Author Topic: You want a digital scale for What??  (Read 10014 times)

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Offline edy

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Re: You want a digital scale for What??
« Reply #50 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.

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:

« Last Edit: August 13, 2020, 03:33:47 pm by edy »
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Offline HighVoltage

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Re: You want a digital scale for What??
« Reply #51 on: August 13, 2020, 03:49:51 pm »
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.






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Offline edy

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Re: You want a digital scale for What??
« Reply #52 on: August 13, 2020, 04:55:35 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.

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.
« Last Edit: August 13, 2020, 04:57:14 pm by edy »
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Online jfiresto

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Re: You want a digital scale for What??
« Reply #53 on: August 13, 2020, 05:42:33 pm »
I read through the entire thread but didn't seem to find anyone questioning the accuracy of these scales....

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.

« Last Edit: August 13, 2020, 05:53:59 pm by jfiresto »
-John
 

Offline edy

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Re: You want a digital scale for What??
« Reply #54 on: August 13, 2020, 07:25:14 pm »
Perhaps that answer your questions.

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!)

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. 
« Last Edit: August 13, 2020, 07:54:01 pm by edy »
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Online Bud

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Re: You want a digital scale for What??
« Reply #55 on: August 13, 2020, 08:10:26 pm »
Learn what this youtuber used his precision scale for. Though the scale is optomechanical, not digital, but it is a quite elaborate device The way he sourced the test materials for the experiment may make you throw up though :o

https://youtu.be/eKsEmukmByI
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Offline SilverSolder

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Re: You want a digital scale for What??
« Reply #56 on: August 13, 2020, 08:32:16 pm »
[...]
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.
[...]

The Muesli that I buy, is sold by weight, not volume - so weighing it wouldn't help me! :D
 

Offline HighVoltage

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Re: You want a digital scale for What??
« Reply #57 on: August 14, 2020, 08:17:02 am »
One other applications for precision scales I had over the years was to certify magnets
I had a magnetic disc above the magnet on the scale and measured the difference in weight.
The disk height can be adjusted by a micrometer.

For this I used a precision scale from Bosch



There are 3 kinds of people in this world, those who can count and those who can not.
 
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Offline Circlotron

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Re: You want a digital scale for What??
« Reply #58 on: August 14, 2020, 08:30:42 am »
Useful for weighing several tens of grams of mass to add to a loudspeaker to measure Thiele and Small parameters.

My spreadsheet for calculating such:
https://www.diyaudio.com/forums/multi-way/24864-parameter-spreadsheet.html#post353269
 

Offline GlennSpriggTopic starter

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Re: You want a digital scale for What??
« Reply #59 on: August 16, 2020, 12:49:04 pm »
O.P. here...
To various posters/replies, yea I doubt the ones I first mentioned would really be that accurate, but who knows!  ;D
My main point was that being the size/look of a Car Remote on a keyring, indicated the 'intended' market, haha...   8)
Mind you, I'm glad to hear from others that there are so many other real & practical uses for a need for small measurements!!
Actually, I just had flash-backs to High-School Chemistry, (nearly 50 years ago!), when we had to weigh the resultant components after
certain reactions/combustions, as a 'proof' of the calculated atomic results. No such accurate digital 'scales' back then!!   :)
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Offline HighVoltage

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Re: You want a digital scale for What??
« Reply #60 on: August 16, 2020, 01:47:04 pm »
One thing that usually is overlooked when using a precision scale is air weight displacement by the part that is being measured.
There are 3 kinds of people in this world, those who can count and those who can not.
 
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Online jfiresto

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Re: You want a digital scale for What??
« Reply #61 on: August 16, 2020, 02:11:15 pm »
From Robert W. Shaw (1980) Balance Corrections for Buoyancy, Journal of the Air Pollution Control Association, 30:8, 908-909, DOI: 10.1080/00022470.1980.10465130:
Quote
In conclusion, conditions may occur when buoyancy corrections to weight changes become significant. An object with a specific gravity of 1 or 2 and a volume of several cubic centimeters may appear to change its weight by amounts on the order of 0.2 mg merely because of changes in the weather and consequent changes in air density. Anyone involved in high accuracy weight determinations should calculate the appropriate buoyancy corrections and keep track of local air density during gravimetric determinations.
-John
 

Offline David Hess

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Re: You want a digital scale for What??
« Reply #62 on: August 17, 2020, 01:58:04 am »
One thing that usually is overlooked when using a precision scale is air weight displacement by the part that is being measured.

