Decent laboratory balances?

My adivce is not to see how cheap you can be. Go with a recognized brand such as Ohaus. Ohaus also makes an excellent triple beam balance, but the one I have is not digital.

For less than 120 gm I have an Acculab balance, good to 0,001 gm. I check it regularly with mg calibration weights and it's very close. But it cost about $ 250 IIRC.

Im sorry I know my post don't help much but this thread is bringing a tear to my eye missing my triple beam with accuracy down to .01. Rest in Piece in the evidence room ol' trusty scale you will never be forgoten

Quote: Originally posted by Lambda-Eyde

I've been drooling over some of these balances. They're relatively cheap and affordable by a hobbyist. Where I live, these "brand" scales cost in the thousands of NOK. For example, a Kern 420 g/1 mg scale costs a little below 10000 NOK including VAT, with todays currency rate that's about 1600 USD. Buy used, you say? In a country with barely 5 million inhabitants the market for used laboratory equipment is fairly non-existent...

Thanks for that website, the "My Weigh iBalance 500" scales look perfect for my needs.

I recently bought a cheap digital balance on eBay from a company in Germany and have been very impressed with it. It arrived within a couple of days and for the incredibly cheap price of £70 it is is both precise and accurate to the tolerance that I require.

Here is a picture of the item and the name of the eBay company selling it. It has a user guide in English but it is fairly basic, however I found I didn't need it as it is quite simple to use.

I have no relationship with this company other than being a satisfied customer.

Pocket drug dealer scales get John's vote for 0.01g

I have posted about this before, but you would be surprised just how accurate those cheap drug dealer pocket scales are.

I spent hour upon hour checking one and various household objects against a calibrated 0.01/0.1mg balance I have; which usually retails at £3k, as opposed to the £6.99 the pocket balance costs.

The results were that the £6.99 balance, reading to 100g at a resolution of 0.01g, is less than 1% off. IMPRESSIVE!

Neither was I using any form of draft shield on the pocket scale, or levelling it. I simply weighed a coin on the calibrated balance, then put it on the pocket scale.

I produced big spreadsheets listing tens and tens of readings across the weight range for that, as well as checking how well things like change functioned as a reference mass, how well balance beams made from rulers functioned as well as dividing things by eye and using digital kitchen scales. Again, the results are far more accurate than you'd imagine, particularly the change. I seem to remember the error on a coin typically being something like 0.05g, regardless of age. Also, because the error is periodic and even, stacks of coins cancel each individual mass error, so it goes down. The error is not from wear and tear, but the Royal Mint dies wearing and the machine tolerances being adjusted. I can see the sine wave over the years on the graph as it's kept in tolerance.

Digital kitchen scales are horribly inaccurate when dealing with a few grams. But their error drops to, again, about 1% as the weight goes over 100g. Meaning, you can use the pocket ones for accurate work up to 100g, then the kitchen ones for hundreds to a kilo.

I then lost all of that work as I formatted the computer, so I need to redo it all. This time I may make a video of it as, with the fridge pumps, I see the question of accurately determining mass appearing fairly often.

Here are the £6.99 pocket scales I was testing

Here is the balance I was checking them against - which showed a <1% error on the £6.99 balance. I did this work so others wouldn't have to spend so much or could get more fun for their money. I was skeptical that these plastic things could even get close to their claimed resolution; accurately. Particularly as they've never been calibrated and I've spilt agar and other rubbish on them, and knocked them around. But I have checked it for you. And they do.

Balances come in fairly standard ranges of accuracy, 0.01g, 0.01/0.1mg and the micrograms. Both the 0.01/0.1mg and micrograms are significantly harder to use in terms of maintaining their accuracy. They need mechanically isolating, to be level, temperature stable, left on for long periods of time and in a humidity and temperature known environment, or the errors from those factors can swamp their resolution. Buying an accurate balance ain't enough.

I also discovered just how much that level of accuracy begins to infiltrate the rest of your work. As a very simple example, I can easily produce huge changes in the mass I'm weighing depending on the amount of water of crystallisation present in a salt. If I produce the anhydrous salt, as soon as it's out the bottle the mass will be visibly going up, quickly, on the 0.01mg/0.1mg balance as it picks up moisture from the atmosphere. It's trickier than you'd imagine.

