ScienceHideout
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Obtaining a Decent Balance
I've been looking everywhere for a balance that can achieve readability of a thousandth of a gram... But I just spent a hundred bucks on a fume hood
and don't want to pay an arm or a leg. Where did you all get your good balances? Do you have any tips?
hey, if you are reading this, I can't U2U, but you are always welcome to send me an email!
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Endimion17
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There are those relatively cheap 0.001 g balances with 20 g maximum load, but I don't think they're reliable.
How about building one yourself? 
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Megamarko94
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thousandth of a gram thats gonna cost you...
i wanted to buy a good one but when i saw the price 1200e,,,
i dont think ill spend that much on scale..
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Steve_hi
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milligram balances are expensive no way of getting around it.
really for most home chemists a centigram balance should be enough they are around 50$ at home science tools I did a lot of searching and milligram
balances from china are a lot cheaper but by the time you add the freight you haven't gained much.
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Mercedesbenzene
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dudadiesel has a decent centigram balance for $18, i suggest checking it out
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Endimion17
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Beware of those digital scales with errors greater than their sensitivity. Yeah, they exist. -_-
Chinese scales are often very bad because their sensitivity changes with temperature so badly that you have to calibrate them all the time, and
calibration weights cost money. I was lucky enough to get a hold of one decigram scale that actually works, but I'd recommend you to buy the real
stuff.
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peach
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By far the most economic and useful at home balance is, one of these;
Dirt cheap (£7.50 - 10), remarkably accurate for the money (I measured well below 1% error when comparing them with a 0.1mg
balance), practical resolution.
My two tips would be;
- Get one of the models with a bigger weighing pan. The tiny, tiny pocket one's can be tricky to even fit 10g on them, unless you're weighing lead.
- Get one with about 100g of capacity. Once you are weighing over 100g, a set of digital kitchen scales can achieve 1% or less error.
There are endless variations on the cases they come in, but they're the same thing inside. Some companies want £80+ for them when it's the same
sensor element and circuit as you'll get in the cheaper ones.
Try searching eBay for 'jewellery scale' or 'pocket balance', sort them by price (lowest first) then scroll down until you find one with a decent
sized pan and 50 / 100g capacity.
[Edited on 10-10-2011 by peach]
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Zander
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Strangely enough, the best, most sensitive balance I own was found completely by accident, at a used music store/head shop. Apparently stoners like
their scales precise and accurate. Go figure.
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Endimion17
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Then by far best solution is to find a drug dealer. You know, heroin and cocaine people. They must have the best scales ever.
The downside of this is that you might eventually get killed. :/
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peach
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That's what the scale in the photo is primarily used for, drug dealing.
If the police find those in your pocket out on the street, they will immediately assume that is what you're doing.
That aside, they still feature excellent resolution and accuracy for the money.
There is also another, more amusing, characteristic of them. And that is, when I checked their accuracy, they were consistently positive; e.g. the
amount of mass weighed out on them would always be very slightly more than the display read.
Which reminds me of 'the bakers dozen'. In ye olde England, a baker dispensing less buns of bread than were they paid for was punished by having
fingers removed. To make sure that never happened, bakers would always give customers 13 instead of 12 when they asked for a dozen.
However, the incredibly slight, constant, positive bias on the scales does not quite amount to the 90% sugar & benzocaine you get with your
cocaine.
There are certainly higher resolution balances, such as the micrograms. But there are so few people on here who have an environment in which they can
work to those accuracies that I could count them on one hand. Which still, thankfully, has all five fingers in tact.
[Edited on 10-10-2011 by peach]
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dann2
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I once seen a project from Scientific American Magazine that made a micro gram (or perhaps sub micro gram) balance from a current meter (moving coil
meter). The glass of the meter was removed. You hung the thing to be weighed on the end of the pointer and the current through the meter needed to
bring the needle back to zero (or perhaps the mid point) was a measure of the weight. It was very sensitive but could only weigh a very small item.
Not much use I suppose but at least I got it off my chest...........
I could look up the artical if anyone is interested.
Dann2
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peach
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Here it is, the newer PWM version of the Sci Am article.
Erm.... hmmmm, no needle.
Mettler vacuum chamber balance. 0.1ug resolution. It'll cost an absolute fortune!