"Ha, look!  After pressing down on the scale, it did not return to zero!"

"That is the weight of your fingerprint."
 
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Offline bson

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Re: You want a digital scale for What??
« Reply #63 on: August 17, 2020, 03:20:40 am »
I have several gram scales and use them for all kinds of things...  Most recently I was curious exactly how much 2 g of salt (NaCl) is.
 

Offline coppercone2

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Re: You want a digital scale for What??
« Reply #64 on: August 17, 2020, 05:28:06 am »
I have several gram scales and use them for all kinds of things...  Most recently I was curious exactly how much 2 g of salt (NaCl) is.

you know, if you have health problems, its a good way to measure how much salt you are adding to your food in a restaurant. Or sugar, for diabetics.

There is too many options, sea salt, granuated sugar, powdered sugar, crystal sugar (brown), syrup packets, honey packets, kosher salt (served in a bowl often), different grinds of salt. You can't measure it with a spoon to medical requirements. I.e. salad bar food prep (temporarily out of style due to disease). Nothing there should be seasoned, theoretically you can get a vegetable salad, add only oil, then salt it to the correct amount for taste and diet. Some doctors argue you should meter the amount of salt you eat very well, even if you have no medical problems. So many people have high blood pressure.
« Last Edit: August 17, 2020, 05:47:04 am by coppercone2 »
 

Offline jh15

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Re: You want a digital scale for What??
« Reply #65 on: August 21, 2020, 12:01:28 pm »
I would like a discrete scale you could use at a restaurant.
     Is it cheaper by the cup or bowl for example.
     A flat load cell/platform that wouldn't be noticeable.
Somehow a readout with tare after food is consumed. These days to your phone, but any readout is good for me.
     Been thinking decades ago of using a strain gauge, but recently adapting these mini scales.
    There. Now someone start a kickstarter.
Also to be fancy, could automatically go to a spreadsheet to figure cost per weight of steak at restaurant A compared to B, etc.
     
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Offline ace1903

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Re: You want a digital scale for What??
« Reply #66 on: September 17, 2020, 11:46:59 am »
I looked for long time for precise measurement of NaOH that I am using as a developer for Positiv20 spray.
Found device that audiophiles use for turntable evaluation.

Does anyone know if this device can be reused for measuring small quantities in chemistry?
https://www.amazon.com/Cuiedailqhb-Portable-Digital-Turntable-Tracking/dp/B0832ZV5KR?th=1

Anyone that made tear-down or knows measurement principle used in that device? S shaped aluminium with resistive sensors is very unlikely to be used. 
 

Online jfiresto

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Re: You want a digital scale for What??
« Reply #67 on: September 17, 2020, 01:51:12 pm »
That is only a 500 count scale which probably keeps the cost down. You might ponder a scale's uses and aim for one that is a little more ambitious if you think it might have other uses.

Commercial and even consumer scales typically do better, offering 3000 and 1000 counts, respectively. Good industrial and laboratory scales can routinely manage two to three orders of magnitude better, with a lab scale offering half a million useful counts of resolution being nothing extraordinary.
-John
 

Online jogri

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Re: You want a digital scale for What??
« Reply #68 on: September 17, 2020, 09:21:37 pm »
I looked for long time for precise measurement of NaOH that I am using as a developer for Positiv20 spray.
Found device that audiophiles use for turntable evaluation.

Does anyone know if this device can be reused for measuring small quantities in chemistry?
https://www.amazon.com/Cuiedailqhb-Portable-Digital-Turntable-Tracking/dp/B0832ZV5KR?th=1

Anyone that made tear-down or knows measurement principle used in that device? S shaped aluminium with resistive sensors is very unlikely to be used.

Protip from a guy that has done that: Never try to weigh your NaOH if you want accurate measurements, that stuff is highly hygroscopic and trying to measure it accurately is a royal PITA as you have to remove the crust of every single pellet you are going to use as the crust mostly consists of water, screwing over your calculations... Oh, and it also collects the CO2 in the air to form sodium carbonate, and you won't get that stuff off by simply heating it.

