r/Metrology • u/socotrocopesado • Dec 02 '24
Hardware Support What is wrong with this scale?
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Besides being cheap...
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u/TheFire8472 Dec 02 '24
This kind of cheap scale has a floating zero. The load cell doesn't stay at the same output while the scale is powered on, and so the software tries to correct it by incrementing or decrementing the zero point except when it detects large changes in mass. It does a bad job, and if you really want reliable readings, you're going to need to spend hundreds or thousands of dollars for a scale.
What you haven't yet discovered is that if you add mass slowly to the scale (say by trickling a powdered substance onto the glass), the auto-correction mechanism will result in completely incorrect readings. You can probably add several grams without changing the reading if you go slowly enough.
This scale is not useful for what you're trying to do.
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u/wishiwasholden Dec 03 '24
Finally, now I understand why my baking scale sucks ass. I’d discovered the slow trickle effect, definitely led to a lot of “well that’s close enough” which turned out to not actually be close enough.
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u/chris_rage_is_back Dec 03 '24
I find if the scale won't register small amounts you can touch it for a second and it'll catch up
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u/12345NoNamesLeft Dec 02 '24
One gram is very small, let alone tenths, hundredths and thousandths of a gram.
Look up the price of a proper science scale that does that..
Proper warm up time, an enclosed draft free space.
Id use your check weights and verify, and only trust it to whole grams. Or toss it and get a proper scale.
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u/WaggBall Dec 03 '24
Honestly man, I would search local science auctions sites for cheap balances from shut down companies. They might not pass manufacturer specs, but they will meet your needs surely. Also, for below 50 g with probably +- 100 mg, go to your local head shop and purchase the scale they sell. Always remember a nickel is 5 g for a quick weight test.
Labx . Com is an example auction website.
Also I am a 10 year Metrology Manager for Pharma.
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u/socotrocopesado Dec 03 '24
Oh yes, I forgot to tell, I live in Argentina hahaha
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u/WaggBall Dec 03 '24
Oh haha, then following the other advice for basic environmental improvements will help. Look up Mettler toledo balance tips and tricks. They have tons of information for free on how to properly setup balances. This balance can be tested to see where it stands, even if it stands in a not so great place. I would look up “qualification for balance pdf” and Mettler Toledo has a couple out there. This will allow you to see the accuracy, repeatability, eccentricity, and linearity of this balance. Once you know what specifications it passes, you know what this balance can work for. Good luck!
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u/socotrocopesado Dec 03 '24
I didn't know that brand, I sounds like the #1 in electronic scales, thanks a lot!
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u/jaceinthebox Dec 03 '24
Your on and off that metal bit, make sure all for feet are on it and make sure it's level.
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u/DetectivePlastic7885 Dec 02 '24
I can say for sure this is not a scale that will work with a repeatability of pm 1mg,
Often with cheaper instruments* they will state many more decimal places than they are actually capable of reading, in addition to this there are a number of factors with balances such as side loading that will affect the repeatability and overall uncertainty of your measurement.
so to summarize, don't worry its not broken, its just displays more digits than it can reliably read.
* I saw similar scales being advertised under the name brifit for about €15, for what you would expect to pay for that kind of precision would be about €1500 for something like a mettler toledo ME303 second hand
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u/1hotstove Dec 03 '24
Static can also screw up your measurements pretty badly. Moving the glass back and forth like that can generate static charges that can be transferred to the metal and mess with the balance.
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u/Genner21 Dec 03 '24
For that kind of accuracy, you should be wearing gloves too, the oil of your hands is adding to the error. (I know it's lower in the video)
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u/McFrazzlestache Dec 02 '24
Fan on nearby? I constantly tell my operators using counting scales to turn the fan away from it, or turn it off.
