[time-nuts] Cheap Rubidium

Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Dec 23 13:01:25 UTC 2009


Try an insulated water cooled metal block for the baseplate heatsink
The water can be recirculated and heated/cooled as required.

With a recirculating system and say 25W dissipation with no temperature 
control you will only need about 5 cubic meters (5 tons) of water to 
maintain a temperature rise of less than 0.01C for 3 hours. Assuming 
that the 25W rubidium dissipation is the only significant source of 
heating for the water.
That means you need a well insulated swimming pool in your basement.

Controlling the temperature of a smaller amount of recirculating water 
is probably a simpler proposition.

Bob Camp wrote:
> Hi
>
> Water might work. It would take quite a bit of it.
>
> Here's my "wild guess" level math:
>
> 1) The basement moves 0.1 to 1 C short term / over a day.
>
> 2) I want to get to<  0.01
>
> That takes the time constant out to>= 10X the time I'm interested in.
>
> 3) The time period of interest is 3 to 30 hours.
>
> That gets to a time constant of at least 10 days.
>
> At the same time you have>10 watts coming out of the gizmo. You can't put the thermal mass inside a vacuum  bottle.
>
> I suspect that some combination of thermal mass and active stabilization will be needed.
>
> So much fun ....
>
> Bob
>
>
> On Dec 23, 2009, at 2:18 AM, Don Latham wrote:
>
>    
>> sheesh! How about a right-sized water jug?
>> Don
>>
>> ----- Original Message ----- From: "Bob Camp"<lists at cq.nu>
>> To: "Discussion of precise time and frequency measurement"<time-nuts at febo.com>
>> Sent: Tuesday, December 22, 2009 8:23 PM
>> Subject: Re: [time-nuts] Cheap Rubidium
>>
>>
>>      
>>> Hi
>>>
>>> I agree that if you simply bolt the rubidium to an old engine block and toss a blanket over it, you might get some pretty good thermal stability in the "hour to couple hours" time period. That's certainly a better approach than putting some kind of DC heater (and it's varying magnetic field) near the rubidium.
>>>
>>> I'm still wondering if they do indeed hit 1x10-13 (as in almost 1x10-14) or not. I suspect not. I'm sure that they do indeed get into the 1x10-13's, just not sure they get to the bottom of that region.
>>>
>>> Bob
>>>
>>>
>>> On Dec 22, 2009, at 8:26 PM, Bruce Griffiths wrote:
>>>
>>>        
>>>> Bob Camp wrote:
>>>>          
>>>>> Hi
>>>>>
>>>>> If I randomly pick up a FE 5680A data sheet, I find that it's short term stability is 1.4/sqrt(Tau) x 10-11.  Since I never doubt anything I see on a data sheet, this immediately tells me I should get 1.4x10-12 at 100 seconds, and I only have to wait for 10,000 seconds to get to 1.4x10-13.
>>>>>
>>>>> Since the temperature performance is at the 1x10-12 / C level, I would need a room that's stable to *much* better than 0.1 C over a 3 hour period to get there. I suspect that 0.01C might not be good enough ...
>>>>>
>>>>> So here's the question:
>>>>>
>>>>> Has anybody run any of the cheap rubidiums (FE or Efratom)  in a *very* stable temperature environment to see how close they get / what the floor is?  I've run through a lot of data on the web, but I haven't really found what I'm looking for.
>>>>>
>>>>> Thanks!
>>>>>
>>>>> Bob
>>>>>
>>>>>
>>>>>            
>>>> Figure 7 on the FE5680 page (also on the data sheet) indicates that you may need somewhat less than 3hours to achieve  ADEV ~1E-13.
>>>> 0.01C stability should be adequate.however its not necessary to control the room temperature to this stability if the FE5680 is in an enclosure with a sufficiently high time constant whilst having a sufficiently low thermal resistance so as to avoid overheating the FE5680.
>>>>
>>>> Bruce
>>>>
>>>>
>>>> _______________________________________________
>>>>          





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