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'OT: Wanted: schematic of (quartz) thermostat on th'
1998\11\07@142806 by Peter L. Peres

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Hello,

 I'm trying to look at as many quartz oven schematics as I can, on the
web, and in books, as I'm making one and I'd like to avoid the hot water,
wheel, etc reinvention. Also a pointer to an electronic design book or two
with relevant chapters would help.

 I understand that if one does not use a thermistor one can rely on a
bandgap type self-regulating supply where its own Pd supplies the heat and
some of the junctions involved supply the reference.  Anyway this is the
direction I am headed for.

thanks,

Peter

1998\11\07@171943 by Scott Newell

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>  I'm trying to look at as many quartz oven schematics as I can, on the
>web, and in books, as I'm making one and I'd like to avoid the hot water,
>wheel, etc reinvention. Also a pointer to an electronic design book or two
>with relevant chapters would help.

bul.eecs.umich.edu/uffc/quartz/vig/vigtoc.htm
http://bul.eecs.umich.edu/uffc/uffc_fc.html
http://www.wenzel.com/


Here are a couple of good books:

Frerking, M. E., Crystal Oscillator Design and Temperature Compensation,
Van Nostrand Reinhold Company, 1978.

Parzen, B., Design of Crystal and Other Harmonic Oscillators, Wiley, New
York, 1983

There's another good oscillator design book I borrowed recently, but I
can't recall the details.  I could look it up in a day or so, if you're
interested.  However, I don't recall a lot of oven schematics in these
books.  (The above books do show some of the early microprocessor
controlled TCXO circuits.)


>  I understand that if one does not use a thermistor one can rely on a
>bandgap type self-regulating supply where its own Pd supplies the heat and
>some of the junctions involved supply the reference.  Anyway this is the
>direction I am headed for.

I've got some stuff from Wenzel for building an oven (which I really am
going to get around to doing, one of these days...), including thermistors.
Seems to me the increased sensitivity would make for a better oven than
trying to use the (relatively) insensitive transistor junctions to measure
the oven temp.  After all, linearity isn't a concern.


Just curious: will you be using an AT or SC-cut overtone rock?


newell

1998\11\08@112346 by Peter L. Peres

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Thanks, Scott ! (scroll down for more)

On Sat, 7 Nov 1998, Scott Newell wrote:

- many great pointers snipped -

{Quote hidden}

Hmm. The ovens I had to do with had thermistor/transistor oven drive PLUS
thermistor/varicap compensator on the rock for startup performance.

> Just curious: will you be using an AT or SC-cut overtone rock?

I don't think it will be overtone. I'll have to read the relevant things
for a coherent answer. I'll go for a mid-range oscillator and make it as
good as possible, with options to use it as a PLL timebase etc.

I'd like to use an off the shelf crystal and correct for its misbehaviors
with (many ?) other standard components, preferrably all SMD, about the
size of the HC crystal case. I expect to spend a lot of time on this one
and learn a great deal about what can and cannot be done this way.

Peter

1998\11\08@130251 by Scott Newell

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>Hmm. The ovens I had to do with had thermistor/transistor oven drive PLUS
>thermistor/varicap compensator on the rock for startup performance.

That's a new one for me.  I never was too concerned with start-up time, so
maybe that's why I missed that technique. :-)

BTW, I just checked my 5345 book.  It's got a block diagram of the HP 10544
OCXO and a schematic of the optional room temp oscillator.  I could scan if
you're interested, but there's not a lot of detail there (especially the
OCXO).


>I don't think it will be overtone. I'll have to read the relevant things

>From what I've read, overtone rocks are less pullable.  Seems like if
you're going to use an oven for better stability, might as well use an
overtone crystal as well.  (Unless you need to be able to pull it, as in a
PLL...)


>I'd like to use an off the shelf crystal and correct for its misbehaviors
>with (many ?) other standard components, preferrably all SMD, about the
>size of the HC crystal case. I expect to spend a lot of time on this one
>and learn a great deal about what can and cannot be done this way.

Can you get off the shelf crystals with turning points of 80¡ C?  If not,
here's an option that you could explore (I've considered it, but I decided
that if I was going to all the trouble of building an oven, I wasn't gonna
stick some low-Q fundamental mode piece of crap in there):

http://www.sonic.net/~shageman/pco.html

It even uses a PIC!


newell

1998\11\08@173440 by Reginald Neale

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I've just been re-reading a twenty-year-old article in SCIENTIFIC AMERICAN
on fitting a pendulum clock with a crystal-controlled device that tweaks
the pendulum period to make the clock super accurate. The author doesn't
use an oven; he uses a "tuning capacitance" that has a special tempco,
along with a selected 3 mHz crystal. Is anyone familiar with this article?
Does anyone know whether the author's crystal recommendations are still the
best available? He claimed an accuracy of about one second per year for his
setup. That seems pretty incredible.

