Crystal oven theory...

[server]

John Dope <always.look@message.header> wrote in news:t6hvrj$kq3$3@dont-
email.me:

Bob Widlar was a big engineer.

Now, what is the significance of \"Anybody can count to one\"?

Seems not to be a famous quote.

John Dope is still in the dark. You never knew electronics and have
been a mere interloper all these years, at best.

The actual quote is \"Every idiot can count to one.\"

So even your google skill sucks. John Dope lives up to his name
every time he posts into SED.

 

[John Larkin]

On Tue, 24 May 2022 11:06:16 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

jlarkin@highlandsniptechnology.com wrote:
On Tue, 24 May 2022 08:41:01 +0100, Mike Coon
gravity@mjcoon.plus.com> wrote:

In article <t6hrnr$2ac$1@dont-email.me>, pNaonStpealmtje@yahoo.com
says...

On a sunny day (Mon, 23 May 2022 17:34:33 +0100) it happened Mike Coon
gravity@mjcoon.plus.com> wrote in
MPG.3cf5c7f82510056d9896bf@usenet.plus.net>:

In article <t6fga4$f2p$1@dont-email.me>, pNaonStpealmtje@yahoo.com
says...

On a sunny day (Sun, 22 May 2022 22:51:09 +0100) it happened Mike Coon
gravity@mjcoon.plus.com> wrote in
MPG.3cf4c0956a87c90d9896be@usenet.plus.net>:

My design for a foyer quartz clock back in the early 1960s included a
crystal in a thermostatic oven made from Perspex. I have a sketch and
isometric of the oven and a note that there were five thermistors in a
bridge, but no schematic. I do remember that on first testing the
control circuit initially ran at full power heating, then cut off, then
gradually settled on steady warmth!

Yes that is overshot, maybe over-compensated

My definition of over-compensated would be indefinite oscillation, which
is what I was concerned about when I was monitoring the behaviour... No
theory involved!

http://panteltje.com/pub/under_and_over_compensated_IXIMG_0818.JPG

Thanks for that idiosyncratic illustration! You could also have reminded
me of the calculus of feedback theory which I studied for my degree back
in the early 1960s. It was merely the modern (?) terminology I was
querying. \"Windup\" indeed; that\'s a gramophone!

We usually tune thermal loops in the classic linear style, for
critically-damped small signal disturbance. They will typically
overshoot at cold-start powerup because the integrator winds up and
rails. Rob did a lot of fancy math to define the software control
loop; I just Spice things like that.

The oven that I pictured has a 2nd order plant response, about 75
minutes tau for the huge aluminum block and about another 17 for the
platform and e/o modulator inside. Spacers set the second time
constant; aluminum, stainless, or plastic.

One goal was to force minimal thermal gradients along the length of
the Mach-Zender electro-optical modulator.

https://www.dropbox.com/sh/knkoywpv6563mj5/AACy1sLNcyqIO8Eik4NRCC9Da?dl=0

We have lots of heater power available so we can stabilize to
millikelvins in about a half hour.

One of the less-frequently remarked advantages of thermoelectrics is
that anywhere near room temperature they can have considerably better
forcing resistance than heater-only loops with a given bandwidth.

A heater-only loop gets its negative slewing exclusively from the heat
leak, which of course leaks in both directions, whereas a TEC can pull
as well as push, so a TEC-based loop can be better insulated for the
same control bandwidth and slew rate.

Cheers

Phil Hobbs

We only run at 30c, and ambient is very reliably 22. We considered
TECs but that was too complex and expensive. We sure don\'t want a fan
anywhere close to our optics.

The dpak mosfet heaters are cheap!

--

If a man will begin with certainties, he shall end with doubts,
but if he will be content to begin with doubts he shall end in certainties.
Francis Bacon