5
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 wave are invisible and their
strength increases as one approach 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 scooter like the Travelux Infineon. 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, cellular phones and alarm systems of shops. 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
scooter’s control system. The intensity of the EM energy can be measured in volts per
meter (V/m).Each powered scooter can resist EMI up to a certain intensity. This is called
“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 scooter 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 scooter 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 scooter off as soon
as it is safe.
4. Be aware that adding accessories or components, or modifying the powered scooter,
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
scooter).
5. Report all incidents of unintended movement or brake release to the powered scooter
manufacturer, and note whether there is a radio wave source nearby.
