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Electromagnetic Interference (EMI) from Radio Wave Sources
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 waves 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). This 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 HP-1:
Power wheelchairs and motorized scooters (in this section, both will be referred to
as powered wheelchairs) may be susceptible to electromagnetic interference
(EMI), which is interfering electromagnetic energy emitted from sources such as
radio stations, TV stations, amateur radio (HAM) transmitters, 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. 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 the
"immunity level". The higher the immunity level, the greater the protection. 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.
Following the warnings listed below should reduce the chance of unintended
brake release or powered wheelchair movement that could result in serious injury:
1. Do not turn on hand-held personal communication devices such as citizens band
(CB) radios and cellular phones while the powered wheelchair is turned on.
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
wheelchair, 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 wheelchair).
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.
SAFETY INSTRUCTIONS
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