Re: [time-nuts] backfill

[Charles Steinmetz]

Poul-Henning wrote:


Next down the line is hydrogen, which comes with a shitload of issues.


No argument there.  But other methods all have their own shitloads -- it 
just depends on which shitload the designers dislike the least.



you will find little love for hydrogen cooling [today]

In 1993 Siemens put the first 170MVA air-cooled generator optimized
by computer simulations of the flow-fields and since then
hydrogen cooling has been confined to an ever-decreasing top tier
of name-plate power.


Certainly there are other ways, and hydrogen cooling may have decreased 
in popularity in the decades since I was paying attention (I consulted 
for a turbine generator manufacturer in the late '80s). But there are 
lots of hydrogen-cooled alternators in service, and it appears that they 
are still being built.


Best regards,

Charles


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Re: [time-nuts] backfill

[Neville Michie]

My memory of high vacuum work is that you need to pump for 4 hours 
at 300C to remove the water monolayer from glass.
On top of the that water monolayer is another water monolayer that comes off 
more easily,
and on top of that another………..

cheers,
Neville Michie


> On 9 Jun 2017, at 10:57 AM, Richard (Rick) Karlquist  
> wrote:
> 
> 
> 
> On 6/8/2017 5:08 PM, Bob kb8tq wrote:
>> Hi
>> In this case hydrogen + oxygen (like from oxidized metal) goes to H20. You 
>> very much do
>> not want water running around inside your crystal holder… Helium is inert.
>> Bob
> 
> Exactly right Bob.  The 10811 guys used to go nuts
> about keeping water out of their vacuum system.
> There were certain temperatures known as "water
> points" at which some water was released.
> The retained water was in spite of the temperature
> already being above 100 degrees C (boiling).
> It has something to do with monolayers of
> water molecules not boiling away.
> 
> Rick N6RK
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Re: [time-nuts] backfill

[Bruce Griffiths]

alpha quartz to beta quartz phase transition at 573C amongst other factors.

Bruce

> 
> On 10 June 2017 at 12:31 Hal Murray  wrote:
> 
> > > 
> > You can’t quite process a crystal at 300C, but you can get close.
> > 
> > > 
> What happens if you get it too hot or too long? What's the limiting 
> factor?
> 
> --
> These are my opinions. I hate spam.
> 
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Re: [time-nuts] backfill

[Hal Murray]

> You can’t quite process a crystal at 300C, but you can get close.

What happens if you get it too hot or too long?  What's the limiting factor?


-- 
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Re: [time-nuts] backfill

[Bob kb8tq]

Hi

You can’t quite process a crystal at 300C, but you can get close.

Bob

> On Jun 9, 2017, at 7:38 PM, Neville Michie  wrote:
> 
> My memory of high vacuum work is that you need to pump for 4 hours 
> at 300C to remove the water monolayer from glass.
> On top of the that water monolayer is another water monolayer that comes off 
> more easily,
> and on top of that another………..
> 
> cheers,
> Neville Michie
> 
> 
>> On 9 Jun 2017, at 10:57 AM, Richard (Rick) Karlquist  
>> wrote:
>> 
>> 
>> 
>> On 6/8/2017 5:08 PM, Bob kb8tq wrote:
>>> Hi
>>> In this case hydrogen + oxygen (like from oxidized metal) goes to H20. You 
>>> very much do
>>> not want water running around inside your crystal holder… Helium is inert.
>>> Bob
>> 
>> Exactly right Bob.  The 10811 guys used to go nuts
>> about keeping water out of their vacuum system.
>> There were certain temperatures known as "water
>> points" at which some water was released.
>> The retained water was in spite of the temperature
>> already being above 100 degrees C (boiling).
>> It has something to do with monolayers of
>> water molecules not boiling away.
>> 
>> Rick N6RK
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Re: [time-nuts] backfill

[Bob kb8tq]

Hi

Well one thing that happens is that the glue that holds the blank in the holder 
turns to ash ….

