Breaking News
Comments
Oldest First | Newest First | Threaded View
Page 1 / 3   >   >>
MeasurementBlues
User Rank
Blogger
Ampere's long arm
MeasurementBlues   4/11/2014 10:05:47 AM
NO RATINGS
The Ampere is one of just seven basic units of measurement. Others are the kilogram, meter, Kelvin, second, Mole, Candela. But, the ampere is used to derive many other units of measurement such as the Farad, Ohm, Henry and yes, even the volt.

 

MeasurementBlues
User Rank
Blogger
Re: Ampere's long arm
MeasurementBlues   4/11/2014 10:07:07 AM
NO RATINGS
Here's a link to NIST about the SI units.

http://physics.nist.gov/cuu/Units/units.html

 

Sheepdoll
User Rank
Blogger
Re: Ampere's long arm
Sheepdoll   4/11/2014 1:58:37 PM
NO RATINGS
I have a number of old science text books. Some dating as far back as the 18th century. Most of this relates to static electricity.  What I found interesting was how the quantities were measured.  Franklin's spark gap was used.  The length of the spark was what we call voltge.  The diameter of the spark was the current.  To measure the current a card was placed into the gap.  The spark would then burn a hole through the card.

 

MeasurementBlues
User Rank
Blogger
Re: Ampere's long arm
MeasurementBlues   4/11/2014 2:29:19 PM
NO RATINGS
@Sheepdol,

Franklin flew his kite on a Philadelphia night;
He saw that lightning was electricity.
Coulomb could tell that like charges repel
By the inverse square of their distance.
Orsted saw magnetic fields make a compass needle yield
When current passed through a nearby wire.


From my song, Electrical Heroes


MeasurementBlues
User Rank
Blogger
Re: Ampere's long arm
MeasurementBlues   4/11/2014 2:30:39 PM
NO RATINGS
@Sheepdoll,

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

pseudoid
User Rank
Manager
How Odd...
pseudoid   4/11/2014 3:50:48 PM
NO RATINGS
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
User Rank
Blogger
Re: How Odd...
MeasurementBlues   4/11/2014 4:03:48 PM
NO RATINGS
I would trust NIST over Wikipedia any day.

MeasurementBlues
User Rank
Blogger
Re: How Odd...
MeasurementBlues   4/11/2014 4:07:37 PM
NO RATINGS
From the University of North Carolina, Again I would go with this over Wikipedia.

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

 

MeasurementBlues
User Rank
Blogger
Re: How Odd...
MeasurementBlues   4/11/2014 4:08:30 PM
NO RATINGS
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".

pseudoid
User Rank
Manager
Re: How Odd...
pseudoid   4/11/2014 4:41:28 PM
NO RATINGS
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!

Page 1 / 3   >   >>


EE Life
Frankenstein's Fix, Teardowns, Sideshows, Design Contests, Reader Content & More
Max Maxfield

Creating New Faceplates for Antique Analog Meters
Max Maxfield
40 comments
I've currently got a couple of hobby projects on the go that feature the use of antique analog meters. For example, there's my Inamorata Prognostication Engine and its companion, the ...

EDN Staff

11 Summer Vacation Spots for Engineers
EDN Staff
11 comments
This collection of places from technology history, museums, and modern marvels is a roadmap for an engineering adventure that will take you around the world. Here are just a few spots ...

Glen Chenier

Engineers Solve Analog/Digital Problem, Invent Creative Expletives
Glen Chenier
11 comments
- An analog engineer and a digital engineer join forces, use their respective skills, and pull a few bunnies out of a hat to troubleshoot a system with which they are completely ...

Larry Desjardin

Engineers Should Study Finance: 5 Reasons Why
Larry Desjardin
45 comments
I'm a big proponent of engineers learning financial basics. Why? Because engineers are making decisions all the time, in multiple ways. Having a good financial understanding guides these ...

Flash Poll
Top Comments of the Week
Like Us on Facebook
EE Times on Twitter
EE Times Twitter Feed

Datasheets.com Parts Search

185 million searchable parts
(please enter a part number or hit search to begin)