Reg Neale

{Quote hidden}

1998\11\08@180151 by Dave VanHorn

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Reginald Neale wrote:
>
> I've just been re-reading a twenty-year-old article in SCIENTIFIC AMERICAN
> on fitting a pendulum clock with a crystal-controlled device that tweaks
> the pendulum period to make the clock super accurate. The author doesn't
> use an oven; he uses a "tuning capacitance" that has a special tempco,
> along with a selected 3 mHz crystal. Is anyone familiar with this article?
> Does anyone know whether the author's crystal recommendations are still the
> best available? He claimed an accuracy of about one second per year for his
> setup. That seems pretty incredible.

Seems reasonable. It also sounds like something that wouldn't work if
you made 1000 of them. That "tuning capacitance" is nothing more than a
cap that had a tempco exactly matching, but in the opposite direction,
that of the xtal. To the degree that you can get all your tempcos to
match, you don't need an oven.

I'd bet that this is not a commercially available part, but something he
made.

The basic technique sounds a lot like injection locking, where you can
hold a 10 Ghz source stable by feeding in a little of a stable lower
frequency.

Your power line is at least that accurate, if not more. They tweak the
generator speed by hand, so that in the long term, it's dead on to wwv.
In the short term though, it could be dramatically off.

1998\11\09@105930 by Peter L. Peres

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On Sun, 8 Nov 1998, Reginald Neale wrote:

> I've just been re-reading a twenty-year-old article in SCIENTIFIC AMERICAN
> on fitting a pendulum clock with a crystal-controlled device that tweaks
> the pendulum period to make the clock super accurate. The author doesn't
> use an oven; he uses a "tuning capacitance" that has a special tempco,

And is totally impossible to get.

> along with a selected 3 mHz crystal. Is anyone familiar with this article?

No, but I can tell you that the guy had access to an astronomical
precision timebase offhand, from how he specs his error. He also does not
say how many hours he spent tweaking the compensation. It would be nice to
know more details though, there may be something to it. My hunch: He used
the differential error of the crystal and pendulum. Other hunch: he did
not compensate for gravity variation induced pendulum problems.

Peter

1998\11\09@105935 by Peter L. Peres

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On Sun, 8 Nov 1998, Dave VanHorn wrote:

> Your power line is at least that accurate, if not more. They tweak the
> generator speed by hand, so that in the long term, it's dead on to wwv.

Historically perhaps. Nowadays the hand has no body behind it, and it has
a legend that says 'IBM' on the side, or something like that.

> In the short term though, it could be dramatically off.

Not really. In a modern country-wide coordinated network operating within
its normal specs all you get is phase slip, else the whole shebang goes to
hell very quickly.

Peter

1998\11\09@111309 by Dave VanHorn

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> Historically perhaps. Nowadays the hand has no body behind it, and it has
> a legend that says 'IBM' on the side, or something like that.

Whichever..

> Not really. In a modern country-wide coordinated network operating within
> its normal specs all you get is phase slip, else the whole shebang goes to
> hell very quickly.

A few degrees at 60 hz is quite a lot of variability at 10 MHz.
Point being, you wouldn't want to lock your color subcarrier to it.

Many areas aren't (or can't) be tied to national grids, but have the
long term compensations in place. In Hawaii, we had (until '87 or so) a
steel mill that would load our system enough to visibly slow clocks. My
father in law ran the furnace there, and I've seen the slowdown myself,
both by eye and by scope.

Still, they were dead on in the long term.

1998\11\09@155056 by Gordon Couger

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If you want good time use a Rockwell Jupiter GPS it has 1 Hz and 10KHz
signals
that are very very accurate. It give the time in ASCII every second. There
is a
known deviation from GMT. But that is published and can be easily accounted
for.

Gordon
{Original Message removed}

1998\11\09@161336 by Sean Breheny

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At 08:50 AM 11/9/98 +0000, you wrote:
>> In the short term though, it could be dramatically off.
>
>Not really. In a modern country-wide coordinated network operating within
>its normal specs all you get is phase slip, else the whole shebang goes to
>hell very quickly.

I recently listened to a lecture by the head of our EE dept. here who is a
power systems expert, and he showed us data of the U.S. Eastern power grid.
The plot was freq. vs. time. It looked to me from the graph that it DOES
vary by as much as 0.3% over short periods of time. The graph had rougly as
many spikes under the 60.000Hz line as above, though, so it would average
out very well in the long run.

Incidentally, he told us that occasionally if a whole bunch of factories
power down at once, it can throw the whole system off. There was a 1% freq.
variation when the O.J. Simpson verdict was read <G>. This corresponded to
5 GW which was instantly wasted before the network could compensate. The
capacity of the whole U.S. Eastern grid is 400 GW. The grid is phase locked
together very well using GPS time standards, A/D convertors,
microcontrollers, and fiber optic lines. So, if even the power company uses
GPS time, I think that we can take a cue from that. Although, it is still
easier to just use 60Hz power as a time base than have a 1.5GHz GPS receiver.

Sean



>
>Peter
>
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