Bob

> On Jun 9, 2017, at 8:31 PM, Hal Murray  wrote:
> 
> 
>> You can’t quite process a crystal at 300C, but you can get close.
> 
> What happens if you get it too hot or too long?  What's the limiting factor?
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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Re: [time-nuts] PPS sync

[Hal Murray]

je...@hanler.com said:
> It’s interesting how it jumps around from PPS to PPS.  

You can work out what the offset will look like.

Assume your clock is roughly 10 MHz.  So you divide by 10,000,000 to get a 
PPS.  If your clock is 2.001 HZ fast, then you need to divide by 10,000,002.  
That gets close, but it will drift by 0.001 HZ or 1 ms per second.  So every 
1000 seconds you will have to skip an extra cycle.

If you plot the offset, you get a ramp going down.  If your clock is 
10,000,001.999 you get a ramp going up.  (I hope I got the sign right.)

It gets more complicated if your clock is not near an integral number of 
cycles/second.  Suppose it is 10,000,002.501.  Now you have to skip an extra 
cycle every other second.  You get 2 lines offset by a half-second.

That all assumes you have a good GPS antenna and such so that there isn't 
much noise/jitter on the calculated time.

If the temperature on your crystal is changing, you can get hanging bridges.

Neat graphs here:
  http://www.leapsecond.com/pages/m12/sawtooth.htm


-- 
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Re: [time-nuts] backfill

[Charles Steinmetz]

Bob wrote:


In this case hydrogen + oxygen (like from oxidized metal) goes to H20. You very 
much do
not want water running around inside your crystal holder… Helium is inert.


The insides of mains alternators are almost entirely metal -- tons and 
tons of copper tubing, and the casings and rotor shaft are steel.  And 
the alternators must operate at a relative humidity of absolute zero. 
The problem is far from insurmountable, even at that huge scale. 
Dealing with it should be very much easier at a scale of cubic centimeters.


They use condensers to remove the water during the hydrogen purge cycle, 
which (for mains alternators) lasts several weeks.  I watched the 
procedure several times 25 years ago, but I don't recall the particulars 
now.


Best regards,

Charles


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Re: [time-nuts] backfill

[Bob kb8tq]

Hi

Cold traps and vac-ion pumps were very common on precision crystal seal setups 
50 years ago. 
They have gotten better since then….

Bob

> On Jun 9, 2017, at 9:13 AM, jimlux  wrote:
> 
> On 6/8/17 1:19 PM, Bob kb8tq wrote:
>> Hi
>> 
>> If you look at the thermal conductivity vs very low pressures, the 
>> conductivity
>> comes up pretty quickly from a hard vacuum. There is essentially no impact
>> on Q.
>> 
> 
> basically, when the mean free path gets to be shorter than the distance to 
> the wall, the thermal conductivity drops off.
> 
> MFP = 65 nm at 1013 hPa = 760 torr
> 
> So at 10-4 Pa/0.75E-3 micron (start of very high vacuum) the MFP is 65 cm
> 
> High vacuum usually starts around 0.1 Pa (close to 1 micron), where the MFP 
> is 65 mm - this is where the MFP is comparable to the size of the stuff 
> you're pumping down, and where you can't use a "pump", but rather you need 
> something that flings the air molecules toward the exit (diffusion or turbo 
> molecular pump) or something that is like flypaper for molecules (sorption, 
> cold finger, etc.)
> 
> 
> If you've got a "refrigeration" vacuum pump, they pull down to about 30-40 
> microns - MFP is a few millimeters
> 
> 
> 
> 
> 
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Re: [time-nuts] backfill

[Bob kb8tq]

Hi

My guess is that crystals are more sensitive to moisture than the alternators…. 
The level of “clean” 
you need in a precision crystal enclosure is way beyond what is required in a 
number of other areas.
One layer of water molecules is way to much in a modern crystal.  can and do 
use crystals as detectors 
of low levels of “stuff” for this very reason. 

