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

Richard (Rick) Karlquist richard at karlquist.com
Thu Oct 2 00:03:55 EDT 2014


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.

Rick Karlquist N6RK




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