Geller Labs
Geller Labs


GELLER Labs "Backyard Science"

Thoughts on a proton precession magnetometer design - a Proton Magnetometer Project. Build an Earth's field magnetometer.

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)

(some materials / code not available until publication of the project article)


Want to build your own FDM Proton Precession Magnetometer?

FDM Proton Precession Block Diagram

A block diagram discussion of the project FDM Proton Magnetometer PART III Article

Block Diagram: PDF

Prototype Pictures

Working FDM magnetometer prototype: JPG All three power supplies from an eBay $50 surplus supply! See Feb. 10, 2012 journal entry, it appears feasible (still under study) with our relatively low duty cycle and voltage to change the current limit from 1.1A to our all season recommended polarization current of 1.5 A. This might make the old hp 6237B an ideal and very cost effective power solution for the FDM PPM geomagnetic observatory! (The battery in the background is for a prototype of an optional air temperature sensor) JPG, JPG, JPG, JPG (using an external polarization supply for slightly more current) older version: JPG1, JPG2

Dave Eubanks finished packaging his FDM PPM geomagnetic observatory in a super nice looking custom built aluminum cabinet PDF, PDF. Dave Eubanks' coil stand pics JPG, JPG.

Coils: counter-wound coil pair JPG1 JPG2 JPG3 JPG4, older coils, JPG1 JPG2 Discussed May 19, 2010

Very Important => FDM Magnetometer electronics System Grounding.


Building a Sensor Stand and Winding the Sensor Coils PART IV Article , See also Jan. 26, Jan. 27, 2011 journal notes. We have been using about 650 to 700 turns of AWG # 19 200 c enameled magnet wire for about 21 to 23 milli Henry inductance.

Use this new bobbin design: JPG January 25, 26, new 2.5" counter-wound coil pair JPG1 JPG2 JPG3 JPG4 coil form on winder and first turn JPG JPG JPG (form on winder is an outdated design, just to show how the PVC bobbin mounts on the winder and how to route the first turn)

Detailed Coil Stand Assembly Instructions contributed by Carl Olsen PDF

Detailed Coil winding Instructions contributed by Carl Olsen PDF

Another example of a well built coil stand by Mark Haun in Washington state: JPG1, JPG2, JPG3. Mark is using paralleled pairs in a shielded outdoor CAT-5 ethernet cable for the cable between his sensor stand and the indoor switch control module.

Testing and balancing FDM Proton Precession Magnetometer Counter-Wound Coils for Dave Eubanks of Iowa and Alaska (David manufactured and wound the coils, we just helped out by balancing them) JPG, JPG. Balancing was done prior to this picture out in the middle of a room on pair of plastic saw horses and 3/4" sheet of plywood using an Agilent 1733C LCR meter. Dave Eubanks' coil stand pics JPG, JPG.

NBLNA Module (Narrow Band Low Noise Amplifier) Ver. 0.9.4 NEW => JPG JPG (old JPG 0.9.3)

Building and Testing the Analog Board - Partial Draft on NBLNA testing PART V Article Johson Noise Worksheet: See Articles

Detailed NBLNA Assembly Instructions contributed by Carl Olsen PDF, see also, our Nov. 12 NBLNA assembly notes.

NBLNA Test and Calibration Procedure, See Also the NBLNA article.

NBLNA analog board: Ver. 0.9.2 JPG (October 23, 2010), older Ver. 0.8 JPG Discussed July 17, 2010.

Narrow Band Low Noise Amplifier (NBLNA)

NBLNA Ver. 0.9.4 Schematic PDF (showing input Ls replaced with 0.1 uf film capacitors PDF)

NBLNA Ver. 0.9.4 Printed circuit board PDF

NBLNA Ver. 0.9.4 Parts List PDF (revises the old chokes at input positions "R1" and "R2" to film C's as described below)

Input R1 and R2 (two ferrite bead chokes) change to 0.1 uF film capacitors to AC couple the input to the SSM2019 creating a high pass filter having a -3 dB point at about 160 Hz. See the May 29, 30 2012 journal pages.

NBLNA errata: just before Ver. 0.9.4 Parts List: R13 should be 49.9 ohms, R11 499 kohms for Rev. 0.9.4

Sample Gain measurements PDF, Marked up schematic PDF, Marked up schematic Ver. 0.9.5 PDF, and corresponding Johnson Noise Worksheet PDF (see Feb. 15, 2011) This was Rev. 0.9.3, some minor differences, e.g. the frequency (filter) trim circuit changed in Ver. 0.9.4

Use resistor noise to characterize a low-noise amplifier, Measure gain or noise with an AC voltmeter, Joe Geller, edited by Martin Rowe and Fran Granville, EDN, June 23, 2011.

