Calibrating ebay 0.001 scales

[naja naja]

G'day all. I just purchaced sum 0.001 scales from ebay. I actually bought them 2 months or so ago, but just got them back from where I'd left them. Long story, but picked em up and left em at a mates house in a safe spot, but they been on holiday and only just been able to get them to testem out.

I only payed $60 and now there $115, so I'm pretty happy bout that, but can sum1 help explain how to use them properly?

As u can see, the 5g weight is weighing out by 0.020g, the 10 g weight weighs 10.033. SO is this just my scales or is it just poorly manufactured weights? Can I calibrate these scales? the instruction manual doesn't say u can.

If it is just my scales, how do I work around this prob? Id there any way to adjust for difference or will every gram weighed be out by upto 0.004g?

cheers all

Naja

Edited after a typo was pointed out. Thanks BB

Edited September 5, 2006 by naja naja

[bloodbob]

As u can see, the 5g weight is weighing out by 20g, the 10 g weight weighs 10.033. SO is this just my scales or is it just poorly manufactured weights? Can I calibrate these scales? the instruction manual doesn't say u can.

No actually I can't see if you were out by 20grams I'd be hell suprised thankfully I looked at the picture. 0.033 really ain't that much it could be the weights. However this might not be really much a of a problem. 0.4% probably isn't going to matter that much in the end.

[Tripitaka]

should be able to calibrate them using the Mode function. If you cannot, which i doubt,, I am sure you could get around it using the TARE function.

What could you possibly be measuring that requires such accuracy,lol?

Should be able to post your parcel soon mate, have been quite busy!

[sobriquet]

G'day all. I just purchaced sum 0.001 scales from ebay. I actually bought them 2 months or so ago, but just got them back from where I'd left them. Long story, but picked em up and left em at a mates house in a safe spot, but they been on holiday and only just been able to get them to testem out.

I only payed $60 and now there $115, so I'm pretty happy bout that, but can sum1 help explain how to use them properly?

As u can see, the 5g weight is weighing out by 20g, the 10 g weight weighs 10.033. SO is this just my scales or is it just poorly manufactured weights? Can I calibrate these scales? the instruction manual doesn't say u can.

If it is just my scales, how do I work around this prob? Id there any way to adjust for difference or will every gram weighed be out by upto 0.004g?

cheers all

Naja

Hi Naja.

The error does seem excessive. 0.4% in the case of the 5g weight being out by 0.020 grams.

Your scale appears to be similar to a Chinese OEM type:

http://digitalscalestore.stores.yahoo.net/20gx01csihip.html

and that indicates an accuracy of 0.002 grams which is 10 times more accurate than what you are getting. The good news is that it says that that scale is capable of being calibrated.

So it might be just a simple calibration is needed.

Edited August 29, 2006 by eNo

[naja naja]

should be able to calibrate them using the Mode function. If you cannot, which i doubt,, I am sure you could get around it using the TARE function.

What could you possibly be measuring that requires such accuracy,lol?

Should be able to post your parcel soon mate, have been quite busy!

Cheers Tripitaka, lookin 4ward to it.

When I press funtion it just swaps between, g, gr, ct and oz. How do other scales work?

Anywayz, I guess I can live with a 0.4% discrepency.

And these are the 10g x 0.001 model not the 20g x 0.002 model.

ebay scales

This is not the seller I got mine from. My seller sold scales only and had over 1000 sales and 99.9% positive feedback.

They are the same brand though and they must be calibratable, otherwise wats the point of sending me calibration weights?

Edited August 29, 2006 by naja naja

[PD.]

This is from my scales naja,

1, turn scales on.

2, wait till display reads 0.00 (or in your case this would be 0.000) then push and hold down the units key (g, oz etc) for 3 seconds and the LCD will display "CAL".

3,Press the units key again and the screen will display "CAL" followed by the required calibration weight.

4, Place the required weight on the plate and the screen will display "PASS" then return to normal mode.

Done.

hope that helps.

Edited August 29, 2006 by Passive Daemon

[Auxin]

1st, did you read the instruction booklet? lol, if there is one start there

Did you touch the calibration weights? Calibration weights should never contact skin- clean them off real good, handle them 'only while wearing a clean lint free static free cotton glove' (ok, I use a clean cloth lol). If mode doesnt bring up a calibration option try holding down mode, if that works it will start blinking a request for a specific calibration weight or give you a choice. Oh and re-calibrate every 6-12 months.

