Crystal oven theory...

[Phil Hobbs]

Gerhard Hoffmann wrote:

Am 24.05.22 um 17:06 schrieb Phil Hobbs:
jlarkin@highlandsniptechnology.com wrote:
he 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.

But a TEC has a thermal low-impedance-path from inside to the
outside. That is unwanted and one of the reasons for their bad efficiency.
That means that heat transients on the outside get in
immediately and must be activly regulated away, AFTER they have happened.

I invite you to compute the ratio of the bandwidth available to a TEC
loop vs a heater loop as the delta-T goes to zero.

Yes, one could insulate the outside of the TEC, but that is somewhat ill?

You can get TECs in all sorts of sizes.

Heater loops work fine at larger delta-T.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Chris Jones]

On 25/05/2022 04:35, Gerhard Hoffmann wrote:

Am 24.05.22 um 17:06 schrieb Phil Hobbs:
jlarkin@highlandsniptechnology.com wrote:
he 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.

But a TEC has a thermal low-impedance-path from inside to the
outside. That is unwanted and one of the reasons for their bad efficiency.
That means that heat transients on the outside get in
immediately and must be activly regulated away, AFTER they have happened.

You could put another temperature sensor on the outside end of the TEC,
and do some sort of feed-forward as well, to remove most of the effect
before it gets in.

 

[Phil Hobbs]

Chris Jones wrote:

On 25/05/2022 04:35, Gerhard Hoffmann wrote:
Am 24.05.22 um 17:06 schrieb Phil Hobbs:
jlarkin@highlandsniptechnology.com wrote:
he 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.

But a TEC has a thermal low-impedance-path from inside to the
outside. That is unwanted and one of the reasons for their bad
efficiency.
That means that heat transients on the outside get in
immediately and must be activly regulated away, AFTER they have happened.

You could put another temperature sensor on the outside end of the TEC,
and do some sort of feed-forward as well, to remove most of the effect
before it gets in.

A really important tool in high-stability temperature control is a local
feedback loop around each actuator. Proportional-only is fine, but what
you really want is super high speed. These days we do a lot of
TEC-based controllers. Our favourite method is to put a bare ENIG pour
on the bottom side of the cold plate board (which usually has a laser or
one or more photodetectors). This contacts the cold side of the TEC via
(usually) silver grease.(*) One end of an 0603 thermistor is soldered
to the pour, and the other goes via a longish skinny trace to the loop amp.

Doing that costs next to nothing, and allows us to make a much faster
simulated actuator with much much lower effective thermal conductance.

Feedforward to the outer loop can also be done, but requires much more
tuning because the speed of the outer loop changes dramatically with
delta-T and Qdot.

Cheers

Phil Hobbs


(*) Thermal silver grease has much much more silver than
electrically-conductive silver paste.

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[server]

On Wed, 25 May 2022 23:17:29 +1000, Chris Jones
<lugnut808@spam.yahoo.com> wrote:

On 25/05/2022 04:35, Gerhard Hoffmann wrote:
Am 24.05.22 um 17:06 schrieb Phil Hobbs:
jlarkin@highlandsniptechnology.com wrote:
he 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.

But a TEC has a thermal low-impedance-path from inside to the
outside. That is unwanted and one of the reasons for their bad efficiency.
That means that heat transients on the outside get in
immediately and must be activly regulated away, AFTER they have happened.

You could put another temperature sensor on the outside end of the TEC,
and do some sort of feed-forward as well, to remove most of the effect
before it gets in.

Bad ovens sometimes sense ambient temp and feed-forward into the
setpoint, to shotgun compensate the badness.

The SRS SC10 is a good example of an oven done wrong. The manual of
rev L is available online.



--

Anybody can count to one.

- Robert Widlar

 

[Chris Jones]

On 25/05/2022 23:34, Phil Hobbs wrote:

Chris Jones wrote:
On 25/05/2022 04:35, Gerhard Hoffmann wrote:
Am 24.05.22 um 17:06 schrieb Phil Hobbs:
jlarkin@highlandsniptechnology.com wrote:
he 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.

