[time-nuts] Poor man's oven
albertson.chris at gmail.com
Mon Jun 5 19:48:53 EDT 2017
On Mon, Jun 5, 2017 at 3:38 PM, Charles Steinmetz <csteinmetz at yandex.com>
> Chris wrote:
> Today all you need is a reliable way to measure the error
>> between the crystals' current temperature and the set point.
> That's all that's ever been needed. But it is devilishly difficult to
> measure the actual quartz temperature, or even to find a good proxy that is
> easier to measure.
> There is a fair body of published research on these topics, including
> Rick's (et al.) work on zero-gradient ovens.
> Keep this in mind when someone says they are controlling the "oven
> temperature" to 0.001C (or even 0.1C). They are measuring *something*, and
> may even be holding whatever it is "constant" within fairly tight
> tolerances. But they have no idea what the quartz temperature is, and no
> way to know with precision the relationship between the measured
> temperature and the actual quartz temperature.
How much does this matter? What we measure is the ambient temperature
inside the insulated box that contains the crystal. The assumption is
that given some time the temperature will be uniform. OK, so the assumption
is not 100% correct but lets say the crystal is held to a range of 0.1C
This is a reasonable goal for a home shop made controller.
Here is another question:
Lets assume we place the operating point on the flat part of the curve with
say a 1.0 C absolute error and can hold the relative temperature to 0.1C
What does this mean in terms of frequency.?
This is a "Poor Man's" oven. So really the question is this: I have a
$10 budget, shouldI blow half my budget on a better sensor or is the 75
cent part good enough. Or is it worth buying a second 75 cent sensor so I
can detect a temperature gradient With a poor man's budget, I think the
trick is to use a good size thermal mass, chunks of scrap meter are cheap.
> Some years ago, I consulted for a research group that was using a number
> of non-contact technologies to measure the temperature of oscillating
> quartz crystals. The results were promising, but there were some issues
> with measuring the temperature (which is, essentially, quantifying tiny
> random molecular motions within the crystal lattice) against the background
> of the hugely greater macro motion of the vibating quartz. I never knew
> the final conclusions, nor am I aware of any systems designed using these
> principles or methods. But it is something to think about if you *really*
> want a temperature-stable oscillator.
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Redondo Beach, California
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