Journal notes, NBLNA and SWCTRL 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, August 21, 2010
Overnight: PDF, TXT, Last few days: PDF. Sample spectra, log spectra.
late evening / early morning, more quiet: PDF, PDF2, PDF3 (1nT / div) (some noise might at the 1 nT levels might have been caused by the running A/C compressor, ~20 feet from the sensor).
Monday, August 23, 2010
Overnight: PDF, TXT. After days of extreme quiet, there are signs of a little geomagnetic activity this evening (6:30 pm), PDF. hmm, stare at your local magnetograms long enough, and I guess you get a 6th sense for when activity is picking up (8:00 pm), still modest however: PDF, Costello Index PDF, Space Weather Now PDF, SWN Alert, PDF. Every power plant should have one of these displays in their control room! (shameless plug for a product kit that is not yet available.)
Very late evening, early morning 24th, still active compared to recent days, but at sub-storm levels, PDF, Costello PDF, Costello 7 day PDF. In recent days, the 12 am period has been very quiet, almost a "DC" field, yet tonight the field fell from over 53,780 nT to under 53,760 in an hour, not especially noteworthy, except in comparison to the last week. This 2 day view shows the contrast of yesterday's overnight period to this morning's disturbed or active period, PDF.
The Costello model seems to be predicting more activity PDF ... SWN is still at K4 (1:56 am) PDF.
It looks like the prototype zero-current switching hybrid FET-relay blank boards should be here Tuesday or Wednesday.
Wednesday, August 25, 2010 (G1 Minor Magnetic Storm)
Very late evening (24th), early morning: Another active period with a minor G1 geomagnetic storm, PDF, TXT, PDF couple of days (compare today's 12 am activity to 12 am on 8/23), NRCan OTT, PDF, Space Weather Now PDF, Costello model PDF. This storm appears to be winding down now (3:41 am) PDF, TXT.
Thursday, August 26, 2010
Ran another short test run with the new prototype Zero-Current Hybrid FET-Relay Switching Board PDF, TXT. There are no apparent changes directly attributable to the change-over from the hand wired prototype board to the first prototype PCB (which is a good thing).
PDFs of the Zero-Current Hybrid FET-Relay Switching prototype SWCTRL PCB !!!
No matter how many hours I spend checking a new PCB design, I almost never get everything right on the first prototype run. this switch/control (SWCTRL) board was no exception. I spent part of today working on the next revision: SWCTRL BOARD PDF, SWCTRL schematic PDF. Recall that the small signal relay never changes state when there is coil current flowing in the powered coil of the counter-wound sensor coil pair (only one of the two coils of the counter-wound pair is powered during polarization). The power FET does all of the active swtching, and runs only when the relay is already in a stable closed position . When the relay returns to its un-powered (nc) state, it also configures the counter-wound pair as a balanced center-tapped coil "secondary". The timing (discussed in previous posts) is provided by the National Instruments USB 6008 module.
The ground plane on the left is the digital ground. It is directly connected to the Zero-Current Hybrid FET-Relay Switching aluminum enclosure (presently a Hammond 1590BB, a classic metal box in electronic music, such as for foot switches), the polarization power supply common, and the USB 6008 digital common. The ground plane on the right is connected to the center-tapped connection of the two counter-wound coils, which is connected to the analog ground of the analog PCB via the shield of the analog signal cable between the Zero-Current Hybrid FET-Relay Switching aluminum enclosure and the analog aluminum enclosure (also a Hammond 1590BB). The right hand side ground plane of the SWCTRL board is not connected to anything else! This is very important so as to avoid a ground loop involving the tiny microvolt exponentially decaying precession signal. Note that we are avoiding ground loops, however, there is no galvanic system isolation (between the digital and analog grounds) since the analog ground and the digital ground are tied together (only ONCE!) at the chassis common terminal of the analog power supply. The active section of the polarization power supply (the "high side") is galvancally isolated, only coupled together by the ~5 picofarads of the small signal relay contacts, relay socket pins, and coupling between traces. Unlike more conventional designs that most of us have done over the years where we conservatively avoided ground loops as good practice, this system -does not work, period- in some ground loop configurations!
PDFs of the Narrow Band Low Noise Amplifier (NBLNA) PCB !!!
While we are discussing PCBs, here are my latest thoughts on the NBLNA analog PCB and the NBLNA Analog circuit schematic diagram. Note the "front end" cut in the analog ground plane to further isolate ground currents near the input stages. R1 and R2 are a single loop through a ferrite bead. The output transformer is another very important ground-break to avoid a ground loop (which is fatal in this system). Also note that the front end first amplifier V+ and V- supply connections are separately filtered with their own RC filters. This is a standard technique for low level and/or noisy EMI/RFI evnvironment applications, we used it extensively at the National Lab in the mid eighties. (One just has to be careful that there is enough head room in the analog rails to compensate for the voltage drops across the series resistors for a given amplifier stage's current draw.)
Comments welcomed!
BETA TESTING (beta testers wanted, NOT YET, THOUGH :-)
We test every new product and project kit with beta testers. We will eventually select about five beta testers for this project. We will supply free of charge the PCBs and boxes of parts. The testers will need to supply a USB 6008 (from NI, eBay, etc), power supplies (just +/- 6V to +/- 12V, milliamps, and about 12V, 2A, depends on your cable run, more later), the sensor shielded cable (I got my first several hundred foot roll for $9, not including shipping, on eBay), copper wire (beta testers wind their own counter-wound coil pair), PVC parts (we got ours at "Lowes"), wood parts for the coil stand (also Lowes, pressure treated 2"x2"), and a PC (probably a Win7) machine that can be used at least part time or simaltaneously for the test (does not need to be a dedicated machine). There will be no waranty or guarantees related to software performance or interaction, however it will likely be well tested compiled National Instruments code, hopefully not all that risky). More later. We already have some names for this project, and we might select some from the Yahoo group. Generally we use a scientist, an engineer and/or a skilled electronics technician, a serious hobbyist and/or amateur scientist, and a non-scientist/non-engineer. At least one of the beta testers should be a ham (amateur radio operator).
Beta testers do not get paid. However, they do get a lot of free parts and technical support and a lot of my time (which isn't always a good thing, although I think I am beginning to mellow out with age)
Stay tuned.
Friday, August 27, 2010
Overnight: PDF, TXT. A little activity, nothing over K4. The spikes are the usual Friday morning garbage trucks stopped for a pickup.
Sunday, August 29, 2010
Overnight: PDF, TXT. Very quiet. The Costello model appeared to overestimate peaks in the geomagnetic activity last week PDF, although the predictions were generally consistant with trends on a scale of hours. It will be interesting to see how it does for higher K events as we approach the sun spot maximum. Quiet evening: PDF.
Project Documentation (very early stages)
QUESTIONS/COMMENTS/notice of typos, etc. send email to joegeller at gellerlabs dot com
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