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Weight - Good mg scales to buy

Discussion in 'Research Chemicals' started by Geofragment, Nov 16, 2007.

  1. Geofragment

    Geofragment Newbie

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    I just have a question about milligram scales. I need to buy some, and I was just wondering if anyone would be able to offer some advice on what scales are a good investment if they are being used for weighing research chemicals.
    Thanks
     
  2. bl0whydr0420

    bl0whydr0420 Newbie

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    to what accuracy? and how many grams, maximum, would you need?

    i personally use a "digiscale" that goes max 50grams, to a 0.01gram accuracy.
    or 50g x 0.01.


    found mine as a "jewelers scale" so i can weigh out my diamonds perfectly. ;):laugh:
     
    Last edited by a moderator: Apr 28, 2010
  3. radiometer

    radiometer bananadine addict Platinum Member & Advisor

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    Tanita used to be the best price for performance, but they are no longer available. Look for scales made by Gempro or Acculab. For weighing individual doses with any degree of accuracy whatsoever you need to have a scale which is sensitive to .002 g or less. A .01 g scale is only good for weighing larger amounts such as 100 mg for further liquid measurement. The adage "you get what you pay for" applies to super cheap scales advertising this sort of accuracy costing under $100. Expect to pay $200 or more for a quality scale.
     
  4. Alfa

    Alfa Productive Insomniac Staff Member Administrator

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    To handle Research chemicals which often have dosages in the milligram(0.001) range, one needs a scale with a microgram (0.0001) range. But since scales in the microgram range are mega-expensive, most will settle for a milligram scale or even a two milligram scale (0.002). This means that the milligram scale will display a weight of 0.006 for both 0.0055 and 0.00649.
    With the two milligram scale this means that the scale will display a weight of 0.006 for both 0.005 and 0.0069.
    To accurately measure weights of milligrams one needs sub-milligram scales, plus the function to adjust the feet of the scale, plus a cap to stop the influence of wind.

    Tanita scales are available.
     
  5. anaesthetics

    anaesthetics Newbie

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    A Tanita 1230 Professional Mini Diamond Scale would be ideal. SWIM obtained one on eBay for half its retail value and hasn't been disappointed in the slightest. Said scale is accurate to 0.002g. SWIM mentioned the importance of handling scale and product with latex gloves as oil and other residues will interfere with accurate calibration.
     
  6. Pino

    Pino Gold Member

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    [SIZE=-1][SIZE=-1]Swim just bought a Proscale Gemological 10g/0.001g, which comes with a calibration set. Would this be appropriate to use for chemicals with dosages around 5 to 20 mg. I amn't really deep into the scale thing. He would say the scale has a precision of +/- 0.5 mg, which is an error of 10% in the smallest dose encountered. This should be enough, I thought.
     
    Last edited by a moderator: Sep 9, 2017
  7. trptamene

    trptamene Platinum Member & Advisor

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    Considering DOx's are active in the submilligram range, me thinks one should go for a micro scale or use the milligram in conjunction w/ a volumetric method.
     
  8. Pino

    Pino Gold Member

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  9. Stimulants

    Stimulants Gold Member

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    Accuracy is a misnomer.

    Just because the scale can count to 1mg doesn't mean it is accurate to 1mg. One count is called 1d, meaning one division.

    Many scales specify a repeatability of +/- 1 to 2d and linearity of 2-4d

    Slightest vibration and draft will affect the measurement, so you can't realistically expect a reliable, stable mg scale that weighs less than 5 lbs

    Accuracy of calibration weight is not THAT important since the skew is proportional. So, if you calibrate a 20g scale with a 19.900g mass, it will just read 19.9mg as 20mg, 1.99 as 2.00g and so on. It isn't going to cause a 0.1g error across the entire measurement.

    To be accurate to nearest mg, then +/- 1mg repeatability is not acceptable. One should always have something with 10 times the resolution of the desired reading.

    Analytical balances are almost always 0.1mg resolution with +/- 0.1mg repeatability. It should be adequate for measuring to nearest 1mg with a margin of error of 10 to 20%. Microrange scales that go into 1µg or 0.1µg range is not warranted unless the sample measured is say, a single dose of pure triazolam (125µg)

    Scale should be line powered, should have a bubble level, glass draft cover and based on the magnetic force restoration sensing method or an old optical mechanical type.

    Old optical mechanical type is affordable, however there's a steep learning curve. 0.1mg analytical balance is around US $1000.

