Empathy List Archives

E

EWKehren@aol.com

Mon, Jul 18, 2011 12:37 AM

I monitor and fan cool the base plate, stays nice and constant at 45 C
which I can not say with heat sink only. I am considering lowering the base
plate to 40 C. I have a heat sink on the base plate with the fan blowing over
it. Makes good heat exchanger. I have experimented with heat pipes from Lap
Tops but never fit for mechanical reasons. May work with a LPRO's. Al my
Rb's are Efratom.
A variable speed fan will reduce any ambient temperature influence. That is
why I chose to use a fan.
Use a dual Op Amp for temp. control. Nothing special. Fans are $ 3.00 I
have monitored points inside the Rb's and they are within 1 C over time.
Bert Kehren

In a message dated 7/17/2011 6:37:50 P.M. Eastern Daylight Time,
phk@phk.freebsd.dk writes:

Cooling Rb's is a much misunderstood discipline.

Most Rb's have a specified "base plate temperature range".

For instance the PRS10 specifies -20..+65°C

Cooling Rb's should happen only through the base-plate.

Cooling other surfaces creates unwanted temperature gradients inside
the Rb unit.

The colder you run a Rb, the more power it uses to keep important
bits inside warm.

Running it near the top end of the range wears out the electronics
in it faster.

No matter what kind of cooling, it is important that it offers
sufficient cooling capacity for the internal ovens to have a
margin to work with.

For frequency stability, you should strive to have a constant
baseplate temperature.

Putting a fan on anything, will generally speed up and amplify the
effects of any ambient temperature changes.

For optimal frequency stability, you want to do is mount
your Rb on a huge lump of iron which you can keep at a
constant temperature around 35-40°C by natural convection.

Iron is better than Cu/brass/Al because it conducts heat slower and
less eagerly, thus attenuating ambient temperature fluctuations.

--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.

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I monitor and fan cool the base plate, stays nice and constant at 45 C which I can not say with heat sink only. I am considering lowering the base plate to 40 C. I have a heat sink on the base plate with the fan blowing over it. Makes good heat exchanger. I have experimented with heat pipes from Lap Tops but never fit for mechanical reasons. May work with a LPRO's. Al my Rb's are Efratom. A variable speed fan will reduce any ambient temperature influence. That is why I chose to use a fan. Use a dual Op Amp for temp. control. Nothing special. Fans are $ 3.00 I have monitored points inside the Rb's and they are within 1 C over time. Bert Kehren In a message dated 7/17/2011 6:37:50 P.M. Eastern Daylight Time, phk@phk.freebsd.dk writes: Cooling Rb's is a much misunderstood discipline. Most Rb's have a specified "base plate temperature range". For instance the PRS10 specifies -20..+65°C Cooling Rb's should happen only through the base-plate. Cooling other surfaces creates unwanted temperature gradients inside the Rb unit. The colder you run a Rb, the more power it uses to keep important bits inside warm. Running it near the top end of the range wears out the electronics in it faster. No matter what kind of cooling, it is important that it offers sufficient cooling capacity for the internal ovens to have a margin to work with. For frequency stability, you should strive to have a constant baseplate temperature. Putting a fan on anything, will generally speed up and amplify the effects of any ambient temperature changes. For optimal frequency stability, you want to do is mount your Rb on a huge lump of iron which you can keep at a constant temperature around 35-40°C by natural convection. Iron is better than Cu/brass/Al because it conducts heat slower and less eagerly, thus attenuating ambient temperature fluctuations. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.

CH

Chuck Harris

Mon, Jul 18, 2011 3:59 AM

For all of this attention to cooling the oven on the Rb standards,
has anyone seen any failures that are attributable to heat?

I sort of doubt it.

