...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<[email protected]> 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 [email protected]:
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,
[email protected] 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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