This is the Sartorius version. It's used as a mass comparator with the International Prototype Kilos (the definition of a kilo). Again, vacuum
chambers, no motors near the weigh stage (in case they produce any thermal interference, so the platforms move on pulleys instead). 0.1ug resolution.
The amount of care and attention to detail in these two is state of the art, which is why I doubt 1ug is realistic at home with something like the Sci
Am idea. But I would be very interested to see it go head to head with an official ug balance.
[Edited on 10-10-2011 by peach]
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dann2
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What's yer opinion of this beast?
http://www.ebay.co.uk/itm/ws/eBayISAPI.dll?ViewItem&item...
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jsc
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Berzelius, probably the best chemist in history along with Davy, used a very simple blade balance that a boy could make. For visitors to his lab it
was a real eye opener: they saw that a simple tool is often better than a more complex one--what is important is your skill in using it.
You would be surprised what a good machinist can do with just a file.
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Hexavalent
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What are your thoughts on this;
http://www.ebay.co.uk/itm/Digital-Precision-Electronic-Scale...
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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Dr.Bob
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The price is great, but 20 g is not much. Most small glass beakers weigh more than that, so you would have to weigh everything on paper and then
dispense to containers. I think 200 g limits are much more practical if you intend to do much real chemistry. I use one of those daily, and I
still have to have a larger balance for many tasks. I would prefer to have a 200 g balance that has only 0.01 g resolution than a 20 g with 0.001,
unless I only did microscale work. I have seen some postal or kitchen scales that read in grams and have quite impressive resolution for $60 or so.
I like Mettler balances, but their prices are insane, so if I was buying my own balance, I would go with another brand, unless it was used or marked
down a lot.
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Hexavalent
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What I already have in my lab is;
A kitchen scale - 3kg capacity, 2g resolution
A basic balance - 500g capacity, 0.1g resolution
A better balance - 100g capacity, 0.01g resolution
and I use each one in proportion of the scale of work that I'm performing. So, do you think the above, considering the price, would be a nice addition
for microscale etc. work?
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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Fleaker
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I love my 1100 g X 0.001 g capacity Mettler Toledo. It does the trick very well. You can usually score a scale like that for $700-1000 used/refurb'd.
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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Lambda-Eyde
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Wow, that's a huge capacity for such a high resolution! Is it a digital model or an older analog one?
This just in: 95,5 % of the world population lives outside the USA
Please drop by our IRC channel: #sciencemadness @ irc.efnet.org
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garage chemist
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I recently got myself a Kern PCB 350-3 scale:
http://www.pkelektronik.com/kern-praezisionswaage-pcb-350-3-...
This is the best scale I've ever had: 350g range and 1mg resolution. It has a huge array of functions, the most important of which I consider the
ZERO-TRACKING option: if this is switched on, then the scale automatically tares small weight changes and produces a constant stable reading with
slowly changing weights, also known as digital drift. If this is switched off, then there is absolutely ZERO digital drift! You can leave a little
dish of water or calcium chloride on the scale and watch the milligrams slowly fall or rise. This is tremendously important for exactly weighing
liquids or tiny amounts of powders.
For this scale to produce a stable reading with deactivated zero-tracking, it needs a warm-up time of 2 hours, meaning that you have to switch on the
scale 2 hours before you can weigh something with one-milligram accuracy.
Every good scale has this property, read the manuals.
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Hexavalent
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Nice, garage chemist! Do you find minor fluctuations with air currents (opening closing doors etc.), and if so, would you considering installing a
wind shield?
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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garage chemist
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Yes there are fluctuations with air currents. If you walk up to the scale then the reading fluctuates, and you have to stand or sit still for 20-30
seconds and not exhale in the direction of the scale until the air currents have died down for the reading to become stable again.
The scale already has a windshield- it's the ring shaped shield around the plate. Without it, it is even more sensitive against air movement than now.
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Hexavalent
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Oh, I thought that was an additional weighing cup! What's the linearity like at the miligram level and how well does it cope with cornerload errors?
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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Hexavalent
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This site could be useful for beginners in balance usage;
http://balances.net/applications/glossary.html
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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garage chemist
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The linearity is given as +/- 0,003g. A cornerload error is not given in the manual, and I have not observed any difference in the reading when I
place the object in the center or at the corner of the weighing plate.
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