[time-nuts] Thunderbolt stability and ambient temperature
Joseph M Gwinn
gwinn at RAYTHEON.COM
Wed Jun 10 21:23:43 UTC 2009
time-nuts-bounces at febo.com wrote on 06/10/2009 03:13:19 AM:
> In message <4A2EFC6D.4020205 at xtra.co.nz>, Bruce Griffiths writes:
> >>> The thermal time constant (not the thermal impedance per se) is what
> >>> matters [...]
> That is pretty much exactly the (mis-)definition of thermal impedance.
> Thermal timeconstant or thermal corner-frequency had been much
> better names.
> >>> It is possible to construct an enclosure with a long thermal time
> >>> constant together with relatively low thermal resistance so that the
> >>> temperature of a GPSDO or similar device within the enclosure only
> >>> increases by a relatively small amount.
> >> Nope. This is essentially a thermal low pass filter.
> Well, yes you can, but it is not very useful:
> A really huge block of metal will do that: It can transfer a lot
> of heat (=low resistance), but will take a long time doing so (=high
I read somewhere the suggestion to take the cast iron block from an old
automobile engine and put it in a heavy insulated wooden cabinet: ~250 Kg
of iron in an insulated box. Cracked blocks are useless in an engine, and
so are available in junkyards quite cheap.
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