Air Quality Sensor
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In MQ135 sensor's datasheet , which line on the curve is used to find out the concentration of benzene?
@bhavika said:
In MQ135 sensor's datasheet , which line on the curve is used to find out the concentration of benzene?
MQ135 is sensitive to particle size, benzene is one of these. I rememer someone who used the chinese datasheet and found a chinese to translate it.
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@epierre I am testing a stripped-down version of your code from your AirQuality-MQ135.ino. I stripped it to make it run just stand-alone.
What I don't understand is how to do the calibration. When I run it in outside environment (with 10k resistor), I get these values:valr 223 Vrl / Rs / ratio:13387 / 20875.00 / 0.00What would be the next step for calibration?
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@epierre I am testing a stripped-down version of your code from your AirQuality-MQ135.ino. I stripped it to make it run just stand-alone.
What I don't understand is how to do the calibration. When I run it in outside environment (with 10k resistor), I get these values:valr 223 Vrl / Rs / ratio:13387 / 20875.00 / 0.00What would be the next step for calibration?
@supersjimmie replace MQ135_DEFAULTRO by your value 20875 in the sketch
z-wave - Vera -> Domoticz
rfx - Domoticz <- MyDomoAtHome <- Imperihome
mysensors -> mysensors-gw -> Domoticz -
@supersjimmie replace MQ135_DEFAULTRO by your value 20875 in the sketch
@epierre Thanks, I thought it would be something like that, but that didn't work.
I then gotvalr 242 Vrl / Rs / ratio:5464 / 8520.00 / 0.00Nothing like around 400ppm.
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yes for the code must be updated, the value is the CO2 (or something else) detected above the 399 in atmosphere
gw.send(msg.set(MQ135_DEFAULTPPM+(int)ceil(valAIQ))); -
Thanks, but when calibrating something strange happens when I put the module outside:
valr 270 Vrl / Rs / ratio / ppm 61355 / 95673.00 / 0.00 / 399.00 valr 265 Vrl / Rs / ratio / ppm 62928 / 98126.00 / 0.00 / 399.00 valr 260 Vrl / Rs / ratio / ppm 64561 / 100673.00 / 0.00 / 399.00 valr 256 Vrl / Rs / ratio / ppm 378 / 589.00 / 0.00 / 399.00 valr 252 Vrl / Rs / ratio / ppm 1773 / 2764.00 / 0.00 / 399.00As you can see, the valr decreases slowly, but suddenly Vlr and Rs jump over.
Vlr is the value of 'val', which is: uint16_t val = ((float)22000*(1023-valr)/valr);
uint16_t is 16bit, so max 65535. It looks like my environment needs more than that?
(in fact, your code defines the defaultro as 68550, which is also too much for a uint16?) -
Thanks, but when calibrating something strange happens when I put the module outside:
valr 270 Vrl / Rs / ratio / ppm 61355 / 95673.00 / 0.00 / 399.00 valr 265 Vrl / Rs / ratio / ppm 62928 / 98126.00 / 0.00 / 399.00 valr 260 Vrl / Rs / ratio / ppm 64561 / 100673.00 / 0.00 / 399.00 valr 256 Vrl / Rs / ratio / ppm 378 / 589.00 / 0.00 / 399.00 valr 252 Vrl / Rs / ratio / ppm 1773 / 2764.00 / 0.00 / 399.00As you can see, the valr decreases slowly, but suddenly Vlr and Rs jump over.
Vlr is the value of 'val', which is: uint16_t val = ((float)22000*(1023-valr)/valr);
uint16_t is 16bit, so max 65535. It looks like my environment needs more than that?
(in fact, your code defines the defaultro as 68550, which is also too much for a uint16?)@supersjimmie said:
Vlr is the value of 'val', which is: uint16_t val = ((float)22000*(1023-valr)/valr);
yes and this is why I did rewrite it to https://github.com/empierre/arduino/blob/master/AirQuality-Multiple_Gas_Sensor1_4.ino but did not updated this one...
z-wave - Vera -> Domoticz
rfx - Domoticz <- MyDomoAtHome <- Imperihome
mysensors -> mysensors-gw -> Domoticz -
@supersjimmie said:
Vlr is the value of 'val', which is: uint16_t val = ((float)22000*(1023-valr)/valr);
yes and this is why I did rewrite it to https://github.com/empierre/arduino/blob/master/AirQuality-Multiple_Gas_Sensor1_4.ino but did not updated this one...
