Atrum
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Help choosing a lab scale
I've been learning chemistry for a while now and I am making steady progress. However I feel I have run into a wall. My scale is pretty limited and I
think it is time to upgrade.
I have been looking for a good lab scale, but most with a readability of .001g or more cost a lot more than my budget allows.
Can anyone recommend a lab scale with .001g readability and good accuracy/precision that is under $500.00 usd?
Thanks,
Atrum
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Texium
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I think that you mentioned in another thread that your current scale is capable of measuring to .01 g? Well, I have always had a .01 g scale and it
hasn't caused any problems. It really depends on what you're doing. Unless you're planning some super precise quantitative stuff, you'd probably be
better off putting your budget towards other stuff.
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Zombie
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It might sound ridiculous to you but I found a .001 scale that has worked great for $23.00.
"American Weigh Scales GEMINI-20 Portable MilliGram Scale, 20 by 0.001 G"
http://www.amazon.com/American-Weigh-GEMINI-20-Portable-Mill...
The reviews on it are excellent, and it is calibratable.
They tried to have me "put to sleep" so I came back to return the favor.
Zom.
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Texium
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Oh yeah, on second thought, that is really nice. I might have to get one of those too!
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Atrum
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Thanks Zombie, I'll check it out.
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Sulaiman
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My workmate bought one of those 20g x 0.001g scales, (mainly for black powder weight in grains)
and I bought a 300g x 0.01g scale for general purpose use.
Both are useful, both need frequent (every use) re-calibration for best accuracy.
re-callibration is quick and easy.
Neither are absolutely reliably accurate but both especially good for relative measurements such as mixing ingredients
just don't assume that the last digit is correct,
re-weighing the same object multiple times often gives +/- 2 least significant digit results.
Neither of us have checked the whole range linearity of the scales.
I checked mine at 10, 20, 50, 100, 200 and 300g and they seem within +/-2 digits often better.
I'd love a class E0 callibration weight  http://www.haefner.de/fileadmin/images/pdfs/14-10-29_Haefner...
I cannot say what the absolute accuracy of the eBay Chinese callibration weights are
but they are consistent relative to each other.
For practical purposes you can rely on better accuracy and resolution than
a Class A volumetric flask or burette, so more than good enough for amateur chemistry.
[Edited on 8-3-2015 by Sulaiman]
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Artemus Gordon
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I have the <a href="http://www.scalesgalore.com/sartorius_m_prove.cfm#mprove">Sartorius AY303</a> 300g capacity 0.001g readability $355.
I like it a lot. It has a built-in bubble level and its own calibration weight, so it is easy to set up and calibrate. I found out its calibration is
quite sensitive to temperature changes, so it is best if you can keep it in a permanent location. If you have to move it from storage to your lab as I
do, you need to allow 1-2 hours for it to acclimate. Other than that, it is very easy to use.
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Sulaiman
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Artemus Gordon, would you mind doing a simple experiment?
After your scale is horizontal, thermally stabilised and calibrated,
could you weigh a something a few times and report on the fluctuation in the last digit?
then sometime later (longer = better) without re-calibration re-weigh the same something a few times
and report on the difference, if any?
[Edited on 9-3-2015 by Sulaiman]
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Amos
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The earlier-mentioned 0.001 gram scale sounds nice, but only measures weights up to 20.0 grams. I've found that the scale below works great; it
measures up to 200 grams with 0.01 gram increments. Together, the two could cover you on lab scales without putting you over $50 for the pair: http://www.amazon.com/American-Weigh-Chrome-Digital-Pocket/d...
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WeaponsRx
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I just picked up an AWESOME .001 balance that really works so good, is exact on all my weights, it may be Chinese, but for the price it was dam well
worth it for its legit. hang on.
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Zombie
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That is the ONLY weigh (nice pun) to go.
If you are weighing Mg's, then you have no need for more than a few grams on that scale.
They tried to have me "put to sleep" so I came back to return the favor.
Zom.
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WeaponsRx
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http://www.ebay.com/itm/391023258683?_trksid=p2057872.m2749....
thats her! haha 89.00 works flawlessly and up to 300g
[Edited on 9-3-2015 by WeaponsRx]
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WeaponsRx
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heres the same one ending in 30 min. comes with a shield and all.
http://www.ebay.com/itm/300G-0-001G-LCD-Digital-Balance-Labo...
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Atrum
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Thanks for all the suggestions guys.
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Artemus Gordon
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Quote: Originally posted by Sulaiman  | Artemus Gordon, would you mind doing a simple experiment?
After your scale is horizontal, thermally stabilised and calibrated,
could you weigh a something a few times and report on the fluctuation in the last digit?
then sometime later (longer = better) without re-calibration re-weigh the same something a few times
and report on the difference, if any?
[Edited on 9-3-2015 by Sulaiman] |
OK. I'll try to do that tonight, and report on it tomorrow.
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DFliyerz
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I use a 100g / 0.01g pocket scale for most measurements, but since my smallest beaker weighs about 50g, I often need to use an old WeightWatchers
scale I found lying around which has a much larger capacity at 2g increments.
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Sulaiman
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I use 1g resolution kitchen scales sometimes too
(mainly when my wife is not around !)
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Artemus Gordon
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| Quote: Originally posted by Sulaiman | Artemus Gordon, would you mind doing a simple experiment?
