General > General Technical Chat
You want a digital scale for What??
edy:
I read through the entire thread but didn't seem to find anyone questioning the accuracy of these scales.
1. What method do they use to measure weight?
2. How well are they calibrated?
3. Has anyone independently checked how accurate they are?
4. Does weight differ depending on where on the scale it is placed?
5. How will repeated use/battery levels, etc... change the sensitivity/accuracy over time?
It is interesting to have a tiny scale (maybe more useful to have the 500g version although not as portable, https://www.ebay.com.au/itm/Portable-500g-x-0-01g-Mini-Digital-Scale-Jewelry-Pocket-Balance-Weight-Gram/223652841494)...
....but in as much as these ARE MEASUREMENT DEVICES, the only thing that matters to me is that they actually do the job accurately, consistently and do not drift over time. Has anyone bothered to check or test this out yet?
Besides drug use, they can be used to measure out quantities of gunpowder and other materials for use in reloading ammunitions:
HighVoltage:
A few years ago, I bought a used precision KERN scale, Made in Germany, that was offered as broken.
And I thought I could easily repair it.
But it was a one-chip system with epoxy (Like in cheap calculators) and the wires were so stiff that they all broke during the disassembly process.
After that I bought a real precision scale from Mettler Toledo, Made in Switzerland.
This one can measure down to 0.1 mg and is made rock solid.
I use these scales for mixing of chemicals and measuring the loss of metal on electrodes during electrolysis.
edy:
--- Quote from: HighVoltage on August 13, 2020, 03:49:51 pm ---After that I bought a real precision scale from Mettler Toledo, Made in Switzerland.
This one can measure down to 0.1 mg and is made rock solid.
I use these scales for mixing of chemicals and measuring the loss of metal on electrodes during electrolysis.
--- End quote ---
Exactly my point... yes sure for measuring street drugs I don't think people care about the accuracy. Maybe even gunpowder grains, if you are off a bit you might not have a huge difference. So these cheap-o scales may be good enough. But how good/bad? I'd like a thorough side-by-side to a quality instrument.
Like when Dave does a side-by-side with a cheap-o $100 pocket oscilloscope's claims against one of his $2000 oscilloscopes, or the cheap-o multimeters. Sure it may be worth the price... nothing wrong there. But I'd still like to know what kind of error I'm dealing with.
jfiresto:
--- Quote from: edy on August 13, 2020, 03:30:50 pm ---I read through the entire thread but didn't seem to find anyone questioning the accuracy of these scales....
--- End quote ---
I bought a Soehnle, 1000 count, 0-2000 gram kitchen scale, back when they were still made in Switzerland. It uses a simple strain gauge sensor which over the last 27 years has drifted about 1%, so that a 1000 gram calibration weight now reads 1011 gram. Unfortunately, like most consumer scales, the end user has no way to recalibrate it.
After the drift had become noticeable, I picked up a lightly used, 21000 count, 2100 gram, Mettler Toledo industrial balance, along with a class F1, 2 kg calibration weight.
The balance has a bubble level to help you get the pan horizontal and calibration modes to adjust for long term drift and the local gravitation acceleration. You can run the balance off battery, but it is really prefers to run off AC and left on standby and stabilized. The balance is sensitive to temperature rather than supply voltage changes.
The balance has an internal calibration weight, which matched and still matches the 2 kg weight. A couple years ago, our friendly local Eichamt (office of weights and measures) compared the 2 kg weight to their standard and found them in agreement to within F2, the next looser accuracy class. So, I am reasonably confident that the balance is within somewhat more than 100 mg of true. For fun, I have made up packages so that they weigh 999.7 g, taken them to our local postal agent and watched as they eventually round up to 1000 g on their scales.
I use the balance for cooking, weighing adhesive and such, but also to weigh out my Muesli each morning. I started doing that after the Muesli makers reduced the amount they put in a box. Now when they do that, I reduce the amount I eat (and buy) proportionally. Tit for tat.
Perhaps that answer your questions.
edy:
--- Quote from: jfiresto on August 13, 2020, 05:42:33 pm ---Perhaps that answer your questions.
--- End quote ---
I'm sure the Soehnle and Mettler Toledo are much higher quality, accuracy and with a commensurately higher cost than the $8 hand-held "car remote" scales being sold on eBay. So my question is partly answered... that is, if these much better scales still drift and have inaccuracies and need some calibration and lots of adjustments for different environmental/geographic conditions, what chance does a cheap-o eBay pocket scale have?
We need a head-to-head "weigh off" with a bunch of known standards across the entire range of such a scale, and compare it to a professional quality or even medium-range cost scale. The fact that the cheap-o scale gives me readings down to the 0.01g means nothing. Here is an example:
Here is the listing, all yours for $6.99:
https://www.ebay.com/itm/Portable-LCD-Mini-Digital-Scale-Jewelry-Pocket-Balance-Weight-Gram-0-01g-500g/283934412103
Read in the description:
--- Quote ---Capacity: 0.1g~500g; 0.01~500g;0.01-200g
Division value: 0.01g/(Note: if The precision is 0.1g, but the minimum measuring weight is 0.5g
If The precision is 0.01g, but the minimum measuring weight is 0.05g and it is true of all the digital scales, pls kindly note it, tks!)
--- End quote ---
What does that even mean? I think they are saying for scales that say 0.01g you can measure down to 0.05g (so you don't expect to be measuring 0.04g and below). And for scales that say 0.1g, you can't actually measure anything less than 0.5g.
So let's take our $6.99 500g/0.01g scale and put it head-to-head with an actual quality scientific instrument and see how it does measuring everything from 0.05g up to 500g in various increments. It's easy to make a set of weights... just divide and conquer... get these standard weights and then put one or several on the scale and you can get to any possible weight range within 500g:
250g
125g
60g
30g
15g
10g
5g
2g
1g
0.5g
0.1g
0.05g
I'd like to know how accurate the $6.99 scale is. Hey, it may be worth $6.99 even if it comes with a HUGE ERROR... just depends what you want to use it for. But it seems nobody seems to know. After some testing we may find the error even varies along the range of weights. We may find the last few "precision digits" are complete garbage. If the scale is GREAT at say between 100-200g, and I have trivial tasks I need that are not high precision, then wonderful. But who actually has tested anything out?
I'll give you another example... say you buy a cheap-o eBay mechanical watch that has pretty bad time keeping. If you are someone who just wants to know the "approximate" time at a glance and the watch was cheap and looked nice, you wouldn't care. But what if accurate time was more critical? What if a watch that cost 2x more but would be 10x more accurate made the difference between you miss a train or not? Before you bought the watch that was $5, $10, $20 or $100, wouldn't you want to really KNOW?
I feel like these cheaper scales are not possible to trust the specs on. They may be fine, or they may be lying. They may actually be quite good for the price.... but who has bothered to test any of them?
And here is an excellent article about someone who loads up gunpowder in his ammunition which I assume has to be a very accurate procedure as they say explicitly on the page that THEY DON'T USE ELECTRONIC SCALES due to their inaccuracy/inconsistency:
https://www.celnav.de/muzzleloaders/powder_measurement.htm
On the topic of rifles... another example could be 2 air-rifles, one that lets you shoot a dime consistently at 20 yards, versus another cheap-o air-rifle which no matter how hard you try aiming, has an error that will not tighten your shot grouping to less than a beer bottle. How far off from the center-target would be your accuracy (which you should be able to correct with a well-calibrated scope), and the tightness of your shot groupings would be your precision.... That may be a function of the quality of your air-rifle, due to the machining of the barrel, the shape and consistency along the length, how reproducible the air pressures are for each shot, and so on.
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