In message <4a2efc6d.4020...@xtra.co.nz>, Bruce Griffiths writes: Bruce,
>>> 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 impedance). >Adding just a little insulation to the added thermal mass can >dramatically increase the thermal time constant combined with a modest >increase in operating temperature. Isn't that exactly what I explained initially ? A huge block of aluminium, encased in 1" of styrofoam ? >>> Readily available inexpensive aluminium foil is a cheaper alternative to >>> expensive noble metal foils. But it does not stay as reflective. By the time you add this layer to the construction I mentioned, you care about the difference between 0.98 and 0.99. Poul-Henning -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@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.
