The most extreme example of slow ovenized oscillator warm-up I've seen is the vintage hp106. These mid-1960's oscillators were designed as the ultimate, "hp way", pre-atomic, frequency standard -- expected to be powered up, uninterrupted, for years and decades. So there was no hurry in the (perhaps once-in-a-lifetime) initial warm-up. Here's a plot/photo of one I recently tested:
http://leapsecond.com/museum/hp106a/ These HP-106 oscillators are among the best I have ever measured: stability and daily drift rates in the very low -13's. Like the SR-71, these were designed by gut and slide rule. And yet achieved extreme performance, even by today's standards. The amazing thing -- as you know from your enviable career at HP -- is that an instrument produced in 1964 can still work 50 years later in 2014. No blown fuses, no electrolytics, no filaments, no f/w upgrades, no Y2K, no decaying EEPROM, no batteries, not even any IC's. No user s/w, no USB, no drivers, no OS. Not even an on/off switch! Just a 5-pin 24VDC backup or 2-prong AC cord in and a pure 5 MHz BNC out, that's all. How many of the instruments we use today will still work out-of-the-box in 2064? /tvb ----- Original Message ----- From: "Richard (Rick) Karlquist" <rich...@karlquist.com> To: "Discussion of precise time and frequency measurement" <time-nuts@febo.com> Cc: <hmur...@megapathdsl.net> Sent: Wednesday, October 01, 2014 9:03 PM Subject: Re: [time-nuts] How long do ovens take to cool to ambient after power is removed? > On 10/1/2014 1:04 PM, Hal Murray wrote: >> >> drkir...@kirkbymicrowave.co.uk said: >>> Anyway, later today (tomorrow ??) I will post a plot of frequency vs time. >>> The question is though, how long is thing thing likely to take too cool? >> >> I'd expect an exponential decay so you need to specify how close to ambient >> you want to get. I'd guess a ballpark of 10x the warm up rate. >> >> You can probably measure it if you have the warmup graph. Turn it off, wait >> a while, turn it on, measure the freq, consult warmup graph. > > When I was still with Agilent, I did some experiments with unpowered > 10811's. Both the oven and oscillator were unpowered and I measured > the temperature by looking at the B mode resonance of the crystal. > I wanted to get rid of any linear frequency drift. As a rough > rule of thumb, 1 hour of cool down is pretty good for most purposes. > For extreme measurements, I would allow 10 hours. This reduced > any exponential tail to below the ability to measure temperature and/or > below the effects of the ambient. I had to put a box over it to > reduce the effects of air currents. If I did not do that, then 1 hour > was all I needed. > > Rick Karlquist N6RK _______________________________________________ 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.
