On 10/1/2014 1:04 PM, Hal Murray wrote:
drkir...@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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