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EMC in the Medical Industry
By Gary Fenical
As the electromagnetic spectrum becomes more congested, the need for electromagnetic
compatibility (EMC) among electrical and electronic equipment
becomes increasingly important. In addition, because of the
proliferation of electronic devices, these devices must work
in close proximity to and with each other.
One particularly critical class of device is electrical and
electronic medical equipment. It is essential that these perform
as intended and not emit levels of electromagnetic energy
that interfere with other equipment. Currently, medical facilities
are packed with all sorts of electronic medical equipment
that must work in unison. In addition, many of these devices
rely on wireless communications to relay their data. Incidences
of interference in MRI imaging systems, malfunctions in patient-connected
medical equipment, and even problems with electric wheelchairs
and scooters are becoming more prevalent.
Some electro-medical devices are required to operate in a
wide variety of environments. These include: hospitals, helicopters
and other aircraft (i.e., commercial, private, military),
ground vehicles, boats, ships and others. Many such devices
are life-support equipment that must operate without interruption
and without susceptibility issues. It is imperative that these
devices do not interfere with the operation of the support
vehicle. In emergencies requiring airlifting of a patient
such devices cannot be shut down during takeoff and landing
as is required by FAA regulations for personal electronic
devices.
IEC 60601-1-2: The Core Standard
Electromagnetic emissions standards are essential for the
protection of the public radio and telecommunication services.
Emissions standards are also required to have some assurance
that other electrical and electronic equipment will operate
as intended if they have reasonable levels of immunity built
in.
The International Electrotechnical Commission is a worldwide
body that promotes international cooperation on all questions
concerning standardization in the electrical and electronic
industries. Hence, the IEC has published a document, IEC 60601-1-2:2001
“Medical Electrical Equipment - Part 1: General requirements
for safety - 2. Collateral Standard: Electromagnetic Compatibility
- Requirements and Tests.”
It must be realized, however, that this document gives certain
levels for immunity that are tailored to the medical environment.
For emissions the levels are not changed from the reference
standards. This means that in a challenging environment such
as a hospital the limits may or may not be sufficient for
assuring that equipment continues to operate as intended.
In applying these emissions and immunity levels, tailoring
of the requirements outlined in IEC 60601-1-2 is common practice
for most medical-electrical equipment. The specification should
only be used as a guideline for producing product-specific
test plans.
It is also important that testing is performed to the current
revision of the document. Some manufacturers are still asking
for tests based upon the 1993 edition of the standard. The
latest and current edition of IEC 60601-1-2 is significantly
different from the first edition as it establishes a minimum
baseline of performance in the presence of expected levels
of Electromagnetic Disturbance. A detailed chart is available
from Laird Technologies.
Suggestions for Manufacturers
Identify products that are currently under development or
those that are ready to go to market but have not yet been
tested, or that have been tested to the older version of the
standard. Have these products tested to the requirements of
the new standard. Although grandfathering is acceptable until
the date-of-withdrawal (DOW) of the original document, the
liability issues of placing products onto the market that
do not meet current standards are a key factor.
Identify non-compliant areas or components. Some component
manufacturers may already have products available that are
compliant with IEC 60601-1-2:2001. Power supply component
manufacturers, for example, are already faced with two of
the new standards added to IEC 60601-1-2:2001: IEC 61000-3-2
(Harmonics) and IEC 61000-3-3 (Voltage Fluctuations and Flicker).
This benefits manufacturers by reducing their time to re-develop
compliant products. Be sure to ask for the complete declaration
of conformity for the component. Many times suppliers unknowingly
declare their device compliant to various standards but have
not addressed all the necessary basic standards that may apply
to your device.
Testing of medical devices or systems requires time to complete
the conformity assessment phase. In real life, products seldom
pass EMC testing on their first pass. Experience has shown
that manufacturers often delay testing until the last moment.
There are hundreds of manufacturers and only a few conformity
assessment organizations that are accredited to perform the
testing.
It is wise to choose a testing facility that has experience
in mitigating EMC problems. This way, fixes or strategies
to resolve EMI issues can start during the initial testing,
ultimately shortening the redesign cycle and the time to market.
Many facilities provide you with only a pass/fail report and
send you on your way. Engineers and technicians experienced
in the EMC field can greatly decrease your learning curve
in dealing with such problems as redesign and component choice.
A wiser choice is to design EMC into the product from the
beginning. History has shown that the longer you wait to deal
with EMC design, the harder it is to implement and the more
it will cost. Remember, it is always more efficient and less
expensive to correct the problem at the source. Generally,
this can only be done efficiently during the design stages.
It is much too late to try to apply devices such as PC board
shields after the PCBs have been laid out, designed, and ordered.
Component changes and physical position are difficult to deal
with unless addressed at the beginning. Basic design factors
such as loop areas are of paramount concern and can only be
effectively minimized during the initial design stages. It
cannot be expressed too strongly how important it is to “design
in” EMC. Today’s standards demand it.
For information, contact Laird Technologies, P.O. Box 650,
Shielding Way, Delaware Water Gap, PA 18327, (800) 843-4556,
www.lairdtech.com.
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