Grounding and system commons for a Proton Magnetometer
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
(be sure to hit refresh to pick up our latest changes and entries)
I created a new Proton Magnetometer Group at Yahoo groups for those interested in discussing proton magnetometers with an emphasis on Earth's field measurements. I will try to keep it as open as possible without getting attacked by spam. I will also try first with no review of posts, let's see what happens. Please keep it friendly and professional. Use of real names is preferred, possibly required in the future.
Project Documentation, Links and References (very early stages)
Journal Notes:
Wednesday, January 5, 2011 - More on System Grounding:
Note: Grounding and commons are particularly important for a fixed based geomagnetic observatory because it is powered by line (mains) connected power supplies. Many of the ground related problems faced by a line connected observatory are non-issues for portable battery powered field survey proton magnetometers.
Update on FDM Magnetometer system grounding: At present, all power supplies are grounded as normal via the standard three prong power cords. The USB 6008 electronics common is via the USB cable back to the computer ground. The +5 V systems of the SWCTRL module are grounded to the USB 6008 digital common and find Earth ground via the computer. The polarizaton power supply common is conneted to the USB 6008 common and therefore is also earth grounded by the computer ground.
There is no connection between the common of the polarization power supply and the analog common.
The analog common is directly connected to Earth ground at the analog power supply. The SWCTRL and the NBLNA box (chassis) grounds are connected to the Earth ground via analog common by one mounting hole on each board. The analog common is broken from the USB 6008 psuedo differential input by the output transformer on the NBLNA board.
The USB 6008 common does not connect to the SWCTRL box.
Our PART IV article on the coils and sensor stand has been updated to reflect the current grounding configuration. We make changes often, always do a refresh on your browser to update links before downloading a document to be sure to get the latest version.
To review your grounding configuration, stop or pause the FDM supervisory program (at a time other than during a polarization cycle when there is current flow in the powered coil). Disconnect the USB cable from the computer, and turn off both the analog and polarization power supply. Use a battery operated hand held ohm meter to explore and confirm the common and Earth ground connections. There should be a high resistance between the USB 6008 common and analog common (with the USB cable pulled).
Afternote: - For a "Floating" or ungrounded laptop type computer- "The polarizaton power supply common is connected to the USB 6008 common and therefore is also earth grounded by the computer ground." If your installation uses a net book, notebook, or laptop computer without an earth ground, then you need to experiment with the local polarization controller/SWCTRL common. It might work, only where the computer is "floating" from earth ground and there is no other earth ground for the USB 6008, to tie the SWCTRL common to the analog common at the analog power supply.
Afternote: - Several of us have noted significant reduction in noise at the NBLNA output and/or a solution to system noise problems by going to a dedicated earth ground. At least for the analog common common connection at the analog power supply, builders should probably consider a dedicated cold water pipe or dedicated ground rod for best performance. Where a dedicated earth ground is used, do not also connect the analog common connection to the local AC power ground (which might cause a ground loop).
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 is the name of our website)) 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.
Project Documentation, Links and References (very early stages)
QUESTIONS/COMMENTS/notice of typos, etc. send email to joegeller at gellerlabs dot com
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