Bob wrote:
EFC is essentially instantaneous at the "many seconds" level. There's not
much settling left to do after 20 time constants.
ALL mostly true, although I have not seen any TCs as long as 50 ms.
EFC inputs on most Osc I've tested, including the 10811, are essentially
instantaneous at <100us TC. (BW > 2 KHz)
BUT
I find it amazing how a few true statements of basic principal can be used
to counter the facts.
I should of made it more clear, I was NOT talking about TC settling.
The long "resettling" time of hrs I was referring to is of a similar effect
as turning the unit off for a while and then back on.
I suppose that according to your book formula, that should only take 20
seconds also to come back to within 1e-12.
Maybe the problem is that the Osc does not read the same books,
OR maybe the problem is just that some of us are getting more performance
from them than they were ever designed to give,
and at that level there are a few new unexpected and unknown secondary
effects.
ws
*******************
Hi
On a properly working crystal oscillator, EFC is essentially instantaneous
at the "many seconds" level. The main delay you see is from the R/C time
constant between the R's in the tuning attenuator and any bypass C's that
are present. Time constants rarely get over 50 ms. Twenty * tau would only
be 1 seconds at the 50 ms case. There's not much settling left to do after
20 time constants.
Bob
******************
WarrenS wrote:
I should of also said; when care is taken, turning the Osc unit over is
repeatable,
if just looking at a graph plot where the resolution is several parts in
e-11.
Pete2
Addressing your first question only, I'll let the experts address the why.
Yes, I 'think' it does in principal, I would not guess on how long it
takes though.
But
I have not checked that close to be sure.
I'd never do something that gross during the middle of a test that I was
trying to see 1e-12 things.
I do that first thing, long before the high resolution test starts and
then let things resettle before proceeding.
Any change in cable position or the Osc moving a bit in its Box or a dozen
other things could also change
it that much, including temp gradients in the box, so Don't do that if you
want 1e-12 results.
Use the wedge, that I have tested, and is completely reversible and
repeatable at those levels.
I have noticed that the OSC will EVEN take a long time to RESETTLE
(HRS+ ) if the EFC voltage is change a lot and then put back.
Which is why I limit the clamp voltage of my Tbolt to typ + - 100 mv or
less from its nominal.
ws
********************
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.
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