Air Quality Sensor

[alexsh1]

@epierre

This is what I discovered. When nobody is around the sensor 'settles' on a particular value. However, when there is anyone around in the room, the sensor reading goes up and down - see the snapshot attached. Any idea what the problem may be?

[epierre]

@alexsh1 hard to say, could be something moving inside if someone makes vibration around and thus this strange reaction... the down curve at the end is correct, the in between not

[Elfnoir]

Hi,
Can you check the reception level?
I had same behaviour with an old temperature/humidity module; need to move it to another place in the room, and works perfectly now :-)

[epierre]

@Elfnoir said:

; need to move it to another place in the room, and works perfectly now

temp/hum are "less" sensitive on environment, here the sensors heats up to 40-60° (or more) so temp/hum is not the most impacting (I can be wrong anyway ;-)

[alexsh1]

@epierre I wonder if you looked at this sensor Figaro TGS8100:

http://www.figarosensor.com/products/entry/tgs8100.html

Looks like it is perfect for a low-powered platform.

[epierre]

@alexsh1 said:

@epierre I wonder if you looked at this sensor Figaro TGS8100:

http://www.figarosensor.com/products/entry/tgs8100.html

Looks like it is perfect for a low-powered platform.

as a replacement for MQ in low power yes could be... the bad part is how to get one ?

[alexsh1]

@epierre said:
the bad part is how to get one ?

How about http://www.soselectronic.com/?str=371&artnum=170939&name=figaro-tgs8100 ?

[Vir]

Hi, It all make sense, I am just confused that in your code once your multiply and once you divide...

case CO:
{
if(ratio1 < 0.01) ratio1 = 0.01;
if(ratio1 > 3) ratio1 = 3;
//c = pow(10, 0.6) / pow(ratio1, 1.2);
** c = pow(ratio1, -1.179)4.385; //mod by jack*
break;
}
case NO2:
{
if(ratio2 < 0.07) ratio2 = 0.07;
if(ratio2 > 40) ratio2 = 40;
//c = ratio2 / pow(10, 0.8);
** c = pow(ratio2, 1.007)/6.855; //mod by jack**
break;
}
SO, what is the actual formula?

Vir

@epierre said:

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...

[Vir]

What does 37143 represents, Rs? and -3.178 is a second value from your regression method, but what about the first value?
Can you elaborate on ppm line, please
Vir

here the formula is a simplification of this:

float Vrl = val * ( 5.00 / 1024.0 ); // V
float Rs = 20000 * ( 5.00 - Vrl) / Vrl ; // Ohm
int ratio = Rs/Ro;
ppm = 37143 * pow (ratio, -3.178);

[Vir]

@bhavika said:

I am confused with MiCS 4514 sensor. What I had done is :

using MiCS quick start evaluation board, measured ADC value
calculated Vout and from that calculated R0.
Rs/R0 concentration gives me high value, which is not possible, My data is as follows
clean air file is used for the purpose of R0 value
https://drive.google.com/file/d/0B8sF8a6FHoseWjhWOHRoYzIxakk/view?usp=sharing
and Polluted file is used to calculate the actual pollution
https://drive.google.com/file/d/0B8sF8a6FHoseR1BnclhCUHdibEU/view?usp=sharing

I am confused. Please help me

I am confused by the formula you are using, could you please explain?
Pollution NO2 = (POWER((RS/R0)*(1/POWER(10,0.8068)),(1/1.01)))

Pollution CO = POWER((RS/R0)*(1/POWER(10 , 0.5476)),(1/-0.8497)))

is the actual formula like this?:

pollution = POWER((ratio *(1/POWER(10, curve[0])),(1/[curve[1])))

This is different than any other formulas discussed in this thread...
Vir

[Vir]

so does 37164 represents the scaling factor and -3.178 the exponent?
Vir
@Vir said:

What does 37143 represents, Rs? and -3.178 is a second value from your regression method, but what about the first value?
Can you elaborate on ppm line, please
Vir

here the formula is a simplification of this:

float Vrl = val * ( 5.00 / 1024.0 ); // V
float Rs = 20000 * ( 5.00 - Vrl) / Vrl ; // Ohm
int ratio = Rs/Ro;
ppm = 37143 * pow (ratio, -3.178);

[alexsh1]

@epierre I have the problem with the dust sketch (shinyei ppd42ns). The following code does not work in MySensors 1.5

...
gw.send(msgPM10.set("ppm"));
  ...
gw.send(msgPM25.set("ppm")); 
...