But a TEC has a thermal low-impedance-path from inside to the
outside. That is unwanted and one of the reasons for their bad
efficiency.
That means that heat transients on the outside get in
immediately and must be activly regulated away, AFTER they have
happened.

You could put another temperature sensor on the outside end of the
TEC, and do some sort of feed-forward as well, to remove most of the
effect before it gets in.

A really important tool in high-stability temperature control is a local
feedback loop around each actuator.  Proportional-only is fine, but what
you really want is super high speed.  These days we do a lot of
TEC-based controllers.  Our favourite method is to put a bare ENIG pour
on the bottom side of the cold plate board (which usually has a laser or
one or more photodetectors).  This contacts the cold side of the TEC via
(usually) silver grease.(*)  One end of an 0603 thermistor is soldered
to the pour, and the other goes via a longish skinny trace to the loop amp.

Doing that costs next to nothing, and allows us to make a much faster
simulated actuator with much much lower effective thermal conductance.

That scheme makes a lot of sense.

 

[Phil Hobbs]

Chris Jones wrote:

On 25/05/2022 23:34, Phil Hobbs wrote:
Chris Jones wrote:
On 25/05/2022 04:35, Gerhard Hoffmann wrote:
Am 24.05.22 um 17:06 schrieb Phil Hobbs:
jlarkin@highlandsniptechnology.com wrote:
he 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.

But a TEC has a thermal low-impedance-path from inside to the
outside. That is unwanted and one of the reasons for their bad
efficiency.
That means that heat transients on the outside get in
immediately and must be activly regulated away, AFTER they have
happened.

You could put another temperature sensor on the outside end of the
TEC, and do some sort of feed-forward as well, to remove most of the
effect before it gets in.

A really important tool in high-stability temperature control is a
local feedback loop around each actuator.  Proportional-only is fine,
but what you really want is super high speed.  These days we do a lot
of TEC-based controllers.  Our favourite method is to put a bare ENIG
pour on the bottom side of the cold plate board (which usually has a
laser or one or more photodetectors).  This contacts the cold side of
the TEC via (usually) silver grease.(*)  One end of an 0603 thermistor
is soldered to the pour, and the other goes via a longish skinny trace
to the loop amp.

Doing that costs next to nothing, and allows us to make a much faster
simulated actuator with much much lower effective thermal conductance.

That scheme makes a lot of sense.

With the thermistor hanging five right at the edge of the pour (right
next to the edge of the cold side of the TEC) the response is faster
than 100 ms.

Thermal diffusion is quadratically slow at large distances, so of course
it\'s quadratically fast at small ones!

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[bitrex]

On 5/23/2022 9:48 AM, Phil Hobbs wrote:

The interesting test would be to measure heater power with and without
the foam.

Air at room temperature has an alpha of about 0.026 W/m/K.  High-density
styrofoam (the kind that crunches when you poke it with your finger) is
about 0.040, and low-density styrofoam (the kind that squeaks) is around
0.030.

Cheers

Phil Hobbs

The way I would describe the \"insulating\" (or whatever it does) foam in
the HP oven is sort of the consistency of freeze-dried ice cream.

 

[server]

bitrex <user@example.net> wrote in news:QaTiK.4601$8T.2667@fx40.iad:

On 5/23/2022 11:46 AM, jlarkin@highlandsniptechnology.com wrote:
On Mon, 23 May 2022 14:11:54 -0000 (UTC),
DecadentLinuxUserNumeroUno@decadence.org wrote:

jlarkin@highlandsniptechnology.com wrote in
news:4hjl8hd5d42lhge1c7lu0kt7m29led31kd@4ax.com:

On Sun, 22 May 2022 16:46:44 -0400, bitrex <user@example.net
wrote:

On 5/22/2022 2:21 PM, jlarkin@highlandsniptechnology.com
wrote:
On Sun, 22 May 2022 13:24:02 -0400, bitrex <user@example.net
wrote:

On 5/22/2022 4:31 AM, Anthony William Sloman wrote:
On Sunday, May 22, 2022 at 1:15:05 PM UTC+10,
jla...@highlandsniptechnology.com wrote:
On Sat, 21 May 2022 20:50:12 -0400, bitrex
us...@example.net> wrote:

Here\'s a paper on the theory of crystal ovens:

http://www.karlquist.com/oven.pdf

He didn\'t survey the literature all that well.

