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3. EMI/RFI
This section provides the user with basic information about the
problems with EMI, known sources of EMI and protective measures
either to reduce the possibility of exposure or to minimize the degree of
exposure. This section also shows some conditions in which unexpected
or erratic wheelchair movements may occur.
3.1 Electromagnetic Interference From Radio Wave Sources
3.1.1 Powered vehicles may be susceptible to electromagnetic
interference (EMI), which is interfering electromagnetic energy
(EM) emitted from sources such as radio stations (Radio
Frequency Interference), TV stations, amateur radio (HAM)
transmitters, two-way radios, and cellular phones. The
interference (from radio wave sources) can cause the powered
vehicle to release its brakes, move by itself, or move in unintended
directions. It can also permanently damage the powered vehicle's
control system. The intensity of the interfering EM energy can be
measured in volts per meter (V/m). Each powered vehicle can
resist EMI up to a certain intensity. This amount of resistance is
called its immunity level. The higher the immunity level, the
greater the protection. At this time, current technology is capable
of achieving at least a 20 V/m immunity level, which would
provide useful protection from the more common sources of
radiated EMI. This powered vehicle model, with no further
modification, has an immunity level of 20 V/m without any
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