Biomedical Engineering Reference
In-Depth Information
TABLE 4.4
EN-55011 Conducted Emissions Limits for Group 1 Devices
a
Maximum RF Line Voltage (dBµV)
Class A
Class B
Frequency (MHz)
Quasi-peak
Average
Quasi-peak
Average
0.15-0.5
79
66
66, decreasing with log
56, decreasing with
of frequency to 56
log of frequency to 46
0.5-5.0
73
60
56
46
5.0-30.0
73
60
60
50
a
The limit decreases linearly with the logarithm of the frequency in the range 0.15 to 0.5 MHz. The lower limits apply at
the transition frequencies.
TABLE 4.5
EN-55011 Sample Worksheet for Testing Conducted Emissions
Line measured: phase
Frequency
Reading
Correction
Correction
Limit
Detector
Input (MHz)
input (dBµV)
Factor (dB)
Reading (dBµV)
(dBµV)
Margin (dB)
Function
0.257
45.5
0.8
46.3
66
19.7
Peak
0.323
42.7
0.7
43.4
66
22.6
Peak
0.195
41.9
1.0
42.9
66
23.1
Peak
0.385
38.8
0.6
39.4
66
26.6
Peak
0.451
34.8
0.6
35.4
66
30.6
Peak
20.100
57.3
1.8
59.1
60
0.9
Peak
18.100
56.0
1.5
57.5
60
2.5
Peak
18.500
53.1
1.6
54.7
60
5.3
Peak
19.000
50.8
1.7
52.5
60
7.5
Peak
SUSCEPTIBILITY
It is really surprising that regulatory agencies around the world took so long to take steps
that would protect patients and health-care providers from EMI-induced medical-device
failures. Although the military and aviation industries had been developing hardware
immune to EMI for many years, it was only in 1994 that the FDA started taking action by
warning the medical device industry about their concerns regarding EMI-induced failures,
as well as by making speci
c recommendations for immunity levels for critical devices. In
1998, European agencies advanced this process by making it mandatory for medical devices
to comply with a fairly comprehensive EMC standard to be marketable in Europe. Today,
most nations which require medical devices to comply with EMC requirements make use
of standards based on the EN-60601-1-2 immunity requirements shown in Table 4.6, which
cover electrostatic discharge (ESD), radio-frequency interference (RFI), and a variety of
power disturbances. IEC-60601-1-2 itself cites extensively the test methods and immunity
levels of the basic IEC-61000-4 series of standards.
At the time of this writing, EN-60601-1-2, pass/fail criteria are ultimately de
fi
ned by
the manufacturer. This is because the current immunity criteria for medical products are
de
fi
ned in this standard as “equipment and/or system continues to perform its intended
function as speci
fi
fi
ed by the manufacturer or fails without creating a safety hazard.” A safety
hazard is then de
ect on the patient, other persons,
animals, or the surroundings arising directly from equipment.” As a result, the manufacturer
fi
ned as a “potentially detrimental e
ff
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