2016-04-24 14:44:19.438 Error: MySensors: Unknown/Invalid sensor type (43)
2016-04-24 14:44:19.438 Error: MySensors: Unknown/Invalid sensor type (43)

So far both PM10 and PM25 are showing zero. However, if I upload the following code, it works fine (one channel though):

// Watch video here: https://www.youtube.com/watch?v=a8r4CeQopfY

/* 
 Connection:
 
 JST Pin 1 (Black Wire)  => Arduino GND
 JST Pin 3 (Red wire)    => Arduino 5VDC
 JST Pin 4 (Yellow wire) => Arduino Digital Pin 8

 Green Led connected to Arduino D7
 Yellow Led connected to Arduino D6
 Red Led connected to Arduino D5
 
 
Dust Sensor possible application:
- Applications of customer
- Air quality sensor
- Dustlessness workshop
- Cigarette detector
*/

/*
Sensor is to create Digital (Lo Pulse) output to Particulate Matters (PM). Lo Pulse Occupancy time (LPO time) is in proportion
to PM concentration. The output is for PM whose size is around 1 micro meter or larger. We can use the sensor to detect the dust in clean room.
Minimum detect particle: 1um
http://www.seeedstudio.com/wiki/Grove_-_Dust_Sensor
 Grove - Dust Sensor Demo v1.0
 Interface to Shinyei Model PPD42NS Particle Sensor
 Program by Christopher Nafis 
 Written April 2012
 
 http://www.seeedstudio.com/depot/grove-dust-sensor-p-1050.html
 http://www.sca-shinyei.com/pdf/PPD42NS.pdf
 */

int pin = 8;
unsigned long duration;
unsigned long starttime;
unsigned long sampletime_ms = 1000;//sampe 1s ;
unsigned long lowpulseoccupancy = 0;
float ratio = 0;
float concentration = 0;
int gLed = 7;
int yLed = 6;
int rLed = 5;

void setup() {
  Serial.begin(9600);
  pinMode(8,INPUT);
  pinMode(gLed,OUTPUT);
  pinMode(yLed,OUTPUT);
  pinMode(rLed,OUTPUT);
  starttime = millis();//get the current time;
}

void loop() {
  duration = pulseIn(pin, LOW);
  lowpulseoccupancy = lowpulseoccupancy+duration;

  if ((millis()-starttime) > sampletime_ms)//if the sampel time == 30s
  {
    ratio = lowpulseoccupancy/(sampletime_ms*10.0);  // Integer percentage 0=>100
    concentration = 1.1*pow(ratio,3)-3.8*pow(ratio,2)+520*ratio+0.62; // using spec sheet curve
    Serial.print("concentration = ");
    Serial.print(concentration);
    Serial.print(" pcs/0.01cf  -  ");
    if (concentration < 1.0) {
     Serial.println("It's a smokeless and dustless environment"); 
     digitalWrite(gLed, HIGH);
     digitalWrite(yLed, LOW);
     digitalWrite(rLed, LOW);
  }
    if (concentration > 1.0 && concentration < 20000) {
     Serial.println("It's probably only you blowing air to the sensor :)"); 
     digitalWrite(gLed, HIGH);
     digitalWrite(yLed, LOW);
     digitalWrite(rLed, LOW);
    }
    
    if (concentration > 20000 && concentration < 315000) {
     Serial.println("Smokes from matches detected!"); 
     digitalWrite(gLed, LOW);
     digitalWrite(yLed, HIGH);
     digitalWrite(rLed, LOW);
    }
      if (concentration > 315000) {
     Serial.println("Smokes from cigarettes detected! Or It might be a huge fire! Beware!"); 
     digitalWrite(gLed, LOW);
     digitalWrite(yLed, LOW);
     digitalWrite(rLed, HIGH);
  }
    
    lowpulseoccupancy = 0;
    starttime = millis();
  }
}

[AnneFR]

@epierre hi, could remove some doubts regarding the mq131 sensor?
thanks,
Anne

[epierre]

