4 SO2, o3 eggs. One working. URGENT


Hi, we’ve just got four so2-o3 eggs, ordered 9th Sept. They are hooked up, publishing to opensensors:

egg nos.: egg008012a84a8880130, egg00802a54700b0123, egg0080287351180112, egg00802a84a90a0130.

They are all measuring SO2, only one measuring O3. These were due for deployment on a project next week monitoring ozone levels. Any suggestions? Please reply asap.


It appears that your eggs are working fine. Here’s a short narrative of the steps that you can go through to determine that in case you ever need to sleuth this down in the future.

Egg data can be downloaded from here. The first serial number in your list is incorrect - a “1” has been added in. egg00802a84a8880130 should be used instead.

Once you have downloaded the data, you can graph it here by uploading the files that you get from the download web page above. Just select the four files in your file browser/chooser. It takes about a minute to crunch the data, and then you will be able to choose some values to display. Under “Primary plot” choose SO2 and say “add to plot”. You should see something like this after half a minute. You can clearly see that all the units are reporting, as you say, and they are going through a typical warm up cycle, stabilizing towards the end of the plot. So I’d guess you turned the units on today.

Now select O3 under “primary plot”. You should see something like this. All the Eggs are reporting data, although at very different levels. But interestingly, one seems very low, and hidden by the other plots. Now click on each egg in the legend to remove it from the plot, until you just have one, Egg …a0130. It takes several seconds to react to each click, because there is a lot of data.

Hmmm … that’s interesting. Although that egg is reporting data, it’s always zero. Let’s look into that a little more. Under “Primary Plot”, choose o3[V] and say “add to plot”. This shows us the voltages, rather than the reported concentrations, and will show if a sensor is broken and reading zero.

The results should look something like this. Again, you can click on the legend to remove Eggs you don’t want.

We can see that the egg is actually reporting a voltage. That means that the sensor is working, but it is not detecting enough Ozone to report a concentration. Again, we see the very typical warm up cycle in the beginning. (Aside: Be a little careful interpreting the raw voltage values. Sensors are individually calibrated, so they aren’t necessarily comparable).

So why might the unit not be reporting data? The most likely reason is that it is working fine. All sensors have some variance built in. Ozone measures PPB (per billion), which is an extremely low concentration, and there is a margin of error. So it is quite possible for there to be a small (eg: 10ppb) of ozone, and the sensor to report 0, and be working completely correctly.

In conclusion, I would say that your units are working fine, they should be left on for a day or so to warm up, and seem to be reporting data correctly. Does this answer your questions?


Not really, dirk. One egg is measuring 40ish ppb , other three, zero. All four giving so2. Would warm up time exceed 5hours or so? If so, why( just out of interste). Ive already succeasfully grabbd data from opensensors.io…i just need to know qhu o3 readings so low


Can you share the data downloads you have via email? I just pulled the data again from the eggs 2 minutes ago and I’m just not seeing anything consistent with ‘other three, zero’. Can you share your data over email (support@wickeddevice.com) so we can get to the bottom of why you are seeing zeros.


Dirk, any progress with this? I sent you a data file, and no response in a few days. At the moment, I have three eggs in my office, reading ozone values of 80+ppb, 0.0ppb, 9.7ppb, and one in a workshop downstairs reading 0.0ppb. I expected a degree of uncertainty in the eggs, but not to this degree. they have been running for 2.5 days at this stage. Please advise asap.


Hi Liz. My apologies for the slower than usual reply. I’m on the road right now, which causes me to lag. Please can you review the documents here for information about the variation of the sensors. This is the web page of the sensor manufacturer, Spec, and is all the information we have. I’ll respond to you directly via email as well when I get a chance later today.


Hi Dirk. I looked through the documents. It appears I’ll have to recalibrate the eggs, getting new bias and slope for voltage to ppb conversion. If you have any information on this please send on. Yes, I’m writing custom software for visualising the data.


Dirk -can you point me towards information on calibrating o3/so2 sensors? Thanks


Let me check that I understand what you are asking, as this is quite a large topic. There is a temperature dependent zero calibration and a temperature INdependent sensitivity, and also a sample window (number of samples).

The Egg user interface has to enter calibrated information (change all the configuration parameters). Do you have a temp chamber with a zero air filter? Also, are you available on the phone - I’d like to get to the bottom of what you are actually asking. If so, please email it to me outside of the forum.