How they made EXTREMELY precise universal voltage reference ?

Willen

Well-Known Member

• Nov 25, 2015

• #1

Talking about very basic thing: People say the Fluke DMMs are very accurate for measurement. I used few cheap DMMs and and they show different voltages for same supply like 5.01V, 4.98V, 4.99V etc.

Maybe the exact reference of time is the rotation of earth. Same way what is the exact reference of voltage (etc) measurement so people say the fluke or etc expensive tools are very accurate?

How I can compare the accuracy of my poor DMMs?

 

Nigel Goodwin

Super Moderator

Most Helpful Member

• Nov 25, 2015

• #2

Those values are VERY close to each other, well within the tolerance of any reasonably priced (including Fluke) multimeters.

 

alec_t

Well-Known Member

Most Helpful Member

• Nov 25, 2015

• #3

Willen said:

Maybe the exact reference of time is the rotation of earth.

Click to expand...

That would be a very poor reference. The atomic clock is the usual reference.

 

MikeMl

Well-Known Member

Most Helpful Member

• Nov 25, 2015

• #4

Look up "Precision voltage reference". **broken link removed** a few.

 

Willen

Well-Known Member

• Nov 25, 2015

• #5

Like atomic clock for time, are there any precise way to measure potential difference?

 

crutschow

Well-Known Member

Most Helpful Member

• Nov 25, 2015

• #6

Ultimately, in the US, voltage references are traced back to the National Institute of Standards and Technology lab where I believe they use a Josephson junction primary voltage reference.
It's a little pricey for home use.

 

MikeMl

Well-Known Member

Most Helpful Member

• Nov 25, 2015

• #7

crutschow said:

Ultimately, in the US, voltage references are traced back to the National Institute of Standards and Technology lab where I believe they use a Josephson junction primary voltage reference.
It's a little pricey for home use.

Click to expand...

But how do they "measure" the primary reference? It seems that all they can do is bring in another reference, and compare it to the standard.

 

AnalogKid

Well-Known Member

Most Helpful Member

• Nov 25, 2015

• #8

A primary standard is different from other references because its absolute value is determined by the nature of its physics with more accuracy and less variation than anything else we know of. When in the correct environment, it makes a voltage that just plain does not vary because of the quantum mechanics of the Josephson effect.

ak

 

jpanhalt

Well-Known Member

Most Helpful Member

• Nov 25, 2015

• #9

Needless to say,"Volt"is not a primary SI unit. Can a derived unit have a primary standard?

 

crutschow

Well-Known Member

Most Helpful Member

• Nov 25, 2015

• #10

According to this, the Josephson junction has been developed as the US primary standard for the volt.
It apparently defines the volt as determined by an accurate frequency and two constants of nature.
Of course this depends upon the accuracy of the frequency, derived from the second, which is the duration of 9,192,631,770 cycles of radiation corresponding to the transition between two energy levels of the caesium-133 atom.
I think perhaps that's as primary as it gets.

 

jpanhalt

Well-Known Member

Most Helpful Member

• Nov 26, 2015

• #11

The time is primary. The volt is derived. That does not mean you cannot measure it accurately. My comment was simply related to the comments regarding a primary standard.

"Primary" standards have been defined by international consensus.

John

 

Willen

Well-Known Member

• Nov 27, 2015

• #12

I am in confuse in a phrase 'volt is derived'. Derived from man made source instead of physics's fact?

For general (very simple) voltage reference, what about 7805, or TL431. I guess TL431 is more precise.

 

crutschow

Well-Known Member

Most Helpful Member

• Nov 28, 2015

• #13

Common accurate voltage references are the semiconductor ones such as the TL431 precision reference. Those can be used as a calibrate check for your multimeter for one voltage.
Some are available with 0.1% accuracy.
Voltage regulators such as the 7805 or the LM317 are not as accurate or stable.