Hi The zero g thing comes from the stress / strain relationships on the crystal. It's a function of the crystal cut, the blank orientation and the way the blank in mounted inside the crystal package. It all gets pretty involved and there are multiple patents on various ways to get around this or that mounting effect.
If you know the cut, the blank orientation, the mounting approach of the blank in the holder, and the holder's orientation relative to the outside of the oscillator, you can make some informed guesses weather the X, Y, or Z plane will have the lowest shift when the oscillator is rotated through 360 degrees. None of them will be zero G by themselves unless you are lucky. Finding the zero G axis always involves careful rotation on each principle axis and some vector math. In most real environments vibration is a three axis sort of thing. In order to optimize you would also need vector information about your vibration environment to really make use of your knowledge about the oscillator. Even lining up with your major vibration axis will normally only help a bit. Things tend to move up / down, left / right and front / back all at the same time. If you are on a platform with predictable high G acceleration characteristics like an artillery shell, then the zero G orientation thing may be more helpful. Bob On Mar 27, 2010, at 11:51 AM, Peter Vince wrote: > Warren, > > If you turn over an oscillator, is the frequency change > completely reversible (to your "under 1e-12 resolution") when it is > restored? Thinking aloud, if an hour-glass is turned over twice, the > final level will be the same, but the grains will be mixed. A quartz > crystal, however, is solid, so hopefully nothing actually moves. > Presumably the zero-G axis is with the axis of oscillation at 90 > degrees to gravity? > > Peter (the "other" one :-) > > > >> Another thing I use it for is to test high resolution Freq meters. >> Using a calibrated wedge that I can then slide under one edge of the zero-G >> Osc box, I can >> make small, variable, repeatable, freq changes of under 1e-12 resolution, >> something pretty hard to do otherwise. >> If I want to make BIG changes like 1e-10, I can rotate the box on any of its >> sides and still use the wedge, >> and for a quick check of new equipment, I just turn the box over which then >> gives a couple of parts in 1e-9 freq change. >> It makes a weird but simple and indispensable variable freq source that is >> useful for many things, such as checking the LOOP TC of a TBolt. > > _______________________________________________ > 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.