Nice scale

[naja naja]

Yeah, instuction book had no info on calibrating. and ofcourse I touched them with my fingers , I'll use my cotton gloves from now on.

I'll go try calibrate now.

Glad u like the scales Auxin. I took my time and bought what I thought was the best quality for the price range. For $60, I rekon it's a sweet deal, even if they arn't 100% milligram acurate.

Cheers all

Naja

Edited August 29, 2006 by naja naja

[hairyplant]

Yeah, ya gotta calibrate em, but there will always be an error with any type of scales. A $1000, 0.001g laboratory balance will have an error of around +or-0.005 to 0.001g. I have a very similar set of ebay scales to those pictured, and I dont expect anything close to this kind of accuracy from them. The thing to aim for is repeatability

And always use a flat surface.

A reliable set of scientific scales will set you back at least AU$1000.

imo that error of 0.02g is not all that bad!!

[naja naja]

yeah kewl, and since it's +0.4%, it will only give me higher weights than wat I'm weighing, not the dangerous lower reading, that could result in an unwanted higher dose.

In theory, weighing 100mg or less won't even register the discrepency.

And no matter wat combo of holding down button I try, no cal setting comes up. When I hold TARE it turns off, but nothing special happens when I turn it back on. Guess the weights are just to give u an Idea of accuracy. It does have a QC sticker on it.

[mark80]

yeah kewl, and since it's +0.4%, it will only give me higher weights than wat I'm weighing, not the dangerous lower reading, that could result in an unwanted higher dose.

In theory, weighing 100mg or less won't even register the discrepency.

And no matter wat combo of holding down button I try, no cal setting comes up. When I hold TARE it turns off, but nothing special happens when I turn it back on. Guess the weights are just to give u an Idea of accuracy. It does have a QC sticker on it.

Try taring a beaker. Then add exactly 5ml of DH2O (use a micropipette) and see what it comes up with. Really depends on your accuracy of volumetric measures. I know this method works great for less accurate scales.

[Tripitaka]

DH2O

Are you crazy man, dont you realise how dangerous this stuff is???

[mark80]

DH2O

Are you crazy man, dont you realise how dangerous this stuff is???

Aghh yeah

Not heavy water!

Sorry this just my free hand coming into play I mean distilled water.

[naja naja]

2 probs, scales only go up to 10g. Where to find a beaker small enough, and then where the fuck am I supposed to find a micropipette?

Naja

But I'm happy for now, 1000ug would only be 996ug. Even if I were lucky enough to have to weigh up cid, this would be accurate enough, me thinks. For every 100ug I'd only be 99.6ug. I can live with that sort of accuracy. Now to find sum fluffy white cid(in my dreams).

But, Since 10mg would be the lowest weighed, she'll be right.

Edited August 29, 2006 by naja naja

[reshroomED]

Naja, I'd check your 'standard' weights on something accurate.

'Real' standards are worth *far* more than you paid for the scales.

Instrument accuracy should be stated as +- % of the range (range being scope of measurement ie. +-1% @ 0-1kg would mean a 50g standard weight should display between 49g and 51g. Linearity and repeatability are other important factors that are generally not mentioned with cheaper scales.

That being said, you've probably got a reasonable deal. Just don't expect them to be quite as accurate as advertised.

All instruments are 'calibratable' to some degree. Electronic devices more-so.

I (used to) design measurement and controls systems for the oil/gas industry (tightest specs you'll see this side of NASA). If you're willing to take the back off one of these I can guide you through a calibration as long as you have quality 'standard weights'. pm me for more.

cheers

ed

2 probs, scales only go up to 10g. Where to find a beaker small enough, and then where the fuck am I supposed to find a micropipette?

Naja

But I'm happy for now, 1000ug would only be 996ug. Even if I were lucky enough to have to weigh up cid, this would be accurate enough, me thinks. For every 100ug I'd only be 99.6ug. I can live with that sort of accuracy. Now to find sum fluffy white cid(in my dreams).

But, Since 10mg would be the lowest weighed, she'll be right.

