Part No 1143151 40 Invacare 3G Storm Series®
5.4 Electromagnetic Interference (EMI) From Radio Wave Sources
Powered wheelchairs and motorized scooters (in this text, both will be referred to as 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.
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 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: citizens
band (CB) radios, “walkie talkie”, security, fire and police transceivers, cellular telephones, and other personal communication devices).
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.
Some cellular telephones and similar devices transmit signals while they are ON, even when not being used.
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, so far as we know, are not likely to cause EMI
problems to your powered wheelchair.
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