Biomedical Engineering Reference
In-Depth Information
TABLE 4.6
EN-60601-1-2 Immunity Requirements
Susceptibility
Test Requirements
Relevant Standard
Electrostatic discharge (ESD)
3-kV contact to conductive accessible parts and coupling planes; 8-kV air
IEC-61000-4-2
discharge to nonconductive accessible parts
Radiated emissions (EMIs)
3 V/m, 26 MHz to 1 GHz, modulated at passband or 1 kHz
IEC-61000-4-3
Conducted emissions
Test from 150 kHz to 80 MHz into power line to 3 V/m; bulk current injection
IEC-61000-4-6
for patient cables
Power line voltage dips,
100% dropout for
1
2
cycle, 60% sag for 5 cycles, 30% sag for 25 cycles;
IEC-61000-4-11
interruptions, and variations
low-powered equipment maintains clinical utility, high-powered equipment
remains safe
Electrical fast transients (EFTs)
1 kV at power line for plug-connected equipment; 2 kV at power line for
IEC-61000-4-4
permanently installed equipment; 0.5 kV for signal lines longer than 3 m
Surge
1 kV di
ff
erential mode at power line, 2 kV common mode at power line;
IEC-61000-4-5
signal lines not tested
Magnetic
fi
fields
10 A/m at power line frequency
IEC-61000-4-8
may chose to classify a failure mode that does not pose a risk to the patient (or other sur-
rounding targets) as a
pass
. For example, the manufacturer may pass a device that fails to
start operating or stops operating when exposed to EMI threats as long as these modes do
not pose a threat to the patient. A common classi
fi
cation for device performance during
testing is as follows:
•
Criteria level A:
normal performance within equipment speci
cations
•
Criteria level B:
degradation or loss of function or performance which is self-
recoverable when the interfering signal is removed
•
Criteria level C:
degradation or loss of function or performance that requires system
reset or operator intervention when the interfering signal is removed
fi
In the United States, the FDA is adopting many of the IEC-60601-1-2 requirements but
imposes restrictions on the manufacturer's ability to adopt pass/fail criteria. The FDA pre-
scribes that a passing result corresponds to maintaining clinical utility. Some of the same
concerns are also being adopted for revised versions of IEC-60601-1-2 and drafts show
that the failure criteria will change in focus from the safety hazard to speci
fi
ed perform-
ance compliance. Because of the fast-changing nature of this
field, we present this section
as a primer on the issue of immunity to EMI, but strongly advise you to keep updated on
the latest versions of applicable standards.
fi
Susceptibility to Electrostatic Discharge
Do you know what is the potential di
erence between you and the doorknob before you
shout “ouch!” on those winter days that electrostatic charges seem to love? 6 kV! But there
are also occasional 15-kV discharges—the kind that make you hope that someone else will
open the door for you. Regardless of the speci
ff
fi
c number of kilovolts, such discharges
su
ce to fry many static-sensitive ICs. However, the primary concern with ESD events is
the large amount of RF energy they convey over an extremely wide band of frequencies.
IEC-61000-4-2 considers ESD between a human being and a medical device as the pri-
mary source of ESD-related failures. Testing is done by delivering 3-kV discharges
directly to a device's exposed conductive components and 8-kV air discharges to parts that
may be recessed.
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