ELECTROMAGNETIC COMPATIBILITY AND MEDICAL DEVICES - Design and Development of Medical Electronic Instrumentation - page 154

TABLE 4.2 EN-55011 Radiated Emissions Limits for Group 1 Devices a

Field Strength (dBµV/m)

Frequency (MHz) Test Distance (m) Class A Class B

30-230 10 40 30

230-1000 10 47 37

a The lower limits apply at the transition frequency.

plane. The table is typically centered on a motorized turntable that allows 360° rotation. A
measurement antenna is positioned at a distance of 10 to 30 m as measured from the clos-
est point of the device under test. The radiated emissions are maximized by con guring

and rotating the device under test as well as by raising and lowering the antenna from 1 to
4 m. A spectrum analyzer with peak detection capabilities is used to

fi

fi find the maxima of the

radiated emissions during the testing. Then, final measurements are taken using a spectrum

analyzer with quasi-peak function with a measurement bandwidth of 120 kHz. The test
setup is shown in Figure 4.4. The limits for radiated emissions per EN-55011 for group 1
devices are presented in Table 4.2.
In reality, devices to be tested are not usually taken directly to the open-

fi

fi eld test site.

Rather, they are ensive radiated emissions in a small shielded

room. The compliance testing is then conducted in the 10-m open-

fi first scanned for potentially o ff

eld test site, paying
special attention to peak emissions detected in the shielded room. This is almost a practi-
cal necessity, because open-

fi

eld test sites, even when located far from large metropolitan
areas, are still inundated by human-made RF signals. As an example, Table 4.3 shows
results obtained recently when testing an implantable-device programmer for radiated
emissions. The speci

fi

fi c frequencies selected for testing were identi fi ed the night before

taking the device to an open- eld test site in the middle of Texas's hill country. Figure 4.5

shows the device being tested at the open-

fi

eld site. The device sits atop a motorized
turntable. A biconical antenna can be seen placed 10 m away from the device under
test. At the 10-m distance speci

fi

fi ed for the tests, radiated emissions have their electric- fi eld

1 TO 4 METERS

3 TO 30 METERS

EUT

COAXIAL CABLE

80 cm

NON-CONDUCTIVE TABLE

TURNTABLE GROUND PLANE

eld test site. The device under test is placed on a noncon-
ductive table 0.8 m above a ground plane, and the distance between the device and the antenna is 10 m.

Figure 4.4 Setup for conducting radiated-emission measurements in an open- fi