[time-nuts] Z3805A cooling requirements?

Volker Esper ailer2 at t-online.de
Fri Dec 21 18:16:54 UTC 2012


...and we do not know how much air flow and how turbulent each of us 
applied. We can only give an _idea_ of what happens and in which order 
of magnitude it could be.

When Stu started the thread (elderly time nuts can surely recall) his 
question was about cooling a Z38xx unit. I recommended building a wind 
shield between the oven and the power supply bricks and cool the bricks 
with a fan. When my current test is completed, I'll try that, too.

The power supply most often seems to be the weak spot, so some 
additional cooling wouldn't be wrong (apart from acoustic noise).

Yes, I bear in mind the warnings about a non ventilated seperate oven 
chamber and the hints about maximum temperature vs oven temperature. So 
I measured the temperature in the closed original aluminium case (which 
however has some ventilation slots). It was about 45°C=113°F, at a room 
temeprature of 21°C=70°F. With an oven temp of about 80°C=176°F I don't 
expect problems, even if the oven chamber temp will increase some degrees.

Till then...

Volker





Am 21.12.2012 18:27, schrieb Said Jackson:
> Great plots guys!
>
> Looking at these results I think my original claim still holds: ADEV goes up when a fan is involved versus no fan, even on a double oven 10811..
>
> Clearly visible on the 10811, maybe not so much on the MV89 but that unit seems to have frequency moves into the xE-010 region on Marks plot so maybe the effect is just a bit hidden?
>
> Bye,
> Said
>
> Sent from my iPad
>
> On Dec 21, 2012, at 5:44 AM, Volker Esper<ailer2 at t-online.de>  wrote:
>
>> ...and the picture of the experiment...
>>
>>
>>> The picture enclosed can give you a first impression. What we see is
>>> the difference time between the GPS signal and the OCXO (blue)
>>> ("PPS-TI"), which is an HP 10811. In red we can see the EFC. The total
>>> span is 24 h.
>>>
>>> Before I applied the fan, the noise was at a maximum of about +/- 20 ns.
>>> Some hours after starting the fan the noise is much greater. That should
>>> have a significant impact on the ADEV.
>>>
>>> I don't put the ADEV curves here, I make up for it when the EFC
>>> compensation is completely out of the scope, that will be in about 12
>>> hours. I don't have the ADEV at 1 s, but the ADEV at 10 s has been
>>> almost constant. The ADEV at about 1000 s has a nasty bump now.
>>>
>>> IMHO that fits to the physical facts: the airflow will surely not affect
>>> the 10 s ADEV since the OCXO tries its best to isolate the oscillator
>>> from short time temperature influences. However, the turbulent air flow
>>> that I applied will influence the longer time ADEV.
>>>
>>> Have a nice solstice
>>>
>>> Volker
>>>
>>>
>>>
>>>
>>> Am 21.12.2012 12:44, schrieb Volker Esper:
>>>>
>>>> Yes, I made such a setup, it's now running 22 hours. I'll post the
>>>> results in two hours or so (if nothing evil happens to the earth,
>>>> meanwhile).
>>>>
>>>> Volker
>>>>
>>>>
>>>> Am 21.12.2012 03:35, schrieb SAIDJACK at aol.com:
>>>>> Wish I had more time to play with this setup.
>>>>>
>>>>> How about fellow time nuts spend some time and present similar test
>>>>> data on
>>>>> their OCXO's to compare?
>>>>>
>>>>> I was interested in the 1s to 100s ADEV, and my runs were from 8
>>>>> minutes to
>>>>> 20 minutes, certainly enough time to capture data for 1s to 100s ADEV
>>>>> measurements..
>>>>>
>>>>> bye,
>>>>> Said
>>>>>
>>>>>
>>>>> In a message dated 12/20/2012 14:17:59 Pacific Standard Time,
>>>>> magnus at rubidium.dyndns.org writes:
>>>>>
>>>>> On 12/20/2012 01:34 PM, Bob Camp wrote:
>>>>>> Hi
>>>>>>
>>>>>> Temperature transients are not a good thing for an OCXO. If you
>>>>> deliberately use the fan to create a transient, then yes the OCXO will
>>>>> not be
>>>>> happy. The question it - what happens after the transient has settled
>>>>> out? The
>>>>> plot you have still looks a lot like a step function.
>>>>>
>>>>> I agree. Temperature steps stresses the OCXO oven loop and easily
>>>>> creates a gradient over the crystal. As the oven loop tracks in, the
>>>>> frequency returns to around normal. The trouble with forced air over a
>>>>> crystal is that the metal shield couples very well and acts like a heat
>>>>> sink. A think plastic cover over it and forced convection doesn't have
>>>>> the same effect. There is even being used by at least one vendor. Works
>>>>> very well for the extra cents of manufacturing cost.
>>>>>
>>>>> The HP10811 is recommended to be put in a airflow-quiet corner of the
>>>>> world. Look at it's mounting in the HP5370A/B for instance.
>>>>>
>>>>> Cheers,
>>>>> Magnus
>>>>>
>>>>>
>>>>> _______________________________________________
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>>>>
>>>>
>>>>
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