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5
Electromagnetic interference (EMI) from Radio Wave Sources
1.
The rapid development of electronics, especially in the area of communications, has
saturated our environment with electromagnetic(EM) radio waves that are emitted by
television, radio and communication signals. These EM wave are invisible and their
strength increases as one approaches the source. All electrical conductors act as
antennas to the EM signals and, to varying degrees, all power wheelchairs and scooters
are susceptible to electromagnetic interference(EMI). The interference could result in
abnormal, unintentional movement and/or erratic control of the vehicle. The United States
Food and drug Administration (FDA) suggests that the following statement be incorporated
to the user’s manual for all power wheelchairs like the P20RTL
2. Be aware of nearby transmitters such as radio or TV stations and try to avoid coming close
to them.
3. If unintended movement or brake release occurs, turn the powered wheelchair off as soon
as it is safe.
4. Be aware that adding accessories or components, or modifying the powered wheel-chair,
may make it more susceptible to interference from radio wave sources.(Note: It is difficult to
evaluate the effect on the overall immunity of the powered wheel-chair).
5. Report all incidents of unintended movement or brake release to the powered wheelchair
manufacturer, and note whether there is a radio wave source nearby. Power wheelchairs
and motorized scooters (in this section, both will be referred to as powered wheelchairs)
may as susceptible to electromagnetic interference (EMI), which is interfering
electromagnetic energy emitted from sources such as radio stations, TV stations, amateur
radio (HAN) transmitter, two-way radios and cellular phones. The interference (from radio
wave sources) can cause the powered wheelchair to release its brakes, move by itself or
move in unintended directions. It can also permanently damage the powered wheelchair’s
control system.
6. The intensity of the EM energy can be measured in volts per meter(V/m).Each powered
wheelchair can resist EMI up to a certain intensity. This is called “immunity level”. The
higher the immunity level, the greater the protec
t
ion. At this time, current technology is
capable of providing at least 20 V/m of immunity level, which would provide useful
protection against common sources of radiated EMI.
