Bob Camp wrote:
Hi
Regardless of weather it's a single or double oven, you want the crystal
to be at it's "turn temperature". If you have a BT cut crystal, that's
going to be the highest frequency you find as you move the oven around.
With either a double or single oven, you should be able to "map out" a
parabolic plot of frequency versus temperature. That's only close to
"right" since the electronics contribute something to the temperature
performance. To really get it *right* you need to vary the external
temperature and see what happens ....
On a double oven, the outer oven is set for some "nominal" amount of
inner oven current. The idea is to keep the inner oven controller from
either cutting off or saturating as the external temperature is varied.
Often the inner oven is set to the "low side" of it's power range.
The outer oven can't have a too high temperature, since then the inner
oven can't remove excess heat through conduction and reduction of
heating power and you want sufficient balance between conduction and
heating so that it does not cut-off since that way it becomes
unregulated and loss of thermal gain is achieved. In a similar sense,
too low outer oven temperature will saturate the heating power and again
loss of thermal gain. The exact temperature of the outer oven is not
that important as long as it provides the thermal gain and is within
some temperature range that allows the inner oven to function properly.
There is no magic to it, just some physics and control laws in action.
Cheers,
Magnus
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