Ideas for magnetometer torsion thread

Alexander Avtanski · 2011-09-12T18:39:45+00:00

Hello,I'm building a torsion magnetometer (you know the type: mirror &magnet hanging on a thread, light bouncing off the mirror, position ofthe bounced light spot tracked and recorded). Things pretty much work,but I have difficulties with finding the right material for thethread.Let me first explain what the problem is... The magnetometer is verysensitive and any slight changes in the thread cause it to drift. Iused at first (naively) some sewing thread, but this is twisted andany slight change in temperature or humidity make it twist/untwist abit, messing up the measurements. Then I tried the thinnest fishingcord I could find, hoping that since this is not twisted, it won't beaffected by temperature, and since it's waterproof, humidity won'tcause problems. It still drifts, as shown on this recording from lastnight:Notice the red line - the minor ups and downs are real disturbances inthe magnetic field, but the general trend up is caused by the threadslowly [un]twisting under the weight of the mirror/magnet. Thisrequires recalibration every few hours.I'm now experimenting with dental floss, hoping that it will provideless resistance to twisting (and hopefully less drift) than thefishing cord. Unfortunately, my wife just called me from home to tellme that the readings went off the scale again in just a couple ofhours.I've read suggestions of using guitar string (I think it won't work,because metal is way too stiff) or hair (reaction to humidity changesworry me). I've tried extremely thin fibers pulled out from twine -they break way too easily.Please, if you have any suggestions about suitable material for thethread, let me know. Any idea is fine - don't be hesitant to givesuggestions that are untried. I hope to get a lot of suggestions anddo some brainstorming.Thanks,- Alex