Inexpensive Ozone sensor ?

john_s

I'm looking for some low cost O3 handheld meter that can sense indoor environment and alarm when it's over certain level.
A quick search (see ozonesolutions.com) has confirmed that there's very little below $500 range.

Did anybody try a diy approach or knows where to start?

Thanks,
John

RDL2004

There is an MQ131 ozone sensor which looks like it's from the same series as the CH4, LPG, etc. sensors that Parallax sells. These use a heater, so power requirements may be an issue for portable use. Not an actual meter though, so you'd have to diy something.

john_s

That one looks quite right - any ideas what might be the life span of the O3 sensors?

erco

I also thought Parallax sold an O3 sensor, but I don't see one right now, and curiously, the "search" feature isn't working. http://www.parallax.com/catalog/sensors/gas

But they are all over EBay China for $20 and "long life" is listed as a feature... http://www.ebay.com/itm/MQ131-Semiconductor-Sensor-for-Ozone-Also-Sensitive-To-O3-CL2-NO2-/181239089579

john_s

I found the answer to so called "long life" by calling the equipment manufacturer directly. According to them it's about 2 years for metal oxide sensors (I figure that MQ131 uses SnO2); while the O3 monitoring equipment using the same sensor needs to be returned for calibration every 12 months.

Tracy Allen

Before you get too deep into it, dig into comparative evaluations of these sensors. It comes down to a case of you get what you pay for--But why, right? These cheap metal oxide sensors have been of great interest to the citizen science community, projects such as the Air Quality Egg. After being lulled by the apparently nice specs, people generally come away from the metal oxide sensors disappointed and perplexed. Here is NO₂ Sensors Report.pdf, a laboratory comparison of "low cost" sensors funded by the US Environmental Protection Agency. The title refers to NO₂, but it also has a lot to say about ozone sensors, as well as others. Ozone and NO₂ sensors typically have a large cross-interference. You can see that in figure 3 of the MQ-131 data sheet. There is also sensitivity to humidity, unit to unit variability, and long term drift. It's utility will depend on what you want to do with it. It might be okay if you you are mainly interested in the presence of short term fluctuations, but not for accuracy and long term monitoring.

The next step up in cost and performance are the electrochemical cells such as the ones from Citytech and Alphasense. Those do require a potentiostat circuit, which will increase your cost an/or your electronic acumen. There are integrated solutions such as the LMP91000 analog front end from TI. For something that is going to be a portable instrument, compare an electrochemical cell at µA to a metal oxide sensor at hundreds of mA. The jury is still out on how good they really are in field apps. Interferences and drift have to be accounted for, so the manufacturers offer a range of premium sensors, at higher cost.

john_s

After some reading I can envision more and more caveats and obstacles in designing a "reliable and inexpensive" O3 detector.

I observed an erroneous operation of 2 detectors placed in what supposed to be a neutral environment inside a sealed building.

Then suddenly it came to me that it might be just because of high concentration of seemingly non-existent vapours from freshly painted walls or fuming brand new Oriented strand board (OSB) material from which the building was made just few months ago. From http://www.hc-sc.gc.ca/ewh-semt/air/in/poll/construction/organi-eng.php

"Volatile organic compounds are chemicals that easily become gases at room temperatures, and therefore are released into indoor air in homes from a variety of products."

And that is exactly what those O3-sensors are sensitive to.