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Air quality monitors: paying more does not get you more accuracy

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Re: Air quality monitors: paying more does not get you more accuracy

#191

Post by s1artibartfast »

mecsred wrote: post #152
whamlastxmas wrote: post #139

Earlier quoted context omitted.

There is zero way your body is losing a quarter pound at night through either process in a room at 70 degrees

According to [0], humans exhale about 11.0L of CO2 per hour at night. 02 in, CO2 out, so we can get mols of gas with ideal gas law and mass loss with molecular weight of carbon. If I did my math right, it comes out to 53.9g over 8 hours of sleep (if you can get that much ). (Americans: 0.118 lb/night). Not quite a quarter pound but maybe closer than you thought! [0] https://onlinelibrary.wiley.com/doi/10.1111/ina.129…

Another way to look at this is the human body stores energy in glucose and fat

Fat is 77% carbon by weight, and glucose is 40% carbon by weight (C18H34O2, C₆H₁₂O₆) . All off that carbon is broken down to CO2 and removed by the blood and lungs.

2000 calories of fat is 0.57 lbs, and 0.44lbs of carbon. 2000 calories of glucose is 1.14 lbs, and 0.46lbs of carbon.

The carbon masses are similar because the energy we use comes from breaking the carbon-carbon bonds these molecules.

This means you exhale about a 0.45 lbs of carbon per day for baseline metabolism. Each pound of fat you lose is another 0.77 lbs of carbon on top of this (over however long you lost it).

Compairing to your numbers, the approach above means you exhale 200g of carbon a day, and 8.3g/hr. If you sleep for 7 hours, that is 58 grams of carbon exhaled (pretty close).

Re: Air quality monitors: paying more does not get you more accuracy

#192

Post by mnw21cam »

83 wrote: post #185
mnw21cam wrote: post #117

Earlier quoted context omitted.

Please could you consider changing the CSS on the article. At the moment, the web page has "display: block" on almost everything, which does exactly what it says on the tin and produces a blank white page, which does make it a little difficult to read the content.

https://www.w3schools.com/cssref/pr_class_display.php

I stand corrected. But anyhow, something in the css is making it show just a blank white page.

Re: Air quality monitors: paying more does not get you more accuracy

#193

Post by sacnoradhq »

ARandomerDude wrote: post #26
sacnoradhq wrote: post #25

PMS9003M is $15 shipped, add another $6 for an Arduino and a display. You can bet the $1000 ones are Better Technology Through Beautiful Marketing and Design(tm). Anyone who pays that deserves to be separated from their money.

> Anyone who pays that deserves to be separated from their money. This a sad statement and simply untrue. The vast majority of people are in other fields, don’t know anything about hardware, and have never even heard the word “Arduino.” They don’t deserve to be scammed by con artists using fancy packaging as the hook.

Ignorance isn't something to be defended, celebrated, or excused. Find hypothetical victims elsewhere because you're preaching against the ethos of this community.

Re: Air quality monitors: paying more does not get you more accuracy

#194

Post by gsliepen »

criddell wrote: post #180
gsliepen wrote: post #134

Earlier quoted context omitted.

You don't even need the Wii itself! You can connect to the balance board via Bluetooth, and there are several libraries out there that can read out its data (and that of the Wiimotes as well).

Do they give you the same feedback about shifting your weight so that you get an acceptably small deviation between the four sensors?

Yes, you get all the data. Sometimes you can see even more than what the Wii shows you. For example, with the Wiimotes, it actually shows you the position and brightness of the top 3 or 4 infrared light sources in its field of view (from that it can derive the position of the "sensor" bar).

Re: Air quality monitors: paying more does not get you more accuracy

#195

Post by justsomehnguy »

ilyt wrote: post #189
mrguyorama wrote: post #183

Earlier quoted context omitted.

If your scale doesn't give you a different weight from one day to the next, either you are a very unusual human that doesn't ever change weight somehow, the scale only gives two sig figs, or it's lying to you. Humans are constantly changing weight, with every single breath you take.

I eat once a day and weight myself in the morning before eating or drinking anything, hence the consistency. If I weight myself in other parts of the day I get different results so it isn't just weight stuck at same level. So I can see the trend based on what I ate last few days pretty quickly. I also tested on small weight and what my kitchen weight calls 3.016KG my bathroom weight calls 3.0KG so I'm pretty sure it'…

> I also tested on small weight

You need to weight youself and then weight yourself again with something of known weight in your hands.

Floor scales usually aren't good at a small weights, though I wouldn't be surprised if they are not bad at it nowadays.

Re: Air quality monitors: paying more does not get you more accuracy

#196

Post by michaelcampbell »

hammock wrote: post #18
ahaucnx wrote: post #3

Author here. I wrote this article a few weeks ago after discovering that a well known air quality monitor in the market that retails for more than USD 1000 actually uses a PM module that costs less than USD 20. Often people assume that the more expensive, the better but as you can see in the article this is often not the case -especially when it comes to the accuracy of the monitor. If you are looking for an open sou…

The same is true of digital bathroom scales. In fact almost all consumer grade digital scales have “fake accuracy” built into the firmware that ensures the same exact weight shows up when you step on the scale twice in a row, even if you pick up e.g a quarter-pound weight in your hand the second time

The one I have at least registers ~1 or 1.5#, uhmmm, shall we say "sudden losses of weight".

Re: Air quality monitors: paying more does not get you more accuracy

#197

Post by michaelcampbell »

ImaCake wrote: post #130
mnw21cam wrote: post #121

The article is about PM2.5 consumer units, and I can well believe that price doesn't make much difference. However, I'd like to point out CO_2 - there are two kinds of sensor. One of them measures volatile organic compounds and assumes that CO_2 correlates with them, and the other actually measures CO_2. The second type costs around £40 for the raw sensor - if your sensor is cheaper than that then it probably isn't a…

If it's measuring VOCs and you live in a city then chances are it would be measuring car exhaust!

Is that bad? I mean, VOC's are VOC's regardless of source, no?

Re: Air quality monitors: paying more does not get you more accuracy

#198

Post by criddell »

gsliepen wrote: post #194
criddell wrote: post #180

Earlier quoted context omitted.

Do they give you the same feedback about shifting your weight so that you get an acceptably small deviation between the four sensors?

Yes, you get all the data. Sometimes you can see even more than what the Wii shows you. For example, with the Wiimotes, it actually shows you the position and brightness of the top 3 or 4 infrared light sources in its field of view (from that it can derive the position of the "sensor" bar).

If you have a link, it would be much appreciated. When I looked I didn’t see anything that came close to the functionality that the Balance Board had when attached to the Wii. It’s nice that the raw data is available, but unless it’s presented in a way that’s useful, it’s not that interesting.

The only project I found was FitScales and it has been dead for a long time now because Android Bluetooth changes made it incompatible with newer devices.

Re: Air quality monitors: paying more does not get you more accuracy

#199

Post by supermatt »

ahaucnx wrote: post #103
supermatt wrote: post #68

Earlier quoted context omitted.

What is the difference between the indoor/outdoor kit? It seems the outdoor one contains more sensors but is less expensive? (or is this a nod to the article in some way ;)) My partner has a pottery studio with a kiln, it can get pretty smoggy in there when a firing is taking place (its unoccupied during, but it takes a while to settle afterwards), so I want to get a sensor. Are there any add-on sensors you can think…

The outdoor kit focuses on PM measurements with dual PM modules for enhanced accuracy. The indoor kit has in addition CO2 and an optional TVOC sensor. I think for a pottery studio to measure PM and VOCs is a good start (and CO2 to see how well the ventilation works).

Thanks! Order placed :)
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