[time-nuts] How long do ovens take to cool to ambient after power is removed?

Magnus Danielson magnus at rubidium.dyndns.org
Thu Oct 2 02:06:50 EDT 2014



On 10/02/2014 06:03 AM, Richard (Rick) Karlquist wrote:
> On 10/1/2014 1:04 PM, Hal Murray wrote:
>>
>> drkirkby at kirkbymicrowave.co.uk said:
>>> Anyway, later today (tomorrow ??) I will post a plot of frequency vs
>>> time.
>>> The question is though, how long is thing thing likely to take too cool?
>>
>> I'd expect an exponential decay so you need to specify how close to
>> ambient
>> you want to get.   I'd guess a ballpark of 10x the warm up rate.
>>
>> You can probably measure it if you have the warmup graph.  Turn it
>> off, wait
>> a while, turn it on, measure the freq, consult warmup graph.
>
> When I was still with Agilent, I did some experiments with unpowered
> 10811's.  Both the oven and oscillator were unpowered and I measured
> the temperature by looking at the B mode resonance of the crystal.
> I wanted to get rid of any linear frequency drift.  As a rough
> rule of thumb, 1 hour of cool down is pretty good for most purposes.
> For extreme measurements, I would allow 10 hours.  This reduced
> any exponential tail to below the ability to measure temperature and/or
> below the effects of the ambient.  I had to put a box over it to
> reduce the effects of air currents.  If I did not do that, then 1 hour
> was all I needed.

Just putting a card-board box around the oscillator does indeed make 
short term deviation (breath, hand-waving, walking around and pushing 
air) reduce significantly. What is needed to get anything decent out of 
crap oscillators. Doesn't do as much for longer term shifts (AC, 
day-variations etc)

Your cool-off numbers is about where I would guess for better ovens.

Naturally, a fan can speed the process up, but let it sit there for some 
time without the fan to have less temperature gradients.

Cheers,
Magnus



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