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Operational method of Sensys sensors
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John Forester
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Jul 20, 2009 20:30 PDT
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This is a further item of information that, perhaps, has not been
noticed by some of you. The Sensys sensors operate, so Sensys says on
their website, by passively disturbing the earth's magnetic field, and
then broadcasting that disturbance to a nearby data-gathering item.
The only common materials that will disturb the earth's magnetic field
are iron and steel. No other common materials will do so. Many modern
bicycles contain very small amounts of these materials. Probably the
most are in the chain, the control cables, and, in most, but not all
cases, the spokes.
This is an entirely different situation than exists with the loop
detectors, for they detect materials that form loops of electrically
conductive material. There have been many misguided claims over the
years that loops detect magnetic materials, but that is false; the
detection of iron or steel depends, in their case, only on their
conductivity, not on their magnetic material.
--
John Forester, MS, PE
Bicycle Transportation Engineer
7585 Church St. Lemon Grove CA 91945-2306
619-644-5481 fore-@johnforester.com
www.johnforester.com
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