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I wouldn't say it's the same. Low cost air quality measurement is difficult. PM is tricky but almost manageable with laser scattering, toxic gases at typical i

by aulin 3y ago

I wouldn't say it's the same. Low cost air quality measurement is difficult. PM is tricky but almost manageable with laser scattering, toxic gases at typical inquinant concentrations are almost impossible to get right with electrochemical sensors, no matter how much money you throw at them. Weight measurement is easy, they could give you precise and accurate results but most customer base doesn't understand anything of physical quantities measurement and would panic they gained 50g in a minute if they showed up the real fluctuating values by stepping on the scale twice.

q87b 3y ago
Easy solution though, just limit the scale's display to a magnitude that it can accurately measure reproducible.
- riskable 3y ago
  This is how the market for scales works: You buy a scale for the weight class you're planning on measuring. For example, you can't buy a scale made for weighing humans and expect it to be useful for weighing herbs or jewelry. It's because of how load cells (and scales) are manufactured. They're made for weight classes like 100g, 1kg, 2kg, 3kg, 5kg, 10kg, etc. So to make a scale for a particular weight you pick the load cells you'll need for the range you want. Higher quality scales don't select higher quality load cells; they're all the same (reasonable quality) for the most part! Instead they just use more load cells and just take an average of all their values, multiplied by the number of cells, to measure weight. So if you want a damned accurate industrial scale for measuring weights around 1kg you'd use like twelve 100g load cells rather than a single 2kg load cell or two 1kg load cells. Of course, then the hard part becomes, "how do I distribute this weight perfectly evenly across all of them?" so you have to take tolerances into account to make sure that at no point can weighing part of your scale rub against the side of its container or accidentally get something wedged between the scale part and the case. There's loads of other things to consider as well but for the most part the accuracy of the scale is a factor of how many load cells its using, not the quality/manufacturing tolerances of the load cells themselves. Because even with the most precise manufacturing methods load cells will still drift and be impacted by temperature. All you can do is calibrate regularly, test them, and hope for the best (or use a completely different technology).
- aulin 3y ago
  Easy solution if your customer understands accuracy. They don't. They want the highest resolution so they can see their 10 gram progress when dieting. But they want the measurement to be stable enough to not cause them too much anxiety.
  - pnt12 3y ago
    >They want the highest resolution so they can see their 10 gram progress when dieting. Do they? 100g is already quite granular, and you can lose that in a day. I have two scales which are giving me different measures - I've been weighting myself and assume I'm in the middle of both. It's a bit annoying, but works for my goals.
jjoonathan 3y ago
No, they lie to cover up the cheapness and inadequacy of their flextures. "Users can't handle the truth" is a bullshit excuse and you should be ashamed for making it.
- pagana 3y ago
  That seems like an unnecessary escalation. It's possible that OP has observed what they're describing before.
  - jjoonathan 3y ago
    Yeah, but I've observed patronizing excuses for corporate misbehavior before and they trigger me a bit, what can I say.
    - aulin 3y ago
      My point was not to patronize anyone. My point was that one measurement (air quality) is difficult from a physics and technology standpoint. Low cost accurate air quality measurement at consumer level is not possible no matter how much you are willing to spend. The other one, weight, is easy enough and if it's not accurate it is for commercial reasons. Either because what I said or what you said. Both could be true.
- riskable 3y ago
  Whoah there: Your typical (cheap) consumer scale will have four (50kg) load cells hooked up to an hx711 (or clone) and the cheapest microcontroller the manufacturer could find that can drive an LCD directly. Even the cheapest load cell is pretty damned accurate and the average between the four of them is going to be accurate within 0.1kg (~0.22lbs). Having said that, load cells have this problem where their values drift over time but only if there's a constant weight on them. If you step off the scale and allow it to re-calibrate itself (which is what it does every time it turns on) there will definitely not be enough drift to matter from a, "how much do I weigh?" standpoint. All it takes is like 2 seconds without weight for a load cell to "settle down" back to its not-actually-very-noisy resting position. I've tested loads of the cheapest possible load cells money could buy along with some load cells I took from an expensive transparent scale that had cracked. They were all far more accurate than I was expecting and any differences between them was negligible. The longer you wait before weighing something the less accurate it'll be but only by tiny, negligible amounts. Like, if you're weighing something that's 100kg and you waited ten minutes after calibration (something most scales won't allow because they all have something like a 30-second timeout) you'd still get a value that's within 0.01 of 100kg. They don't drift that much at rest unless there's some serious temperature variations or you had something resting on the scale the entire time.