There\'s a lot more to it than just slapping a crystal &
heater in a metal box and calling it a day! There are
probably some pathologically bad geometries even a really
fast control loop can never stabilize very well.

The part about the outer can acting like a Faraday shield
is interesting, shunting ambient gradients around the
core. Does anyone know how they make the negative space
look like a linear tehrmal resistance over a wide range?
There\'s some kind of insulating foam in there, is main
heat thermal transfer radiative or conduction?

Conduction. Foam pretty much stops convection.

It was mentioned on another thread that the thermal
resistance of radiation between two concentric blackbodies
at 300K is about 6mm, interestingly that\'s very close to the
same thickness of foam-filled negative space between the
outer and inner shells of the OCXO module on my 5334B.

Don\'t know if that\'s a coincidence or not, obviously the two
aren\'t at exactly 300K. The interior I think runs about
355K, while the exterior (I haven\'t measured it) seems cool
enough to keep your hand on a while.


In a reasonably close-fitting box, without a lot of space for
convection, air is a better thermal insulator than foam or
fiberglass.


Here\'s a glamour shot of the internals:

https://imgur.com/a/W4hmKt4

Don\'t know what the foam is. It doesn\'t seem to conduct heat
too good.



The interesting test would be to measure heater power with and
without the foam.




The foam is for physical shock absorption, silly.

None of my ovens depended on foam for mechanical support.
Sometimes long lead wires are bad news too.

I did mount one OCXO on some custom springs. Mating and unmating
an nearby SMB test connector made my PLL lose lock.

https://www.dropbox.com/s/0k8agdfyiqlwn84/Spring_2.JPG?raw=1

https://www.dropbox.com/s/l2gr4fxas2k05fz/Sprung_Osc_2.JPG?raw=1



Hard to protect against that \"floating in air\". They should
try
some nice aerogel inserts. I think it has pretty good thermals
compared to foam.

Have you done that? Is aerogel rigid enough to support a
subassembly? Would mechanical shocks scrunch it down?

The foam inside the HP oven is stiff & brittle. I think it may
just be to separate the bits from each other and provide
mechanical support, but I don\'t think I\'d want to rely on it to
absorb much shock.

Compared to being suspended in air, I am sure it wil absorb more.
Just what do you think \"mechanical support\" is?

 

[bitrex]

On 5/23/2022 6:05 PM, DecadentLinuxUserNumeroUno@decadence.org wrote:

bitrex <user@example.net> wrote in news:QaTiK.4601$8T.2667@fx40.iad:

On 5/23/2022 11:46 AM, jlarkin@highlandsniptechnology.com wrote:
On Mon, 23 May 2022 14:11:54 -0000 (UTC),
DecadentLinuxUserNumeroUno@decadence.org wrote:

jlarkin@highlandsniptechnology.com wrote in
news:4hjl8hd5d42lhge1c7lu0kt7m29led31kd@4ax.com:

On Sun, 22 May 2022 16:46:44 -0400, bitrex <user@example.net
wrote:

On 5/22/2022 2:21 PM, jlarkin@highlandsniptechnology.com
wrote:
On Sun, 22 May 2022 13:24:02 -0400, bitrex <user@example.net
wrote:

On 5/22/2022 4:31 AM, Anthony William Sloman wrote:
On Sunday, May 22, 2022 at 1:15:05 PM UTC+10,
jla...@highlandsniptechnology.com wrote:
On Sat, 21 May 2022 20:50:12 -0400, bitrex
us...@example.net> wrote:

Here\'s a paper on the theory of crystal ovens:

http://www.karlquist.com/oven.pdf

He didn\'t survey the literature all that well.

There\'s a lot more to it than just slapping a crystal &
heater in a metal box and calling it a day! There are
probably some pathologically bad geometries even a really
fast control loop can never stabilize very well.

