Kilogram reference

[Wartex]

[IanB]

And?

[AntiProtonBoy]

Actually I think that reference will be soon be (or maybe already is) obsolete.

Scientists are working on polishing a near perfect sphere out of pure silicon. The idea is to count the number of atoms in the sphere and thus compute the exact weight from that.

http://www.theage.com.au/news/national/making-an-exact-difference/2007/06/14/1181414466901.html

[saturation]

Yes, soon, due to chronic instabilities:


http://en.wikipedia.org/wiki/Kilogram

[SeanB]

You mean my 1g calibration masspiece is no longer valid? 1.00000g on last certification against a national standard. I almost never use it, rather the 100g in the same box, or the 20, 10 and 5kg masspieces. Nice having a standards lab nearby, they have a lovely display of old standards and comparators in the foyer. Interesting to look into the metrology lab as well.

[Uncle Vernon]

And?

Would be more interesting in the form of sausages!

[saturation]

A common problem is every time its taken out of its protective case, the metal absorbs some water vapor or dirt, increasing its weight.  So the cleaning has to standardized and effective, to maintain its tolerances.  A bigger problem is if the cleaning removes small amounts of the metal, and also reduces its weight.

The importance of this trivial issue is that the standard is a kg, not a mg or ug, so small variations may influence the smaller values quiet largely.

You mean my 1g calibration masspiece is no longer valid? 1.00000g on last certification against a national standard. I almost never use it, rather the 100g in the same box, or the 20, 10 and 5kg masspieces. Nice having a standards lab nearby, they have a lovely display of old standards and comparators in the foyer. Interesting to look into the metrology lab as well.

[SeanB]

I think the errors divide and multiply to scale with the measurand. Only problem is the other reference masses are gaining with respect to the reference, so they are looking to do a final change to reference to a physical constant. That will allow reproduction of the standard mass anywhere, and will mean a large sale of polished Si balls that are flat down to the atomic level, and whose mass is known down to the atom.

No effect on the gross scale, just a thing to do if you are measuring at the limits of resolution. At least now you will have the Whole SI measurement system in a form that can be reproduced without any other than physical properties of matter and physical constants.