    If a 0.01mg resolution scale is set to display only to 1mg, then that is what can be expected, for for a 1mg readability scale with 1mg internal resolution
    that's not the way it works. For a 1mg readability scale with 20g capacity and 1mg repeatability, when you measure 0.50000g (+/- 0.025mg) OIML E1 calibration weight many times and take the standard deviation, it should be within 1mg. If the reproducibility is 2mg, then the scale may report the 0.50000g mass as 0.498g to 0.502g

    There are some scales with internal resolution higher than display resolution and these scales will have a much better displayed value repeatability and it may have a spec like d=0.1g, reproducibility =0.03g, though such scales are not common. The region of up to about 5-10 counts from zero can not be used reliability as it is likely to get set back to zero as a part of internal zero drift corrective system.

    2mg with +/- 2-4mg repeatability would report 10mg actual weight as 6-14mg or 8-12mg. Unfortunately, readability does not equate accuracy. If the scale does not come with a detailed specifications, then it should be questioned.
     
    Last edited: Jun 8, 2009
  10. jihan_nyhn

    jihan_nyhn Newbie

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    Hi guys,

    I've joined this forum specifically to post this:

    search google for 'chapter 9 A Homemade Microgram Balance' without quotes and click on the first site (I'm not allowed to post links hence roundabout way of linking).

    this website explains a technique for making you's own analogue scales that would give You sufficient accuracy for 2Cx's, DOC, DMT etc.

    all the materials can be had for £20 or so. I recognise that there's a lot of expertise on this forum so I'd like to know what peoples opinions are on this design. Specifically I am considering making scales like this and using it to weigh doses of 2CB, does this seem sensible?

    Also, calibrated weights are expensive, is it a reasonable plan to get 60 g/sq.m graph paper and cut 4mm by 4mm squares (approx) to calibrate the scale, obviously I would make say 50 such weights and calibrate using the average.

    If SWIM's scales registered 20mg for example and it was actually 19 or 21 that would not concern SWIM very much.

    Any feedback appreciated. Thanks.
     
  11. Terrapinzflyer

    Terrapinzflyer MDMA, RC & News Forums Platinum Member & Advisor

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    ^^^ -hmmm- the place is called science toys- and probably for good reason. Would definitely advise against using something like this for anything like RC's, especially anything active in the milligram range and especially not for things like DO'x's that are active in the microgram range. This just screams "danger!"

    A decent scale is far cheaper then the harm one can do mis-weighing many of these substances.
     
  12. jihan_nyhn

    jihan_nyhn Newbie

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    ^^^ yeah point taken. However this guy has a photo at the end of the article where a 450 microgram weight is pulling the scale down by 2 large notches. You might be right that that's still not good enough for safe weighing of DO'x's and other low dose RC's, but ultimately this guy claims this scale will weigh 10 microgram intervals, multiply that by a factor of 100 for the sake of 'better safe than sorry' and I could still weigh 2CB to, say 20mg and be sure it was within 19.5 - 21.5

    Even if accuracy were outrageously bad and what weighed in at 20mg was actually 40mg I would be freaked out but far from dead...

    I completely understand why people are saying I should buy proper scales but if he can't afford it he can't afford it and this strikes him as really not a very dangerous option if he sticks to 2CB...

    Cheers
     
  13. Seaquake

    Seaquake Gold Member

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    if You can afford to buy the chemicals You can afford to wait to buy the chemicals and buy the scales first.
     
  14. jihan_nyhn

    jihan_nyhn Newbie

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    If someone constructed these scales and used calibrated weights to repeatedly test them for accuracy and reliability I don't see why that someone couldn't then depend on the results obtained from future weighing. Ultimately science is just the application of careful reason and a few material instruments, the fact that some scales don't have a brand name and aren't made in a factory doesn't necessarily mean their results can't be depended on. If all the appropriate principles are applied, all the appropriate physical and mathematical aspects are considered, why shouldn't these scales be as good as any others?
     
  15. Stimulants

    Stimulants Gold Member

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    A scale that measures with 1mg resolution up to 10g isn't exceptionally hard. In scientific use, a greater range is needed and measuring mg range resolution is more difficult with heavier objects.

    For example, two drill bits weighing somewhere around 20g (but is precisely recorded to the 1/10mg). They have different heat treatments. After ten uses, the change in weight is recorded to observe wear. For such use, the procedures usually call:

    1.) calibrate and adjust
    2.) weigh
    3.) use the tool for few days
    4.) calibrate again
    5.) reweigh

    Much of engineering and science experiments are set up to observe change, so if the bit only wears 5mg but the scale reports +/- 5mg on 20g, it's a failed experiment.

    If the application is simply weighing substance in the few mg range with a 10% margin of error, it is much easier, however, the scale needs to display calibration stability to be dependable.
     
