Re: [time-nuts] Improving the stability of crystal oscillators

[SAIDJACK]

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In a message dated 10/14/2007 23:07:04 Pacific Daylight Time,  
[EMAIL PROTECTED] writes:

>Thermal transients propagate into the ground on a different  law,  
>Gauss' Error Function.
>If the ground is cleared of  trees, one hundred years later at a depth  
>of 100 metres  or
>so there will be a record of the change in average soil  temperature.
>The Cave was Saltpetre Cave in Carter Caves  Park.
>Just thought you might like to know.
>Neville  Michie



Hi Neville,
 
your post made me remember stuff from my University days!
 
Gauss' Error Function is also used to calculate diffusion depth of  
semiconductors.
 
HP/Agilent makes a semiconductor tester to measure this depth.
 
One interesting fact I remember from this: the form of the diffusion  profile 
depends on the speed (time) of the actual diffusion process into the  bulk 
material.
 
I bet there is a nice analog to temperature transients progressing through  
soil.
 
I love it when micro and macro effects show mathematical  similarities.
 
bye,
Said 



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Re: [time-nuts] Improving the stability of crystal oscillators

[Neville Michie]

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Enough speculation on ground temperatures.
The attenuation of cyclic variations of surface temperature die away
at an exponential rate with depth.
The thermal diffusivity of soils does vary but not so you can not  
generalise.
For daily changes, the temperature variation is attenuated to 1% of  
the surface swing between
0.3 and 0.6 metres.
For the annual swing, the distances are about 20 times greater.
I once was investigating a limestone cave climate, and I was  
delighted by
a pure sine wave of temperature that showed up on a data logger after  
a year
of measureing the temperature of the cave roof. It would not have  
been noticed except
that the logger was a high resolution model.
It was about 15 metres underground.
Higher frequencies have much higher attenuation, so the harmonics of  
daily and
annual  cycles are quickly lost.
Thermal transients propagate into the ground on a different law,  
Gauss' Error Function.
If the ground is cleared of trees, one hundred years later at a depth  
of 100 metres or
so there will be a record of the change in average soil temperature.
The Cave was Saltpetre Cave in Carter Caves Park.
Just thought you might like to know.
Neville Michie





On 15/10/2007, at 1:18 PM, Hal Murray wrote:

>
>> I've heard there is some depth that building foundations need to  
>> be so
>> they  don't get winter frost heave that might be on the order of a
>> couple of feet,  but that's far different from an constant  
>> temperature
>> depth.
>
> That depends on where you live.
>
>> I'm guessing that 10 or 15 feet may be required to get fractional
>> degree temp  stability where I am.  The Wisconsin data was in loam
>> which I think means a  fairly good insulator.  They had the widest
>> temperature variation (15 c delta @  120 cm down).  I've got sand and
>> clay after the first foot or so which may be a  better thermal
>> conductor implying less variation.
>
> The math is the same as for skin depth on RF on metal.  The  
> temperature
> fluctuation decays exponentially with depth.  Lower frequencies  
> (years vs
> days) go deeper.
>
>
>
>
> -- 
> These are my opinions, not necessarily my employer's.  I hate spam.
>
>
>
>
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Re: [time-nuts] Improving the stability of crystal oscillators

[Hal Murray]

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> I've heard there is some depth that building foundations need to be so
> they  don't get winter frost heave that might be on the order of a
> couple of feet,  but that's far different from an constant temperature
> depth.

That depends on where you live.

> I'm guessing that 10 or 15 feet may be required to get fractional
> degree temp  stability where I am.  The Wisconsin data was in loam
> which I think means a  fairly good insulator.  They had the widest
> temperature variation (15 c delta @  120 cm down).  I've got sand and
> clay after the first foot or so which may be a  better thermal
> conductor implying less variation. 

The math is the same as for skin depth on RF on metal.  The temperature 
fluctuation decays exponentially with depth.  Lower frequencies (years vs 
days) go deeper.




-- 
These are my opinions, not necessarily my employer's.  I hate spam.




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Re: [time-nuts] Improving the stability of crystal oscillators

[Brooke Clarke]

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Hi Bruce:

All the papers are for depths on the order of a few feet, aimed at plant 
growth, nevertheless in all cases the temperature was changing by at least 1 
deg c at the deepest depth recorded.

I've heard there is some depth that building foundations need to be so they 
don't get winter frost heave that might be on the order of a couple of feet, 
but that's far different from an constant temperature depth.

I'm guessing that 10 or 15 feet may be required to get fractional degree temp 
stability where I am.  The Wisconsin data was in loam which I think means a 
fairly good insulator.  They had the widest temperature variation (15 c delta @ 
120 cm down).  I've got sand and clay after the first foot or so which may be a 
better thermal conductor implying less variation.

Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.precisionclock.com
http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Cam


Bruce Griffiths wrote:
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> 
> Brooke Clarke wrote:
> 
>>Hi Bruce:
>>
>>Details on your experiment please.
>>Hole/pipe diameter, material?
>>Depth?
>>Delta T at different depths vs surface ambient?
>>Soil type?
>>
>>
>>Have Fun,
>>
>>Brooke Clarke
>>  
> 
> Brooke
> 
> Unable as yet to find my data, it was published in some very obscure
> publication if I remember correctly.
> However there was extensive series of records kept in England from the
> time of Lord Kelvin.
> 
> More recent data is available from the US forest service among others:
> http://ncrs.fs.fed.us/pubs/rn/rn_nc032.pdf
> Above is for Wisconsin, not directly applicable to California.
> http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?letter=.&classic=YES&bibcode=1952AuSRA...5..303W&page=&type=SCREEN_VIEW&data_type=PDF_HIGH&send=GET&filetype=.pdf
> 
> Above paper by CSIRO is for an Australian site.
> Analysis is fairly comprehensive.
> 
> http://www.mmm.ucar.edu/mm5/lsm/soil.pdf
> 
> http://www.ias.ac.in/epsci/mar2002/Esb1439.pdf
> 
> Bruce
> 
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Re: [time-nuts] Time-Nuts Archive?

[Jason Rabel]

> Is there an archive of past digests that I can search
> for useful tidbits of information?

Yes!!!

http://www.febo.com/pipermail/time-nuts/

I've spent hours on end sifting through them. Google hasn't indexed the info
completely for some reason (maybe too many links per page?). But if you know
what you are searching for it never hurts to use the 'site:...' command to
search just the archives.


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[time-nuts] Time-Nuts Archive?

[Tom Clifton]

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Is there an archive of past digests that I can search
for useful tidbits of information?


  

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Re: [time-nuts] Improving the stability of crystal oscillators

[Magnus Danielson]

From: "John Miles" <[EMAIL PROTECTED]>
Subject: Re: [time-nuts] Improving the stability of crystal oscillators
Date: Sun, 14 Oct 2007 14:15:10 -0700
Message-ID: <[EMAIL PROTECTED]>

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> 
> 
> > The required depth depends on the soil diffusivity and the temperature
> > stability required.
> > It is instructive to install thermometers at depth intervals of a foot
> > or so and record the temperature fluctuations experienced by each
> > thermometer.
> > This was first done around 1860 by Forbes.
> > I repeated the experiment in 1966.
> 
> There was an interesting bit in the last Agilent Measurement Journal about a
> product that uses an ordinary communications-grade fiber as a thermometer.
> >From what I remember, they send a laser pulse down the fiber, then look at
> the backscatter, correlating time-of-flight with the Raman-scattering lines
> (Stokes and anti-Stokes).  One of those spectral lines is
> temperature-dependent while the other isn't, so by recording the separation,
> they end up with is a graph of temperature versus distance along the fiber,
> gathering up to a few kilometers' worth of data with what looked like
> sub-meter resolution.
> 
> No doubt this effect is old hat to physicists on the list, but I'd never
> heard how it worked before.  So if you buried a fiber like this, you'd
> presumably get a great picture of what happens with temperature at various
> depths.  Plotting the temperature-versus-distance on a waterfall display
> gives a nice diurnal picture.  The article used it to study water
> temperature along the course of a stream, but you could think of plenty of
> other uses for 2D remote temperature sensing.

Bell Labs have made measures on soil temperature at different deps and also
fiber-delay as it varies with temperature. As it happends, the delay is part
due to fiber length change due to temperature and most part due to change of
delay due to change in dielectrics which converts into changes in the wave-
equation.

It naturally depends on temperature, laser wavelength and accumulates over
distance. I haven't seen any paper on non-chromatic delay shifts, but I haven't
looked too closely.

Cheers,
Magnus

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Re: [time-nuts] Improving the stability of crystal oscillators

[John Miles]

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> The required depth depends on the soil diffusivity and the temperature
> stability required.
> It is instructive to install thermometers at depth intervals of a foot
> or so and record the temperature fluctuations experienced by each
> thermometer.
> This was first done around 1860 by Forbes.
> I repeated the experiment in 1966.

There was an interesting bit in the last Agilent Measurement Journal about a
product that uses an ordinary communications-grade fiber as a thermometer.
>From what I remember, they send a laser pulse down the fiber, then look at
the backscatter, correlating time-of-flight with the Raman-scattering lines
(Stokes and anti-Stokes).  One of those spectral lines is
temperature-dependent while the other isn't, so by recording the separation,
they end up with is a graph of temperature versus distance along the fiber,
gathering up to a few kilometers' worth of data with what looked like
sub-meter resolution.

No doubt this effect is old hat to physicists on the list, but I'd never
heard how it worked before.  So if you buried a fiber like this, you'd
presumably get a great picture of what happens with temperature at various
depths.  Plotting the temperature-versus-distance on a waterfall display
gives a nice diurnal picture.  The article used it to study water
temperature along the course of a stream, but you could think of plenty of
other uses for 2D remote temperature sensing.

-- john, KE5FX


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