[time-nuts] Double ovened 10811-60158 on ebay
namichie at gmail.com
Sun Jul 20 10:29:31 EDT 2008
Silicon rubber is quite transparent to water vapour, at least in the
concentrations that are
important to the HP 10811. The seal on the screw will only slow the
response of the oscillator to humidity.
Epoxy is a much better barrier but not perfect. Vapour barriers must
Water vapour adheres to oxygen atoms, so has an affinity to all
metals which have an oxide film.
It will also adhere to quartz being SiO2. The glass frequency trim
capacitor is a good candidate for humidity sensitivity,
but so are all the insulating materials.
Solder seals are good against humidity as are glass to metal seals.
The way to make a HP10811 immune to humidity is to seal it in a metal
container with glass leadthrough seals
after it has been flushed with dry nitrogen for a few days.
Another method is to seal a small quantity of P2O5 in it as a
humidity "getter". An added improvement is to wind
two platinum wires on a P2O5 containing fibre glass pad, and
electrolyse any water absorbed to oxygen and hydrogen gas
after it is sealed.
Vacuum tube sealing and evacuation works well.
cheers, Neville MIchie
On 20/07/2008, at 8:54 PM, Mike S wrote:
> At 01:17 AM 7/20/2008, Ed Palmer wrote...
>> If their intent was to hermetically seal the oscillator, why would
>> leave the screw in the front that covers the adjustment hole (which
>> nobody could possibly get to!)? Would the seal around the screw be
>> enough to make it worth the effort to seal the rest of the unit?
> That screw has a silicone (?) o-ring on it. Why do you think that
> wouldn't make a sufficient seal?
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