@epierre I striped-down that AirQuality-Multiple_Gas_Sensor1_4.ino to use only MQ135.
When used inside, the analogRead is 473, so a reasonble value.
But the MQCalibration function returns 0. Which means the MQResistanceCalculation also returns 0.MQResistenceCalculation only does one calc:
return (long)((long)(1024 * 1000 * (long)rl_value)/raw_adc-(long)rl_value);
rl_value = float RL4 = 0.990
raw_adc = 473 (measured as said above)
(1024 * 1000 * 0.990) / 473 - 0.990 = 2142.266
I checked that raw_adc is filled with the correct value (to be sure it is not lost somewhere).What looks to fix this, I changed everything to float . So:
return (float)((float)(1024 .* 1000. * (float)rl_value)/raw_adc-(float)rl_value);
Which can be simplyfied as:
return ((1024 * 1000*rl_value)/raw_adc-rl_value);
I went to float, because the function is created as float MQResistenceCalculation.This now gives some ppm values that are within a reasonable range (about 2000 here).
Now I have to figure out how to do calibration on this method again...
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looks like I have to rework something... but not in the todo list right now... Imperihome is now back on top, and Particle on lipo/solar also...
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@tantt2810 as explained above, if the datasheet has a logarithmic scale, you can use the power regression to approximate the curve. One tool for example to do this calculus:http://www.xuru.org/rt/powr.asp
for a sensor discussed above I read this on the datasheet:
H2
1.3 50
0.8 100
0.28 400
0.16 1000
0.05 4000The xuru website gives me this:
y = 73.59123879 x-1.355617483
Residual Sum of Squares: rss = 87393.44418and thus I have::
H2Curve[3] = {73.5912, -1.355617};z-wave - Vera -> Domoticz
rfx - Domoticz <- MyDomoAtHome <- Imperihome
mysensors -> mysensors-gw -> Domoticz -
@tantt2810 as explained above, if the datasheet has a logarithmic scale, you can use the power regression to approximate the curve. One tool for example to do this calculus:http://www.xuru.org/rt/powr.asp
for a sensor discussed above I read this on the datasheet:
H2
1.3 50
0.8 100
0.28 400
0.16 1000
0.05 4000The xuru website gives me this:
y = 73.59123879 x-1.355617483
Residual Sum of Squares: rss = 87393.44418and thus I have::
H2Curve[3] = {73.5912, -1.355617}; -
So tonight with these new formulae, I updated my mega sketch to get :
MQ2 :LPG :0ppm CO :0ppm SMOKE :0ppm MQ6 :LPG :0ppm CH4 :0ppm MQ131 :CL2 :1ppm O3 :1ppm TGS2600:H2 :0ppm C2H5OH:0ppm C4H10 :0ppmGoing through the "clean air calibation" I have:
float MQResistanceCalculation(int raw_adc) { return ( ((float)RL_VALUE*(1023-raw_adc)/raw_adc)); }Here are the readings without:
MQ2:5.28 MQ6:36.94 MQ131:3.61 TGS2600:0.04and with all is 0... BTW...
What do you think of that ? nothing indicated that MQ6 should be so big, and tgs so low... same for MQ131 that should be 100k-200k per datasheet....
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Hello,
I'm don't understand the recipe below. Why RL_Value(Load Resistance)(1023-raw_adc)/raw_adc)? Can you explain for me?
Thank you so much !!!
/***************** MQResistanceCalculation ****************************************
Input: raw_adc - raw value read from adc, which represents the voltage
Output: the calculated sensor resistance
Remarks: The sensor and the load resistor forms a voltage divider. Given the voltage
across the load resistor and its resistance, the resistance of the sensor
could be derived.
