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The Ampere, Redefined

4/11/2014 00:01 AM EDT
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Sanjib.A
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Re: Ampere's long arm
Sanjib.A   4/12/2014 11:04:53 AM
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@Sheepdoll: Wow! That is a very interesting!! Do you have the title of the book and author's name on it? Could you please share those details if you have?

@MeasurementBlues: Thank you for recommending the book. That would definitely be my next one on the list! 

_hm
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Does this effect Volt and Ohm
_hm   4/12/2014 9:09:33 AM
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Since Amp is redefined, will it effect volt and ohm too?

 

pseudoid
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The more accurate "Second"
pseudoid   4/11/2014 6:59:10 PM
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Our college days have taught us that there is a difference between 'accurate' and 'precise'.

OffTopic#2 [But not way off since the following relates to both one of the 7 units of measure and NIST]:

The US Department of Commerce's National Institute of Standards and Technology (NIST) [has] launched the new atomic clock, called NIST-F2, to serve as a new US civilian time and frequency standard, along with the current NIST-F1 standard. NIST-F2 would neither gain nor lose one second in about 300 million years, making it about three times as accurate as NIST-F1, which has served as the standard since 1999, NIST said.  NIST-F2 is now the world's most accurate time standard, NIST said in a statement. For now, NIST plans to simultaneously operate both NIST-F1 and NIST-F2.

 "If we've learned anything in the last 60 years of building atomic clocks, we've learned that every time we build a better clock, somebody comes up with a use for it that you couldn't have foreseen," said NIST physicist Steven Jefferts, lead designer of NIST-F2.

Both clocks use a "fountain" of cesium atoms to determine the exact length of a second.  Both NIST-F1 and NIST-F2 measure the frequency of a particular transition in the cesium atom - which is 9,192,631,770 vibrations per second, and is used to define the second, the international (SI) unit of time.

The key operational difference is that F1 operates near room temperature (about 27 degrees Celsius) whereas the atoms in F2 are shielded within a much colder environment (at minus 193 degrees Celsius).  This cooling dramatically lowers the background radiation and thus reduces some of the very small measurement errors that must be corrected in NIST-F1.   Pasted from <http://www.business-standard.com/article/pti-stories/new-super-accurate-atomic-clock-developed-114040400488_1.html>

Measurement.Blues
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Re: How Odd...
Measurement.Blues   4/11/2014 4:46:24 PM
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Unless your VOM has nanoamp resolution, you won't see the difference.

pseudoid
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Re: How Odd...
pseudoid   4/11/2014 4:41:28 PM
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Oh forget it! 

I am just gonna stick with the old Triplett VOM to measure Amps.  It can't be that inaccurate of a reading!  I know all about parallax and how to compensate for it! 

How many digits of accuracy would you like with your french fries, Sir?  LOL!

MeasurementBlues
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Re: How Odd...
MeasurementBlues   4/11/2014 4:08:30 PM
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And from the source itself

http://www.bipm.org/en/si/history-si/name_kg.html

The reason why "kilogram" is the name of a base unit of the SI is an artefact of history.

Louis XVI charged a group of savants to develop a new system of measurement. Their work laid the foundation for the "decimal metric system", which has evolved into the modern SI. The original idea of the king's commission (which included such notables as Lavoisier) was to create a unit of mass that would be known as the "grave". By definition it would be the mass of a litre of water at the ice point (i.e. essentially1 kg). The definition was to be embodied in an artefact mass standard.

After the Revolution, the new Republican government took over the idea of the metric system but made some significant changes. For example, since many mass measurements of the time concerned masses much smaller than the kilogram, they decided that the unit of mass should be the "gramme". However, since a one-gramme standard would have been difficult to use as well as to establish, they also decided that the new definition should be embodied in a one-kilogramme artefact. This artefact became known as the "kilogram of the archives". By 1875 the unit of mass had been redefined as the "kilogram", embodied by a new artefact whose mass was essentially the same as the kilogram of the archives.

The decision of the Republican government may have been politically motivated; after all, these were the same people who condemned Lavoisier to the guillotine. In any case, we are now stuck with the infelicity of a base unit whose name has a "prefix".

MeasurementBlues
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Re: How Odd...
MeasurementBlues   4/11/2014 4:07:37 PM
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From the University of North Carolina, Again I would go with this over Wikipedia.

http://www.unc.edu/~rowlett/units/sifundam.html

 

MeasurementBlues
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Re: How Odd...
MeasurementBlues   4/11/2014 4:03:48 PM
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I would trust NIST over Wikipedia any day.

pseudoid
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How Odd...
pseudoid   4/11/2014 3:50:48 PM
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OffTopic >> Thank you for the link but I find it quite odd that NIST (old NBS) calls out the unit of mass as being the Kilogram (kg) rather than a gram (g).

Wikipedia provides the following historical perspective:

In 1921 the Convention of the Metre was revised and the mandate of the CGPM (Conférence générale des poids et mesures) was extended to provide standards for all units of measure, not just mass and length. In the ensuing years the CGPM took on responsibility for providing standards of electric current (1946), luminosity (1946), temperature (1948), time (1956) and molar mass (1971).  Those are not too far away in the rear view mirror!

MeasurementBlues
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Re: Ampere's long arm
MeasurementBlues   4/11/2014 2:30:39 PM
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@Sheepdoll,

I recommend reading The Story of Electrical and Magnetic Measurements by Joseph F. Keithley.

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