[time-nuts] FE-5680A heat sink

Chuck Harris cfharris at erols.com
Mon Jun 8 09:31:08 EDT 2009

Hi Poul,

By replying to my reply to Leigh, and clipping out everything
that I wrote (but my name), you seem to be attributing to me,
what Leigh wrote.

You then rephrased my statement about heaters in the physics
package, restated my statement about extra cooling increasing
the power drawn by the heaters.

You then clarified things greatly by advising to not run the Rb
too hot, but also don't cool it too much.


If you have so much to say to the original author, and nothing to
say about my reply, wouldn't it have been be better to just reply
to his message, instead of mine?

-Chuck Harris

Poul-Henning Kamp wrote:
> In message <4A2CFCE2.5020107 at erols.com>, Chuck Harris writes:
>>> I ran the device today for about half an hour, and used an infrared 
>>> sensing thermometer to measure the external case temperature.
> Be very careful about trusting this:  you need to do some tricky
> calibrations to get anywhere near precise when you measure metal
> surfaces.
> The easy way, is to put a piece of duc[kt]tape on the metal surface
> and make sure your thermometer can see only that surface.
> Unfortunately, the tape will also act as insulation, so the result
> you get is not precise even then.
>>> It got up to 48 C externally in the physics package area.
> That's quite normal.
> Those small Rb's keep the internal temperature constant using
> heaters, which can raise the temperature and by being able to dump
> excess heat through their heat-sink to lower the temperature.
> You shouldn't run your Rb too hot, as this decreases the electronics
> lifetime and reduces the wiggle-room of the thermal management
> inside the device.
> On the other hand, cooling it too much will only increase the
> power drain for the heaters and increase the thermal gradients
> inside the unit, likely degrading thermal stability.
> Poul-Henning

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