Interestingly, the packing instructions for the Solartron 7081 81/2 digit voltmeter shows two "thermal inertia bottles" close to the instument. These provide a thermal mass that works with the insulation to reduce the rate of temperature change at the unit. This will also filter short duration transients. So a cardboard box with a couple of bottles of water in it would make a good enclosure. Or just leave the beer in the cooler :-)
Robert G8RPI. --- On Tue, 9/6/09, Poul-Henning Kamp <[email protected]> wrote: > From: Poul-Henning Kamp <[email protected]> > Subject: Re: [time-nuts] Thunderbolt stability and ambient temperature > To: "Discussion of precise time and frequency measurement" > <[email protected]> > Date: Tuesday, 9 June, 2009, 9:03 PM > In message <[email protected]>, > Mark Sims writes: > > >I think that using a well insulated box [...] > > The point for timenuts is not just the thermal resistance, > but more > importantly the thermal *impedance*: you want to low-pass > filter > the thermal changes so that they all happen in the area > where the > PLL can cope with them. > > Thermal resistance is about insulation, thermal impedance > is > about (thermal) mass. > > So you significant mass and volume (like a fridge) not > light and > small (like a cardboard box). > > When metrology people really want to keep things at the > same > temperature, they mount them in oil-baths (for good thermal > contact) > in the middle of a block of aluminium, typically 2'x2'x1' > (for > thermal impedance) which is again insulated with 1" > styrofoam, all > of this mounted in a plywoodbox, set on rubber-wheels to > get it off > the floor (for thermal resistance). > > If they are really into this, they cover the plywood with > high-quality > (noble-) metal foil, to maximize reflectivity and minimize > emissivity, > so that the black-body radiation from devices and humans in > the lab > does not affect the temperature interface as much. > > Then they leave it alone for "some weeks" in their > temperature > controlled lab so the temperature can stabilize. > > At this point they may start to wonder how they can verify > the pt100 > temperature sensor they put in the middle of it all > actually works > when the temperature never changes... > > Poul-Henning > > -- > Poul-Henning Kamp | UNIX > since Zilog Zeus 3.20 > [email protected] > | 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 -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