by aulin 3y ago

q87b 3y ago

Easy solution though, just limit the scale's display to a magnitude that it can accurately measure reproducible.

riskable 3y ago
This is how the market for scales works: You buy a scale for the weight class you're planning on measuring. For example, you can't buy a scale made for weighing humans and expect it to be useful for weighing herbs or jewelry. It's because of how load cells (and scales) are manufactured. They're made for weight classes like 100g, 1kg, 2kg, 3kg, 5kg, 10kg, etc. So to make a scale for a particular weight you pick the load cells you'll need for the range you want. Higher quality scales don't select higher quality load cells; they're all the same (reasonable quality) for the most part! Instead they just use more load cells and just take an average of all their values, multiplied by the number of cells, to measure weight. So if you want a damned accurate industrial scale for measuring weights around 1kg you'd use like twelve 100g load cells rather than a single 2kg load cell or two 1kg load cells. Of course, then the hard part becomes, "how do I distribute this weight perfectly evenly across all of them?" so you have to take tolerances into account to make sure that at no point can weighing part of your scale rub against the side of its container or accidentally get something wedged between the scale part and the case. There's loads of other things to consider as well but for the most part the accuracy of the scale is a factor of how many load cells its using, not the quality/manufacturing tolerances of the load cells themselves. Because even with the most precise manufacturing methods load cells will still drift and be impacted by temperature. All you can do is calibrate regularly, test them, and hope for the best (or use a completely different technology).
aulin 3y ago
Easy solution if your customer understands accuracy. They don't. They want the highest resolution so they can see their 10 gram progress when dieting. But they want the measurement to be stable enough to not cause them too much anxiety.
- pnt12 3y ago
  >They want the highest resolution so they can see their 10 gram progress when dieting. Do they? 100g is already quite granular, and you can lose that in a day. I have two scales which are giving me different measures - I've been weighting myself and assume I'm in the middle of both. It's a bit annoying, but works for my goals.

jjoonathan 3y ago

No, they lie to cover up the cheapness and inadequacy of their flextures. "Users can't handle the truth" is a bullshit excuse and you should be ashamed for making it.

pagana 3y ago
That seems like an unnecessary escalation. It's possible that OP has observed what they're describing before.
- jjoonathan 3y ago
  Yeah, but I've observed patronizing excuses for corporate misbehavior before and they trigger me a bit, what can I say.
  - aulin 3y ago
    My point was not to patronize anyone. My point was that one measurement (air quality) is difficult from a physics and technology standpoint. Low cost accurate air quality measurement at consumer level is not possible no matter how much you are willing to spend. The other one, weight, is easy enough and if it's not accurate it is for commercial reasons. Either because what I said or what you said. Both could be true.
riskable 3y ago
Whoah there: Your typical (cheap) consumer scale will have four (50kg) load cells hooked up to an hx711 (or clone) and the cheapest microcontroller the manufacturer could find that can drive an LCD directly. Even the cheapest load cell is pretty damned accurate and the average between the four of them is going to be accurate within 0.1kg (~0.22lbs). Having said that, load cells have this problem where their values drift over time but only if there's a constant weight on them. If you step off the scale and allow it to re-calibrate itself (which is what it does every time it turns on) there will definitely not be enough drift to matter from a, "how much do I weigh?" standpoint. All it takes is like 2 seconds without weight for a load cell to "settle down" back to its not-actually-very-noisy resting position. I've tested loads of the cheapest possible load cells money could buy along with some load cells I took from an expensive transparent scale that had cracked. They were all far more accurate than I was expecting and any differences between them was negligible. The longer you wait before weighing something the less accurate it'll be but only by tiny, negligible amounts. Like, if you're weighing something that's 100kg and you waited ten minutes after calibration (something most scales won't allow because they all have something like a 30-second timeout) you'd still get a value that's within 0.01 of 100kg. They don't drift that much at rest unless there's some serious temperature variations or you had something resting on the scale the entire time.