Chapter 10
Electromagnetic Interference (EMI)
D82014014B 10/15
Chapter 10
45
Our environment is saturated with radio (electromagnetic) waves that
originate from transmitters of television, radio and communication signals.
The waves are invisible and their strength at any location is unknown but in
general, the strength of a given e.m. wave increases as you move toward
the transmitting source. All electrical conductors act as antennas to the
e.m. signals. To varying degrees, all power wheelchairs and scooters are
susceptible to electromagnetic interference. Abnormal operation in the
form of unintentional movement and/or erratic control of the vehicle
could result if the interference is such as to override the control system of
the vehicle. The U.S. F.D.A. has suggested that the following statement be
incorporated to the owner’s manual for all power wheelchairs.
Electromagnetic Interference ( EMI ) From Radio Wave Sources.
Power wheelchairs and motorized scooters (in this text, both will be
referred to as power 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 power wheelchair to release its
brakes, move by itself or move in unintended directions. It can also
permanently damage the power wheelchair’s control system. The
intensity of the interfering EM energy can be measured in volts per meter
(V/m). Each power 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 Teknique XHD power wheelchair model, as
shipped, without any further modification has a tested immunity level of
at least 20 V/m. There are a number of sources of relatively intense
electromagnetic fields in the everyday environment. Some of the sources
are obvious and easy to avoid. Others are not so obvious and exposure is
unavoidable. However, we believe that by following the warnings listed
below, your risk to EMI will be minimized.
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