The part about the outer can acting like a Faraday shield
is interesting, shunting ambient gradients around the
core. Does anyone know how they make the negative space
look like a linear tehrmal resistance over a wide range?
There\'s some kind of insulating foam in there, is main
heat thermal transfer radiative or conduction?

Conduction. Foam pretty much stops convection.

It was mentioned on another thread that the thermal
resistance of radiation between two concentric blackbodies
at 300K is about 6mm, interestingly that\'s very close to the
same thickness of foam-filled negative space between the
outer and inner shells of the OCXO module on my 5334B.

Don\'t know if that\'s a coincidence or not, obviously the two
aren\'t at exactly 300K. The interior I think runs about
355K, while the exterior (I haven\'t measured it) seems cool
enough to keep your hand on a while.


In a reasonably close-fitting box, without a lot of space for
convection, air is a better thermal insulator than foam or
fiberglass.


Here\'s a glamour shot of the internals:

https://imgur.com/a/W4hmKt4

Don\'t know what the foam is. It doesn\'t seem to conduct heat
too good.



The interesting test would be to measure heater power with and
without the foam.




The foam is for physical shock absorption, silly.

None of my ovens depended on foam for mechanical support.
Sometimes long lead wires are bad news too.

I did mount one OCXO on some custom springs. Mating and unmating
an nearby SMB test connector made my PLL lose lock.

https://www.dropbox.com/s/0k8agdfyiqlwn84/Spring_2.JPG?raw=1

https://www.dropbox.com/s/l2gr4fxas2k05fz/Sprung_Osc_2.JPG?raw=1



Hard to protect against that \"floating in air\". They should
try
some nice aerogel inserts. I think it has pretty good thermals
compared to foam.

Have you done that? Is aerogel rigid enough to support a
subassembly? Would mechanical shocks scrunch it down?

The foam inside the HP oven is stiff & brittle. I think it may
just be to separate the bits from each other and provide
mechanical support, but I don\'t think I\'d want to rely on it to
absorb much shock.



Compared to being suspended in air, I am sure it wil absorb more.
Just what do you think \"mechanical support\" is?

Do u require mechanical support:

<https://www.mayoclinic.org/tests-procedures/penis-pump/about/pac-20385225>

 

[John Larkin]

On Mon, 23 May 2022 17:41:12 -0400, bitrex <user@example.net> wrote:

On 5/23/2022 5:40 PM, bitrex wrote:

  Hard to protect against that \"floating in air\".  They should try
some nice aerogel inserts.  I think it has pretty good thermals
compared to foam.

Have you done that? Is aerogel rigid enough to support a subassembly?
Would mechanical shocks scrunch it down?

The foam inside the HP oven is stiff & brittle.

Basically the consistency of dehydrated \"astronaut\" ice cream if you\'ve
had that stuff..

Dehydrated ice cream? I\'m glad I didn\'t become an astronaut.

--

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

 

[bitrex]

On 5/23/2022 6:54 PM, John Larkin wrote:

On Mon, 23 May 2022 17:41:12 -0400, bitrex <user@example.net> wrote:

On 5/23/2022 5:40 PM, bitrex wrote:

  Hard to protect against that \"floating in air\".  They should try
some nice aerogel inserts.  I think it has pretty good thermals
compared to foam.

Have you done that? Is aerogel rigid enough to support a subassembly?
Would mechanical shocks scrunch it down?

The foam inside the HP oven is stiff & brittle.

Basically the consistency of dehydrated \"astronaut\" ice cream if you\'ve
had that stuff..

Dehydrated ice cream? I\'m glad I didn\'t become an astronaut.

Yeah, freeze-dried. No idea if this stuff was actually used on space
flights or when. My mother used to buy it for me at science museum gift
shops when I was a kid, we didn\'t have much money but she didn\'t like to
turn me down for a few souvenirs so long as they were \"educational\"!

It was sweet at least and most sweet stuff tastes good to an 8 y/o:

<https://youtu.be/gmGDBmeyBIs>

The pull-back racer Space Shuttle toy was another classic gift shop
crowd-pleaser.

