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

Post by mrguyorama » Thu, Jun 08, 2023, 4:51 PM UTC

riskable wrote: post #176

jjoonathan wrote: post #169

Earlier quoted context omitted.

When you cheap out on flextures, it's not the accuracy under ideal perpendicular loads that goes, and cheap housings struggle to provide ideal perpendicular loads. These are not particularly difficult things to get right, but the construction of even relatively expensive ($150) scales is so cheap that it screws this up and results in >1% deviation over the surface of the scale if you bypass the digital cheating mecha…

What the heck are you talking about? The only flexure to speak of is within the load cell itself and... Can you even call that a flexure? It's a teeny tiny strain gauge mounted on a piece of steel that's going to bend ever so slightly when a weight is put on it. Even the cheapest load cells are precision-manufactured well within the tolerances necessary for the strain gauge to give you damned accurate results. I've n…

Post by mrguyorama » Thu, Jun 08, 2023, 4:58 PM UTC

ilyt wrote: post #107

Luc wrote: post #71

Earlier quoted context omitted.

I have looked for this myself, and come to the conclusion that it doesn't exist unless you're willing to buy a second hand, bulky hospital scale. Measuring human weight is harder than it seems (we don't stay still). Most scales use a strain gauge sensor that detects bending of a metal arm through changes in resistance. It's pretty noisy and needs averaging. There's some integrated circuits to relate the resistance to…

My $10 +decade old one CR2032 powered one does that just fine. Accurate enough for weight control (doesn't drift from day to day), no "stuck weight" problem mentioned either. Just need to wait 2 seconds for self calibration to finish

Post by 83 » Thu, Jun 08, 2023, 5:23 PM UTC

mnw21cam wrote: post #117

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…

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.

Post by rkagerer » Thu, Jun 08, 2023, 5:37 PM UTC

Luc wrote: post #71

sidmitra wrote: post #19

Earlier quoted context omitted.

Yes, but do you(or someone else) have a recommendation of which scale does not do this? Something that's not consumer grade, but not "enterprise cost"

I have looked for this myself, and come to the conclusion that it doesn't exist unless you're willing to buy a second hand, bulky hospital scale. Measuring human weight is harder than it seems (we don't stay still). Most scales use a strain gauge sensor that detects bending of a metal arm through changes in resistance. It's pretty noisy and needs averaging. There's some integrated circuits to relate the resistance to…

Post by ilyt » Thu, Jun 08, 2023, 5:57 PM UTC

mrguyorama wrote: post #183

ilyt wrote: post #107

Earlier quoted context omitted.

My $10 +decade old one CR2032 powered one does that just fine. Accurate enough for weight control (doesn't drift from day to day), no "stuck weight" problem mentioned either. Just need to wait 2 seconds for self calibration to finish

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.