@alexsh1 said:

(shinyei ppd42ns)

I corrected the following sketch which had bad yg/m3 to ppm conversion thanks to LouiS22 from Domoticz forum remark (type conversion errors leading to 0 values).

https://github.com/empierre/arduino/blob/master/DustSensor_SamYoung_DSM501.ino

I guess I'll have to do the same here (but I lack time...):
DustSensor_Shinyei_PPD42NS.ino

[alexsh1]

@epierre Thanks - I'll have another go at Shinyei PPD42NS sketch once I have time. Ideally, I'd like to combine it with MH-Z14A sketch.

[epierre]

@alexsh1 which is a good idea, also a temp/him is quite usefull though I didn't added the impact in the formulas so far.

[alexsh1]

@epierre I have combined the two sketches - works just fine, but need to find a spare temp sensor.The hardware setup looks messy so adding an extra i2c sensor will complicate it even more. I'll come back with the combined three-in-one sketch shortly.

BTW, this

gw.send(msgPM25.set("ppm"));

still throws the following error. What version MySensors are you using?

 MySensors: Unknown/Invalid sensor type (43)

[alexsh1]

@epierre I started looking at the formula you have used in ppmv calculation. Why do you need ppmv? All values in EPA or Europe are in μg/m3.

The ppmv equation is:

ppmv = mg/m^3 * (0.08205*T)/M 

T = atmospheric temperature in kelvins = 273.15 + °C
M = molecular weight of the air pollutant = 28.97
(http://www.engineeringtoolbox.com/molecular-mass-air-d_679.html - this is a good link)
0.08205 = Universal Gas Law constant in atm·l/(mol·K)

Your code for this equation is:

ppmv=(float)(((concentrationPM25*0.0283168)/100) * ((0.08205*temp)/0.01))/1000;

Now, I think it should be as follows:

1. temp = °C + 273.15

int temp=273.15 + 22;

22C - is a typical temp inside though the intention is to use a sensor

2. The amended ppmv equation is going to be:

ppmv=(((concentrationPM25*0.0283168)/100) * ((0.08205*temp)/28.97))/1000;

I have not changed 0.0283168 /100 - not sure that this is. And the whole thing is divided by 1000? why?

IMPORTANT UPDATE:

I have just received the following result:

PM10: 7373

send: 11-11-0-0 s=0,c=1,t=37,pt=7,l=5,sg=0,st=ok:1.744

If I use the following web-site http://www.herramientasingenieria.com/onlinecalc/ppm-mg_m3.php and the result is
mg/m3 = 7373 * 0.283168/100 = 2.08 mg/m3
The molecular weight is 28.97 for dry air

2.08 mg/m3 is equivalent to 1.74ppm for a gas with molecular weight=28.97 Pressure=1013.25, Temperature=22C 

Success!
Now I have found a spare BMP280 (temp and pressure sensor) which I can use here.
Additionally, I need to use 24-h and 1 year averages - https://www3.epa.gov/airquality/particlepollution/2012/decfsstandards.pdf

Stay tuned!

[epierre]

@alexsh1 said:

@epierre I started looking at the formula you have used in ppmv calculation. Why do you need ppmv? All values in EPA or Europe are in μg/m3.

because domoticz only knows ppm... and many AIQ like use only that except for particles.

1. temp = °C + 273.15
   int temp=273.15 + 22;
   22C - is a typical temp inside though the intention is to use a sensor

not for me ;-)

2. The amended ppmv equation is going to be:
   ppmv=(((concentrationPM250.0283168)/100) * ((0.08205temp)/28.97))/1000;

I have not changed 0.0283168 /100 - not sure that this is. And the whole thing is divided by 1000? why?

was a volume conversion

The molecular weight is 28.97 for dry air

2.08 mg/m3 is equivalent to 1.74ppm for a gas with molecular weight=28.97 Pressure=1013.25, Temperature=22C 

Success!

success for the mysensors value ?

MySensors: Unknown/Invalid sensor type (43)

Domoticz doesn't recognize this command... I use 1.5.x but I have my own gateway to domoticz

[alexsh1]

@epierre Yes, all works fine now. I modified the combined sketch and here is the final result.