That piece of tinfoil, as another example, shouldn't really be there - turbulence.

{edit}I should check into having the 0.01/0.1mg one recalibrated. Then I could buy a pack of those pocket balances, check them all and pass them on with a stamp of tolerance. Possibly with bits of nickel or stainless as a reference mass. Problem there being, 0.01/0.1mg and below recalibration is usually pretty darn expensive.



[Edited on 24-1-2011 by peach]

Quote: Originally posted by peach

Both the 0.01/0.1mg and micrograms are significantly harder to use in terms of maintaining their accuracy. They need mechanically isolating, to be level, temperature stable, left on for long periods of time and in a humidity and temperature known environment, or the errors from those factors can swamp their resolution.

Build your own...

Or, if you're good with electronics...

I'm afraid all balances are affected by the numerous instabilities in temperature, air pressure, humidity, the gravimetric field, electrical fields, magnetic fields, vibration and so on, electrobalances included. Question would be whether or not it's a big enough effect to be bothered about in the range you're interested in. For the pocket 0.01g balance, next to zero care is needed.

If a balance displays a stable reading, it doesn't necessarily mean it is the correct reading.

[Edited on 25-1-2011 by peach]

Quote: Originally posted by peach

I'm afraid all balances are affected by the numerous instabilities in temperature, air pressure, humidity, the gravimetric field, electrical fields, magnetic fields, vibration and so on, electrobalances included.

Quote: Originally posted by peach

If a balance displays a stable reading, it doesn't necessarily mean it is the correct reading.

The people who define the kilo and who make the balances for doing so seem to have a difference of opinion.

The microgram comparator used by BIPM; the people who have the IPK in their vault


The 0.1ug FB-2 balance they built.


Sartorius microgram balance, available with metal shielding to counter electrostatic fields, deioniser and a synthetic stone vibration damping table. This is their latest version, which doesn't include a handle, but does include levelling feet. It's $20k+


The Mettler microgram balance. Note the sight glass for levelling. This is because mass is measured by the force it exerts, and the force is directly related to gravity. If the mass isn't directly on axis, it's no longer a scalar value but a vector

The standards for calibration also list room conditions.

This is the International Prototype Kilo (IPK), made in 1879 in London and then sent to France, it is a platinum / iridium alloy with a double chamfered edge for dimensional stability. Platinum provides it with a substantial level of chemical resistance and the 10% iridium (also a platinum group metal) makes it harder to scuff. The IPK was declared by international law to be the kilo, so copies are checked against it by mass comparators (dual pans). The copy always display the error, not the IPK; due to the IPK being considered the definition. The dual pan comparator measures the incremental error between the two, not the absolute mass of the copy alone. The IPK is very rarely outside those three bell jars. Countries buy copies and then maintain them, using those to calibrate their country's balances. There are six primary copies in the vault with the IPK. Calibration certificates are available with traceability back to the IPK, for when mass matters.


In an attempt to put a finite measurement on what a kilo is, the Avogadro project chose to use spheres of silicon, as the semiconductor industry can produce ultra high purity, defect free, monocrystalline boules of it across the globe. Two years worth of polishing and error cancelling later... the lattice spacing of the silicon can be measured with X-ray diffraction and then the sphere's size by interferometry


To end the discussion for good, work is under way to produce a Watt balance to replace the fallible masses with a scientifically solid definition based on physical constants. This has already occurred for the majority of other units. The metre, for instance, is now defined by the speed of light in a vacuum, as opposed to a stick of platinum in the BIPM vault. The watt balance will define the kilo based on a mass's response to voltage and current, both of which have also been defined by physical constants.

Quote: Originally posted by peach

The Mettler microgram balance. Note the sight glass for levelling. This is because mass is measured by the force it exerts, and the force is directly related to gravity. If the mass isn't directly on axis, it's no longer a scalar value but a vector

I don't know if that is a response to my post or what..the Cahn balances require none of that crap...ultra-fine measurement seems a bit off-topic here...I'm not saying that Mettler and Sartorius balances aren't sensitive to problems...I thought I was saying the opposite...I own both brands, not exactly those models...the old 0.1 mg. models of mine have enough drift problems...I have had opportunities to take isolation tables home but I have a bad back...now let's look at the Cahn electrobalance which only requires no trucks driving by:
(also off-topic really because a used one that works may be a little pricey.)
(Cahn Instruments was sold to Thermo Electron...who became Thermo Fisher Scientific in 2006 and had no further interest.)
(I am unaware of any available manual for my model 25, but this model was its replacement.)

