brooke at pacific.net
Tue Aug 17 13:23:07 EDT 2004
HP did quite a bit of research on isothermal oven design. The idea is
that you can draw a line in three dimensional space where the
temperature is constant. Since you can not have the temperature sensor
and the device being controlled in the same place it's important to have
them both on an isothermal line. Then the trick is to get the system
gain as high as possible.
I have found that cork makes an excellent insulator for crystal ovens.
Another option is to dig a hole that goes down in the ground maybe 5
feet and put a large diameter pipe in the hole that's capped to keep out
water. The temperature will be about 50 some degrees and very well
regulated. One of the local wineries has been working for the last
couple of years to make a cave to store their wines. Probably because
of safety regulations it needs to have two entrances.
Brooke Clarke, N6GCE
Poul-Henning Kamp wrote:
>In message <4122376B.2080706 at usa.net>, Alberto di Bene writes:
>> 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
>>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
>>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...
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