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Electromagnetic compatibility (EMC) is the ability of an electrical device to work satisfactorily in its electromagnetic environment without influencing the surrounding devices. An additional goal of EMC standards, testing, and design is to ensure the safe and correct operation of other devices in the same electromagnetic environment. This article will discuss some of the changes that have taken place in EMC standards for medical devices.

The parent standard for medical device testing is IEC 60601-1 Medical Electrical Equipment - Part 1: General Requirements for Safety. IEC 60601-1-2 is a Collateral Standard: covering Electromagnetic Compatibility - Requirements and Tests. This article will deal with IEC 60601-1-2:2001 (2^nd edition), Amendment 1:2004, and IEC 60601-1-2:2007 (3^rd edition). The article will also describe the specific reference standards related to immunity and emissions testing for medical devices.

History of IEC60601-1-2 Electromagnetic Compatibility of Medical Electrical Equipment
In 1993, the first edition of IEC 60601-1-2 was published, covering electromagnetic compatibility for medical devices.

The second edition, which was published in 2001, was a major rewrite of the first edition. It made the following changes:

Addressed intentional transmitters, statistical testing, and large equipment;
Required application of IEC 61000-3-2, IEC 61000-3-3, IEC 61000-4-6, IEC 61000-4-8, and IEC 61000-4-11;
Based the immunity requirements upon “essential performance” and basic safety;
Gave greater detail on testing and requirements;
Excluded non-medical equipment that would not adversely affect “essential performance of the medical electrical (ME) equipment or ME system.”

Amendment 1:2004 removed the defined term “essential performance,” leaving it up to the user to determine how the essential performance of his device would be defined. The guidance provided in Annex GGG was changed to refer to the draft of IEC 60601-1, 3^rd edition, for information on essential performance concepts. Both versions of the standard require the identification of essential performance in order to determine whether a medical device has properly passed electromagnetic immunity testing. This also suggests performing a risk analysis using ISO 14971:2000 to make this determination. Essential performance is safety-related criteria, the absence or degradation of which would result in an unacceptable risk.

The third edition was published in March of 2007. The principle technical changes are in Clause 4, which now harmonizes the defined term “essential performance” with that of the general standard, IEC 60601-1:2005, (3^rdedition) (now published).

EMC compliance is an important part of the design and evaluation of medical devices for all regulated medical markets. Most markets refer to IEC 60601-1-2 to determine acceptable performance in the presence of electromagnetic phenomena. Please keep in mind that, strictly speaking, IEC 60601-1-2:2001, with or without Amendment 1:2004, and IEC 60601-1-2:2007 are safety standards that maybe used to ensure basic safety and essential performance of ME equipment and ME systems in the presence of electromagnetic phenomena. The intended performance of the device may not be tested because the absence or degradation of this performance may not present an unacceptable risk.

It is also important to review any national deviations.

In the European Union, EN 60601-1-2:2001 is the harmonized standard under the Medical Device Directive (93/42/ECC). EN 60601-1-2:2001 is identical to IEC 60601-1-2:2001, and compliance with EN 60601-1-2:2001 is required for CE mark of a product. IEC 60601-1-2 Amendment 1:2004 and IEC 60601-1-2:2007 (3^rd Edition) are not yet harmonized under the Medical Device Directive.

In the United States, the Food and Drug Administration (FDA) is responsible for EMC compliance. The FDA recognizes ANSI/AAMI/IEC 60601-1-2-2001 as the consensus standard, which has identical requirements to IEC 60601-1-2-2001.
The FDA has indicated it will accept declaration of conformity, in support of pre-market submissions, to ANSI/AAMI/IEC 60601-1-2:2001, with or without Amendment 1:2004, until September 3, 2007. After September 3, 2007 all submissions must be to IEC 60601-1-2:2001 with Amendment 1:2004.

Note that the FDA considers ANSI/AAMI/IEC 60601-1-2 as a baseline for all the appropriate device areas. If the FDA’s Center for Devices and Radiological Health (CDRH) has issued guidance documents with additional EMC specifications, these will supersede the ANSI/AAMI/IEC requirements. (These can be found at the FDA website, www.fda.gov.)

As an example, the FDA provides guidance to FDA investigators regarding Electromagnetic Compatibility (EMC) and how it is likely to be addressed in a medical device manufacturer’s Quality System and current Good Manufacturing Practices.

Requirements: Emissions and Immunity
The requirements in IEC 60601-1-2 fall into two categories, emissions and immunity. Emissions deals with both radiated and conducted electromagnetic (EM) energy generated by the device. Immunity in IEC 60601-1-2 addresses the basic safety and essential performance of medical devices in the presence of EM disturbances. A detailed listing of the emissions standards is shown in Table 1.

