[time-nuts] 10811-60105 and -60111

buehl buehl at superlink.net
Tue Aug 17 13:33:15 EDT 2004

HI all:

I'm not so heavily into 'time', but do dabble in control circuits/ systems.

The limiting factor is going to be the ON-OFF temp delta of the internal 
ovens.  The raising of the external temp (with your external heaters) will 
delay the time it takes for the internal to cool off and turn on; However, 
once the internal oven turns ON, it will stay on until the temp rises 
enough to turn it off.  This temp change is beyond your control.

What you have gained is a very slow cooling, thus less short term drift 
during the cooling half of the cycle.  This is the reason Poul-Henning Kamp 
found passive insulation to be just as good as an external heater; He has 
slower cooling.

To outperform the original regulation, you need to enclose within an 
external oven which is a degree warmer than the TURN-ON temp of the 
internal (original).  Then you have control, but you need to design a 
regulator better than the original.  You would place your temp sensor on 
the outer case of the original oven:  This gives you a system similar to 
the 'aluminum block' system Poul-Henning Kamp found on the net.

Tom Buehl

At 01:09 PM 8/17/2004, you wrote:
>In message <4122376B.2080706 at usa.net>, Alberto di Bene writes:
> >Tom,
> >
> >  thanks for the answer. I was asking as often I see the -60105 submodel
> >offered on eBay at attractive prices. Now I know why, but maybe you are
> >right,
> >aged OCXOs can give surprises.
> >
> >Talking of OCXOs, supposing I want to build an outer oven around a 10811,
> >which could be the right temperature ? Anybody knows the outer oven
> >temperature
> >of the double ovenized 10811 used in the Z3801A ?   Thanks.
>I experimented a bit with this.
>The temperature you choose is not important as long as it is not
>close to or higher than the internal oven temperature.  Simple
>physics dictate that if you OCXO is rated 0..70C you can trust the
>internal oven to be above 70C.
>I found that passive insulation of 5..10cm high quality foam performed
>as well as any kind of heating I could come up with.
>Hunt around metrology information and find out how they construct
>the ovens they use when they calibrate equipment and you will find
>some serious temperature regulation:  I saw one which consisted of
>an internal block of aluminium approx 30x30x10cm (with a small
>hole in the center for the device under test) packed in 10cm of foam
>inside a box of 2.5cm thick aluminuum which was peltier regulated
>on all six sides and then encapsulated inside another layer of
>10cm foam.  They still thought they could do it better...
>Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
>phk at 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.
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