Electromagnetic Compatibility (EMC) Information
3 Electromagnetic Compatibility
(EMC) Information
3.1
Electromagnetic Interference (EMI) From
Radio Wave Sources
Powered wheelchairs and motorized scooters (in this text, both
will be referred to as powered wheelchairs) 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 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 interfering 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 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 wheelchair.
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 powered wheelchair's control system while using these
devices. This can affect powered wheelchair movement and braking.
Therefore, the warnings listed below are recommended to prevent
possible interference with the control system of the powered
wheelchair.
1143190-N-03
25
