At 07:13 PM 8/6/2011, Hal Murray wrote:
new...@cei.net said:
> The general shape and bumps in the plots track nicely, but I'm wondering
> why there's so many cycles difference after 36 hours.
How are you collecting the data? What's the time between samples?
First off, your TEC data was an inspiration. I thank you sir.
The embedded box sends a string with every sample, so 60Hz. The
computer timestamps the arrival and logs the time, count, and
frequency data to a file. (I'm actually generating two files now,
one with every sample, one downsampled 60:1. Other neato stuff too:
sync start, auto file rotation at top of day, etc.)
One possibility is that one system is picking up extra clock ticks. If your
data is dense enough, that should be pretty obvious if you zoom in on the
I think that's what happened to the setup at location "tock". Friday
I threw iron at the situation--a consumer grade UPS in front of a
Sola line conditioner. Both sites got new embedded firmware with the
new detection scheme. (Wait for edge, start 15.something ms hardware
timer, send data to computer, wait for timer expiration,
repeat). That should reject a lot of noise.
Glitches like that are easy to spot if you plot the frequency. It's the
difference in counts divided by the difference in times between a pair of
samples. At 10 second sampling rate, you get 600 counts per sample. 601
counts turns into 60.1 Hz. That 0.1 Hz is well above the noise. (at least
with my setup)
I'm sorta doing this now. The logging program has a FIFO for the
count and timestamp, so I'm calculating the frequency over the last
1s, 60s, 600s, and 3600s intervals. Every minute or so the frequency
data is written to a file for Munin to plot (so that I have a live
picture to look at). But yes, the data is in the file, so I can also
gnuplot it.
55779 data is downloading now, so I'll put some graphs up in an hour
or so. I can already tell from the Munin plots over the last 24
hours that the two sites are tracking very closely. (Right now, tock
shows -25.13 cycles at 00:35, and sparc is at -24.87.)
There's another PC at site "sparc" doing the webcam thing. Still
using the Windows XP powertoy to timelapse, so the intervals aren't
exactly 60s. If I can get a few hundred cycles of error, it should
be obvious from the picture . (There's an old 60 Hz clock and a WWVB
clock in the frame, so the measurement is limited by the flashing
color, maybe +/- 0.5s or so.)
Both site's computers have Debian supported audio hardware, so it's
tempting to add that into the mix...
--
newell N5TNL
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