-Chuck Harris

EWKehren@aol.com wrote:

I monitor and fan cool the base plate, stays nice and constant at 45 C
which I can not say with heat sink only. I am considering lowering the base
plate to 40 C. I have a heat sink on the base plate with the fan blowing over
it. Makes good heat exchanger. I have experimented with heat pipes from Lap
Tops but never fit for mechanical reasons. May work with a LPRO's. Al my
Rb's are Efratom.
A variable speed fan will reduce any ambient temperature influence. That is
why I chose to use a fan.
Use a dual Op Amp for temp. control. Nothing special. Fans are $ 3.00 I
have monitored points inside the Rb's and they are within 1 C over time.
Bert Kehren

For all of this attention to cooling the oven on the Rb standards, has anyone seen any failures that are attributable to heat? I sort of doubt it. -Chuck Harris EWKehren@aol.com wrote: > I monitor and fan cool the base plate, stays nice and constant at 45 C > which I can not say with heat sink only. I am considering lowering the base > plate to 40 C. I have a heat sink on the base plate with the fan blowing over > it. Makes good heat exchanger. I have experimented with heat pipes from Lap > Tops but never fit for mechanical reasons. May work with a LPRO's. Al my > Rb's are Efratom. > A variable speed fan will reduce any ambient temperature influence. That is > why I chose to use a fan. > Use a dual Op Amp for temp. control. Nothing special. Fans are $ 3.00 I > have monitored points inside the Rb's and they are within 1 C over time. > Bert Kehren

NM

Neville Michie

Mon, Jul 18, 2011 4:06 AM

The manufacturers data sheet presents MTBF figures for the LPRO
and they decline considerably with higher temperatures.
Against that the power required decreases with rising temperature,
so that at 19 volt supply and 40-45*C the unit takes much lower
power and has
still has most of its expected life.
cheers,
Neville Michie

On 18/07/2011, at 1:59 PM, Chuck Harris wrote:

For all of this attention to cooling the oven on the Rb standards,
has anyone seen any failures that are attributable to heat?

I sort of doubt it.

-Chuck Harris

EWKehren@aol.com wrote:

I monitor and fan cool the base plate, stays nice and constant at
45 C
which I can not say with heat sink only. I am considering lowering
the base
plate to 40 C. I have a heat sink on the base plate with the fan
blowing over
it. Makes good heat exchanger. I have experimented with heat pipes
from Lap
Tops but never fit for mechanical reasons. May work with a
LPRO's. Al my
Rb's are Efratom.
A variable speed fan will reduce any ambient temperature
influence. That is
why I chose to use a fan.
Use a dual Op Amp for temp. control. Nothing special. Fans are $
3.00 I
have monitored points inside the Rb's and they are within 1 C over
time.
Bert Kehren

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time-nuts
and follow the instructions there.

The manufacturers data sheet presents MTBF figures for the LPRO and they decline considerably with higher temperatures. Against that the power required decreases with rising temperature, so that at 19 volt supply and 40-45*C the unit takes much lower power and has still has most of its expected life. cheers, Neville Michie On 18/07/2011, at 1:59 PM, Chuck Harris wrote: > For all of this attention to cooling the oven on the Rb standards, > has anyone seen any failures that are attributable to heat? > > I sort of doubt it. > > -Chuck Harris > > EWKehren@aol.com wrote: >> I monitor and fan cool the base plate, stays nice and constant at >> 45 C >> which I can not say with heat sink only. I am considering lowering >> the base >> plate to 40 C. I have a heat sink on the base plate with the fan >> blowing over >> it. Makes good heat exchanger. I have experimented with heat pipes >> from Lap >> Tops but never fit for mechanical reasons. May work with a >> LPRO's. Al my >> Rb's are Efratom. >> A variable speed fan will reduce any ambient temperature >> influence. That is >> why I chose to use a fan. >> Use a dual Op Amp for temp. control. Nothing special. Fans are $ >> 3.00 I >> have monitored points inside the Rb's and they are within 1 C over >> time. >> Bert Kehren > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/ > time-nuts > and follow the instructions there.

CH

Chuck Harris

Mon, Jul 18, 2011 4:40 AM

I understand that, but you didn't answer my question:

Has anyone seen any failures that are attributable to heat?

50 year theoretical life vs 75 theoretical year life probably
isn't going to be too significant. 1 year life vs 10 year would
be.

These GPSDO's are made to run with their ovens powered, and hot.
Surely the manufacturer took a little time to select parts that
would survive the intended operating environment.

Cooling down an oven is not a good thing, as it simply ups the
power the oven control circuitry dumps into the oven to keep it
hot.

-Chuck Harris

Neville Michie wrote:

The manufacturers data sheet presents MTBF figures for the LPRO
and they decline considerably with higher temperatures.
Against that the power required decreases with rising temperature,
so that at 19 volt supply and 40-45*C the unit takes much lower power
and has
still has most of its expected life.
cheers,
Neville Michie

On 18/07/2011, at 1:59 PM, Chuck Harris wrote:

For all of this attention to cooling the oven on the Rb standards,
has anyone seen any failures that are attributable to heat?

