[time-nuts] Thunderbolt stability and ambient temperature

Don Latham djl at montana.com
Wed Jun 10 15:04:18 EDT 2009


In one of my other incarnations, radio astronomy (definitely amateur if
not downright amateurish) an automotive 12 v thermoelectric cooler was
converted by one of the group into a servoed "constant" temperature box.
Those of time persuasion might want to try that. Note the small auto
coolers can just as well be converted to a constant temperature heated box
as well.
Don

Robert Atkinson
>
> Interestingly, the packing instructions for the  Solartron 7081 81/2 digit
> voltmeter shows two "thermal inertia bottles" close to the instument.
> These provide a thermal mass that works with the insulation to reduce the
> rate of temperature change at the unit. This will also filter short
> duration transients. So a cardboard box with a couple of bottles of water
> in it would make a good enclosure. Or just leave the beer in the cooler
> :-)
>
> Robert G8RPI.
> --- On Tue, 9/6/09, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:
>
>> From: Poul-Henning Kamp <phk at phk.freebsd.dk>
>> Subject: Re: [time-nuts] Thunderbolt stability and ambient temperature
>> To: "Discussion of precise time and frequency measurement"
>> <time-nuts at febo.com>
>> Date: Tuesday, 9 June, 2009, 9:03 PM
>> In message <BLU125-W9E23FDF3E1618C93E603ECE440 at phx.gbl>,
>> Mark Sims writes:
>>
>> >I think that using a well insulated box [...]
>>
>> The point for timenuts is not just the thermal resistance,
>> but more
>> importantly the thermal *impedance*: you want to low-pass
>> filter
>> the thermal changes so that they all happen in the area
>> where the
>> PLL can cope with them.
>>
>> Thermal resistance is about insulation, thermal impedance
>> is
>> about (thermal) mass.
>>
>> So you significant mass and volume (like a fridge) not
>> light and
>> small (like a cardboard box).
>>
>> When metrology people really want to keep things at the
>> same
>> temperature, they mount them in oil-baths (for good thermal
>> contact)
>> in the middle of a block of aluminium, typically 2'x2'x1'
>> (for
>> thermal impedance) which is again insulated with 1"
>> styrofoam, all
>> of this mounted in a plywoodbox, set on rubber-wheels to
>> get it off
>> the floor (for thermal resistance).
>>
>> If they are really into this, they cover the plywood with
>> high-quality
>> (noble-) metal foil, to maximize reflectivity and minimize
>> emissivity,
>> so that the black-body radiation from devices and humans in
>> the lab
>> does not affect the temperature interface as much.
>>
>> Then they leave it alone for "some weeks" in their
>> temperature
>> controlled lab so the temperature can stabilize.
>>
>> At this point they may start to wonder how they can verify
>> the pt100
>> temperature sensor they put in the middle of it all
>> actually works
>> when the temperature never changes...
>>
>> Poul-Henning
>>
>> --
>> Poul-Henning Kamp       | UNIX
>> since Zilog Zeus 3.20
>> phk at 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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>
>
>
>
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-- 
Dr. Don Latham AJ7LL
Six Mile Systems LLP
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304
www.lightningforensics.com
www.sixmilesystems.com





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