On 3/14/2012 1:35 PM, Chris Howard wrote:
These pretty ADEV/Tau plots, do people have an automated
system to produce these things? How much work is involved?
How many samples are taken? Sample for a month, omputer crunching
for weeks?
I have no feel for what the process is like.
I have two oscillators and a Racal 1992 counter. If I were
to hook up the computer to the counter would I have the minimum
amount of "stuff" needed?
The stuff on my pages at febo.com come primarily from two sources:
1. Screenshots from the TSC analyzer's display (actually, I trick the
TSC into thinking it's network printing to a Postscript device, then I
grab the incoming bitstream and convert it to .png -- not a pretty process.
2. Phase or frequency data from the TSC or other counters manually
massaged using a *nix WYSIWIG graphing tool called Grace. In a few
cases, I've also munged a way to automatically generate Grace plots
every X minutes from live data. That, also, is not pretty.
However, lately I've been using John Miles' TimeLab software (even
though it's Windows...) because it is so damn easy to capture data from
lots of counter types, and display multiple runs and various plot types.
It just takes all the work out of it.
Length of capture depends on what you're trying to do. Generally, you
want a minimum data length of X times the longest tau, where X can range
from 3 (but huge error bars) on out to perhaps 8 - 10 for good
reliability. So if you want to plot stability out to 100K seconds,
you're going to be collecting data for at least a week or two.
I've had PPS measurement setups where I took data perhaps every 10
minutes for several months. That starts to be an exercise in "design
for reliability"!
John
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