Bob

> On Jun 9, 2017, at 2:55 AM, Charles Steinmetz  wrote:
> 
> Bob wrote:
> 
>> In this case hydrogen + oxygen (like from oxidized metal) goes to H20. You 
>> very much do
>> not want water running around inside your crystal holder… Helium is inert.
> 
> The insides of mains alternators are almost entirely metal -- tons and tons 
> of copper tubing, and the casings and rotor shaft are steel.  And the 
> alternators must operate at a relative humidity of absolute zero. The problem 
> is far from insurmountable, even at that huge scale. Dealing with it should 
> be very much easier at a scale of cubic centimeters.
> 
> They use condensers to remove the water during the hydrogen purge cycle, 
> which (for mains alternators) lasts several weeks.  I watched the procedure 
> several times 25 years ago, but I don't recall the particulars now.
> 
> Best regards,
> 
> Charles
> 
> 
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Re: [time-nuts] backfill

[Neville Michie]

It is possible that the ageing of a crystal is associated with the 
redistribution of the surface water
monolayer, under the influence of the minute temperature gradient of an 
oscillating crystal.
Some energy is dissipated in the quartz, so some gradient may exist.
When a crystal is resting, the water may redistribute in the sealed package, 
but when run again, the water 
redistributes due to the temperature differences.
Adsorbed water is in equilibrium with its environment, and, given time, will 
migrate along temperature gradients.
It could be just one more mechanism in frequency drift.
I would try using a reactive metal getter in the package to pick up any mobile 
water molecules.

cheers, 

Neville Michie

> On 10 Jun 2017, at 9:52 AM, Bob kb8tq  wrote:
> 
> Hi
> 
> You can’t quite process a crystal at 300C, but you can get close.
> 
> Bob
> 
>> On Jun 9, 2017, at 7:38 PM, Neville Michie  wrote:
>> 
>> My memory of high vacuum work is that you need to pump for 4 hours 
>> at 300C to remove the water monolayer from glass.
>> On top of the that water monolayer is another water monolayer that comes off 
>> more easily,
>> and on top of that another………..
>> 
>> cheers,
>> Neville Michie
>> 
>> 
>>> On 9 Jun 2017, at 10:57 AM, Richard (Rick) Karlquist 
>>>  wrote:
>>> 
>>> 
>>> 
>>> On 6/8/2017 5:08 PM, Bob kb8tq wrote:
 Hi
 In this case hydrogen + oxygen (like from oxidized metal) goes to H20. You 
 very much do
 not want water running around inside your crystal holder… Helium is inert.
 Bob
>>> 
>>> Exactly right Bob.  The 10811 guys used to go nuts
>>> about keeping water out of their vacuum system.
>>> There were certain temperatures known as "water
>>> points" at which some water was released.
>>> The retained water was in spite of the temperature
>>> already being above 100 degrees C (boiling).
>>> It has something to do with monolayers of
>>> water molecules not boiling away.
>>> 
>>> Rick N6RK
>>> ___
>>> time-nuts mailing list -- time-nuts@febo.com
>>> To unsubscribe, go to 
>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>> 
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Re: [time-nuts] backfill (was: Poor man's oven)

[Didier Juges]

The difficulty with hydrogen is to keep it where you want it. It does not
take very much for it to leak out (or in, as the case may be)

On Jun 8, 2017 4:58 PM, "Alan Melia"  wrote:

> Hi Bob, it also depends on what you allow to leak into the vacuum.
> Hydrogen is a pretty effective remover of heat :-))
> Alan
> G3NYK
>
> - Original Message - From: "Bob kb8tq" 
> To: "Discussion of precise time and frequency measurement" <
> time-nuts@febo.com>
> Sent: Thursday, June 08, 2017 9:19 PM
> Subject: Re: [time-nuts] backfill (was: Poor man's oven)
>
>
> Hi
>>
>> If you look at the thermal conductivity vs very low pressures, the
>> conductivity
>> comes up pretty quickly from a hard vacuum. There is essentially no impact
>> on Q.
>>
>> Bob
>>
>> On Jun 8, 2017, at 4:03 PM, Attila Kinali  wrote:
>>>
>>> On Thu, 8 Jun 2017 06:55:07 -0400
>>> Bob kb8tq  wrote:
>>>
>>> The simple answer is that the backfill is done because it does matter in
 a lot of
 cases.