I sort of doubt it.

-Chuck Harris

I understand that, but you didn't answer my question: Has anyone seen any failures that are attributable to heat? 50 year theoretical life vs 75 theoretical year life probably isn't going to be too significant. 1 year life vs 10 year would be. These GPSDO's are made to run with their ovens powered, and hot. Surely the manufacturer took a little time to select parts that would survive the intended operating environment. Cooling down an oven is not a good thing, as it simply ups the power the oven control circuitry dumps into the oven to keep it hot. -Chuck Harris Neville Michie wrote: > The manufacturers data sheet presents MTBF figures for the LPRO > and they decline considerably with higher temperatures. > Against that the power required decreases with rising temperature, > so that at 19 volt supply and 40-45*C the unit takes much lower power > and has > still has most of its expected life. > cheers, > Neville Michie > > On 18/07/2011, at 1:59 PM, Chuck Harris wrote: > >> For all of this attention to cooling the oven on the Rb standards, >> has anyone seen any failures that are attributable to heat? >> >> I sort of doubt it. >> >> -Chuck Harris

CP

Charles P. Steinmetz

Mon, Jul 18, 2011 4:57 AM

Chuck wrote:

Cooling down an oven is not a good thing, as it simply ups the
power the oven control circuitry dumps into the oven to keep it
hot.

The temperature, thermal mass, and conductivity of the surroundings
determine how quickly an oven cools down when the heater is off. Too
little cooling, and the oven control loop cannot do its job
properly. As others have said, rubidium oscillator manufacturers
specify them for operation within a certain range of baseplate
temperatures. Best performance is often obtained near the middle of
the specified window.

Best regards,

Charles

Chuck wrote: >Cooling down an oven is not a good thing, as it simply ups the >power the oven control circuitry dumps into the oven to keep it >hot. The temperature, thermal mass, and conductivity of the surroundings determine how quickly an oven cools down when the heater is off. Too little cooling, and the oven control loop cannot do its job properly. As others have said, rubidium oscillator manufacturers specify them for operation within a certain range of baseplate temperatures. Best performance is often obtained near the middle of the specified window. Best regards, Charles

MD

Magnus Danielson

Mon, Jul 18, 2011 9:54 AM

On 18/07/11 06:40, Chuck Harris wrote:

I understand that, but you didn't answer my question:

Has anyone seen any failures that are attributable to heat?

50 year theoretical life vs 75 theoretical year life probably
isn't going to be too significant. 1 year life vs 10 year would
be.

These GPSDO's are made to run with their ovens powered, and hot.
Surely the manufacturer took a little time to select parts that
would survive the intended operating environment.

Cooling down an oven is not a good thing, as it simply ups the
power the oven control circuitry dumps into the oven to keep it
hot.

Actually it is two-folded...

You do need a certain amount of cooling such that the oven remain in a
linear control-state. If you have too little cooling, the oven will turn
off completely for periods and then click in and heat up and then turn
off again. I've seen what this does to the frequency and it is not nice.

You do not want too much cooling, or you will draw a lot of current in
the heating regulator and this will shorten the life of that
transistor(s) significantly as it is both hot and operating with high
current, a double-bad situation.

So, instead of just slabbing a big passive radiator there or a strong
cooling fan, what I was discussing and what Charles and Bert has been
implementing is a temperature controlled cooling.

I agree that the temperature needs to be higher than ambient, but with
an active cooling you can have higher cooling dynamics than otherwise be
premisable, so the baseplate temperature may be higher than for a
passive radiator.

If you want to use the iron stabilisation proposed by Poul-Henning,
which can be an additional trick to use, mounting pre-heating resistors
on the iron body to pre-heat it up to operating range may be
recommended, since the heaters of the rubidium oven isn't that powerful
and the heat capacity of a big iron lump can be quite significant.

Essentially, it behaves like an oven, just that the main controlling
mechanism lies in cooling rather than heating. Pre-heating of iron blob
just fits the picture.

