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Topic: MQ8 H2 sensor (Read 977 times) previous topic - next topic

Just curious, if anyone has experience with these.  I have one that was prewired and has a dial to set the sensitivity.  Upon first testing I noticed that I was getting a value in the 600's so I turned the dial and I can change that number and it reads around 60 now, and reaches 100+ when I introduce hydrogen.

What is the best way to translate this value to PPM? Do I need to use a PPM meter to compare values with and make a formula?

Krodal

I have made a page for those sensors : http://playground.arduino.cc/Main/MQGasSensors
But they are not very accurate, and you have to figure out the ppm for the value yourself.

Cool thanks lot of good info on that page.  Did not realize there was that many of those sensors too.  The Carbon monoxide and natural gas ones could also be handy around the house.

I think what I will do is subject it to hydrogen and take note of values, then try to ignite it (with sensor removed).  Once I get ignition then I have a scale to go by.  Are the numbers fairly consistent, or can it change with room temp and other factors?  My test method produces oxygen too if that matters.  (electrolysis)

Krodal

#3
Feb 13, 2013, 10:25 am Last Edit: Feb 13, 2013, 10:30 am by Krodal Reason: 1
After the burn-in time, they are reasonably stable.
But still for just one type of gas and indoors and for a certain air humidity.

I can't find in the datasheet how sensitive the MQ-8 is to oxygen. You have to test that.
Perhaps you need also an oxygen sensor : http://en.wikipedia.org/wiki/Oxygen_sensor
It seems that a galvanic oxygen sensor is used for simple measurements and a lambda oxygen sensor is used in cars.

The MQ-8 sensor uses 5V for the heat element. The sensor could get 50 or 60 degrees celsius (the metal on the outside). That should be avoided. Ask anyone who works at a natural-gas processing plant, they might freak out.

agmudgal

I bought the following MQ8 sensor module.
http://www.ebay.com/itm/MQ8-MQ-8-Hydrogen-Gas-Sensor-Module-for-Arduino-Gas-Sensor-module-/130897191077?ssPageName=ADME:X:AAQ:US:1123
and am using the code given at http://sandboxelectronics.com/?p=196. As per code the RL value after calibration should give values around at 10 k ohm. However I am getting very arbitary values like 20k, 100k etc. Can anyone plz explain this?
Also, about a month back, when hydrogen gas was passed over the sensor, the output(ppm) would change instantly however now the output changes very sluggishly(over several minutes). Also it does not reach the final value.
Could this be the effect of humidity or temperature? Can anyone suggest?

Hi ,

I have known arduino for long but Have not used any untill today. I am working on a project for detecting hydrogen. I will be using the MQ-8 sensor as my sensing element.

Could you please go over how to calibrate the sensor in a lab suggesting a suitable experiment.
Also, How do we convert the digital output into a ppm value.

Thank You.

epierre

Hello,

  See discussion here for calibration in open air:

http://forum.mysensors.org/topic/147/air-quality-sensor/2

  Here are my libraries with curves calculated from datasheets :

https://github.com/empierre/arduino/blob/master/AirQuality-Multiple_Gas_Sensor1_4.ino

  The MQ series are very cheap, variable, and change their values in time. It is a good entry point but no more after. Oftern the knob on the pre-assemble boards are only sed for the digital signal and its led on the board.

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