>>>
>>> This raises the question, why there is backfill (just for thermal
>>> conductivity?)
>>> and how much it affects the Q of the crystal.
>>>
>>> Attila Kinali
>>>
>>>
>>> --
>>> You know, the very powerful and the very stupid have one thing in common.
>>> They don't alters their views to fit the facts, they alter the facts to
>>> fit the views, which can be uncomfortable if you happen to be one of the
>>> facts that needs altering.  -- The Doctor
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>>>
>>
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Re: [time-nuts] backfill (was: Poor man's oven)

[Van Horn, David]

Wouldn't the low density of helium reduce some mechanical friction?
I realize the motions are small but they are motions. 

The "Cousteau effect"?  :)
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Re: [time-nuts] backfill

[jimlux]

On 6/8/17 1:19 PM, Bob kb8tq wrote:

Hi

If you look at the thermal conductivity vs very low pressures, the conductivity
comes up pretty quickly from a hard vacuum. There is essentially no impact
on Q.



basically, when the mean free path gets to be shorter than the distance 
to the wall, the thermal conductivity drops off.


MFP = 65 nm at 1013 hPa = 760 torr

So at 10-4 Pa/0.75E-3 micron (start of very high vacuum) the MFP is 65 cm

High vacuum usually starts around 0.1 Pa (close to 1 micron), where the 
MFP is 65 mm - this is where the MFP is comparable to the size of the 
stuff you're pumping down, and where you can't use a "pump", but rather 
you need something that flings the air molecules toward the exit 
(diffusion or turbo molecular pump) or something that is like flypaper 
for molecules (sorption, cold finger, etc.)



If you've got a "refrigeration" vacuum pump, they pull down to about 
30-40 microns - MFP is a few millimeters






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[time-nuts] Symmetricom Time Source 2700

[Bert Kehren via time-nuts]

Just got a Symmetricom Time Source 2700. Bought it for the PRS 10 to keep.  
. It came with a 48 V power source. Does any one want the rest of the Unit. 
You  pay shipping.  Please off list.
Bert Kehren  Palm City Fl/
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Re: [time-nuts] backfill

[Poul-Henning Kamp]

In message <593a4677.5080...@yandex.com>, Charles Steinmetz writes:

>The insides of mains alternators are almost entirely metal -- tons and 
>tons of copper tubing, and the casings and rotor shaft are steel.  And 
>the alternators must operate at a relative humidity of absolute zero. 

This is close to to being "not even wrong".

There is no requirement for "a relative humidity of absolute zero",
which is theoretically impossible if there is any iron around.

There are however stringent requirements for non-corrosion, dielectric
potential, cooling, corona behaviour etc. etc.

Cooling the stator is a no-brainer, it is almost always water-cooled.

If they could afford to use helium to cool the rotor, they would
jump on it instantly, but the cost is prohibitive at their leakage
rates.

Pure water would also be workable, but its high density means
it cannot be used to cool the rotor without a serious hit to
efficiency.

Next down the line is hydrogen, which comes with a shitload of issues.

Apart from all the obvious issues, lube-oil degradation, polymer
degradation, fire-risk, risk of explosion, health-risk etc.  hydrogen
has "interesting" solubility in metals.

If you want to purify hydrogen, you press it trhough a filter
consisting of a solid slab of palladium, and that takes a lot less
pressure than you would expect.

For iron in particular, hydrogen means embrittlement, so a
major focus in rotor design is to keep the hydrogen away from
the iron.

If you Google "generator hydrogen seal" and and you will find
little love for hydrogen cooling.

In 1993 Siemens put the first 170MVA air-cooled generator optimized
by computer simulations of the flow-fields and since then the
hydrogen cooling has been confined to an ever-decreasing top tier
of name-plate power.

Today fan cooling will take you to approx 400MVA and pressured air
cooling will take you to about 600MVA.

Above that, you are, almost by definition, in a nuclear power plant,
and all problems from hydrogen cooling of your single huge generator
pale in comparison to having a handful of smaller generators in
parallel.

-- 
Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
p...@freebsd.org | TCP/IP since RFC 956
FreeBSD committer   | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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