  16. jihan_nyhn

    jihan_nyhn Newbie

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    ^^^ Brilliant, thanks very much for the reply. Basically these scales that my irresponsible drug-using acquaintance wants to make need to weigh with 1mg resolution but could have a maximum load of literally 30mg and it wouldn't matter cos the only purpose will be to weigh single doses of 2CB.

    Furthermore 10% inaccuracy would be tolerable. In order to avoid anything worse I'll tell this reprobate acquaintance of mine to calibrate repeatedly over and over again and with varied known masses to reassure himself that the scales are reliable prior to using them.

    Just to link this back to the original question which is about mg scales I'd like to point out that someone who only ever wanted mg scales for personal weighing of 2C'x's could save themselves hundreds of pounds with this method, I'm sure this would appeal to a lot of people.

    Thanks for your help everybody, if this dastardly acquaintance of mine ever makes this horrid contraption I'll let you all know how it works out.
     
  17. Stimulants

    Stimulants Gold Member

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    30 count would not be appropriate unless it's absolutely dead on each time with repeatability of less than a scale division. Take a piece of foil, handled by sweeters.

    Weight it ten times and record.

    Weigh the same piece ten times again the next day, preferably after some change in room temperature.

    If it doesn't read the same or very close to the same every time, then it is not good enough.

    Using a mg scale to measure something that only weighs a few mg is like using a 30ton truck scale that reads to nearest ton to weigh a 3-ton truck. For a 25 ton truck, the error maybe acceptable, but for a 3-ton truck, +/- 1 or 2 ton is not.

    When a truck is being weighed, they don't use scales that can read to the nearest ton, but usually nearest 10kg.


    Many instruments will have d spec and e spec. d is the resolution and e is the legal for trade accuracy and there is further restriction stating the minimum sample weight so that e remains within reasonable accuracy. Usually 10d = e, so in my opinion the resolution should be ten times greater than minimum expected precision of measurement. Scales that is spec'd at 1mg(e) and displays 1mg usually have internal resolution that is at least 10 times higher. A good example is a deli scale. It may only bill to nearest 1/100 of a pound, but internal resolution is around 1/1000, so that even the 1/100 lb reading is accurate every time.
    It's not possible to test an instrument without having a control instrument that is of known accuracy and precision.
     
  18. jihan_nyhn

    jihan_nyhn Newbie

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    Yeah that's very sensible cheers.

    Surely not or no one could ever have made the first accurate and precise scale? Is it not equally acceptable and effective to test the instrument with calibrated weights as i suggested?

    If you read the design I linked to at the start, the guy claims resolution of 10 micrograms. He has a photo of a 450 microgram weight pulling his scale down 2 large notches. Allowing for him exaggerating you could fairly say that the resolution is 100 micrograms, in which case that is 10 times the minimum expected precision of the instrument.
     
  19. Stimulants

    Stimulants Gold Member

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    The knife edge wouldn't be able to hold sensitivity consistent enough. Commercially made substitution balances use a set of high precision weights to hold the knife edge under constant load.

    If the capacity is 100g and sample weighs 0.001g, 99.9g of weight is placed on the pan side internally by set of physical weights and the last 1/10g is read on a optical beam which is magnified with lenses.

    If the sample weighs 99.9g, only 0.1g of internal weights are used.

    The end result is that the knife edge always see the same weight regardless of sample weight.

    Two pan balances are hard to use and they must be pre-loaded so that the fulcrum sees about the same load every time. If the capacity is 50g and sample to be weighed is 0.001g, both sides need to be loaded with very precise 50g weights, then the sample is placed on one side. Small weights are used to cancel out the unbalance.

    The knife edges are made of sapphire as steel doesn't provide enough hardness.

    So, it wouldn't weigh 2g+1mg the same as 1g+1mg. There's a need to be able to accept tare weight, because the substance would have to be placed in a container for weighing.

    Calibration drift would be too great to measure accurately to 1mg.

    For accuracy down to 10mg, then a cheapo 1mg resolution balance available only maybe adequate. They're all load-cell based.

    0.1 and 0.01mg (100 and 10µg) scales are based on force restoration sensor and they're inevitably fragile and expensive. 0.01mg semi micro balance is ideal for measuring things below 10mg.
     
  20. jihan_nyhn

    jihan_nyhn Newbie

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    okay, well thanks stimulants, you've succesfully convinced me that I should just spend the money so my friend's chihuaha can have some proper scales and not take any risk. I was really quite convinced by my idea of making these scales but you've changed my mind.

    Cheers for your help