Journal notes, One Year of R&D, early September Quiet
GELLER Labs "Backyard Science"
Thoughts on a proton precession magnetometer design - a Proton Magnetometer Project. Build an Earth's field magnetometer.
The FDM MAGNETOMETER1 project is a low cost high performance proton magnetometer (a digital magnetometer) kit under development for universities and amateur scientists to be able to accurately measure and monitor changes in the Earth's total magnetic F field and to observe geomagnetic storms. Magnetic storms can cause large excursions in the field and are of concern to interests ranging from electrical power grids, radio communications, and satellite operations, to aurora watchers and amateur radio operators.
1 Filter Diagonalization Method "FDM" (harmonic inversion), see Jan 21 and Jan 23 entries, based on: Vladimir A. Mandelshtam, Howard S. Taylor, Harmonic inversion of time signals and its applications, Journal of Chemical Physics (1997), Volume 107, Issue 17, 1997, Pages 6756-6769
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Project Documentation (very early stages)
Journal Notes:
Sunday, September 5 , 2010
It has been about a year now since the first backyard experiments. The experiment has come a very long way from watching the precession signal decay on a hp 400 AC voltmeter analog scale jpg to the commercial instrument prototype jpg to the present working version jpg.
I got back to working with the FDM software module this afternoon. As the FDM windows executable module continues to be customized for the FDM magnetometer application, intermediate values are often displayed for trouble-shooting purposes. Today I realized that the input signal file (the digitized FID signal) has been read incorrectly for some time now. The read error appears to have preserved the fundamental frequency, however calibration tests will need to be redone and the spectrum evaluated over several days, stay tuned.
The present working prototype LabView program calls a FDM windows executable, which writes to "standard output", then continues with LabView using the same standard output as it reenters the main vi. If we continue along these lines with compiled LabView code (if we distribute software for the project using the National Instruments "Application Builder"), the present plan is to also distribute the FDM windows executable. Since the core sections of the FDM module code are owned by others and not our original work, we will probably not be able to distribute the Fortran source code for the FDM module.
The system came back on just in time to record a small impulse (a relatively minor "sub-storm" event so far) following days of quiet: PDF, TXT, NRCan OTT PDF, USGS PDF.
Monday, September 6 , 2010
Overnight: PDF, TXT. Moved the delay before sampling out 200 milliseconds to 350 milliseconds, which has reduced the number of auto-retries compared to overnight (probably need to reduce the analog board gain by ~20%). PDF Sample FDM spectra PDF, log spectra PDF.
The FDM module calibration was tested today using an Agilent 33120A synthesizer locked to a hp Z3801A GPS disciplined oscillator. An unused differential input of the USB 6008 module was used to input the test signal, so no other changes to the prototype were made. With the exponential window (apodization to emphasize the early portion of the FID), a CW sine wave can be used for calibration testing (otherwise, without apodization, FDM only solves for a decaying waveform). For convenience, testing was done for frequencies (2290 Hz to 2286 Hz in 0.5 Hz increments) within the current magnetogram scale of about 53,710 nT to 53,810 nT. The calibration page PDF shows perfect FDM frequency determination to 0.001 Hz (0.01 nT) as can also be seen in the recorded text file TXT. The sample rate calibration constant (the exact USB 6008 sample rate) has not been adjusted since it was initially measured many months ago using a GPS referenced calibration signal. This calibration check was made following correction of a data structure error related to the FDM software module and how it read the raw digitized USB 6008 data.
evening: all is well PDF, TXT.
Tuesday, September 7 , 2010
Overnight: PDF, TXT. There was a relatively constant DC geomagnetic field PDF just after midnight:
9/7/2010 12:09:49 AM 53755.20 2287.995 2.300 0.000000800 31.4
9/7/2010 12:12:17 AM 53755.20 2287.995 1.849 0.000000200 37.2
9/7/2010 12:14:17 AM 53755.08 2287.990 2.038 0.000000100 30.5
9/7/2010 12:16:45 AM 53755.18 2287.994 0.877 0.000000400 16.4
9/7/2010 12:18:55 AM 53755.22 2287.996 1.714 0.000001000 23.7
9/7/2010 12:20:55 AM 53755.04 2287.988 2.196 0.000000900 43.4
9/7/2010 12:23:23 AM 53755.22 2287.996 1.863 0.000000500 29.2
Otherwise, the relatively quiet diurnal cycle is unremarkable: PDF. The auto-retry rate since yesterday afternoon is running around 50% (e.g. 500 measurements survived the FOM filter for 1,000 measurements made), which is somewhat improved from the previous 40% auto-retry rate. We believe that the bulk of the rejected reading were unsuccessful because of environmental reasons, such as magnetic gradients in time (dB/dt) and/or distance (dB/d length and/or width) across the sensor coils, and/or electromagnetic or radio interference. So, it is unlikely that further improvement in the electronics would improve the auto-retry rate.
In fact, many of the measurements rejected by the FOM filter are "good", however to further filter the rejected measurents to find the actual "bad" ones, is believed to be computationally wasteful at our slow measurement rates (presently a 2 minute interval, with auto-retry set at 8 or 9 seconds). Also, since interfering conditions, such as close in passing vehicles or EMI/RFI, typically take several seconds to clear, increasing the auto-retry rate (to less than 8 seconds) just increases the number of rejected measurements.
Wednesday, September 8 , 2010
Overnight: PDF, TXT. A few minor pulses or impulses, otherwise relatively quiet overnight.
Thursday, September 9 , 2010
Overnight: PDF, TXT, very quiet. Sample log spectra PDF, spectra PDF.
Friday, September 10 , 2010
Overnight: PDF, TXT. Continued quiet overnight.
Sunday, September 12, 2010
Overnight: PDF, TXT, NOAA Costello geomagnetic index PDF, Continued quiet. Looks like a picture perfect diurnal cycle developing the evening, PDF. late night, early morning, continued quiet, PDF, Costello PDF, diurnal view PDF.
Project Documentation (very early stages)
QUESTIONS/COMMENTS/notice of typos, etc. send email to joegeller at gellerlabs dot com
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