[time-nuts] One Kg Quartz Resonator

Bob Camp lists at rtty.us
Thu Jan 24 12:41:20 EST 2013


Hi

I think a better analogy would be:

There don't have to be exactly X atoms in the Avogadro ball for it to be a
standard. You simply have to know how many relative to X in order to correct
for your gizmo. The gotcha obviously is you need the count of each isotope.

The same sort of issue applies to a cesium. You actually measure gravity
(and several other things) and correct for them. If there was no way to
measure your local gravity (or magnetic field), you would have a lot of
trouble using Cs as a primary standard.  

That said, the currently accepted primary mass standard is simply an
arbitrary lump of metal. It does not connect to anything other than it's
self. That's not a good thing at all. 

Bob

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Mike S
Sent: Thursday, January 24, 2013 11:50 AM
To: time-nuts at febo.com
Subject: Re: [time-nuts] One Kg Quartz Resonator

On 1/24/2013 10:38 AM, Jim Lux wrote:
> On 1/24/13 7:24 AM, Mike S wrote:
>> On 1/23/2013 3:34 AM, Magnus Danielson wrote:
>>> On 01/23/2013 02:32 AM, Mike S wrote:
>>>> Can you have a Cs under zero acceleration and at zero temperature, the
>>>> only conditions for which the second is defined? Since most metric
>>>> units
>>>> are derived from the definition of the second, are any "primary
>>>> standards," in your opinion?
>>>
>>> Isn't it defined for zero sea-level, that is standard acceleration?
>>
>> "At its 1997 meeting the CIPM affirmed that:
>> This definition refers to a caesium atom at rest at a temperature of 0
>> K." - http://www.bipm.org/en/si/si_brochure/chapter2/2-1/second.html
>>
>> Sea-level would be 1 g of acceleration, would it not?
>>
> which sea?

OK, "roughly 1 g," but that's missing the point. Which is, a real-world 
device that realizes the definition of the second is (currently?) 
impossible. That TAI is a weighted average of many "standards" I think 
supports that - real world devices must be compensated to be close, but 
still imperfect.

My question was in response to a claim that if "the number and type of 
atoms in such a standard" (proposed 1 kg silicon sphere) couldn't be 
counted, "its not a primary standard." The same logic could be applied 
to the second, and all derived units.

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