[time-nuts] Rb cooling

[EWKehren at aol.com]

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 at 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 at 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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