The definition of the ampere is changing.

[Coppersmith]

See this article: https://www.designboom.com/technology/kilogram-grande-k-measurement-weight-standard-11-14-2018/

The relevant paragraph is the last one:

It is expected that the outcome of the vote on friday will see the planck constant put into effect but what does this mean for the regular person? the actual changeover won’t happen until may next year. that is when labs will be able to start making their own measurements of the kilogram using the kibble balance. when it does any other metric defined using the kilogram will be changed and updated too. in total, four units will be given new definitions: the kilogram, the ampere, the kelvin, and the mole. it is true our everyday lives will be essentially unchanged by the shifting of the weight measurement standard, but it is a big deal for organizations and industries that rely on hyper-accurate weight readings.

 

[MAC702]

Good read, except for some incomplete sentences and zero usage of capital letters (except for an initialism), neither for names or to start sentences. It seemed odd for a technical article. I found it annoying.

Worth it for the info and photographs, though.

 

[ggunn]

See this article: https://www.designboom.com/technology/kilogram-grande-k-measurement-weight-standard-11-14-2018/

The relevant paragraph is the last one:

It is expected that the outcome of the vote on friday will see the planck constant put into effect but what does this mean for the regular person? the actual changeover won’t happen until may next year. that is when labs will be able to start making their own measurements of the kilogram using the kibble balance. when it does any other metric defined using the kilogram will be changed and updated too. in total, four units will be given new definitions: the kilogram, the ampere, the kelvin, and the mole. it is true our everyday lives will be essentially unchanged by the shifting of the weight measurement standard, but it is a big deal for organizations and industries that rely on hyper-accurate weight readings.

No big deal unless it changes the 310.15 tables.

 

[Carultch]

See this article: https://www.designboom.com/technology/kilogram-grande-k-measurement-weight-standard-11-14-2018/

The relevant paragraph is the last one:

It is expected that the outcome of the vote on friday will see the planck constant put into effect but what does this mean for the regular person? the actual changeover won’t happen until may next year. that is when labs will be able to start making their own measurements of the kilogram using the kibble balance. when it does any other metric defined using the kilogram will be changed and updated too. in total, four units will be given new definitions: the kilogram, the ampere, the kelvin, and the mole. it is true our everyday lives will be essentially unchanged by the shifting of the weight measurement standard, but it is a big deal for organizations and industries that rely on hyper-accurate weight readings.

I don't understand how the Kelvin, and subsequently the rest of the temperature scales, would be changed by refining the definition of the kilogram. This is based on the triple point of pure water, which doesn't have anything to do with kilograms.

As for how it effects us, unless you are depending on Le Grand K, or a replica of it, as a reference kilogram to calibrate your equipment in the first place, it isn't significant enough to matter.

Similar issue happened when they stopped defining the meter based on a reference stick, and instead used the speed of light. That's why there are 9 digits in the definition of the speed of light, instead of just fixing it to a nice round number (3e8 m/s). They had to keep it consistent with the existing definition of what a meter was at the time.

 

[Coppersmith]

No big deal unless it changes the 310.15 tables.

it isn't significant enough to matter.

Haven't you heard? All 20 amp breakers now have to be relabeled 20.001 amps.

JK

I'm positive it doesn't matter in the least to electricians. I just thought it would be of interest to the group.

 

[JFletcher]

I don't understand how the Kelvin, and subsequently the rest of the temperature scales, would be changed by refining the definition of the kilogram. This is based on the triple point of pure water, which doesn't have anything to do with kilograms.

As for how it effects us, unless you are depending on Le Grand K, or a replica of it, as a reference kilogram to calibrate your equipment in the first place, it isn't significant enough to matter.

Similar issue happened when they stopped defining the meter based on a reference stick, and instead used the speed of light. That's why there are 9 digits in the definition of the speed of light, instead of just fixing it to a nice round number (3e8 m/s). They had to keep it consistent with the existing definition of what a meter was at the time.

I also wonder about why the mole is being redefined... As far as I remember, a mole is Avogadro's number of molecules. And isn't an amp a joule per secon

the article did not state why it lost weight... I wonder if it's because the gravitational pull of the planet has changed (affecting weight not mass), or a tiny fraction of that platinum and iridium was radioactive, and Decay has caused the weight loss.

Since the old weight is going to be obsolete, I wonder if they will put it in a museum somewhere for people to see. a 1 kilogram platinum and iridium cylinder would be something neat to see in the Smithsonian.

 

[rbalex]

This is the International Bureau of Weights and Measures' (the folks that set the standard) statement. They are attempting to define the base units in a manner that does not involve interdependent values. For example, the definition of Ampere currently references Newtons and metres and Newtons are ultimately derived from metres, Kilograms, and seconds. See the BIPM's summary of units. (Save a copy before they change everything)

Side NOTE: Several of the base units were/are defined in terms of seconds (the metre still is) and it took several years to independently define the second.

Added a note to save a copy of the summary of units.

 

[Carultch]

I also wonder about why the mole is being redefined... As far as I remember, a mole is Avogadro's number of molecules. And isn't an amp a joule per secon

the article did not state why it lost weight... I wonder if it's because the gravitational pull of the planet has changed (affecting weight not mass), or a tiny fraction of that platinum and iridium was radioactive, and Decay has caused the weight loss.

Since the old weight is going to be obsolete, I wonder if they will put it in a museum somewhere for people to see. a 1 kilogram platinum and iridium cylinder would be something neat to see in the Smithsonian.

Avogadro's number is not defined directly as a fixed number, and we don't have the precision to know all 24 digits of it. The mole is defined based on 12 grams of Carbon-12 atoms, so if the gram & kilogram are redefined, the dependent unit of the mole is also redefined. One competing idea for redefining the kilogram was to fix Avogadro's number, and use a sphere of silicon 28 atoms to generate the kilogram. It would be much simpler for the general public to understand, but that method couldn't be achieved with enough precision to compete with the fixing Planck's constant method.

