wondering if anyone managed to calibrate their board using the AO of this board, and if so how? I can't seem to get a good resolution, as it has noise of at least in the 10's of ppm.

I'm considering whether its simpler to by pass the board and its amplifier, and directly hook set up onto the sensor itself with the correct resistors.

[epierre]

@Yuki-M said:

Hi,

I've started working with an MQ135 sensor, attached to a board like the disucssion you had from a year ago. I measured some of the resistances between the Aouts and the sensor pins and seems similar with the 1kohm resistance between AO and Gnd, and the pot not changing the output.

I was wondering if anyone managed to calibrate their board using the AO of this board, and if so how? I can't seem to get a good resolution, as it has noise of at least in the 10's of ppm.

I'm considering whether its simpler to by pass the board and its amplifier, and directly hook set up onto the sensor itself with the correct resistors.

Calibration is not possible as it varies between the same sensors of this construction class. Check datasheet on minimal sensibility also on low and max values.

Also without a gas concentration it is not possible to calibrate it. The best guess is that co2now.org gives you that outside (aka clean air) it is 399 for CO2, but that would be only for CO2 and not the other gases !

[Yuki M]

@epierre Thanks for a rapid response!
Yes I've been trying to calibrate it assuming out door air is at 399ppm. I understand each one has variances but would like to know how you guys worked it out.
I'm using
ppm = 116.6020682 (Rs/Ro)^-2.769034857
from davide's blog http://davidegironi.blogspot.ch/2014/01/cheap-co2-meter-using-mq135-sensor-with.html#.VinvWX4rIuU

Since the board show RL, I took that to calculate Rs. This lets me calculate Ro, thus calibrate it.

Not quite sure where I'm going wrong. I had it working 8 months ago, and came back to it and couldn't figure out how i had it working so well.. I was able to get pretty nice graphs and now its very unstable.

I'm having a play around with it, you can see my current points here https://thingspeak.com/channels/31162