Air Quality Sensor

epierre

@hek here is an updated list from the Wunder Weather list of reportable gases:

Carbon Monoxide – CO
Carbon Dioxide – CO2
Oxygen – O2
Methane – CH4
Hydrogen – H2
Ammonia – NH3
Isobutane – C4H10
Ethanol – CH3CH2OH (aka C2H5OH or C2H60)
Toluene – C6H5CH3
Hydrogen Sulfide – H2S
Nitrogen Dioxide – NO2
Ozone – O3
Hydrocarbons – VOC
Chlorine CL2
Ammonium NH4
Ethanol CO2H50H
Methyl CH3
Acetone CH3_2CO
LPG (both C3H8 C4H10)

NO - nitric oxide
NOX - nitrogen oxides
NO3 ion (nitrate, not adjusted for ammonium ion) UG/M3
SO4 ion, sulfate, not adjusted for ammonium ion, UG/M3
SO2 sulfur dioxide, ppb
EC (elemental carbon) – PM2.5 UG/M3
OC (organic carbon, not adjusted for oxygen and hydrogen) – PM2.5 UG/M3
BC (black carbon at 880 nm) UG/M3
UV-AETH (second channel of Aethalometer at 370 nm) UG/M3
PM2.5 mass - UG/M3
PM10 mass - PM10 mass

hek

Thanks!

Still thinking about you gas_type suggestion. It would introduce another level of device types. Hmm..

epierre

@korttoma look above to S_CO2Sensor.json D_CO2Sensor.xml D_CO2Sensor.json, if you can test it...

epierre

@Yveaux I know you are strong at finding datasheet... can you find one for me ? I can't find the 2SH12 sensor altgough I've asked for it to all suppliers on aliexpress...

Same for theWSP1110

Yveaux

@epierre Couldn't find it either, sorry...
I wouldn't buy a $52,- component without a datasheet, if I were you...

epierre

@Yveaux When I asked for the WSP110 they sent me only this (not the same for this one is HCHO and well documented...) :

hek

@epierre

I wonder what the green curve represents :confused:

epierre

@hek that should be the more sensitive, and since it is given mostly for CHCO I guess this is it... (Formaldehyde)

epierre

@hek 甲醛 is formaldehyde, given by google translate so I'm right !

hek

@epierre

Haha :thumbsup:

epierre

Davide answered me, lot of things to read but a warning:

Anyway, for consistent CO2 investigaion, you HAVE to chose a NDIR sensor, those chemical sensor can not be used. They decay in a few year, and they differs a little one from each other.

I've asked him back for precision if he speaks of the organic sensor or the ceramic ones (like MQ...).

For the CO2, it is MH-Z14 which is $66+ priced.

hek

@epierre said:

MH-Z14

Like this little puppy?

epierre

@hek exact !

korttoma

@epierre said:

@korttoma look above to S_CO2Sensor.json D_CO2Sensor.xml D_CO2Sensor.json, if you can test it...

Thanks, found the device files and got the device included again.
Seems like my MQ-2 is always reporting 0 or nothing at all. I guess I need to try to calibrate it again.
It will do the calibration every time the sensor is restarted right?
How can I calibrate the sensor if I put it somewhere where the air is not clean enough? (bring clean air in a jar? ;) )

Maybe it would be an idea to add a calibration button to the mix and when run using the button it would save the calibration related data in the RAM so it can then always use this calibrated value and then it would not re-calibrate every time it loses power.
I have the 10k resistor between GND and A0, is this really necessary?
Does the potentiometer on the sensor board affect the analog out at all or is it only for sensitivity on the digital out?

Sorry for all the questions ;)

epierre

@korttoma said:

Thanks, found the device files and got the device included again.

So you confirm they can be used as is ?

@korttoma said:

Seems like my MQ-2 is always reporting 0 or nothing at all. I guess I need to try to calibrate it again.
It will do the calibration every time the sensor is restarted right?
How can I calibrate the sensor if I put it somewhere where the air is not clean enough? (bring clean air in a jar? wink )

this is the ongoing work, except CO2 which is known to be 399ppm (co2now.org) that should report this in clean air, for the other that should be little, and for deadly gases a full warning if this is high.

@korttoma said:

Maybe it would be an idea to add a calibration button to the mix and when run using the button it would save the calibration related data in the RAM so it can then always use this calibrated value and then it would not re-calibrate every time it loses power.

