ELECTROMAGNETIC COMPATIBILITY AND MEDICAL DEVICES - Design and Development of Medical Electronic Instrumentation - page 148

by which equipment must possess su cient immunity to operate as intended in the pres-

ence of interference [Gubisch, 1995].
Regulatory bodies around the world have developed standards and regulations covering
both emissions and immunity that designers must take very seriously. Failure to comply
with EMI and EMC regulations can have a serious impact on everyone associated with a
product, starting with the designer, through the manufacturer, the marketing and distribu-
tion network, and extending even to customers. The consequences of noncompliance
include halting manufacturing and distribution, levying

fines, and the publication of pub-
lic notices of noncompliance to warn potential customers and other agencies. These con-
siderations become especially important in the case of medical equipment, since it often
involves sensitive electronics that can be a

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ected adversely by electromagnetic interfer-
ence, leading to potentially serious hazards to patients and health-care providers.
The European Community regulates emissions and immunity of medical devices
through the EN-60601-1-2 standard ( Medical Electrical Equipment—Part 1: General
Requirements for Safety ; Section 2: Collateral Standard: Electromagnetic Compatibility—
Requirements and Tests) as well as the EN-55011 standard ( Limits and Methods of Meas-
urement of Radio Disturbance Characteristics of Industrial, Scienti

ff

fi c and Medical Radio

Frequency Equipment ). In EN-60601-1-2, pass/fail criteria are de ned by the manufac-

turer. As a result, the manufacturer may chose to classify a failure mode that does not pose
a hazard to the patient as a “pass.” In the United States, the FDA is adopting many of the
IEC-60601-1-2 requirements but is imposing restrictions on a manufacturer's ability to
adopt pass/fail criteria. The FDA prescribes that a passing result corresponds to maintain-
ing clinical utility. In addition, there are discrepancies between the immunity levels rec-
ommended by European authorities and the FDA. Because of these di

fi

erences in opinion,
as well as because the standards are relatively new, changes occur often, and we advise
engineers to keep updated on the latest versions.
Assuring compliance with the rules involves an extensive series of tests. The EMI and
EMC standards enforced by the various regulatory agencies clearly de

ff

ne the construction
of test sites as well as the test procedures to be followed. Even a fairly spartan facility
capable of conducting these tests ends up costing over $100,000 just to set up, and for this
reason, most companies hire an outside test lab at the rate of $1500 to $3000 per day to
conduct testing. Considering how fast charges can accumulate during testing, it is obvi-
ously not a smart move simply to hire a test lab and wait for the results. Rather, designers
should familiarize themselves with the relevant EMI and EMC standards and make sure
that compliance requirements are considered at every stage in the design process.
In this chapter we present the major EMI/EMC requirements for medical devices, look
at the theory of how circuits produce EMI, and describe some low-cost tools and methods
that will allow you to identify and isolate the sources of EMI that inevitably make it into
a circuit.

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EMISSIONS FROM MEDICAL DEVICES

The FCC's main concern with RF emissions from electronic devices is possible interfer-
ence with communications devices such as commercial radio and TV receivers. From the
point of view of agencies regulating medical devices (in the United States the FDA), the
concern about unintentional electromagnetic emissions extends to the way in which they
could interfere with diagnostic or therapeutic medical devices. Note the word uninten-
tional , since these standards do not apply directly to medical devices that intentionally
generate electromagnetic signals (e.g., telemetry ECG transmitters, electrosurgery equip-
ment, magnetic resonance imagers) which require special emissions that limit exemptions
at speci fi cally allocated frequency bands.