MadSci Network: Engineering

Re: testing an ionizing machine

Date: Thu Apr 6 06:58:04 2006
Posted By: Calvin Cole, Faculty, Engineering Physics, Northeastern State University
Area of science: Engineering
ID: 1142849880.Eg

Just testing to see if the appliance puts out ionized air is one thing. 
Judging the amount produced is likely to be a bit more difficult, if not
impossible, with simple tools.  I don’t have one of these ionizers at hand
to test but what I’m about to suggest should work.  One of the simplest
devices with which to check for charged particles is the electroscope.  You
can find directions for building one of these many places on the web or in
the Boy Scout “Atomic Energy” Merit Badge book.  It is basically two thin
pieces of metal foil hanging from a conductor attached to a metal top,
often the lid of a jar.  Letting the negatively  charged air from one of
these air ionizing machines  blow over the top should cause the leaves to
separate as the charge is collected.  One could also first charge the
electroscope positively by touching its top to a piece of cloth that has
just been used to charge a rubber balloon.  The balloon charges negatively
so the cloth is left positive.  You know the balloon is well charged if it
will stick to the wall or ceiling.  Note these sorts of tests really only
work well on days with low humidity.  A positively charged electroscope
should have the leaves more rapidly fall back together as negatively
charged air is blown across its top than if left alone.  You do not blow
the air directly over the leaves just the top of the closed electroscope.
In principle one could time the rate at which the leaves fall back together
to judge which machine was producing the most ionization.  This could be
complicated by having different rates of air flow from the different
machines as well as the distance from the machines.  Perhaps the best way
to get a good comparison done with proper instrumentation would be to check
out the “Consumer Reports” web site.  They also noted about a year ago that
some of these devices actually put out too much ozone (which can be a lung
irritant) as a byproduct of negative ion production.

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