How to interpret sensor data. Especially VOC
VOC data in the app appears to be in Ppm, but is labelled Pm?
My VOC data suggests VOC levels of 20-50 with the windows open, quickly rising to 300 overnight with windows closed.
As acceptable VOC levels are in the region on 100 Ppm, this would be rather concerning if correct. I'm assuming that either the sensor readings are incorrect, the units are incorrect, or I'm misinterpreting something.
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Some results from the sensors also appear a little impossible, like this one for CO2 (this happened coincidentally with the first time I've added an essential oil to the fragrance stick).
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In addition, what's with the quantised NO2 readings (all either 1 or 2)?
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Hi Fergus,
Thanks for sharing, and for including those screenshots! I'll have our engineer take a look at this and see what he advises.
He did mention that the NOx levels and VOCs are measured on an index, meaning the sensors will need to calibrate to your environment.
For the NOx, this also means that rather than a concentration output, the level is measured in a room relative to the sensor’s recent history. A NOx reading above 1 means that there are more NOx compounds compared to the average (e.g., if you've been cooking on a gas stove), while an NOx reading close to 1 means that there are (nearly) no NOx gases present, which is the case most of the time.
For the VOCs, a VOC Index above 100 means that there are more VOCs compared to the average (e.g., induced by a VOC event from cooking, cleaning, breathing, etc.) while a VOC Index below 100 means that there are fewer VOCs compared to the average (e.g., induced by fresh air from an open window, using an air purifier, etc.). Is your Briiv running overnight when the VOC levels are increasing? It does make sense that with closed windows the VOC levels would increase overnight, though if your Briiv is running I wouldn't expect it to be quite this high!
Please can you confirm which fragrance oils you used? It may be that the sensor mis-interpreted the compounds and read them as CO2, but knowing what you used means we can look into this with more clarity!
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Thank you. That's helpful.
I added a 3 of drops of lavender oil, only really enough to be detectable for a day or so. I only run the briv on level 1 overnight, as it's a bit too noisy for me on level 2 (and it's quite a big room, about 36m3).
Might I request that Briiv put together a document/FAQ explaining how the sensors work and how to interpret the values. That would be really helpful.0 -
Hi, I agree with Fergus. We should have an explanation video or something, as its not clear to me what the data actually means. For instance, I read on the Internet that VOC in the home has a safe level up to 400, but it seems you are saying it's 100. I'm a air quality noob, so need all the help I can get 😁
Also the bottom of the page won't display the information for VOC, NOx and Co² on the app, so tried turning it into landscape, but the app only stays in portrait for me.
Thanks
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With some sadness I think I have to go further Harry.
I believe that the measures on the app are utterly unreliable.
I don’t have a proper monitor to compare with. However for example, the CO2 measure reliably goes up to silly levels (3-4000ppb) if I put a few drops of essential oils in the briiv. This indicates that whatever the sensor is doing, it gets utterly confused.In addition the PM measures are so massively correlated with each other and other measures that it’s difficult to imagine that they are valid.
Briiv I think we really need you to be transparent.
I am happy to accept that I’ve bought something on kickstarter that over promises. I was pretty sceptical of the initial AI claims.In the spirit of transparency. Please let us know:
How the sensor works
How the data we see is derived
What have you done to validate the measures. What are they benchmarked against, in what circumstances
Clarify what the units are for each measure.
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Hey Guys,
Regarding the CO2 data, this is based off of training data, essentially part of the AI function in Briiv 2 Pro. We qualified the data against two different 3rd party sensors, one being a directly equivalent competitor and the other being commercially available. The sensor we use isn't created by us, but we have applied our own training data and other qualifiers. This does also mean we can only share the information that's already publicly available, but hopefully this should be helpful!
For gaseous readings (CO2, NOx, and VOCs), the sensor directly measures the number of gas molecules (or gas mass) flowing past the sensor. If the temperature and pressure conditions are significantly different from the calibration conditions, or training data, there may be a decrease in accuracy. As explained previously, both NOx and VOC levels are measured on an index. The NOx units are in a scale of 1, so any change can appear as a spike. This measurement usually sits around 0 but can spike to 3 or 4Pm. The VOC measurements are more granular and tend to sit around 100Pm and are often affected by things like gas ovens and other combustible items.
Humidity is measured relatively, which is shown as the amount of water vapour in the air relative to what the air is holding at a given temperature.
Particulate matter is measured in a similar way to the CO2, NOx, and VOCs, with a direct measure of particles flowing past the sensor being measured using optical particle counters based on laser scattering. A laser is used as a light source, and when it interacts with the particles the light is scattered to a photodetector. This detector can then convert the signal into a mass concentration value in μg/m3.
We are aware of the issue you’ve highlighted with the CO2 and we are resolving this by refining our training data. This refinement is needed due to the unique nature of the scent diffuser and how it diffuses the oil into your environment. Your first report of this was really helpful in identifying this area for improvement, so thank you for that!
I hope this clears up some of your concerns and we’re more than happy to answer any further questions!
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Apologies Fergus, I missed units! They're as follows:
Temperature: Celsius (unless in US, in which case temp. is measured in Fahrenheit)
Humidity: Relative humidity as a percentage
PMx: μg/m3
VOC: Parts per million, measured on an index
NOX: Parts per million, measured on an index
CO2: Currently listed as parts per billion, but this is being looked into as part of our refinement
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Hi,
Sorry for the slow reply, thanks for getting back to me with a detailed response! Great to have the issues acknowledged and a bit more information on how the sensor works etc.
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