<https://www.amazon.com/5-Diecast-Pullback-Space-Shuttle/dp/B003PATHLU/>

 

[server]

On Mon, 23 May 2022 10:09:23 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

On Monday, May 23, 2022 at 8:46:31 AM UTC-7, jla...@highlandsniptechnology.com wrote:
On Mon, 23 May 2022 14:11:54 -0000 (UTC),
DecadentLinux...@decadence.org wrote:

The foam is for physical shock absorption, silly.

None of my ovens depended on foam for mechanical support. Sometimes
long lead wires are bad news too.

I did mount one OCXO on some custom springs...

Hard to protect against that \"floating in air\". They should try
some nice aerogel inserts. I think it has pretty good thermals
compared to foam.

Have you done that? Is aerogel rigid enough to support a subassembly?
Would mechanical shocks scrunch it down?

Some aerogels are foam-like quartz, quite strong enough for most uses, and
relatively tough. You could use \'em to support, and they\'re good in vacuum (if
you want a good insulator, ditch the air). On the other hand, a perforated
section of fiberglass PCB should likewise be a thermal break. How
stingy on heater power do you want to be?

Heater power is seldom an issue. Heat loss is bad because it makes an
assembly non-isothermal, so that some bits are not at the same
temperature as the feedback sensor. And the difference will vary with
heater power, namely ambient temp.



--

Anybody can count to one.

- Robert Widlar

 

[Anthony William Sloman]

On Friday, May 27, 2022 at 12:09:00 AM UTC+10, Phil Hobbs wrote:

Chris Jones wrote:
On 25/05/2022 23:34, Phil Hobbs wrote:
Chris Jones wrote:
On 25/05/2022 04:35, Gerhard Hoffmann wrote:
Am 24.05.22 um 17:06 schrieb Phil Hobbs:
jla...@highlandsniptechnology.com wrote:
he 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.

But a TEC has a thermal low-impedance-path from inside to the
outside. That is unwanted and one of the reasons for their bad
efficiency.
That means that heat transients on the outside get in
immediately and must be activly regulated away, AFTER they have
happened.

You could put another temperature sensor on the outside end of the
TEC, and do some sort of feed-forward as well, to remove most of the
effect before it gets in.

A really important tool in high-stability temperature control is a
local feedback loop around each actuator. Proportional-only is fine,
but what you really want is super high speed. These days we do a lot
of TEC-based controllers. Our favourite method is to put a bare ENIG
pour on the bottom side of the cold plate board (which usually has a
laser or one or more photodetectors). This contacts the cold side of
the TEC via (usually) silver grease.(*) One end of an 0603 thermistor
is soldered to the pour, and the other goes via a longish skinny trace
to the loop amp.

Doing that costs next to nothing, and allows us to make a much faster
simulated actuator with much much lower effective thermal conductance.

That scheme makes a lot of sense.
With the thermistor hanging five right at the edge of the pour (right
next to the edge of the cold side of the TEC) the response is faster
than 100 ms.

Thermal diffusion is quadratically slow at large distances, so of course
it\'s quadratically fast at small ones!

There\'s a lower limit set by the structure of the thermistor. It\'s finite lump of metal oxides,and it takes a finite time for heat to diffuse from the edges to the middle.

--
Bill Sloman, Sydney

 

[Jan Panteltje]

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

 

[John Doe]

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 <always.look@message.header> wrote in news:t6gdmo$or8$6@dont-
email.me:

jlarkin@highlandsniptechnology.com wrote:

Anybody can count to one.

- Robert Widlar

I don\'t get it.

allintext:\"Anybody can count to one\" \"Robert Widlar\"

Produces four results, all of them from John Larkin.

 

[Mike Coon]

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!

 

[Anthony William Sloman]

On Tuesday, May 24, 2022 at 2:34:46 AM UTC+10, Mike Coon wrote:

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

On a sunny day (Sun, 22 May 2022 22:51:09 +0100) it happened Mike Coon
gra...@mjcoon.plus.com> wrote in
MPG.3cf4c0956...@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!

Clearly not. Most people understand over-compensated to mean very long settling times, and under-compensated to mean ringing. If it is second or or higher order system, a sufficiently undercompensates unit can oscillate.

