Proton Magnetometer

GELLER Labs "Backyard Science"

Thoughts on a proton precession magnetometer design - a Proton Magnetometer Project

The goal of this project is a low cost high performance proton magnetometer (a digital magnetometer) kit for amateur scientists to be able to accurately measure and monitor changes in the Earth's total magnetic F field and to observe geomagnetic storms. There is a regular daily (diurnal) variation in the Earth's magnetic field. During events related to solar activity, there can be sudden changes in the field (such as a sudden impulse) as well as large excursions in the field which can be more than ten times the regular diurnal variation caused by magnetic storms.

(be sure to hit refresh to pick up our latest changes and entries)

Saturday, February 6, 2010

Overnight run: PDF, TXT, USGS PDF. Now that I got some experience running the I/Q FDM configuration, I have returned to the simple single channel USB6008 setup. The relatively large number of failed measurements overnight in the txt file is from nearly dead batteries out at the test stand, especially during the cold early morning hours.

For now, artifacts are not a problem and apodization gives significantly lower FOMs. FDM continues to provide exceptional performance. The amplitude at the desired frequency component is typically five to ten times the amplitude of any nearby spectral components. A first glance at the close-in spectral components indicates that they are all artifact related, however futher study is needed.

Another tuning of FDM parameters yielded little improvement, however FOM values in the e-7 and e-8 range are common now. It is likely that the this is at or near the present noise floor.

Running the USB 6008 full out at 10 kHz, taking 11,000 samples each measurement. Continuing with auto-retry with a 2e-6 FOM threshold with far less retries with the current parameters. Polarize time is 1.8 seconds at about 1.5 A. Measurements are once per 2 minutes with an auto-retry delay at a few seconds. The present working fluid is 125 ml (4 Oz) of Prestone De-Icer windshield washer fluid (no preparation, just pour straight from the bottle which has enough fluid for 30 proton precession magnetometers!).

Sunday, February 7, 2010

Overnight run: PDF, TXT, USGS PDF.

Monday, February 8, 2010

Overnight run: PDF, TXT, USGS PDF. Record includes the now typical Monday morning garbage trucks, school buses, car drop-offs, etc.

Tuesday, February 9, 2010

Overnight run: PDF, TXT, USGS PDF. See the sudden impulse warning at Space Weather Now yesterday PDF and then the pulse at around 2345 UTC on the USGS plot. (Was that the predicted one?) Unfortunately our overnight run began later at around 8 pm EST (0100 UTC).

Interesting failure yesterday afternoon. The program was shutdown, but the USB 6008 was still running on USB and the polarizing power supply was on. The normal cycle lately has been about 1.5 A for 1.8 seconds, every two minutes, except for auto-retry at about 6 seconds if the FOM is > 2e-6. Well, somehow the analog control voltage to the polarize FET went high or was high when I stopped the program (I use program halt, granted a bad habit), and the single powered coil was powered constantly (DC) for several hours. Fortunately it was still chilly, in the 20s F, and apparently Prestone windshield washer fluid isn't too combustable (I should check that!). Anyway the coil and Nalgene 125 ml bottle were both hot to the touch, but there was no burning insulation odor. There probably should be some fail safe mechanism for testing with volatile fluids, fuels, acetone, and the like and/or the power supply/coil should be designed to stay relatively cool at DC operation. Also, at least that coil is completely open on one end (for ease of changing fluid sample bottles), so I strongly recommend for safety reasons against sealing both sides of a thick wall PVC coil form.

Since I had the sensor open, I switched back to RainX (-25F) windshield De-Icer for a while.

An aside, here is an exemplary spectral view of the free induction decay (FID) signal using FDM: PDF of spectrum, raw data set TXT, excel worksheet. The computation for this particular view over a much wider frequency range takes longer (>10 seconds) than the typical narrow spectral range FDM calculation (< 1 second) (on an old Pentium 4).

Friday, February 12, 2010

Just taking data for a few days and thinking about what part of the project to tackle next. The sun is all of a sudden becoming active after many years of quiet. The GOES pictures at Space Weather Now are becoming more interesting.

At some point, I probably need to test a remote sensor where only the two counterwound coils are out at the outdoors test stand, with all of the electronics (polarizing power supply, switching, and amplifiers) in the lab. It would be convenient, although I have a nagging feeling that the first amplifier should be near the coils ... It will be interesting to see what happens to the signal to noise ratio. No doubt, it would make a lot more sense to have all of the electronics indoors in one place.

Sunday, February 14, 2010

A couple of days of run time: PDF, TXT, USGS 24 hour PDF. Spikes are mostly from when the snow plow happens to stop during a measurement to maneuver plowing a nearby corner.

Tuesday, February 16, 2010

Overnight run: PDF, TXT, USGS PDF.

Wednesday, February 24, 2010

Overnight run: PDF, TXT, USGS PDF. Working on other projects, still considering where to go next.

Monday, March 8, 2010

A few days run showing the local diurnal variation (disturbed by vehicles coming and going): PDF, TXT; 24 hours PDF, 12 hours PDF, USGS PDF. We seem to get a really nice ramp from about 12 pm to 3 pm local time. For amateur labs with less instrumentation, these relatively linear ramps might prove useful for testing signal processing techniques such as frequency estimators. Still considering where to go next, tackling a few other projects and waiting for more snow melt.

Tuesday, March 9, 2010

Added a waveform graph of the envelope of the precession signal (before apodization): PDF.

QUESTIONS/COMMENTS/notice of typos, etc. send email to joegeller @ gellerlabs dot com

Geller Labs	Geller Labs
Products	GELLER Labs "Backyard Science" Thoughts on a proton precession magnetometer design - a Proton Magnetometer Project The goal of this project is a low cost high performance proton magnetometer (a digital magnetometer) kit for amateur scientists to be able to accurately measure and monitor changes in the Earth's total magnetic F field and to observe geomagnetic storms. There is a regular daily (diurnal) variation in the Earth's magnetic field. During events related to solar activity, there can be sudden changes in the field (such as a sudden impulse) as well as large excursions in the field which can be more than ten times the regular diurnal variation caused by magnetic storms. (be sure to hit refresh to pick up our latest changes and entries) Saturday, February 6, 2010 Overnight run: PDF, TXT, USGS PDF. Now that I got some experience running the I/Q FDM configuration, I have returned to the simple single channel USB6008 setup. The relatively large number of failed measurements overnight in the txt file is from nearly dead batteries out at the test stand, especially during the cold early morning hours. For now, artifacts are not a problem and apodization gives significantly lower FOMs. FDM continues to provide exceptional performance. The amplitude at the desired frequency component is typically five to ten times the amplitude of any nearby spectral components. A first glance at the close-in spectral components indicates that they are all artifact related, however futher study is needed. Another tuning of FDM parameters yielded little improvement, however FOM values in the e-7 and e-8 range are common now. It is likely that the this is at or near the present noise floor. Running the USB 6008 full out at 10 kHz, taking 11,000 samples each measurement. Continuing with auto-retry with a 2e-6 FOM threshold with far less retries with the current parameters. Polarize time is 1.8 seconds at about 1.5 A. Measurements are once per 2 minutes with an auto-retry delay at a few seconds. The present working fluid is 125 ml (4 Oz) of Prestone De-Icer windshield washer fluid (no preparation, just pour straight from the bottle which has enough fluid for 30 proton precession magnetometers!). Sunday, February 7, 2010 Overnight run: PDF, TXT, USGS PDF. Monday, February 8, 2010 Overnight run: PDF, TXT, USGS PDF. Record includes the now typical Monday morning garbage trucks, school buses, car drop-offs, etc. Tuesday, February 9, 2010 Overnight run: PDF, TXT, USGS PDF. See the sudden impulse warning at Space Weather Now yesterday PDF and then the pulse at around 2345 UTC on the USGS plot. (Was that the predicted one?) Unfortunately our overnight run began later at around 8 pm EST (0100 UTC). Interesting failure yesterday afternoon. The program was shutdown, but the USB 6008 was still running on USB and the polarizing power supply was on. The normal cycle lately has been about 1.5 A for 1.8 seconds, every two minutes, except for auto-retry at about 6 seconds if the FOM is > 2e-6. Well, somehow the analog control voltage to the polarize FET went high or was high when I stopped the program (I use program halt, granted a bad habit), and the single powered coil was powered constantly (DC) for several hours. Fortunately it was still chilly, in the 20s F, and apparently Prestone windshield washer fluid isn't too combustable (I should check that!). Anyway the coil and Nalgene 125 ml bottle were both hot to the touch, but there was no burning insulation odor. There probably should be some fail safe mechanism for testing with volatile fluids, fuels, acetone, and the like and/or the power supply/coil should be designed to stay relatively cool at DC operation. Also, at least that coil is completely open on one end (for ease of changing fluid sample bottles), so I strongly recommend for safety reasons against sealing both sides of a thick wall PVC coil form. Since I had the sensor open, I switched back to RainX (-25F) windshield De-Icer for a while. An aside, here is an exemplary spectral view of the free induction decay (FID) signal using FDM: PDF of spectrum, raw data set TXT, excel worksheet. The computation for this particular view over a much wider frequency range takes longer (>10 seconds) than the typical narrow spectral range FDM calculation (< 1 second) (on an old Pentium 4). Friday, February 12, 2010 Just taking data for a few days and thinking about what part of the project to tackle next. The sun is all of a sudden becoming active after many years of quiet. The GOES pictures at Space Weather Now are becoming more interesting. At some point, I probably need to test a remote sensor where only the two counterwound coils are out at the outdoors test stand, with all of the electronics (polarizing power supply, switching, and amplifiers) in the lab. It would be convenient, although I have a nagging feeling that the first amplifier should be near the coils ... It will be interesting to see what happens to the signal to noise ratio. No doubt, it would make a lot more sense to have all of the electronics indoors in one place. Sunday, February 14, 2010 A couple of days of run time: PDF, TXT, USGS 24 hour PDF. Spikes are mostly from when the snow plow happens to stop during a measurement to maneuver plowing a nearby corner. Tuesday, February 16, 2010 Overnight run: PDF, TXT, USGS PDF. Wednesday, February 24, 2010 Overnight run: PDF, TXT, USGS PDF. Working on other projects, still considering where to go next. Monday, March 8, 2010 A few days run showing the local diurnal variation (disturbed by vehicles coming and going): PDF, TXT; 24 hours PDF, 12 hours PDF, USGS PDF. We seem to get a really nice ramp from about 12 pm to 3 pm local time. For amateur labs with less instrumentation, these relatively linear ramps might prove useful for testing signal processing techniques such as frequency estimators. Still considering where to go next, tackling a few other projects and waiting for more snow melt. Tuesday, March 9, 2010 Added a waveform graph of the envelope of the precession signal (before apodization): PDF. QUESTIONS/COMMENTS/notice of typos, etc. send email to joegeller @ gellerlabs dot com COPYRIGHT © 2009 JOSEPH M. GELLER, All rights reserved.
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