SoylentNews is people
SoylentNews
Technische Universität Ilmenau and the Physikalisch-Technische Bundesanstalt (the National Metrology Institute of Germany) are developing a balance which is required for measuring the redefined kilogram that will be introduced in 2018. Called the Planck balance, this highly precise electronic weighing balance is not based on weights, but refers to the fundamental physical constant called Planck's constant. The balance will be used worldwide for calibrating other scales or balances so that they correspond to the system with this new method. The new balance will also be used in industry for measuring weights.
In many sectors, there is a significant demand for highly precise balances, including pharmaceutical companies for precise dosing of medical products, in official metrology service labs for calibrating scales for food, and in police departments, for the proof of toxic substances and in ballistics.
The original kilogram, a 4 cm cylinder made from platinum and iridium and stored under three glass domes in a safe near Paris since 1889, is becoming lighter. Over 100 years, it has lost 50 millionths of a gram. As all scales worldwide refer indirectly to this unique kilogram, they all weigh incorrectly, even if by minimal and negligible amounts. Although the original kilogram is becoming lighter, structurally identical copies of the prototype are used worldwide – which means that these copies are slowly becoming heavier relative to the prototype. Therefore, a new standard is required that does not change and cannot be damaged or lost.
In 2018, the new kilogram will be adopted at the 26th General Conference on Weights and Measures. It is not defined by an object or a physical mass, but by Planck's constant. The highly precise, continuously measuring Planck balance, developed by the German university Technische Universität Ilmenau, operates on the principle of electromagnetic force compensation. Simply put, a weight on one side is to be balanced by electrical force on the other. This electrical force is inextricably linked with the Planck's constant and can be directly referred to the new kilogram definition. As this balance is the first self-calibrating instrument of its kind, masses determined as reference or standard masses for calibrating scales and balances are no longer required. Another advantage of the Planck balance is its wide measuring range, from milligrams to one kilogram. At the end of the year, the first prototype of the balance will be available and ready for use.
At last, a balanced article.
(Score: 3, Informative) by esperto123 on Wednesday June 21 2017, @11:22AM (4 children)
The kilogram reference weight is not getting lighter because, until the new definition is adopted, it weighs exactly one kilogram by definition.
What is happening is that the sister weights that are used for several countries and institutions as references are brought together from time to time and their weight compared to the reference (calibrated), and it has been noted that the difference in weights are increasing, some more than others (see https://upload.wikimedia.org/wikipedia/commons/thumb/c/c9/Prototype_mass_drifts.jpg/399px-Prototype_mass_drifts.jpg [wikimedia.org]) and this uncertainty, albeit small, is a problem, even worse considering that the kilogram is the only physical reference still tied to a physical object not a absolute parameter, so if you loose or damaged it, we are screwed.
My only question is if it is decided that the watt balance will be the method used to redefine the kilogram, from what I recall there were a few methods competing, including one that uses a sphere made of a single crystal of silicon (of a single isotope) that is polished to an unbelievable level of precision, so you can know the exact (or to a very very very high precision) number of atoms there, and derive from that the atom weight. Derik from youtube channel Veritasium has a couple of very interesting videos about this.
(Score: 2, Disagree) by Thexalon on Wednesday June 21 2017, @01:37PM (1 child)
Except that you can't, due to isotopes: Some forms of hydrogen have extra neutrons, which makes them a lot more massive than the basic 1-proton 1-electron hydrogen, for example. When you're looking for an extremely high level of precision, that's going to matter.
The only thing that stops a bad guy with a compiler is a good guy with a compiler.
(Score: 2) by esperto123 on Thursday June 22 2017, @11:13AM
That's why the crystal is made pretty much of a SINGLE isotope, I guess they cannot say for sure it has only one isotope because they cannot analyze every atom in there, but it is as close as it gets, it's a quite amazing thing.
(Score: 0) by Anonymous Coward on Wednesday June 21 2017, @02:03PM
So if I steal one half of platinum in the Paris kilogram, it would not actually be lighter? Sounds like a perfect crime, which by definition was not committed.
(Score: 2) by esperto123 on Thursday June 22 2017, @04:29PM
For reference, today scientific american posted an article about the silicon sphere https://www.scientificamerican.com/article/sphere-made-to-redefine-kilogram-has-purest-silicon-ever-created/ [scientificamerican.com]