When do two kilogram fields are the same the same? When each goes to another place and adsorbs the different amount of moisture and contamination.
When investigating this issue, the National Institute of Standards and Technology (NIST) of the U.S. and the National Research Council (Canada) is working with measuring laboratories in North, Mid and South America to better understand how the precise weight increases and falls over time.
They hope the results will benefit international trade, where even small measurement inaccuracies can have significant effects.
In order to ensure that a pound of potatoes in the grocery shop actually pound a pound, the balance of shop must be calibrated regularly. For this type of calibration, consumers depend on the ultimate mass artifacts, pieces of metal whose mass has measured in detail. Scientists know the mass because each artiffact is in turn compared with other artifacts in an inverse chain of comparisons that extend to the basic definition of its own mass.
Standards laboratories maintain artificial mass for comparisons such as these, which ultimately used to galibrate everything from food balances to bathrooms. From time to time, these laboratories need extra mass artiffact or replacement for their collection.
In the first few months of life, however, the mass of new artiffact can change dramatically as the new metal breaks its molecules from its environment.
There is some disagreement about how long scientists have to wait before they can be certain that new artificial mass is stable. Therefore, NIST and NRC Canada designed the huge new experiment to help solve this issue.
The experiment consists of 60 pounds one-kilogram the same, which is ordered to make one rod of high quality stainless steel. About half of these 60 units were distributed to 29 countries within the Inter-American Metropolitan System (SIM), a network of national metallurgy organizations (NMIs) located in North, South and Central America, as well as island countries.
For a year or more, each country's SIM representatives will measure the mass of their activity every few months and send the data to NIST and NRC Canada. They will also monitor the environment of each mass, including laboratory temperature, barometric pressure, humidity and volatile organic compounds (VOCs), measure air quality.
"The whole thing will be a massive stable study on a scale that nobody has ever done," said NIST physicist Patrick Abbott. "Because the masks were removed from the same rod of steel, you would expect them to have the same long-term response." However, the conditions in the different SIM laboratories are expected to affect the rate the mass changes, depending on features such as height and amount of salt in the air. For the first few months of their lives, the forces are retained in the USA and Canada. Now, half of them will be stored in laboratories near the equator and well into the southern hemisphere.
"So how do the masses go to change?" Abbott said. "Once they go down there, they are not necessarily going to follow the same pattern as they do in North America."
Cat Hair on Catching Pants
There is a new, freshly broken artiffact, such as a sponge: It collects air molecules, and this increases its mass slightly over time. The new artefacts used in this experiment are less than one year old and, therefore, are in a rapidly fast-paced stage of 7 microgram (million grams) order over six months. This could sound too small to issue, but small changes – even if they are unpredictable – can raise uncertainty in laboratory measurements.
"These pressures change," said Abbott. "They're getting things out of the type of air like the black pair of pits in a house with a white battle."
At some point, that process usually prevents or slows down. The question is, how long does a laboratory have to wait before it can be sure that its mass has reached a fixed period? And how does that change depend on the location of the laboratory and common environmental conditions?
Previous studies have tended to be small scale, carried out in one laboratory. Abbott and his colleagues NIST and NRC Canada thought whether a larger scale effort would help to resolve inconsistencies in earlier results.
"At present, many of the studies that have been made have been very local: one laboratory, one person, under one set of conditions," said Abbott. "But someone else else in another laboratory could do the same study and say, under these conditions, we had something completely different, and" continued. So who is really?
"I hope this study will be able to answer the question: If you buy mass for your laboratory, what is a reasonable expectation of when you could put it into a service, and have confidence in it? " Abbott said.
More Than Single Mass
Before distributing the artefacts, NIST and NRC Canada were fully characterized by measuring their density as well as their magnetic side, the quality of the way the material behaves when it is open to magnetic field. Each organization took half of the masses: NRC Canada even took the numbers, and NIST took the ones that have no numbers.
To measure the intensity of half their weight, Canadian scientists used a hydrostatic technique that consistently pressed each artificially in fluids of different known densities. Meanwhile, NIST conducted their tests aerostatic, using a pressure chamber that could weigh artefacts in different air densities.
Although all the masses were to be the same name, Abbott was surprised to find that the first 15 weight he had had a very different intensity of the second 15. He was worried that he had made a mistake – until he discovered that his counterparts in Canada measure the same inconsistency in their weight.
"It turns out that the manufacturer uses two different bargains of different steel with a slightly different density," said Abbott, "and we saw in our measurements."
When exchanging data to see how close the numbers were aligned, Abbott said, "It was beautiful, but beautiful. We used two very different techniques, and there was an excellent agreement for this study."
Earlier this month, NIST and NRC Canada distributed 29 of the 60 types, one for each of the countries participating in the South and Central America. The remaining artifacts will be saved and monitored by NIST and NRC Canada until the study has been completed.
Until May 19, 2019, the definition of the world of growth will continue to be based on the International Prototype Kilogram (IPK), a metal cylinder that was dropped in the late 19th century and kept in a laboratory outside Paris, France. After this date, the formal definition of a kilogram will be redefined to rely on basic consistency of nature. However, kilogram artifacts are expected to be used in many applications, including the spread of the new mass standard.
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