On Sat, 16 Feb 2002, Dave Dilatush wrote:

> Jinx wrote...
>
> >What I don't understand is that these are parallel cut crystals,
> >the type I use all the time with micros (which require parallel
> >cut), yet the series circuit seems to work so much better
>
> I'm no expert on crystal oscillators; so I could be wrong here.  But
> AFAIK there isn't anything structurally different between "parallel"
> resonant and "series" resonant crystals; all crystals have parallel and
> series resonant frequencies, as I understand it, and a particular unit
> is defined as parallel or series simply because that's the resonant mode
> that'll give you the frequency that's marked on the can.
>
  Well, my clocks and Roman's Bresenham accurate timing methode said that
never the real oscillating frequency are marked on the can...
There are some important diferences about serial and parallel resonant
frequencies. Any cuartz crystal have three major cutting axis. The most
important one is the thermal ax. An unadvised user of a cuartz
oscillator will say: "what big deal ? we use an owen an keep the
oscillator at the same temperature " If you'll have in your hands a
crystal which was cutted on electrical or mechanical axis the
thermostating effect can be worst than keeping the whole oscillator on
ambiant temperature. And everything depends by distance of the cutted
material measured to thermal axis.
Why the quartz producers don't cut only on thermal axex ?
Easy, because of money, 1/3 from the quartz crystall must be dropped to
the garbage. The resonant modes of any cuartz take care about the
thickness of the cuartz and the cutting axis.
BTW, the best accuracy I've got with bresenham methode was +/- 2
sec/month. Could be better ?

best regards, Vasile

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