Peter
Section 11.2 (4.7), IEC 945 (1996), describes a test to determine
the "compass safe" distance for electronic equipment. The idea here
is that a magnetic compass could be influenced by nearby metal or DC
magnetic fields associated with current flows in wires, etc. The
test is to determine the separation distance at which a maximum
acceptable compass deflection will be caused by the DUT (I'm sorry I
don't have the spec available).
As I remember the test parameters chosen were to account for
worst-case geomagnetic field strengths - at the poles.
Military and others are interested in measuring magnetic field
anomalies to determine locations of submarines, hidden vehicles and I
believe oil fields. Measured parameters are very tiny and
interfering fields don't have to be very big to cause errors. Can't
recall where I saw info, you might ask your favorite search engine to
look for SQUID, I believe is the acronym for the supercooled quantum
devices used to measure the variations in earth's magnetic field.
Good luck
Best regards,
Tom Cokenias
EMC Consultant
El Granada, CA
