Will someone beside us use heat pipe. Would love to have an impendent
input. What does it take to get a test going. Scott has done a lot of work, how
about some one else step up to the plate. There are a lot of time nuts out
there  with the 5680A,many for the first time will have a very good
reference and some  of our experts with proper equipment can make a big difference.
Bert Kehren

In a message dated 6/28/2014 12:20:12 P.M. Eastern Daylight Time,
newell+timenuts@n5tnl.com writes:

At 04:32  AM 6/28/2014, wb6bnq wrote:

input ?

No. I've only traced back from  the ADC input to the voltage divider.

I have not.

It does sound messy. I don't think I'm willing to dunk one of  my units.

--
newell  N5TNL

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Hi Bert,

I am thinking about testing a heat pipe on a fan cooled setup I use.
The first temp controlled chassis I did used a peltier and works very
well, but was a lot more work to do and is much more power hungry.

The main problem I find is not the temp controller itself, but rather
the change in the temperature across the chassis as the ambient
changes. However good the temp controller is, it only controls a
single point, but other points further away from the sensing
thermistor can vary a lot.
I noticed you posted a picture of a heat pipe cooler a couple of weeks
ago - did you happen to compare the temperature across the unit with
direct fan cooling and the heat pipe cooler, or with different heat
pipes?

Angus.

On Sat, 28 Jun 2014 12:37:37 -0400 (EDT), you wrote:

keep the heat sensing very close to the heating to avoid thermal control
oscillation ! a thermal time constant is large and no to easy to deal
with it
73
Alex

On 7/3/2014 6:35 PM, Angus wrote:

Hi

There is a bunch of stuff on the Wentzel site about their double wall mini-test chambers. It’s probably the best approach to the gradient issue. You still have a gradient around the inner chamber / box, but it’s consistent. You eliminate the coupling of the gradient to the ambient temperature.

The downside is the higher thermal resistance of the structure. That may force you right back to thermo electric cooling. I’d try a conventional heat pipe designed for high power desktop CPU cooling first. The things are cheap, come with way more fan than you need and the plate that mates to the CPU is about the right size for this application.

Bob

On Jul 3, 2014, at 9:35 PM, Angus not.again@btinternet.com wrote:

At 07:23 AM 7/4/2014, Bob Camp wrote:

I dug around a bit and found this:
http://www.wenzel.com/wp-content/uploads/Sub-pico-Multiplier.pdf

Relevant?

--
newell  N5TNL

Hi

Yes, that’s one of the papers that shows their little chamber. I believe it’s mentioned in a couple of other places. Die cast boxes work pretty well for the enclosures. If you want to zero the gradient in the inner enclosure, put a small fan in there. That adds it’s own issues so it’s probably not really something you want to do.

Bob

On Jul 4, 2014, at 12:46 PM, Scott Newell newell+timenuts@n5tnl.com wrote:

On Fri, 04 Jul 2014 02:35:41 +0100, you wrote:

I finally got around to playing with a couple of laptop heat pipes,
fixed to a 25x50x75mm block of aluminium which is fixed to the 12mm
thick baseplate.
On a quick test of it, a sensor near the end of the baseplate showed
1.5-2x greater variation with temperature compared with just having a
fan blow directly onto the baseplate.
The oscillator also had to be allowed to run a few degrees C hotter
for the heatpipe coolers to work to the same max ambient temp.

One cooler had two heatpipes with about 12cm between the aluminium
block and the heatsink fins (cast in this case) The other had a
single, wider heat pipe with about 5cm between the block and the
heatsink (this time with a lot more fine fins)

The second cooler was rather more efficient, allowing a extra degreee
of cooling at the top end, but more problematic was that it entered
'bang-bang' mode with the analogue temperature controller even sooner,
and the temperature fluctuations there were greater. Both were rather
worse than with the fan just blowing onto the baseplate.

Using a PWM fan controller would help a good bit, but getting more
creative with a microcontroller would be better. That way you can give
the fan a minimum of a small kick every so often, and vary the
repetition rate as well as the duty cycle as more cooling is needed.
With feedback from the fan and even air temperature monitoring, you
could get a good idea of exactly how much cooling was being applied.

Another problem is that the overall temp control range is lower with
the coolers - barely 8-9 DegC compared with 12+ DegC with the fan
blowing directly on the baseplate. That's mainly the result of the
poorer cooling at the top end of the range.

The Rb osc fitted during this test was a SA.22c which takes a good bit
less power than a 5680A, and the fan blowing onto the baseplate was
normally a 60mm one fitted about 50mm away from it. The baseplate was
horizontal with the fan blowing onto it from below.

Maybe fitting a heatsink directly onto the base would help further
with the maximum temp, but it would increase the convection cooling at
the minimum temp, reducing the overall benefit. It could also be more
susceptible to drafts, and would make the fan control much more
delicate.

Anyway, that's the results I got with my setup. Other setups and more
fine tuning could change things a good bit, but I just wanted to get
an idea of how the two cooling methods compared on the same setup.

Angus

Is a heatpipe really appropriate for this application?  The heatpipe
expects that the heat source wants to burn up and so there's lots of
heat available to vaporize the liquid in the pipe.  It's not clear to me
whether that situation exists with these Rb standards.  My tests with an
FE-5680A showed a maximum temperature of about 62C without a heatsink.
That's far lower than a CPU or GPU.  Some of them run at that
temperature with the heatpipe.

I think that a heatsink/fan (maybe from a video card) equipped with a
PWM controller might be a better fit.  Many of those combinations have a
ducted fan to provide better control of the airflow.  That would reduce
the effects of drafts and convection. One nuisance with using a video
card heatsink is that the back side typically has a raised area that
contacts the GPU.  For this application you'd have to have a flat back
over the entire heatsink.

Ed

On 8/18/2014 6:58 PM, Angus wrote: