Journal notes, Second Revision of SWCTRL and NBLNA PCBs
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:
Saturday, October 23, 2010
Overnight: PDF, TXT, active overnight, the geomagnetic field is relatievely active this morning, although the largest field change so far, here at upstate NY, has been about 25 to 30 nT on the F scalar. Here are the recent magnetograms from NRCan OTT PDF and USGS PDF for comparison. NOAA Space Weather Now is predicting a K5 (G1) event PDF, as is the Wing Kp index (Wing Kp Predicted Activity Index 7-Day Model Performance) PDF, however, at least here in upstate NY PDF (and Ottowa, Canada to the north), the geomagnetic field is active, but not at storm levels (as of about noon EST).
Evening: It has been a relatively active day: PDF, TXT.
NBLNA Board Characterization JPG (testing the Version 0.9.2 board) (error: Note that the polarity marking of C7 is reversed.)
GAIN: [500,000] Two 49.9 ohm resistors were connected from the +/- inputs respectively to a common ground. The low side of the output transformer was tied to analog common for these measurements. Using a hp 400 GL meter to monitor the input voltage at the + 50 ohm resistor was set to 10 uV (measured) using a hp 3325B synthesizer at 2288 Hz (NBLNA filter pot peaked for 2288 Hz) and a Kay 837 attenuator. The NBLNA gain trimmer was set to give an output of 5.00 V as measure with an Agilent 34410A DMM. The gain range is about 288,000 to about 1.48 million. The rail voltages were raised from +/-6V to +/-15V for the range test to maintain enough headroom for the 10 uV input test signal. The amplifier is stable throughout this gain range, with no evidence of oscillation as verified with the LeCroy LT344L oscilloscope. The gain was returned to 500,000 for the following testing.
EFFECTIVE NOISE BANDWIDTH: [187 Hz]: Using our automated effective bandwidth test set (the hp 3325B synthesizer, Kay attenuator, the Agilent 34410A DMM and a LabView program) the effective noise bandwidth was measured PDF. For more information on measuring noise bandwidth, see our noise bandwidth tech note. The effective noise bandwidth and gain are needed as input paramters for the noise measurements and calculations which follow.
NOISE FLOOR: [1.8 nV/rt-Hz]: With a short across the +/- input terminals (bias current provided by the onboard 10 kohm resistors to common, the average output AC RMS voltage (statistics on) was measured to be 13.4 mV. Next, using a few known input resistances, we studied the noise characteristics of the NBLNA board using the noise worksheet developed for the JCan experiment. I notice an error in the August 31 report, the input resistances are entered in units of kiloohms and the 9.9 milliohm short was incorrectly entered there. Here is the noise worksheet for this board: PDF. Assuming the 187 Hz eff BW figure is correct, the actual NBLNA gain (now without the two 50 ohm test resistors) was measured to be about 546,000.
Now (about 10:20 pm local time (UTC +4)), I will pause the operational FDM magnetometer and install the new Ver. 0.9.2 NBLNA board and back the gain trimmer down for a maximum output below 2 V for the USB 6008 2 V scale. 10/23/10 10:33:52 pm data point is the first data point with the new NBLNA board.
Sunday, October 24 , 2010
Overnight: PDF, TXT, the geomagnetic field is beginning to quiet down after an active period, albeit at substorm levels. Overnight view on a two day time scale, PDF.
The new analog board (NBLNA) is running well. The new gain trimmer is an old part, not sure if it was 10T or 15T, need to order some new Bourns 20k trimmers. Comments and observations related to the SWCTRL board.
Monday, October 25, 2010
Tuesday, October 26, 2010
Overnight: PDF, TXT, relatively quiet.
Thursday, October 28, 2010
Overnight: PDF, TXT, very quiet.
Friday, October 29, 2010
Here are the new drawings for the zero-current Ver. 0.8.2 switching hybrid switch control board (SWCTRL) schematic PDF, PCB PDF. I took a quick look at temperatures across the SWCTRL board and found the highest rise was under +5C at the relay, since we now run with a duty cycle where the coil is on most of the time. The traces around the relay were increased both for polarization current ampacity (a very conservative layout) and to provide more copper near the coil connections for better heat conduction. The USB 6008 runs warmer than either the SWCNTRL or NBLNA aluminum boxes. Also, we left more room to conveniently fold down the power FET where package height is a consideration (there are no thermal concerns with this FETs ultra low ON resistance, it does not even get warm at our observatory repetition rate).
The field is very quiet this evening / early morning: PDF.
Small signal relay pulls in just before the digitization cycle: Since the revision of the SWCTRL board so that the small signal relay pulls in just before the digitization cycle (see Oct. 24 comments), the FID amplitude is remarkably stable shot to shot (here about 6 hours of data) PDF. There is of course some remaining variation with the tau1 and tau2 sensitivity to ambient temperature at the sensor, a different question than shot to shot variation induced by the electronics. Also, note that as long as there is sufficient amplitude for the FDM method to solve, the amplitude has no direct affect on the frequency and magentic field determination. However, other studies, such as fluid comparisons, should benefit from the new lower scatter in the FID amplitude data.
Saturday, October 30, 2010
Overnight: PDF, TXT, quiet, the step change was a departing parked vehicle.
A slight increase (very small) in activity this afternoon PDF, might correlate well with the new Wing Kp index PDF.
Sunday, October 31, 2010
Overnight: PDF, TXT, a couple of relatively low amplitude pulses (<5 nT), otherwise continued quiet. Early afternoon, more pulses including sinusoidal shaped changes in the field, however, still relatively small at the 5 nT level PDF.
Monday, November 1, 2010
Overnight: PDF, TXT, one small slow level shift after 1 am and one triangular shaped pulse before 4 am, otherwise continued quiet in the geomagnetic field overnigth.
Project Documentation (very early stages)
QUESTIONS/COMMENTS/notice of typos, etc. send email to joegeller at gellerlabs dot com
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