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CHAPTER 10
– EMI WARNING
All types of electrically powered vehicles, such as powered wheelchairs and motorized scooters (in this
text all types will be referred to as “powered vehicles”) may be susceptible to electromagnetic
interference (EMI). This is from sources such as radio and TV stations, amateur radio (HAM)
transmitters, two-way radios and cellular phones. The interference (from radio wave sources) can cause
the powered vehicle to release its brakes, move by itself, or move in unintended direction. It can also damage the
powered vehicle’s control system. The intensity of the interfering EM energy can be measured in volts per meter (V/m).
Each powered vehicle can resist EMI interfering electromagnetic energy (EM) emitted up to a certain intensity. This is
cal
led its “immunity level”. The higher the immunity level, the greater the protection. At this time, current technology is
capable of achieving an immunity level that would provide useful protection from the more common sources of radiated
EMI. This vehicle as shipped, with no further modification, has an immunity level of 20 V/m.
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 warning listed below, your risk of 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: citizen band (CB) radios, “walkie talkies”, 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, 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.
NOTE:
Other types of hand held 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, as far as we know, are not likely
to cause EMI problems to your powered vehicle.
Powered Vehicle Electromagnetic Interference (EMI)
Because EM energy rapidly becomes more intense as one moves closer to the transmitting antenna, the EM field from
hand-held radio wave sources (transceivers) are of special concern. It is possible to unintentionally bring high levels of
EM energy close to the powered vehicle’s control system while using these devices. This can affect powered vehicle
movement and braking.
Therefore, the warnings listed below are recommended to prevent possible interference with the control system
of the powered vehicle.
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 vehicles.
Following the warnings listed below should reduce the chance of unintended brake release or powered vehicle
movement
which could result in serious injury:
1) Do not operate hand-held transceivers (transmitters-receivers) such as citizen band (CB) radios, or turn ON
personal communication devices such as cellular phones, while the powered vehicle is ON;
2) Be aware of nearby transmitters, such as radio or TV stations and try to avoid coming close to them.
3) On appearance of unintended movements or brake release occurrences, switch the powered vehicle OFF
as soon
as it is safe to do so
.
4) Be aware that adding accessories or components, or modifying the powered vehicle, may make it more susceptible to
EMI (since there is no easy way to evaluate their effect on the overall immunity level of the powered vehicle).
5) Please report to us all incidents of unintended movement or brake release and note whether there is a source of EMI
nearby.
Important information
1) 20 volts per meter (V/m) is a generally achievable and useful immunity level against EMI (as of May 1994). The
higher the level the greater the protection;
2) This product delivered to you has an immunity level of 20 V/m.
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