***********************************************************************************/
float MQ2::MQResistanceCalculation(int raw_adc)
{
return ( ((float)RL_VALUE(1023-raw_adc)/raw_adc));
} -
hi
i am new here.
sorry i am a little confused by with these new formulate.
is it the key for module?
@jenbaker said:
sorry i am a little confused by with these new formulate.
is it the key for module?
if you have a module the datasheet gives you the values, yes. Remember this is their """""generic"""" calibration, in fact they all copy the other so don't expect your MQ** would follow this by the letter...
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Hello,
I'm don't understand the recipe below. Why RL_Value(Load Resistance)(1023-raw_adc)/raw_adc)? Can you explain for me?
Thank you so much !!!
/***************** MQResistanceCalculation ****************************************
Input: raw_adc - raw value read from adc, which represents the voltage
Output: the calculated sensor resistance
Remarks: The sensor and the load resistor forms a voltage divider. Given the voltage
across the load resistor and its resistance, the resistance of the sensor
could be derived.
***********************************************************************************/
float MQ2::MQResistanceCalculation(int raw_adc)
{
return ( ((float)RL_VALUE(1023-raw_adc)/raw_adc));
}@tantt2810 said:
Hello,
I'm don't understand the recipe below. Why RL_Value(Load Resistance)(1023-raw_adc)/raw_adc)? Can you explain for me?
Thank you so much !!!
Input: raw_adc - raw value read from adc, which represents the voltage
Output: the calculated sensor resistance
Remarks: The sensor and the load resistor forms a voltage divider. Given the voltage
across the load resistor and its resistance, the resistance of the sensor
could be derived.
float MQ2::MQResistanceCalculation(int raw_adc)
RL_VALUE(1023-raw_adc)/raw_adc));in fact it is above described, you have a voltage, you want a resistance.
https://learn.sparkfun.com/tutorials/voltage-dividersdatasheet needs a value which is the Rs/Ro (called here RL) where
Ro: sensor resistance at 100ppm of NH3 in the clean air.
Rs:sensor resistance at various concentrations of gaseshere 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);z-wave - Vera -> Domoticz
rfx - Domoticz <- MyDomoAtHome <- Imperihome
mysensors -> mysensors-gw -> Domoticz -
@tantt2810 said:
Hello,
I'm don't understand the recipe below. Why RL_Value(Load Resistance)(1023-raw_adc)/raw_adc)? Can you explain for me?
Thank you so much !!!
Input: raw_adc - raw value read from adc, which represents the voltage
Output: the calculated sensor resistance
Remarks: The sensor and the load resistor forms a voltage divider. Given the voltage
across the load resistor and its resistance, the resistance of the sensor
could be derived.
float MQ2::MQResistanceCalculation(int raw_adc)
RL_VALUE(1023-raw_adc)/raw_adc));in fact it is above described, you have a voltage, you want a resistance.
https://learn.sparkfun.com/tutorials/voltage-dividersdatasheet needs a value which is the Rs/Ro (called here RL) where
Ro: sensor resistance at 100ppm of NH3 in the clean air.
Rs:sensor resistance at various concentrations of gaseshere 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);@epierre Hi you,
I think the Rs/Ro is not RL. In the datasheet RL=5kOhm. As I know it is a resistance on board Arduino, and we set it 5kOhm. Is it right? I also don't know why we set it equal 5kOhm. =))
And why 20000 is in "float Rs = 20000 * ( 5.00 - Vrl) / Vrl ; // Ohm" ?
Please help me clearly. Thank you so much !!! -
Hello, I'm working with an MQ-136 sensor, and am interested in measuring H2S and/or SO2 concentrations. I've got a simple sketch written which gives me a fairly consistent value on the serial monitor, but I've tried to run the multiple gas sensor sketch both complete and I also tried picking apart the sketch just to include MQ-136 related variables and algorithms, but I can't get it to work. It's showing too many errors to list here. Does anyone have simple conversions from the serial outputs to usable values for various gases that this sensor can measure?