The Ampere changes, because it is based on the magnetic force between two wires carrying equal current with free space between, and the force unit depends on the kilogram. It is a Coulomb per second, but the Ampere is easier to measure than the Coulomb, so the Coulomb is defined from the Ampere instead of the other way around.

Le Grand K loosing mass is not an illusion because of the gravitational pull. What actually is happening is the replicas of it, stored under the same conditions, diverge in mass as they check each one. Le Grand K lost mass relative to the average. They know gravitational factors vary at that level of precision, and the weighing method compensates for that issue.

 

[romex jockey]

https://simple.wikipedia.org/wiki/Planck_constant

oh boy......hmy:~RJ~

 

[Tony S]

For goodness sake, please don’t start another interminable debate about SI units :weeping:

 

[JFletcher]

Avogadro's number is not defined directly as a fixed number, and we don't have the precision to know all 24 digits of it. The mole is defined based on 12 grams of Carbon-12 atoms, so if the gram & kilogram are redefined, the dependent unit of the mole is also redefined. One competing idea for redefining the kilogram was to fix Avogadro's number, and use a sphere of silicon 28 atoms to generate the kilogram. It would be much simpler for the general public to understand, but that method couldn't be achieved with enough precision to compete with the fixing Planck's constant method.

The Ampere changes, because it is based on the magnetic force between two wires carrying equal current with free space between, and the force unit depends on the kilogram. It is a Coulomb per second, but the Ampere is easier to measure than the Coulomb, so the Coulomb is defined from the Ampere instead of the other way around.

Le Grand K loosing mass is not an illusion because of the gravitational pull. What actually is happening is the replicas of it, stored under the same conditions, diverge in mass as they check each one. Le Grand K lost mass relative to the average. They know gravitational factors vary at that level of precision, and the weighing method compensates for that issue.

:thumbsup: thank you for the detailed reply.

And I meant coulomb per second. Good catch.

Perhaps you or another can answer one final question I have... How far off was the old kilogram to the new? Considering that most of humans achievements up this point have been completed satisfactorily with the old kilogram, in What fields would a billionth or trillionth of a gram difference make? Astrophysics in measuring masses of stars 4 million light years away or something?

 

[MAC702]

I don't think it matters for anything. YET. But in a few million years or so it might, and we now have the technology to define it differently, so might as well. It's making a few people feel really important.

 

[LarryFine]

the article did not state why it lost weight... I wonder if it's because the gravitational pull of the planet has changed (affecting weight not mass), or a tiny fraction of that platinum and iridium was radioactive, and Decay has caused the weight loss.

"There's that word again. "Heavy." Why are things so heavy in the future? Is there a problem with the Earth's gravitational pull?" ~ Doc Brown In Back to the Future

 

[Carultch]

:thumbsup: thank you for the detailed reply.

And I meant coulomb per second. Good catch.

Perhaps you or another can answer one final question I have... How far off was the old kilogram to the new? Considering that most of humans achievements up this point have been completed satisfactorily with the old kilogram, in What fields would a billionth or trillionth of a gram difference make? Astrophysics in measuring masses of stars 4 million light years away or something?

It is more about the "measure of spread" that will change, rather than the "measure of center". Le Grand K has differed from its replicas by about 50 micrograms, which is a relative uncertainty of 5e-8. The new definition will maintain the kilogram as close as possible to what we currently use as the definition. Planck's constant can be measured to a relative uncertainty of 1.8e-8. The new definition no longer references a definition that is a moving target, and the relative uncertainty is only limited by how precise the apparatus can measure.

Astrophysics is probably not where this would matter, as our knowledge of a distant star's mass is very imprecise. As an example, the nearest non-sun star's mass is only known to a relative uncertainty of 1.8%. You can know your own mass more precisely than that, with a household scale. Applications where redefining the kilogram matters, are yet to be determined, but it will matter in research where high precision is important. Maybe eventually in industry it will make a difference, but that could be decades away. Think topics of research in the study of the small, rather than the study of the large, like quantum mechanics, where this change would matter.

Recall those leap seconds that you occasionally hear about, that affect official timekeeping? At one point, the day was exactly 86400 seconds long, and that was how we defined the second. But thanks to atomic clocks, the second's definition is no longer based on the Earth's rotation rate (which is also a moving target). The atomic clock and the precision it offers over conventional clocks, is what allows your GPS to work. The satellites measure distances by atomic clock timing of the time it takes the radio signal to make the round trip to the receiver, and it makes a serious difference in the outcome of your GPS results.

 

[JFletcher]

Thank you again for the detailed explanation, although it is slightly over my head. I can completely understand the GPS though, if there was creeping errors in that, you would either have to reset all of your points to 0 at sometime, or the GPS would indicate you are quite far away from your actual position, which would kind of suck if you were lost, or needed 911... or when your Garmin GPS screams that you need to take an immediate left turn while you're on a bridge LOL

 

[GoldDigger]

Thank you again for the detailed explanation, although it is slightly over my head. I can completely understand the GPS though, if there was creeping errors in that, you would either have to reset all of your points to 0 at sometime, or the GPS would indicate you are quite far away from your actual position, which would kind of suck if you were lost, or needed 911... or when your Garmin GPS screams that you need to take an immediate left turn while you're on a bridge LOL

Fortunately the GPS receiver does not need to know the time, just read differences in the satellite signals. And they can read each others time stamps at any time to make sure no clocks are drifting.
The absolutely essential information that has to be kept updated is the precise orbital path and orbital position of each satellite.