After your scale is horizontal, thermally stabilised and calibrated,
could you weigh a something a few times and report on the fluctuation in the last digit?
then sometime later (longer = better) without re-calibration re-weigh the same something a few times
and report on the difference, if any?
[Edited on 9-3-2015 by Sulaiman] |
OK, I've got some data to report. This is not as complete as I would like, partly because I learned some things as I went along that caused me to
alter my method. I want to go back and redo this.
First, I let the scale acclimate in my lab space for 2 hours unpowered. However, when I turned it on, the initial 0.000 display started climbing (or
possibly falling, the minus sign is hard to read if you don't specifically look for it). So I think self-heating was going on. I left the power on for
20 mins and then zeroed the display. It held 0.000 for 30 secs, so I went on to calibrate. Calibration is normally done with 2 supplied 100g weights
together (i.e. 200g is the cal point chosen). I decided to use one of the 100g weights and a penny and to alternate weighing them. This is what I got:
* 99.999 * 3.062
* 100.001 * 3.060
* 99.999 * 3.061
* 99.998 * 3.061
* 99.999 * 3.064
I let each object settle on the pan for 30 secs, and let the empty pan settle back to 0.000 for 30 secs. I found returning to 0.000 took most of the
30 secs after the 100g weight, it only took a few secs after the penny. Before the final weighing of the penny, the display only returned to 0.004 at
the end of 30 secs. This accounts for the discrepancy in the last measurement. I have said before that the scale is sensitive to temperature changes,
I'm guessing that my non-heated lab might have cooled a bit by then - 9:08pm.
Then, I left the scale powered up with an empty pan, but otherwise untouched for 2 hours. When I returned, the ostensibly zero reading actually said
0.236g (or possibly -0.236g). This was certainly due to the room cooling off. I tried just zeroing the display w/o redoing the 200g cal, but I got
readings of 99.963, 3.001, 99.953, & 3.071, so obviously the scale was out of cal by then. At this point, I had new ideas of how I want to do
this, so I went to bed with plans to redo the whole thing tonight.
Conclusion:
Scale is certainly temperature sensitive. This makes sense because the sensor converts strain to electrical resistance, which is temp dependent. So to
get reliable readings, it is important to let the scale sit powered up for 20-30 mins to reach a stable temp, and to calibrate often. Fortunately,
calibration only requires pressing the "zero" button, then the "cal" button, then placing the calibration weights on the pan, and then waiting a few
seconds, so it is not a huge hassle.
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Zombie
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Do either your storage or use temperatures fall outside these (from the manufacturers page)
"Storage Temperature 4°F to 122°F (-10°C to 50°C)
Operating Temperature 50°F to 86°F (10°C to 30°C)"
I understand the changing temp. in the lab effecting the readings but yours seem pretty severe.
I'm now a little curious...
They tried to have me "put to sleep" so I came back to return the favor.
Zom.
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Sulaiman
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Thanks for doing the experiment, much appreciated.
I had similar results in the last digit but my super cheap 300g x 0.01g scales are in effect an order of magnitude worse !
Regarding warm up, my friend with the 20g x 0.001g scales will (when he has time/motivation)
add an external power supply and modify the scales to not auto turn off to alleviate this problem.
When using mine I get the feeling that the stressed element is made of plastic,
or the thin plastic housing bends, because return to zero is a little slow.
I needed a rough measurement today, the scales were calibrated weeks ago indoors
but were stored and quickly used today at about 10 C.
Power up, zero, 5g weight measured 4.99g ... good enough.
As the cost of my scales was below £5 with p&p I can't complain,
(I have spent more on calibration weights since)
and as I mentioned above, what other quantitative measurement in amateur chemistry is this accurate?
I can definitely recommend the cheap Chinese eBay 20g x 0.001g and 300g x 0.01g scales for amateur chemistry use.
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WeaponsRx
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Yea my $89 ebay balance thats .001 up to 300grams if flawless..... just level the baby out with the adjustable 4 screw in rubber supports, with its
built in level, install the enclosure shield, plug her in, let it sit for an hour or two, calibrate, weight out what you want, come back the next day,
try again no calibrating nothing, weight the same. THANKS CHINA!
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88man1
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I just found this forum and wanted to share what I have found recently. I know some folks are ok with a few of the low cost ebay balances. Personally,
I haven't had much success with those items especially when it comes to durability. Sure they may work for a few weeks but they seem to fail pretty
frequently. Again, just my experiences. One line that I have had some success with is the Tree HRB balances. These are built with pretty high quality
components and in my opinion are the best lab balances available that don't cost a fortune.
http://www.1800scales.com/Balance-1milligram.html
The original poster mentioned needing a 0.001 gram balance and they do have a 300 x 0.001 gram analytical balance available that will easily fit
within his budget. The HRB balances are designed and imported into the U.S. by a veteran in the scale industry who knows his stuff having worked for
several high end manufacturers so that is why I mention that it's worth a consideration if you have a few more dollars.
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Sulaiman
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P.S. calibration weight(s) = essential.
I have three slightly different eBay Chinese 100g calibration weights (one more in post)
With my 300g x 0.01g scales I cannot reliably measure any difference....surprising.
The weights were advertised as M2 class which for 100g is +/-16mg
so the consistency of weight from different sources is excellent.
Has anyone ever had eBay Chinese calibration weights calibrated? ... just curious.
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