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Topic: Gas Sensors MQ Series Principle (Read 157 times) previous topic - next topic

natong

Aug 03, 2016, 09:46 am Last Edit: Aug 10, 2016, 02:12 pm by natong


The virgin sensor require to run for 24 hours (the 1st time initialization).
The heater require 5V 800mW (160mA) which is a bit hot while working.



Updated: The MQ-2 sensor resistance (RS) will vary between 3 - 30 kohm while measuring gas. I don't known what it mean. Normally when measuring the clean air, the MQ-2 sensor resistance (RS) just only 10 kohm and reduce when found the gases. Look at the graph (post #4), if RO is fixed, the RS should be lowest to 0.3 kohm. The prefered range should be 0.3 to 10 kohm.

The MQ-2 sensor resistance will working as the Voltage Dividers.




natong

#1
Aug 03, 2016, 10:02 am Last Edit: Aug 30, 2016, 07:17 am by natong
RS while measuring gas can find from VOUT and the fixed RL.
The best RL value for the entire sensitivity range can find from the equation below:







natong

#2
Aug 03, 2016, 10:17 am Last Edit: Aug 10, 2016, 01:55 pm by natong
Updated: If we choose RS (min) = 0.5 kohm and RS (max) = 10 kohm, the best RL will be 2.2 kohm.



These are the RL calculation from the RS max & min range:

RS (min) = 0.5 kohm
RS (max) = 10 kohm



The best RL value should be 2.2 kohm which give the analog VOUT 649 scales/spreads. It is the highest resolution.






natong

#3
Aug 03, 2016, 10:23 am Last Edit: Aug 10, 2016, 01:53 pm by natong
(Reserved)

natong

#4
Aug 03, 2016, 10:48 am Last Edit: Aug 10, 2016, 01:51 pm by natong
To calibration, we need to find the RO value while measuring the clean air.
Since we known the ratio of the clean air from the graph is 9.83, then we can calculate RO from the equation below:



Now we can find the concentrations (ppm) of any gas from the graph from RS/RO ratio.


natong

#5
Aug 03, 2016, 11:02 am Last Edit: Aug 10, 2016, 02:13 pm by natong
The FC-22 Gas Sensor Module use RL = 1 kohm.
These module will give 589 spreads.
The module also power down the heater by connected the resistor 5.1 ohm.










PS: Some modules use RL = 5 kohm which give 589 spreads too.




natong

#6
Aug 03, 2016, 11:39 am Last Edit: Aug 10, 2016, 02:18 pm by natong
Code: [Select]
const int MQ_PIN = A5;
const float RL = 1.0;    // kohm (FC-22 module = 1.0 kohm)
const float CLEAN_AIR_RATIO = 9.83;    // Taken from datasheet graph
float RS;    // kohm  
float RO;    // kohm
int ADC;    // 0 to 1023
  
ADC = analogRead(MQ_PIN);
RS = ( (float) RL * (1023 - ADC) / ADC );

RO = RS / CLEAN_AIR_RATIO;    // Do only once while measuring clean air.

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