Build a Geomagnetic Observatory ! 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 magnet
ometer) 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, Links and References
Journal Notes:
Monday, November 14, 2011
Overnight: (very quiet) PDF, TXT.
Instrument Health: Polarization Controller PDF, FDM FOM and amplitude PDF.
Tuesday, November 15, 2011
Wednesday, November 16, 2011
Thursday, November 17, 2011
Instrument Health: Polarization Controller PDF, FDM FOM and amplitude PDF.
Friday, November 18, 2011
legend for our TXT files:
Date Time F Scalar Larmor FDM FDM FDM Env. Polr. Msrd. Air Fluid
Frequency Ampl. FOM NBS/N Ampl. Time Tau 2 Temp Temp
11/18/2011 9:44:22 AM 53616.50 2282.030 0.812 2E-7 21.4 0.818 0.609 0.763 34.26 35.40
11/18/2011 9:46:20 AM 53616.33 2282.023 0.808 1E-7 21.0 0.833 0.607 0.750 33.78 35.52
11/18/2011 9:48:18 AM 53615.88 2282.004 0.808 3E-7 13.7 0.831 0.603 0.737 33.11 35.70
FOM-figure of merit; NBS/N-narrow band signal to noise ratio; Ampl.-amplitude; Env.-envelope; Polr.-polarization; Msrd.-measured
Saturday, November 19, 2011
Sunday, November 20, 2011
Overnight: PDF, TXT, sample free induction decay (FID) signal (the precession signal) FDM spectra PDF (post processing), polarization controller plot PDF (post processing from the TXT file).
Monday, November 21, 2011
Tuesday, November 22, 2011
Wednesday, November 23, 2011
FDM PPM software I/O files
Diagram showing the various FDM PPM files and how they relate to the executable files: PDF. For new readers, you do not need to own a copy of LV, we distribute a Windows 7 executable, the "LabView FDM PPM executable".
The LabView FDM PPM executable reads two files (both text readable, for example in MS Notepad), C:\FDM\FDM_FRNG.TXT and C:\FDM\FDM_LV_Panel_Control_Defaults. C:\FDM\FDM_FRNG.TXT provides the working range for the FDM executable, generally a 300 Hz range including the expected range of Larmor frequencies (e.g. 2.1 kHz to 2.4 kHz). These values are later combined with the digitized precession signal and provided to the FDM executable. C:\FDM\FDM_LV_Panel_Control_Defaults provides default control settings for the front panel controls and graph.
Each measurement cycle, the LabView FDM PPM executable writes C:\FDM\signal, a combination of an infomation header including the working range for the FDM executable from above, number of samples, and exact sample rate, followed by the digitized precession signal (the free induction decay (FID) signal).
The FDM executable outputs, each measurement cycle as "standard output" with no file back the LabView FDM PPM executable a single Larmor Freq., FDM Amplitude, FDM figure of merit (FOM), and the FDM NB S/N (narrow band signal to noise ratio).
Each measurement cycle, having received the FDM data from the LabView FDM PPM executable, the LabView FDM PPM executable saves the latest measurement data to the file C:\FDM\field_data.txt. The LabView FDM PPM executable then runs the auto-retry filters and decides whether to accept or reject the most recent data. If rejected, the LabView FDM PPM executable runs a new measurement following a relatively short AR delay period (typically 8 seconds to allow a moving vehicle to pass by). If accepted, the LabView FDM PPM also saves the latest measurement data to the file C:\FDM\field_data_plot.txt and waits for the next regular measurement time interval (we run 2 minutes, it can be much faster). The accepted data is also plottedon the front panel display graph.
Post processsing:
One post processing option is to generate a FDM narrow band spectra PDF and/or log narrow band spectra display PDF for the last saved C:\FDM\signal. While FDM.exe provides and single frequency and other FDM data, F1.exe writes a spectra file of only frequencies and corresponding amplitudes. The resultant file C:\fdms.txt can be read into an available Excel spread sheet to display and print the data.
Another post processing option is to generate a graph showing the performance over many measurements (since last restarted) of the polarization controller data. The polarization data graph shows a plot of FID Peak Envelope Voltage, Polarization Time (seconds), Tau 2 (seconds), Air Temperature, and Fluid Temperature (F) plotting over time (measurement number). PDF
Another post processing option is to generate a graph showing the performance of the FDM PPM in terms of FDM figure of merit (FOM) and FDM amplitude over time (as measurement number). PDF
Thursday, November 24, 2011
Saturday, November 26, 2011
Sunday, November 27, 2011
Overnight: TXT.
Monday, November 28, 2011
Overnight: PDF, TXT (partial record, off for a while for program R&D). There was an interesting positive fast impulse around 5 pm local PDF.
Tuesday, November 29, 2011
Overnight: PDF, TXT. There was another interesting negative fast impulse just before pm local last night. Evening: there was yet another interesting fast waveform at about 9:00 pm (US, NY) PDF.
To demonstrate the noise cancelling feature of the FDM PPM counter-wound coils: I recorded the ambient noise with the polarization power supply turned off (no precession signal) for two measurements, then reversed the connections for -one of the two- counter-wound coils, at the SWCTRL board terminal block, for two more measurements. The differences are dramatic: correct counter-wound coil connection PDF, PDF, one coil reversed counter-wound coil connections PDF, PDF. The exponential decay (time domain graph, upper left) is caused by apodization or exponential windowing. To observe such tests without the exponential windowing, the FDM final value ("FV") value can be set to 1.0.
Wednesday, November 30, 2011
Want to build your own FDM Proton Precession Magnetometer?
Project Documentation, Links and References
QUESTIONS/COMMENTS/notice of typos, etc. send email to joegeller @ gellerlabs dot com
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