Hi Most precision crystals get a high vac bake out prior to seal. It works to drive off some stuff. There's a practical limit to how hot you can get and how long you can afford to pump for. Not quite everything gets removed….
Bob On Jun 21, 2013, at 6:04 AM, Magnus Danielson <mag...@rubidium.dyndns.org> wrote: > On 06/21/2013 06:11 AM, Jim Lux wrote: >> On 6/20/13 4:57 PM, Gary wrote: >>> A common scheme in metal deposition measurement is to measure the >>> frequency of a crystal prior to starting the deposition process, then >>> monitoring the frequency shift of the crystal as the metal is sputtered. >>> >>> I was told crystals are tuned this way at the factory, but don't know >>> this for a fact. >> >> >> it's also how particle counters based on "piezobalance" work. The >> particles hit the crystal and stick, lowering its frequency. > > Which is how one mechanism for frequency drift works, and hence is avoided. > Whatever junk is on the crystal, it get's thrown off by the heating and > operation, and that balance take a long time to shift, until you turn it off > and it deposit back on. Then as you turn it on you experience the same thing > again. By cleaning the crystals and even bake them out, this can be > significantly reduced. BVAs for instance is baked out with a turbopump > operating, and at the end the "stove pipe" is pinched of as in normal vacuum > processes. > > Cheers, > Magnus > _______________________________________________ > 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. _______________________________________________ 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.
