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• # The end of the kilogram we knew or at least how the metrologists knew it.

Discussion in 'Suggest a forum topic' started by rafaelherrera, Jan 12, 2019.

1. ### rafaelherreraMemberEngineeringClicks Expert

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How does this change affect?

On Friday, November 16, the 26th General Conference on Weights and Measures was held in the French city of Versailles, where several dozen countries voted in favor of overthrowing Le Grand Kilo and redefining the kilogram and three other standard measuring units: the ampere, for the electric current; the kelvin, for the temperature, and the mole, which describes the quantity of a chemical substance.

Until now, it had been determined by the grandfather of all kilos: a metal cylinder enclosed in a vault in France. Made of an alloy resistant to corrosion of 90% platinum and 10% iridium. His role has been crucial, as the basis for the world-accepted system for measuring mass, called the Grand K. His copies are distributed around the world, with his own reference, as close as possible to the original

From now on, the seven units in the International System of Units will no longer be defined according to material objects; they will be established only by abstract constants of nature.

So, instead of using the classical kilogram as a criterion, scientists will use the Planck constant to define a kilogram, which would vary the mass by about 50 micrograms less (0.000000005 kg). No one who is outside an advanced physics laboratory will notice the change. Although the new formula will not affect your bathroom scale, the change is expected to have practical applications in computing, nanotechnology, pharmaceuticals, the study of climate change and other sciences where accurate measurements are required.

The Planck constant, h (6.62 * 10-34 m2 kg / s), is the quantum mechanical quantity that relates mass to energy through E = mc2, one of the most popular equations in physics. The redefinition of the kilogram using a universal constant has been an exhausting project, involving decades of research in laboratories around the world, the result of two Nobel prizes in quantum physics and the construction of some of the most intricate machines ever made. How is quantum related to weight in kilos? How will it be measured?

Here is the difficult part. The balance Kibble, invented in 1975 by the physicist Bryan Kibble, has an electromagnet that pulls on one side of the scale and a weight on the other. The electromagnets generate a force, like the cranes that are used to lift and move the old cars. The impulse of the electromagnet, the force it exerts, is directly related to the amount of electrical current that passes through its coils. There is, therefore, a direct relationship between electricity and weight.

Then, in principle, scientists can define a kilogram, or any other weight, in terms of the amount of electricity needed to counteract its strength. By measuring the current flow through the electromagnet with extraordinary precision, researchers can calculate the mass to an accuracy of 0.000001%. This advance has made the Grand K give way to the small h.

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3. ### john12Well-Known MemberEngineeringClicks Expert

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It makes sense to move forwards as technology improves, I reckon. It's just amazing that they can, and they need to, measure things to such precision!

4. ### MSHOfficialWell-Known MemberEngineeringClicks Expert

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That is also what happened in 1952. NIST completed its first accurate measurement of the frequency of cesium clock resonance. It was called the NBS-1. This clock was based on the cesium-133 it was a cesium-beam clock and used as a calibration source, it was built by Louis Essen and Jack Parry in 1955 in the national physical laboratory in England. The cesium standard atomic clock’s calibration was done according to astronomical time scale Ephemeris time. Therefore, internationally this was accepted as the most accurate time and the definition of a second was based on this atomic time clock. The definition of SI second is "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom" (at a temperature of 0 K).

5. ### rafaelherreraMemberEngineeringClicks Expert

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Completely agree. I think the most important thing is the possibility of being as precise as possible. Reduce errors and tolerances. I will be aware of information about projects that already use this method.

6. ### rafaelherreraMemberEngineeringClicks Expert

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Wow, I did not know about it. Good contribution.

I looked over the whole process and what the experiment consisted of and got the image of NBS-1, the first cesium atomic clock built by the US National Bureau of Standards (now the National Institute of Standards and Technology (NIST) in 1952.

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7. ### MSHOfficialWell-Known MemberEngineeringClicks Expert

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If you found that interesting you should also look into fountain atomic clocks. They are the most innovative ones. But still in GPS satellites we use the older cesium and rubidium atomic clocks. Their accuracy is like they don’t miss a second in 300,000 years if I am not wrong. However, even this is not precise enough for the GPS. Can you guess how much error 50ns of time shift can cause in terms of distance on earth?

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Super amazing right? You should also check out how DGPS ( differential GPS ) works. Its another marvelous architecture, its just additional equipment to GPS, to reduce some errors caused by the atmosphere. And the GPS receiver on your phone initializes in a couple of seconds. Thanks to DGPS and mobile service providers. DGPS has land based stations through which it can accurately pinpoint another devices location by calculating the time shift in sending and receiving the signals.

8. ### john12Well-Known MemberEngineeringClicks Expert

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Yeah, I remember during my flying training we had to learn all of the potential errors of GPS. I've forgotten most of them now but I think there's about seven or eight different things, and still it works so well!
Amazing really.

9. ### tmark938ModeratorEngineeringClicks Expert

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What is the view of others on here?

Is this just making change for the sake or it or is it fully justified?

10. ### MSHOfficialWell-Known MemberEngineeringClicks Expert

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Nice to know you took flight training! What do you fly? Did you take a Private pilot license ?

GPS is just getting more and more precise by using more accurate atomic clocks. More number of satellites. Using other systems like DGPS etc

Main sources of error from the principle of work system are multipath error, where signals from GPS first hit a reflective surface before reaching the receiver in your phone. The atmospheric errors like the tropospheric error and ionospheric error, when GPS signals pass through them the signals change wavelength or frequency or both, causing a delay in transferring the signal. Or relativistic effects, like the GPS moving in such high speeds the clocks seem to tick slower than the ones on earth, or general relativity effect where the clocks tick faster on the satellite because they are away from the earths huge gravitational field.

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