I'm wanting to build an environment monitor with an arduino and wanted to add some gas sensors to monitor the air quality. I want to know which sensors should I get. I was looking at the MQ sensors since they seem to be pretty common but I'm also looking at maybe getting the MICS sensors, http://sgx.cdistore.com/
Which one do you guys think I should get to help monitor outdoor air quality?
Any help?
The SGX sensors look like standard electrochemical senors. The data sheets are really good as they give you a lot information regarding the cross-interferences. The solder process seems to be a little bit complicated. Most probably not possible at home.
Regarding your question to measure "air quality". You need to define what you mean by "air quality" or nobody will be able to help you.
Well more measuring Carbon Monoxide and Nitrogen Dioxide and maybe ozone. It's more about the sensors in general which would be more accurate or easier to use. Also if I understand right these sensors won't be able to give me a accurate PPM of the gases in the air but more just when the concentration of these gases changes.
The electrochemical sensors you found are all able to measure in the ppm range. The actual measurement range depends on the measurement species. As for all electrochemical sensors you need to calibrate the sensor in order to get a reasonable measurement. Typically you calibrate the zero point as well as a "high" concentration. Without the calibration you can't even measure changes in the concentration quantitatively (as you don't know which change in measurement signal corresponds to which change in concentration).
hmmm well how can someone at home calibrate these sensors and also the data sheet said that the accuracy will change over time if they are exposed to a gas over a long period.
You need test gas for the calibration. But this you can buy. I have some practical experience with the Dräger sensors. They are used for measuring dangerous gases in order to avoid that you are exposed to critical levels (and they also offer the test/calibration gases). They schedule a daily check of the calibration and a 3 month recalibration interval. Normally you recalibrate no less then once per month. You definitely see the measurement values drift over time. For non safety relevant tasks I would recalibrate every month and trust the sensor in between (recalibration is not much more complicated then checking the calibration).
One example why this calibration is necessary. We once exchanged two sensors in between two measurement units (same type, roughly same age und usage and if I remember correctly they were sensors for explosive gases). The measurement value had an offset of around 30% of the measurement range and the linearity was off a factor of 2. I have no clue how much of this difference is caused by unit to unit differences and how much on different aging/usage. But it clearly states that the sensor is more or less useless without calibration.
For some gases NDIR sensors are much better but also much expensive.