Author Topic: Volt-Nuts, Time-Nuts and the Laws of the Universe!  (Read 1221 times)

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wn1fju

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Volt-Nuts, Time-Nuts and the Laws of the Universe!
« on: November 30, 2016, 09:50:44 am »
Excuse me if this is a naive question, but it has been puzzling me for a while.

In the arena of volts, resistance and current measurement (or generation), achieving 1 ppm accuracy (at least in a home lab situation) is far from trivial and will set you back a lot of money.

Yet, achieving 1 ppm frequency accuracy is very easy (a $5 crystal with perhaps a temperature compensating capacitor), and any$200 GPS-disciplined oscillator will be orders of magnitude better than that.

So, why the fundamental discrepancy?  Is it as simple as SNR (V-I-R measurement needs to fight Johnson noise whereas oscillators don't)?  Or is there some fundamental Law of the Universe in play.

Dr. Frank

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Re: Volt-Nuts, Time-Nuts and the Laws of the Universe!
« Reply #1 on: November 30, 2016, 10:39:43 am »
Excuse me if this is a naive question, but it has been puzzling me for a while.

In the arena of volts, resistance and current measurement (or generation), achieving 1 ppm accuracy (at least in a home lab situation) is far from trivial and will set you back a lot of money.

Yet, achieving 1 ppm frequency accuracy is very easy (a $5 crystal with perhaps a temperature compensating capacitor), and any$200 GPS-disciplined oscillator will be orders of magnitude better than that.

So, why the fundamental discrepancy?  Is it as simple as SNR (V-I-R measurement needs to fight Johnson noise whereas oscillators don't)?  Or is there some fundamental Law of the Universe in play.

Well, achieving 1ppm accuracy for URI is not so expensive, but 1ppm uncertainty for sure is...

Just joking..

The root cause of the many orders of magnitude of uncertainty lies in the difference between analogue and digital techniques, or the mise en pratique, that is the realization in a working laboratory.

Noise is dominant in the analogue world, whereas in the digital world, you are able to mitigate that to many orders of magnitude less.

Anyhow, in 2018, when the new SI will be defined, the Volt and the Ohm will be as uncertain and as stable as the other quantum defined units, like the second and the meter.
The physics behind this stability is always a quantum phenomenon, but for the analogue units, there will still be no such quantum standard at room temperature, so the home lab will still have to live with stability figures on the order of 10^-7.. 10^-9, compared to 10^-13 for the second.

Frank

Smf