GrovePi and Mq9

blademckain · December 2, 2015, 3:28pm

Hi,
someone has more detailed examples of how to use the sensor mq9 ?

how can I measure the various gases detected ( Carbon Monoxide, Coal Gas, Liquefied Gas ) ?

the value printed in the file grove_gas_sensor.py is something similar to

(&#039;sensor_value =&#039;, 43, &#039; density =&#039;, 0.0)
(&#039;sensor_value =&#039;, 43, &#039; density =&#039;, 0.0)
(&#039;sensor_value =&#039;, 43, &#039; density =&#039;, 0.0)
(&#039;sensor_value =&#039;, 44, &#039; density =&#039;, 0.0)
(&#039;sensor_value =&#039;, 47, &#039; density =&#039;, 0.0)
(&#039;sensor_value =&#039;, 45, &#039; density =&#039;, 0.0)
(&#039;sensor_value =&#039;, 45, &#039; density =&#039;, 0.0)
(&#039;sensor_value =&#039;, 43, &#039; density =&#039;, 0.0)
(&#039;sensor_value =&#039;, 43, &#039; density =&#039;, 0.0)
(&#039;sensor_value =&#039;, 43, &#039; density =&#039;, 0.0)
(&#039;sensor_value =&#039;, 39, &#039; density =&#039;, 0.0)
(&#039;sensor_value =&#039;, 45, &#039; density =&#039;, 0.0)
(&#039;sensor_value =&#039;, 45, &#039; density =&#039;, 0.0)
(&#039;sensor_value =&#039;, 39, &#039; density =&#039;, 0.0)
(&#039;sensor_value =&#039;, 45, &#039; density =&#039;, 0.0)
(&#039;sensor_value =&#039;, 45, &#039; density =&#039;, 0.0)
(&#039;sensor_value =&#039;, 45, &#039; density =&#039;, 0.0)

but what is the meaning of sensor_value and density ?

Thx to all

karan · December 8, 2015, 1:22am

The density is just the sensor value between 0-1 representing the value between 0-1023. There seems to be a bug in the code which is why you are getting 0 in density but it can be used as as threshold. Now this sensor is not used a lot for accurate measurement. The wiki on Seeed says that you can use this as a threshold: http://www.seeedstudio.com/wiki/Grove_-_Gas_Sensor(MQ9) or use approximations using the values they provide in the wiki. But even the wiki says: " However, we can’t provide a formula because the relation between ratio and concentration is nonlinear. " .

-Karan