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CHAPTER 6 - 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
interfering
electromagnetic energy (EM)
emitted 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 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 immunity
level, which 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 10 V/m.
There are a number of sources of relatively intense electromagnetic fields in
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, 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, 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.