That is an option, but EEPROM has a 100k write cycle only... this is what citizensensors says about it:

1) Metal oxide gas sensors have intrinsic drift over time i.e. it is necessary to perform calibration on a regular basis.

2) Because of spread in baseline resistance, sensitivity, cross-sensitivity, temperature dependency it is not possible to apply same calibration parameters to all the sensors.

3) This type of sensor is efficient to detect change in concentration but not well adapted to absolute readings because of multiple dependency (T, RH, cross-contaminants).

4) Using smart algorithm allows indicating useful information like the correlation with CO2 in confined space like offices or buildings (see VZ-87 in attachment).

For absolute readings with high accuracy and repeatability I agree with you that you should use another technology.

From this we have the calibration issue... in another post, since they only report resistance, they say they will rebuild all their platform to address callibration issue... but since calibration depends only from a reference gas concentration... only the pre-calibrated sensors remains viable for the low cost MQ/MICS/TGS will never be really calibrated...

@korttoma said:

I have the 10k resistor between GND and A0, is this really necessary?
Does the potentiometer on the sensor board affect the analog out at all or is it only for sensitivity on the digital out?

no you can remove it, I have observed a different behavior when moving it, it looks like it is shared by both digital and analogic for the same reason. What I'd like to find is where to measure the resistance for there are often some more on the board.

@korttoma said:

Sorry for all the questions

good questions are always useful, especially when they meet my current subject of interrest ;-)

korttoma

@epierre said:

@korttoma said:

Thanks, found the device files and got the device included again.
So you confirm they can be used as is ?

well, for the device in Vera I had to change the parameter "device_file" from "D_AirQuality1.xml" to "D_CO2Sensor.xml".
I don't get any errors but I also do not get any values but I guess this is because my node is not sending any values.

I'll try to look in to why my node is not reporting any value and try to remove the 10kR and see if I can measure the load resistance of my MQ-2 sensor board and maybe even remove some unnecessary components from it...

pbo

Hi All. Very interesting stuff, thanks all for sharing! I'm attempting to integrate an MQ-2, MQ-6 and MQ-135 (sensors only, no boards) using parts of epierre's sketch but I'm confused on a few things on how to set it up properly:

What resistor(s) should go between A0 and ground? Keep in mind I'm not using a sensor board with built in protection resistor. Should there be a protection resistor then an adjustable pot for calibration?
define RL_VALUE (5)
-- does this refer to the size of the protection resistor between A0 and ground?
define RO_CLEAN_AIR_FACTOR (9.83)
-- does this value need to change at all?
float Ro4 = 2.511;
-- when you say this needs to be tuned to 10k, does that mean put a pot between A0 and ground and adjust until the calibration R0 is 10k?

Sorry for all the questions, I appreciate any input! Thanks!

epierre

@pbo

1- see http://www.electronicaestudio.com/docs/SHT-114.pdf Fig 2 for wiring, the adjustable resistance is with ground and the sensor.

2- yes

3- Ro is calculated on first launch expecting you do this outside.
Ro = MQCalibration(MQ_SENSOR_ANALOG_PIN);

4- this is a default value I observed here. again the datasheet recommands for MQ135 20K to be in range with their values:
we recommend that you calibrate the detector for 100ppm NH3 or 50ppm Alcohol concentration in air and use value of Load resistance that( RL) about 20 KΩ

pbo

@epierre

Thanks for fast reply! I think i understand all but point #4... What do you mean by the Ro needs to be tuned to 10k? Using the adjustable resistor? Does that mean that the calibration number in fresh air at startup should ideally reach a set number, 10k?

Since I don't have access to properly calibrate the sensor against a know quantity of gas, I thought the rough calibration would occur in clean air at start up, is that correct?

Sorry for all the questions, it's a bit complicated. Thanks again!

epierre

@pbo as stated above, the sensors evolve in their life... let's say that the value recommended by the datasheet is the best if you can.

clean air calibration means that you should have a 0 value in clean air. Let's say that for CO2 the actual value is 399... so it should not be 0, but the clean air calibration is "assumed" quite good for LPG, SO2, NOx... that should be present in very little quantity, and again this is when the value increases a lot that it gets dangerous... there are some discussion on this above.

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