Cheers,
Magnus

On 18/07/11 06:40, Chuck Harris wrote: > I understand that, but you didn't answer my question: > > Has anyone seen any failures that are attributable to heat? > > 50 year theoretical life vs 75 theoretical year life probably > isn't going to be too significant. 1 year life vs 10 year would > be. > > These GPSDO's are made to run with their ovens powered, and hot. > Surely the manufacturer took a little time to select parts that > would survive the intended operating environment. > > Cooling down an oven is not a good thing, as it simply ups the > power the oven control circuitry dumps into the oven to keep it > hot. Actually it is two-folded... You do need a certain amount of cooling such that the oven remain in a linear control-state. If you have too little cooling, the oven will turn off completely for periods and then click in and heat up and then turn off again. I've seen what this does to the frequency and it is not nice. You do not want too much cooling, or you will draw a lot of current in the heating regulator and this will shorten the life of that transistor(s) significantly as it is both hot and operating with high current, a double-bad situation. So, instead of just slabbing a big passive radiator there or a strong cooling fan, what I was discussing and what Charles and Bert has been implementing is a temperature controlled cooling. I agree that the temperature needs to be higher than ambient, but with an active cooling you can have higher cooling dynamics than otherwise be premisable, so the baseplate temperature may be higher than for a passive radiator. If you want to use the iron stabilisation proposed by Poul-Henning, which can be an additional trick to use, mounting pre-heating resistors on the iron body to pre-heat it up to operating range may be recommended, since the heaters of the rubidium oven isn't that powerful and the heat capacity of a big iron lump can be quite significant. Essentially, it behaves like an oven, just that the main controlling mechanism lies in cooling rather than heating. Pre-heating of iron blob just fits the picture. Cheers, Magnus

BC

Bob Camp

Mon, Jul 18, 2011 4:33 PM

Hi

Yes, I have seen several Rb's die from what I believe were temperature
related causes. Since it's an accelerated MTBF sort of thing, proving they
were temperature related is difficult.
Put another way - I believe the manufacturer's data on MTBF vs temperature
is fairly accurate. At elevated temperatures, the life of the device is in
the "few years" (2 to 4) range.

Bob

-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Chuck Harris
Sent: Monday, July 18, 2011 12:00 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Rb cooling

For all of this attention to cooling the oven on the Rb standards,
has anyone seen any failures that are attributable to heat?

I sort of doubt it.

-Chuck Harris

EWKehren@aol.com wrote:

I monitor and fan cool the base plate, stays nice and constant at 45 C
which I can not say with heat sink only. I am considering lowering the

base

plate to 40 C. I have a heat sink on the base plate with the fan blowing

over

it. Makes good heat exchanger. I have experimented with heat pipes from

Lap

Tops but never fit for mechanical reasons. May work with a LPRO's. Al my
Rb's are Efratom.
A variable speed fan will reduce any ambient temperature influence. That

is

why I chose to use a fan.
Use a dual Op Amp for temp. control. Nothing special. Fans are $ 3.00 I
have monitored points inside the Rb's and they are within 1 C over time.
Bert Kehren

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Hi Yes, I have seen several Rb's die from what I believe were temperature related causes. Since it's an accelerated MTBF sort of thing, *proving* they were temperature related is difficult. Put another way - I believe the manufacturer's data on MTBF vs temperature is fairly accurate. At elevated temperatures, the life of the device is in the "few years" (2 to 4) range. Bob -----Original Message----- From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On Behalf Of Chuck Harris Sent: Monday, July 18, 2011 12:00 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Rb cooling For all of this attention to cooling the oven on the Rb standards, has anyone seen any failures that are attributable to heat? I sort of doubt it. -Chuck Harris EWKehren@aol.com wrote: > I monitor and fan cool the base plate, stays nice and constant at 45 C > which I can not say with heat sink only. I am considering lowering the base > plate to 40 C. I have a heat sink on the base plate with the fan blowing over > it. Makes good heat exchanger. I have experimented with heat pipes from Lap > Tops but never fit for mechanical reasons. May work with a LPRO's. Al my > Rb's are Efratom. > A variable speed fan will reduce any ambient temperature influence. That is > why I chose to use a fan. > Use a dual Op Amp for temp. control. Nothing special. Fans are $ 3.00 I > have monitored points inside the Rb's and they are within 1 C over time. > Bert Kehren _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.

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Re: [time-nuts] Rb cooling