The Cahn C-34/C-35 is a very sensitive weight and force measurement instrument. It is designed for weights and forces up to 3.5 grams and is sensitive to changes as small as 0.1 micrograms. The balance may be described as a force-to-current converter. It consists of (1) a balance beam mounted to, supported by, and pivoting about the center of taut ribbon; (2) a torque motor coil located in a permanent magnetic field and also mounted to the taut ribbon; (3) sample suspension fixtures; (4) a beam position sensor system; and (5) controls, circuitry and indicators (See Figure 1).

Weights or forces to be measured are applied to the sample (left) side of the beam which produce a force about the axis of rotation. An electric current flowing in the torque motor also produces a force about the same axis which is equal and opposite to the force from the beam, if the beam is at the beam reference position. This reference position is detected by the beam position sensing system. A greater force on the beam will require a greater opposite force from the torque motor in order to keep the beam at its reference position. Therefore, the current necessary to produce the required torque motor force is a direct measure of the force on the beam. The process of calibration allows this current to be measured in units of weight (grams).

The Cahn C-34 or C-35 may be used in almost any location. It does not require leveling. However, the level should not change after zeroing. Try to avoid exceptionally shaky tables, direct sunlight or drafty locations (such as near air conditioners). For ultimate microweighing, avoid locations near equipment which generate vibrations such as vacuum pumps, air conditioners or heavy machinery.

By 0.1mg, you mean 0.1 milligrams? If so, that's not impossible no.

I do see people purposefully using mg to mean micro, which is u (mu) or, if you're a doctor, mcg - which was introduced to avoid dosing errors due to handwriting.

The Cahn balances claim a resolution of 0.1ug, three orders of magnitude more.

A Cahn 25


BIPM's 0.1ug balance - They are not going to have built that chamber, and the entire balance within, if they could have got the same results from a Cahn out on the desk, unlevelled


[Edited on 26-1-2011 by peach]

Attached is a picture taken minutes ago of a pair of my "old 0.1 mg. models", and the other balances I've mentioned in this thread. Needless to say, I did not pay anywhere near new prices; no one else needs to either if they keep their eyes open. Note the location of the decimal point on the electrobalance; the knob at far left is on the 2 mg. setting. The picture is not good enough to show the pan at A well, or at TARE at all. Edit: I just can't make a post without editing it...I wrote the above before getting the 800 pixel limit message....I thought that applied to the other dimension...so now you'll need some magnification to see that the decimal point is to the left of all the 0's...and the printing right above the readout is: MILLIGRAMS



[Edited on 26-1-2011 by S.C. Wack]

Balance selection

I'm looking to buy a balance with a resolution of 0.01g, and a capacity of 100-200g. So far, I've found a few balances that seem worth it:


1) A $163<a href=http://balance.balances.com/scales/419> Ohaus "Cent-O-Gram"</a>, which is a mechanical balance . Do you think that this is a good idea, or I should stick with digital balances? I couldn't tell if weights were included though. Are weights usually included for mechanical balances?

2) A $99 <a href="http://balance.balances.com/scales/1">My Weigh iBalance 201</a>. Has anyone tried this brand of scales before? I've heard negative things about their pocket scales, but nothing negative so far about this balance. Any opinions?

3) A $184 <a href="http://balance.balances.com/scales/471">Acculab VIC212</a> scale.

What do you think is the best option? Any advice would be greatly appreciated! Thanks!

I wish I had one of these scales . I have been working with this stupid little incredibly inaccurate balance which just doesn't cut it for work requiring a resolution of 5 grams or less.

Quote: Originally posted by Magpie

Or, is it just stupid to buy a cheap scale?

Quote: Originally posted by peach

Here is the balance I was checking them against - which showed a <1% error on the £6.99 balance. I did this work so others wouldn't have to spend so much or could get more fun for their money. I was skeptical that these plastic things could even get close to their claimed resolution; accurately. Particularly as they've never been calibrated and I've spilt agar and other rubbish on them, and knocked them around. But I have checked it for you. And they do.