--
Bill Sloman, Sydney

 

[server]

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.





--

Anybody can count to one.

- Robert Widlar

 

[Phil Hobbs]

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

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[server]

bitrex <user@example.net> wrote in
news:47UiK.3545$vAW9.2843@fx10.iad:

On 5/23/2022 6:05 PM, DecadentLinuxUserNumeroUno@decadence.org
wrote:
bitrex <user@example.net> wrote in
news:QaTiK.4601$8T.2667@fx40.iad:

On 5/23/2022 11:46 AM, jlarkin@highlandsniptechnology.com wrote:
On Mon, 23 May 2022 14:11:54 -0000 (UTC),
DecadentLinuxUserNumeroUno@decadence.org wrote:

jlarkin@highlandsniptechnology.com wrote in
news:4hjl8hd5d42lhge1c7lu0kt7m29led31kd@4ax.com:

On Sun, 22 May 2022 16:46:44 -0400, bitrex <user@example.net
wrote:

On 5/22/2022 2:21 PM, jlarkin@highlandsniptechnology.com
wrote:
On Sun, 22 May 2022 13:24:02 -0400, bitrex
user@example.net> wrote:

On 5/22/2022 4:31 AM, Anthony William Sloman wrote:
On Sunday, May 22, 2022 at 1:15:05 PM UTC+10,
jla...@highlandsniptechnology.com wrote:
On Sat, 21 May 2022 20:50:12 -0400, bitrex
us...@example.net> wrote:

Here\'s a paper on the theory of crystal ovens:

http://www.karlquist.com/oven.pdf

He didn\'t survey the literature all that well.

There\'s a lot more to it than just slapping a crystal &
heater in a metal box and calling it a day! There are
probably some pathologically bad geometries even a
really fast control loop can never stabilize very well.

The part about the outer can acting like a Faraday
shield is interesting, shunting ambient gradients
around the core. Does anyone know how they make the
negative space look like a linear tehrmal resistance
over a wide range? There\'s some kind of insulating foam
in there, is main heat thermal transfer radiative or
conduction?

Conduction. Foam pretty much stops convection.

It was mentioned on another thread that the thermal
resistance of radiation between two concentric blackbodies
at 300K is about 6mm, interestingly that\'s very close to
the same thickness of foam-filled negative space between
the outer and inner shells of the OCXO module on my 5334B.

Don\'t know if that\'s a coincidence or not, obviously the
two aren\'t at exactly 300K. The interior I think runs
about 355K, while the exterior (I haven\'t measured it)
seems cool enough to keep your hand on a while.


In a reasonably close-fitting box, without a lot of space
for convection, air is a better thermal insulator than foam
or fiberglass.


Here\'s a glamour shot of the internals:

https://imgur.com/a/W4hmKt4

Don\'t know what the foam is. It doesn\'t seem to conduct heat
too good.



The interesting test would be to measure heater power with
and without the foam.




The foam is for physical shock absorption, silly.

None of my ovens depended on foam for mechanical support.
Sometimes long lead wires are bad news too.

I did mount one OCXO on some custom springs. Mating and
unmating an nearby SMB test connector made my PLL lose lock.

https://www.dropbox.com/s/0k8agdfyiqlwn84/Spring_2.JPG?raw=1

https://www.dropbox.com/s/l2gr4fxas2k05fz/Sprung_Osc_2.JPG?raw=1



Hard to protect against that \"floating in air\". They
should try
some nice aerogel inserts. I think it has pretty good
thermals compared to foam.

Have you done that? Is aerogel rigid enough to support a
subassembly? Would mechanical shocks scrunch it down?

The foam inside the HP oven is stiff & brittle. I think it may
just be to separate the bits from each other and provide
mechanical support, but I don\'t think I\'d want to rely on it to
absorb much shock.



Compared to being suspended in air, I am sure it wil absorb more.
Just what do you think \"mechanical support\" is?

Do u require mechanical support:

Look at it. It is smaller than the can it is in. So yes, it
requires mechanical support.

snipped retarded link post.

Real mature, twerp.