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Appendix B
– Electromagnetic Interference (EMI)
Electromagnetic Interference (EMI) From Radio Wave Sources
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.
This powered wheelchair model as shipped, with no further modification, has an unknown
immunity. 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 minimised.
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.
**NOTE: 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,
ambulance, and taxis. These usually have the antenna mounted on the outside of the
vehicle; and
3) Long range transmitters and transceivers, such as commercial broadcast transmitters
(radio and TV broadcast antenna towers) and amateur (HAM) radios.
NOTE: Other types of hand-held devices, such as cordless phones, laptop computers,
AM/FM radios, TV sets, CD 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.
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 hand-held 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
.
WARNINGS
Electromagnetic interference (EMI) from sources such as radio and TV stations, amateur
radio (HAM) transmitters, two way radios and cellular phones can affect powered
wheelchairs.
Following the warnings listed below should reduce the chance of unintended brake release
