Blast/Rev F/Feb03
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I I I . E M I / R F I
EMI/RFI
Laboratory tests performed by the Food and Drug Administration (FDA) have shown that radio waves can cause unintended
motion of power chairs. Radio waves are a form of electromagnetic energy. When this energy adversely affects the operation
of an electronic device, it is called Electromagnetic Interference (EMI) or Radio Frequency Interference (RFI).
WARNING! Radio waves may interfere with the control of power chairs.
Frequently Asked Questions (FAQs)
The following FAQs summarize what you should know about EMI/RFI. Use this information to minimize the risk that EMI/
RFI will affect your power chair.
Where do radio waves come from?
Radio waves are emitted from the antennas of cellular phones, mobile two-way radios (such as walkie-talkies), radio stations,
TV stations, amateur radio (HAM) transmitters, wireless computer links, microwave sources, and paging transmitters. Radio
waves are a form of electromagnetic energy (EM). Because electromagnetic energy is more intense closer to the transmitting
antenna (source of emission), the EM fields from two-way radios are of special concern to power chair users.
If my power chair is affected by EMI/RFI, what kind of motion should I expect?
This is hard to predict. It would depend on a number of factors:
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Strength of the radio waves
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Construction of the power chair
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Position of the power chair (whether it is on level ground or on an incline)
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Whether or not the power chair is in motion
An affected power chairs movement can be erratic. It may move by itself or come to a sudden stop. Furthermore, it is possible
for EMI/RFI to unexpectedly release the brakes on a power chair. Some intense sources of EMI/RFI can even damage the
control system of the Blast.
Is there any way to know for sure whether radio waves are responsible for the unintended motion of my power chair?
Unfortunately, interference from radio wave sources may be difficult to recognize, since the signals from these sources are
invisible and may be intermittent. However, the FDA recommends that you report all incidents of unintended motion or brake
release to the power chair manufacturer and, if possible, note whether there was a radio wave source nearby at the time of the
incident.
Has anyone been hurt from erratic, unintended motion of power chairs?
The FDA has reports of injuries that resulted from the apparent uncontrolled motion of power chairs. However, it is unclear
how many of these incidents were actually caused by radio wave interference.
Are all power chairs susceptible to EMI/RFI?
Each make and model of chair differs in its ability to resist electromagnetic interference. That is, each has a particular level of
immunity to interference, measured in volts per meter (Vm). A higher immunity level offers greater protection. In other
words, a power chair with a high immunity level is less likely to be affected by a strong radio source than one with a low
immunity level.
