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Electromagnetic Interference (EMI) From Radio Wave Sources
EMI-RFI
RADIO WAVES MAY INTERFERE WITH THE CONTROL OF THE POWERCHAIR
This is to let you know that laboratory tests performed by the Food and Drug Administration (FDA)
indicated that radio waves could cause unintended motion of powerchairs. Radio waves are a form of
electromagnetic energy. When this energy unintentionally affects the operation of a device, it is called
“electromagnetic interference” (EMI).
The following information summarizes what you need to know about EMI. You can use this information
to minimize the risk that EMI will affect your LIBERTY™ 624 MINI.
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Where do radio waves originate?
Radio waves are emitted from the antennas of cellular phones, mobile two-way radios (like ones
used in police, fire and emergency vehicles), hand-held two-way radios (like walkie-talkies), TV
stations, radio stations, amateur radio (HAM) transmitters, wireless computer links, microwave
sources and paging transmitters. Because electromagnetic (EM) energy is more intense closer to the
transmitting antenna (source), the EM fields from two-way radios are of special concern.
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If my powerchair is affected by EMI, what kind of motion should I expect?
This is hard to predict. It would depend on a number of factors including the intensity of the radio
waves, the construction of the powerchair, whether it is on level ground or on a slope or incline, and
whether it is in motion or stationary. The motion can be erratic with the powerchair moving by itself
or coming to a sudden stop. Further, it is possible for EMI to unexpectedly release the brakes on
a powerchair or cause it to move in unintended directions. Some intense sources of EMI can even
damage the control system of the powerchair.
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Is there any way to definitely know whether radio waves are responsible for the unintended
motion of my powerchair?
Unfortunately, interference from radio wave sources may be difficult to recognize since the signals
from these sources are invisible and may be intermittent. However, FDA recommends that you
report all incidents of unintended motion or brake release to the powerchair manufacturer, and, if
possible, make note whether there was a radio wave source nearby at the time of the incident.
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Has anyone been injured from erratic unintended motion of powerchairs?
FDA has reports of injuries that resulted from uncontrolled motion of powerchairs but it is not clear
how many of these incidents were actually caused by radio wave interference.
