CHAPTER 9 – 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
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 20 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 .
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.