If you want to make a solution with a known concentration you have two options:
-Make the solution and measure the concentration by a titration (can be done at home, but takes a bit of experience). Keep in mind that you will have a bit of sodium carbonate in it, so not a good idea if something is sensitive against that stuff
-Wash your NaOH before you use it: Take a bit of water, rinse the pellets/nuggets and dump that water, then heat it in a drying oven (but not for too long as it will start to collect CO2 from the air), then weigh your dry NaOH and add the required amount of DI water. Not as precise as doing a titration, but more than good enough for most applications
 

Offline ace1903

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Re: You want a digital scale for What??
« Reply #69 on: September 18, 2020, 06:50:13 am »
Usually I buy ecofriendly developer for photoresist that only needs to be diluted with 1l distilled water.
But due to problems with shipping I switched back to local supplier for chemicals.
Fortunately I don't need extremely precise measurement since process is tolerant to range of concentrations.
7g is at low side on those 200g range 0.01g resolution scales and I don't want to keep several liters of NaOH.

Could you please provide info what is used to titrate NaOH? I already have set of lab glassware and maybe 30 chemicals.

I hoped that this 5g scale will have better resolution since I am close to max range. But I didn't notice this 500 counts limit.
Is this resolution limit of the measurement principle or I can override it with some 16bit ADC and nucleo board that I have on disposal?


 

Offline jmh

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Re: You want a digital scale for What??
« Reply #70 on: September 18, 2020, 08:49:07 am »
I got one from eBay of the type you see on 'police camera action' type programmes to weigh gemstones, but the only use it sees these days is to weigh the occasional letter and to weigh our hamsters!
 

Online jogri

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Re: You want a digital scale for What??
« Reply #71 on: September 18, 2020, 10:57:25 am »
Could you please provide info what is used to titrate NaOH? I already have set of lab glassware and maybe 30 chemicals.

The standard approach would be to use muriatic acid with a known concentration, but since you probably don't have that you have to make a primary standard: That's a solution with a known concentration, made by dissolving a substance that isn't hygroscopic (and therefore has a known density and molecular weight)->if you weigh the amount of substance that you dissolved in x litres of water you can calculate the precise concentration of your solution. You then use this primary standard to titrate your NaOH solution.

You could use almost every pure chemical that is stable in air, doesn't have an unknown amount of crystal water and that forms an acid when you toss it in water, but the two substances that get used in chemistry labs for this job are potassium hydrogen phthalate (KHP) and oxalic acid dihydrate. Use phenolphthalein as the indicator, and make sure that you will use between 10-30ml of acid for your titration if you want precise results (you can always dilute your NaOH but the primary standards don't have a great solubility in water so you can't make a really concentrated solution).

Here is a paper that describes the process, just PM me if you have further questions: https://silo.tips/download/chemistry-111-laboratory-experiment-8-stoichiometry-in-solution-standardization

I personally wouldn't go this far just for a film developer as it will probably work just as good even with a +/- 10% deviation in the NaOH concentration, but a titration is a great exercise in precise lab work.
 
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Online tom66

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Re: You want a digital scale for What??
« Reply #72 on: May 25, 2022, 10:58:24 pm »
My father had one of these to weigh jewelry.   He was a gemologist though.
 

Offline magic

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Re: You want a digital scale for What??
« Reply #73 on: May 26, 2022, 01:06:22 pm »
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:

You are going to love this thread:
https://www.eevblog.com/forum/dodgy-technology/i-cracked-the-mystery-of-chinese-precision-jewelry-scales/

I don't recommend using Chinese junk for dosing drugs :P
 

Online coppice

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Re: You want a digital scale for What??
« Reply #74 on: June 14, 2022, 08:46:48 pm »
Why are electronic scales considered the most convenient ?
They are clearly the most convenient, giving a quick numerical readout. However, I think they are mostly attractive because they just work so well. Try putting a kilo of something on several models of electronic scale that cost just a few dollars each and the spread of measurements is usually just 3 or 4 grams, and stays like that for a few years.
 


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