[naja naja]

I'm broke as for the next few weeks and even then can't spend money on calibration weights. When I can, i'll PM u. But until then, I'll just concider them (fairly acurate) and make sure I'm not dealing with anything where small discrepencies can make big differences. The cal weights, certainly do not look great quality, but after fiddling around, cleaning the weights, the weights were reading 5.017 and 10.034 respectively. Both out by the exact same percentage. I rekon the suggests the weights may be accurate and the scales are out by 0.37%. Wat r ur thoughts?

[Auxin]

the weights were reading 5.017 and 10.034 respectively. Both out by the exact same percentage.

Definatly a calibration issue. A scale like that has to be calibratable... look for manufacturers website or google with whatever info is printed on the bottom.

[nmethyl]

I'm not trying to be an advertising whore for my mate, but he has a balance on e-bay. Lots of the lab surplus he picks up doesn't sell well to already established labs, so told him to throw anything like that on e-bay in future.

http://cgi.ebay.com.au/AND-HF-300G-Lab-Bal...1QQcmdZViewItem

[reshroomED]

make sure I'm not dealing with anything where small discrepencies can make big differences.

That's the main point I was getting that.

A few years ago it was a pretty simple rule that 'cheap instruments aren't good and good instruments aren't cheap'. Thesedays I read good reports on a lot of cheap gear (particularly from China). The problem lies in that this equipment hasn't been tested over time, as the reputable brands have.

Perhaps their build-quality provides an 80% 'up-to-spec' turn out, and they're happy to please only 80% of their clientele. Or a 100% 'up-to-spec' , yet won't hold a calibration over time. Or be a good, reliable unit.

If you're looking at mg measurement I'd assume that reliable accuracy is pretty important.

The cal weights, certainly do not look great quality, but after fiddling around, cleaning the weights, the weights were reading 5.017 and 10.034 respectively. Both out by the exact same percentage. I rekon the suggests the weights may be accurate and the scales are out by 0.37%. Wat r ur thoughts?

I'm guessing they're gram weights? For one, the weights may be calibrated to suit the scale, rather than vice-versa. Also you only need a small nick or bit of corrosion to alter their weight.

Regardless, that seems a bit good to be true (not doubting you, just that that neat an error would attract my attention even when calibrating a critical-service device).

To accurately calibrate a device there are several factors that must be taken into account.

Very few devices have a linear input vs output relationship. They're usually a quite complex trig equation.

Calibrating at three pts only really ensures your accuracy at those pts.

Then there's repeatability (pretty self-explanatory) and hysteresis ( % input change to cause a rise/fall in output), and a few others.

This is where quality brands come into it. You can rely on their accuracy be good at all pts of the scale.

I'd recommend measuring your weights on an accurate scale (lab, large jeweller, etc) and calibrating to them. You can take some small, different sized peices of metal etc and weigh them to use as spot checks at different pts.

If you want to weigh something small I'd suggest placing the 5g weight on and using the tare button. Should be reasonably accurate around that pt.

And this is what it comes down to really. How accurate do you need to be?

ed

[naja naja]

Twosee-??????? accurate.

SO 10-30mg range, accurate within a milligram or two would be suitable.

The advert for this brand states" You used to have to pay $1000+ for good jewellery scales previously, but no longer with these" or sumthing to that effect.

The scale repeatably weighs the cal weights the same to the milligram. So repeatability is there. I have a few gemstones that I could easily get the local jeweller to weigh for me to use as extra cal weights. (Also be good to know just for my own interest.)

Edited August 31, 2006 by naja naja

[naja naja]

Yaaaaaaayyyyyyyyyyyy!!!!!!!!!!!1 I found out how to calibrate my scales! For anyone else with these scales or if the instructions don't say how. (like mine)

1. under power off condition, press "TARE" switch till the scale displays the INS (internal statement number)

2. press TARE again, then it displays "0.000g"

3. put standard weight of 5g on the scales

4. press "TARE" after the digital display is stable, then it displays "5.000g"

5. take the 5g weight away til it displays "0.000g", then put a 10g weight on the centre of the weighing area.

6. press "TARE" after digital display is stable, then it displays "10.000g"

7. press "TARE" til power off

8. press "ON/OFF", then test the scale is accurate or not. If not, repeat the process.

SO there ya's go, I did manage to calibrate these 0.001 scales that cost only $60 (now $115) and now they read perfect and repeatable.

I'm stoked. Thanks heaps JJ

Peace out

Naja