I finished my magnetic field survey gizmo. I'm amazed at how well it
works, he said modestly.

The prescribed "safe" level for 60Hz magnetic field is 1 gauss. The
sensor I selected has sensitivity of about 4 millivolts per gauss.
That's in the same ballpark as the levels from magnetic phono
cartridges and some dynamic microphones -- and we all know what
happens when a shield lead comes loose on those, right? BRAMMMM,as
the cones on the woofers come loose.

I selected a sensor that has differential outputs, figuring that'd
help deal with E-field hum.

Boy, did it! With the scope set at 200 mV/cm (half a gauss after x100
gain in the amp) I see about 50 mV of noise (expected) and there must
be some 60 Hz content in there but it sure doesn't stand out. This is
bare board on the bench, it isn't in a shielded box or even on a
ground plane. Dang, this dog is gonna hunt! Can it sense B-fields?
Ohhellyeah! It starts moving when I get within a foot of it with a
teensy little magnet (0.1" x 0.2" x 0.4") I took out of a Sonicare
toothbrush. Tomorrow I'll check it on 60 Hz with a soldering gun.
Then it's time to start taking data.

I have no reason to doubt that the sensitivity is per the spec sheet
but I can calibrate it later, even post implant. I need to get data
from welding situations while I can.

Tomorrow, figure out Fitch's scope-meter and start takin'some data
with MIG and TIG welding in progress. Hooaahhh!

If my data indicates that my welding setup and expectations would
carry more risk of a whack than I'm willing to accept, so be it. I'm
guardedly optimistic.