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Electromagnetic Compatibility (EMC) Information
3 Electromagnetic Compatibility (EMC)
Information
3.1 Electromagnetic Interference (EMI) From
Radio Frequency Sources
Powered wheelchairs and motorized scooters (in this text,
both will be referred to as mobility devices) may be
susceptible to electromagnetic interference (EMI), which
is interfering electromagnetic energy (EM) 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
mobility devices to release its brakes, move by itself, or
move in unintended directions. It can also permanently
damage the mobility devices control system. The intensity
of the interfering EM energy can be measured in volts per
meter (V/m). Each powered mobility device can resist EMI
up to a certain intensity. This 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.
There are a number of sources of relatively intense
electromagnetic fields in the everyday environment. Some
of these sources are obvious and easy to avoid. Others are
not apparent and exposure is unavoidable. However, we
believe that by following the warnings listed below, your
risk to EMI will be minimized.
The sources of radiated EMI can be broadly classified into
three types:
1. Hand-held Portable transceivers (transmitters/receivers
with the antenna mounted directly on the transmitting
unit. Examples include: citizens band (CB) radios,
“walkie talkie”, security, fire and police transceivers,
cellular telephones, and other personal communication
devices).
Some cellular telephones and similar devices
transmit signals while they are ON, even when
not being used.
2. Medium-range mobile transceivers, such as those used
in police cars, fire trucks, ambulances and taxis. These
usually have the antenna mounted on the outside of
the vehicle.
3. Long-range transmitters and transceivers, such as
commercial broadcast transmitters (radio and TV
broadcast antenna towers) and amateur (HAM) radios.
Other types of handheld devices, such as cordless
phones, laptop computers, AM/FM radios, TV sets,
CD players, cassette players, and small appliances,
such as electric shavers and hair dryers, so far as we
know, are not likely to cause EMI problems to your
powered mobility device.
3.2 Powered Wheelchair Electromagnetic
Interference (EMI)
Because EM energy rapidly becomes more intense as one
moves closer to the transmitting antenna (source), the EM
fields from handheld radio wave sources (transceivers) are
of special concern. It is possible to unintentionally bring
high levels of EM energy very close to the mobility devices
control system while using these devices. This can affect the
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