SWCTRL Module (Switch Control) Ver. 0.9.2 (JPG old JPG, JPG )

Operation, Building and Testing the FET-Relay Control Board PART VI Article

Note: Use care that the relay socket pins are all at the same height before soldering. Discard the small signal relay used as the form to align the pins for soldering (Or, open it up to see how it works; we send five with each kit). Use care to not get flux or solder inside the gold pins!

Detailed SWCTRL Assembly Instructions contributed by Carl Olsen PDF

SWCTRL polarization board prototype Ver. 0.8.8: JPG, older versions JPG PDF Discussed April 17, 2010, June 18, 2010

Picture of Relay Socket (gold MillMax pin jacks) PDF Temporary Snubber capacitor: PDF

Zero-Current Switching FET-Relay Hybrid Polarization circuit (SWCNTRL) - Digital Board Switching and Control

SWCTRL Ver. 0.9.2 Schematic PDF

SWCTRL Ver. 0.9.2 Printed circuit board PDF

REVISED => SWCTRL Ver. 0.9.2 Parts List PDF

A 1.5 kW peak pulse power transient suppressor voltage (TVS) device JPG (now on the PCB in 0.9.2) now performs the bulk of the powered-coil energy dump in conjunction with the secondary dump resistor. The MOSFET still controls powered-coil current control, however since the TVS diode voltage is chosen to be lower than the MOSFET reverse avalanche breakdown voltage, the TVS diode, in conjunction with the secondary dump resistor, now performs the discharge of the stored inductive energy of the powered coil. The MOSFET (a IRFI1310N HEXFET ) no longer provides this role. System performance numbers have further improved and stabilized since this change was made. See the Saturday, June 23, 2012 journal entry.

Counter-wound coil connections to SWCTRL board JPG (See also Journal notes June 8, 2012); See Tuesday, November 29, 2011 for how to check for reverse conntected coils.

Concept Drawing of how the counter-wound coil pair is re-configured from a powered coil for proton spin polarization to a center-tapped counter-wound coil pair to pick up the precession signal with ambient RFI/EMI noise cancellation PDF.

Original notes on the Zero-Current Switching FET-Relay Hybrid Polarization circuit: PDF Discussed April 17, 2010

FDM Magnetometer Flow Charts

FDM Magnetometer Software PART VII Article

Overall measurement cycle: PDF Discussed June 8, 2010

The auto-retry process: PDF Discussed June 6, 2010

Polarization and digitization timing: PDF , the small signal relay "pulls in" before digitization, discussed in comments.

Filtered envelope display: PDF Discussed June 17, 2010 (Revised 9/9/2010, added digital filter left off original dwg.)


Copy and Installation instructions (draft). We can send the project files (only with a kit purchase) via email or lately we have been using "Drop Box".

Dec. 2013 All of the relevant source code, vi's and FORTRAN code have been posted to the public DropBox. All copyright and ownership in code, especially as to code not originated by us, such as the underlying FDM code, apply. However, feel free to use for personal use in your own PPM projects.

FDMPPM Ver. 0.9_6_8_3 compiled LabView code and fdm.exe at Drop Box .

>User's without a LabView Development system already installed (the most common installation) need to install a free download "run time" driver for the USB 6008, the NI-DAQmx Configuration Run-Time and the LabVIEW Run-Time Engine. Latest Versions:

REVISED => Very Important => (all Windows users install the 32 bit version) We are presently building the FDM PPM LabView application on a 32-bit Windows 7 machine. It turns out that the choice of run-time engine for users of our application depends on what type of machine the build was created on, not the machine using our compiled application. Users with 64 bit machines, therefore, should still install the core LV 2012 32-bit run-time engine! "This is the download page for the LabVIEW 2012 SP1 (32-bit) Run-Time Engine for Windows. This Run-Time Engine must be installed on any 32-bit or 64-bit Windows system where you plan to run executables that you build with the Application Builder in LabVIEW 2012 or 2012 SP1 (32-bit)". (We build on a 32 bit machine). Soon, we will be moving to LV 2013 with the LV 2013 32-bit run-time engine.

You also need to install either the full featured DAQ-MX . It is huge, but it also installs helpful examples and diagnostic programs to test the USB-6008 or USB-6009 installation.

FDM Testing: Example signal file TXT Rename without "txt" extension (no file name extention) to try with fdm.exe in a Windows Command prompt window. This "test vector" gives the following results: 2277.052 0.428E+04 0.3E-06 35.6 (both fdm.exe and signal in a C:\FDM Windows directory, command prompt: C:\FDM>)

We are happy to share our LabView files (only with a kit purchase) with those experimenters who own a LabView development system (not the usual case). However we are not able to distribute the FDM frequency estimator source code.

Very Important => New installations, please remember to turn-off Windows USB power savings modes under power savings settings. Or, when you go to check the plots and data from your first overnight run, you will probably find that the USB port and the USB 6008/9 turned off!


