Al You should also measure at about 1 inch. It is an inverse square decrease
with distance. The rate of drop off is related to the starting point and the shape of the field. Some have a flat field out to some distance before they start the inverse square drop off. Dwight ________________________________ From: cctalk <cctalk-boun...@classiccmp.org> on behalf of js--- via cctalk <cctalk@classiccmp.org> Sent: Thursday, March 16, 2017 5:06:09 PM To: gene...@classiccmp.org; Discussion@ Subject: Re: AC magnetic field strengths That is in fact how I spot degauss CRT screens, but using a flat wood boring bit (metal, obviously, instead of a paint stick) with the magnet stuck on the end, spun around with a drill. - J. On 3/16/2017 6:37 PM, dwight via cctalk wrote: > It sounds like one can make a fine tape degausser by connecting > > a super magnet to the end of a paint stirring rod and use a drill > > to spin it. > > Dwight > > > ________________________________ > From: cctalk<cctalk-boun...@classiccmp.org> on behalf of Tapley, Mark via > cctalk<cctalk@classiccmp.org> > Sent: Wednesday, March 15, 2017 11:51:07 AM > To: General Discussion: On-Topic and Off-Topic Posts > Subject: Re: AC magnetic field strengths > > On Mar 15, 2017, at 12:01 PM, Al Kossow via cctalk<cctalk@classiccmp.org> > wrote: > >> I bought an AlphaLabs GM-2 Gaussmeter for another project, and measured the >> AC magnetic >> field strength touching these devices yesterday, since I really didn't have >> any idea beyond >> order of magnitude what they might be >> >> Handheld tape head demagnetizer: 40 Gauss >> GC Elec 9317 CRT degausing coil: 70 Gauss >> Audiolab TD-3 desktop bulk eraser: 1000 Gauss >> Inmac 7180 or >> RS 44-233A handheld bulk tape erasers: 2000 Gauss >> >> >> >> also the DC field of a 1/4" button super magnet like on the >> backs of clip on badges is about 3000 Gauss > More context available at: > > https://en.wikipedia.org/wiki/Orders_of_magnitude_(magnetic_field) > > ranging from 50 femtoGauss (what the Gravity Probe B SQUID magnetometers > measured with several days’ averaging) to 100 MegaGauss (strongest pulsed > field ever obtained at Sandia Labs). > > Interestingly that page claims 12.5 kGauss for a "neodymium–iron–boron (Nd2 > Fe14 B) rare earth magnet” (subscripts on the atomic symbols got converted to > plain text during cut-n-paste). Guess the badges have weaker versions? > > Interesting to compare earth field and the badge fastener field to practical > exposure limit for pacemakers - only about a factor of 10 at the poles - and > to loudspeaker coils, which are 5000 times above the recommended pacemaker > limit. > > Now I know why people with pacemakers don’t like rock music (and name tags)! > > :-) > > - > Mark > > >