NavList:

   

Reply

Brad had mentioned the presence of a mumetal shield around the batteries of
the Skyscout instrument.

I had cast a bit of doubt on that, pointing out that the mumetal screen, in
itself, would locally distort the Earth's magnetic field, even as it
shielded any magnetic effects from the batteries.

I've now had a chance to see the manual that went out with the instrument,
and it does indeed refer to the use of mumetal to screen the batteries.
Presumably, then, the evil effect of the magnetism of the batteries is such
that any such perturbation of the ambient field is a price worth paying to
eliminate it. I imagine that the magnetic sensors will have been placed as
far as possible from the battery assembly, so as to take advantage of the
inverse-cube law, which applies in this case.

Does anyone in the list know about the construction of such alkaline
batteries? It's presumably the steel case that is the origin of the
magnetism. Is that a fundamental part of the chemistry, or could they be
encased in another material, non-magnetic, just as well, if at greater
expense? Has any specialist battery maker explored such a niche market, I
wonder (if so, they would be expensive). I'm interested in such effects on
other types of battery too, having substituted LED illumination for the
faded Tritium lighting of a Mini-compass, using a 3 volt coin cell (CR
2032). This has to be spaced several inches outside the hockey-puck profile
of the compass, to preserve magnetic accuracy. Perhaps use of a mumetal
shield, for that little battery, would allow it to be placed against the
compass body. It seems worth investigating. Does anyone have experience? Can
anyone offer a bit of mumetal? I used to use masses of the stuff, in my
working days, for magnetic shielding of photomultiplier tubes, but that was
long ago.

George.

contact George Huxtable, at  george@hux.me.uk
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.


--~--~---------~--~----~------------~-------~--~----~
Navigation List archive: www.fer3.com/arc
To post, email NavList@fer3.com
To , email NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---

   

Reply