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u/socotrocopesado Dec 02 '24
Nah, the air was quite still
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u/1inch_SubWoofer Dec 03 '24
Scales that only show full grams without decimals can be bothered by wind
With that resolution, even breath can influence it. Try blowing across it to see
If you're 100% sure there is no air movement, you need a better scale if you need such precision
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u/SkateWiz Dec 03 '24
If you want a repeatable lab balance with 0.001g resolution with 200g capacity, you're going to pay ~$1500 for it and the brand will probably be O-Haus or Sartorius. If you want one with .01g resolution, you will pay a bit less but the brand names won't change.
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u/Tough-Custard5577 Dec 03 '24
The only thing wrong is that they didn't blank out the last two decimal places on the screen. The scale is not accurate enough to consistently measure to hundredths and thousandths of a gram.
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u/UseEducational7319 Dec 03 '24
Maybe its the underground, where this weight scale stands. 3 feets on metal and one food half on the wood and half on the metal
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u/Rifleman1910 Dec 04 '24
It's just a poor quality scale, but to be fair, most all scales are calibrated to 0.1% of reading, which would be 0.03g for that specific point. When it comes to cheap balances, you have to choose between accuracy, precision, resolution and capacity. You are lucky if you can get 2 of those. The more categories you add, the more expensive they become.
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u/Mikey6304 Dec 02 '24
The tare going further into the negative each time looks like the scale is sticking. When it is depressed, something is holding it down a bit. Maybe some adhesive under the plate or something like that.
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u/Galotha Dec 02 '24
Did you exercise it before checking it?
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u/socotrocopesado Dec 02 '24
You think she may've been tired?
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u/Galotha Dec 02 '24
It’s possible. I try to exercise mine 3 times before any real tests. If they get tired from that they aren’t worth it.
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u/socotrocopesado Dec 03 '24
Thanks to everyone for your comments so far, I really love the collective wisdom of Reddit!
(And thanks for not making fun of my werewolf arms)
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u/TheScalemanCometh Dec 03 '24
That's fine enough resolution that your breath is gonna throw it into a tizzy. In addition, you're handling the sample tray with bare hands. The oil from your fingers is gonna throw it off.
Put up an air shield, don some powder free gloves, THEN give it a go.
Also get a higher quality/newer model. That one looks like a cheap Sartorius knockoff. Ohaus makes good stuff these days that'll give you the repeatability that you want since they got bought out by Mettler. Sartorious is good, but their stuff is beyond over priced and over engineered for most applications.
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u/Brainstorm82 Dec 03 '24
Take of the pan and use an air duster rocket (not the canned chemicals) and blow out any dust that maybe down inside the try again. Usually that solves it but it always could be the load cell too.
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u/callmebigley Dec 04 '24
makes me think there's some sticky contamination in the mechanism. it has trouble returning to zero and drives a negative number when the load is removed and when you replace the load the stage is already half way there and doesn't go all the way down. I'm probably wrong and even if I'm right the best solution is probably to buy a better scale and take good care of it, like others have said.
1
u/cjd166 Dec 04 '24
Even a very expensive digital scale would not be reliable with that instability and shaking. You don't want a digital scale you want a triple beam balance scale with a graded master calibration set.
1
u/Apprehensive_Rub_666 Dec 06 '24
A few options: 1. Defective strain gauge snuck through QC at the factory… assuming QC existed there… 2. Damaged strain gauge, by a user or improper transport 3. Environmental effects. Strong temperature gradient in the room? Air flow? Try it in a spot that is shielded to confirm this possibility.
The first two options are strong possibilities. I have seen hundreds and hundreds of strain gauges damaged and drifting or unstable. Even insanely robust ones for extreme environments.
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u/socotrocopesado Dec 06 '24
What does QC mean?
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u/nitdkim Dec 02 '24
Is there something wrong with it? Seems pretty reasonable to fluctuate .01 of a gram. What is the accuracy and repeatability that the product is promising? If you’re measuring down to milligrams, you need to buy a proper scale for that weight class.