Takamisawa NAS5W-K relay PDF, IRFI1310N MOSFET PDF, TVS diode PDF


Estimate your local Magnetic Field: NOAA's National Geophysical Data Center (NGDC) Estimated Values of Magnetic Field

Input common mode filter: PDF Discussed May 29, 2010 (new: replaced ferrite bead chokes with 0.1 uf film capacitors for AC coupling, 0.1 uf - 10 k ohm high pass filter; old: replaced series 50 ohm Rs with one loop through ferrite bead)

Analog output transformer coupling: PDF Discussed April 21, 2010 (dropped output load resistors)

National Instruments Module

NI USB-6008 digitization (ADC) and control module. Very Important => The USB 6008 must be Dev1 as assigned by NI "Measurement and Automation Explorer". If you are not otherwise a NI user, the USB 6008 should be Dev1 by default. If you use other NI modules or devices, you might need to reassign the existing Dev1 and then rename the USB 6008 to Dev1. We will look into this further, perhaps it can be made more flexible in the future.

Connection from the NBLNA analog output JPG to the USB 6008 pseudo differential input JPG.

Connection from the USB 6008 +5 V, com, and digital outputs JPG to the SWCTRL board digital inputs JPG.

Very Important => FDM Magnetometer electronics System Grounding.

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  9:48:18 AM     53615.88     2282.004   0.808    3E-7   13.7   0.831   0.603   0.737   33.11   35.70
11/18/2011 9:50:29 AM 53615.81 2282.001 0.738 5E-7 23.3 0.778 0.605 0.749 33.09 36.20
11/18/2011 9:52:52 AM 53615.53 2281.989 0.857 6E-8 32.7 0.882 0.632 0.801 33.27 36.91
(removed air temp sensor, fluid temp is calculated from tau2, no temp. sensor)

Date        Time           F Scalar     Larmor     FDM      FDM    FDM    Env.    Polr.   Msrd.  Fluid
                                        Frequency  Ampl.    FOM    NBS/N  Ampl.   Time    Tau 2  Temp

8/15/2012  1:35:46 AM     53527.32     2278.446   0.847    1E-7    9.2   0.916   0.735   1.424   71.82
8/15/2012  1:37:00 AM     53527.36     2278.448   0.773    9E-8   23.6   0.866   0.725   1.447   71.36
8/15/2012  1:37:59 AM     53527.39     2278.449   0.836    1E-7   28.7   0.906   0.718   1.441   71.58

(Added FDM T2* some month ago, forgot to update the legend)

Date      Time           F Scalar     Larmor     FDM      FDM    FDM    FDM    Env.    Polr.   Msrd.   Fluid
                                      Frequency  Ampl.    T2*    FOM    NBS/N  Ampl.   Time    Tau 2   Temp
4/2/2013  5:48:55 AM     53455.40     2275.384   0.822  0.733    4E-7   20.6   0.860   1.161   0.698   31.52
4/2/2013 5:49:55 AM 53455.28 2275.379 0.851 0.715 3E-7 45.3 0.874 1.160 0.701 31.90
4/2/2013 5:50:55 AM 53455.40 2275.384 0.859 0.718 1E-6 21.1 0.875 1.154 0.712 32.18
4/2/2013 5:51:54 AM 53455.35 2275.382 0.853 0.715 7E-7 38.1 0.871 1.149 0.713 32.55

FOM-figure of merit; NBS/N-narrow band signal to noise ratio; Ampl.-amplitude; Env.-envelope; Polr.-polarization; Msrd.-measured

Magnetometer Verification: So, how does our FDM PPM data compare with a professional geomagnetic observatory? Mark Haun's FDM PPM in the Seattle, WA area, is only about 60 miles from NRCan Victoria. Here is a comparson with NRCan VIC for the January 24/25, 2012 G1 geomagnetic storm PDF.

UPDATED => (parked marker)

NEW => (parked marker)

Project Articles!

Project Documentation, Links and References (very early stages)

Past Project Journal Notes


Safety notice: Generally, no earth grounding is needed at a wood sensor stand. However, if there is any possibility for life threatening electrical potentials and/or currents at your individual sensor stand, then a local earth ground is required for safety reasons, at least when working at the stand. Never disconnect a powered coil when the polarization current is on (there will be a high voltage spike). Also, wear safety glasses and observe good electrical grounding practice for any mains operated power tools while assembling the stand and coil pair. In other words, individual experimenters are solely responsible for their own safety and we (GELLER (Geller Labs) are not in any way responsible for or liable for any injuries incurred while performing this FDM magnetometer experiment. Please do not use our plans or kits if you do not agree to accept full responsibility for your own personal safety.


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

COPYRIGHT © 2009, 2010, 2011, 2012 JOSEPH M. GELLER, All rights reserved.

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