[time-nuts] How long do ovens take to cool to ambient after power is removed?
Richard (Rick) Karlquist
richard at karlquist.com
Thu Oct 2 18:29:27 EDT 2014
Len Cutler was pretty much allowed to do whatever he wanted
on the HP106 and he produced the proverbial doomsday machine.
I think the SR-71 analogy is good here, except that Kelly
Johnson had a lot more support from his management. Len always wanted
to make an optically pumped cesium as his ultimate doomsday
machine, but management never funded it.
He proudly had a 106 on display in his office. I wish I
had asked him how he got such low aging crystals. 10811
crystals never got much lower than about 1 part in 10^-10
Rick Karlquist N6RK
On 10/2/2014 11:58 AM, Tom Van Baak wrote:
> 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:
> 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?
> ----- Original Message -----
> From: "Richard (Rick) Karlquist" <richard at karlquist.com>
> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
> Cc: <hmurray at 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:
>>> drkirkby at 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
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