CISPR 11 Ed. 4.1 B:2004	Industrial, scientific and medical (ism) radio-frequency equipment - electromagnetic disturbance characteristics - limits and methods of measurement edition: 4.1
IEC 61000-3-2 (2005-11) Ed. 3.0 Electromagnetic compatibility	Limits - limits for harmonic current emissions (equipment input current ≤ 16 a per phase)
IEC 61000-3-3 (2005-10) Ed. 1.2 Consolidated Edition Electromagnetic compatibility	Limits - limitation of voltage changes, voltage fluctuations and flicker in public low-voltage supply systems, for equipment with rated current ≤ 16 a per phase and not subject to conditional connection

Table 1: Emissions Standards

Emissions testing ensures that, while a medical device is operating, it does not generate electromagnetic or radio-frequency energy of sufficient levels to interfere with the safe operation of other devices in the vicinity. Devices are classified as Group 1 or Group 2 and Class A or Class B according to CISPR 11. Class A or B is determined by the environment in which the device is used, Class A being industrial/light industrial environments such as hospitals, and Class B being all other environments, such as domestic or residential. Class B limits are more restrictive, with lower thresholds for allowed emissions. Class B limits are often used for medical devices used in homes and doctors’ offices.

CISPR 11
Most medical devices must comply with CISPR 11. Some simple devices with circuitry operating under 9 kHz may be tested to CISPR 14. Medical lighting equipment may be tested to CISPR 15. Non-medical devices used in a medical system, such as information technology equipment, can be classified and tested to their applicable standard.

Edition 4.1 of CISPR 11 was published in June of 2004, in which procedures are given for the measurement of radio-frequency disturbances, and limits are given within the frequency range of 9 kHz to 400 GHz. The fifth edition is still a work in progress, with a draft being circulated for vote. It is scheduled to be released by April 2008.

IEC 61000-3-2 Harmonic Emissions
Limits are imposed on harmonic emissions and distortion of the mains supply voltage. This standard covers medical devices with rated input current ≤ 16A per phase, which will be connected to a public low-voltage distribution system and operated at line voltages >220 Vac.

IEC61000-3-3 Voltage Fluctuations and Flicker
IEC 61000-3-3 outlines testing and limits for voltage changes, voltage fluctuations and flicker on the public low-voltage supply system. This standard has the same requirements as IEC 61000-3-2, covering products with an input current of ≤ 16A per phase, connected to a public low-voltage distribution system and operated at line voltages >220 Vac.

Edition 1.2 was published October, 2005 and consolidates Amendments 1 and 2.

The basic immunity standards used in IEC 60601-1-2 are found in Table 2.

IEC 61000-4-2 (2001-04) Ed. 1.2 Consolidated Edition Electromagnetic compatibility	Testing and measurement techniques - electrostatic discharge immunity test
IEC 61000-4-3 (2006-02) Electromagnetic compatibility	Testing and measurement techniques - radiated, radio-frequency, electromagnetic field immunity test
IEC 61000-4-4 (2004-07) Electromagnetic compatibility	Testing and measurement techniques - electrical fast transient/burst immunity test
IEC 61000-4-5 (2005-11) Electromagnetic compatibility	Testing and measurement techniques - surge immunity test
IEC 61000-4-6 (2006-05) Ed. 2.2 Consolidated Edition Electromagnetic compatibility	Testing and measurement techniques - immunity to conducted disturbances, induced by radio-frequency fields
IEC 61000-4-8 (2001-03) Ed. 1.1 Consolidated Edition Electromagnetic compatibility	Testing and measurement techniques - power frequency magnetic field immunity test
IEC 61000-4-11 (2004-03) Electromagnetic compatibility	Testing and measurement techniques - voltage dips, short interruptions and voltage variations immunity tests

Table 2: Basic Immunity Standards

The following are brief descriptions of the basic test methods that are used in the standard. The specific test levels and conditions of test are specified in IEC 60601-1-2.

IEC 61000-4-2 Electrostatic Discharge
This standard outlines test procedures and test levels for the application of electrostatic discharge to conductive and non-conductive parts of the device.

IEC 61000-4-3 Electromagnetic Immunity Testing
This is one of two key immunity tests dealing with radio-frequency sources. The explosion in the use of cell phones and other wireless devices has fueled the requirement for this type of testing.

IEC 61000-4-4 Electrical Fast Transient/Burst Immunity Test
Electrical fast transients (EFT) are created when switches open in the power distribution system, causing an arc. This standard defines test procedures, waveforms, and test levels for this type of EM disturbance. The EFT signal is applied to the power leads and signal lines of the device. Signal lines are tested because EFTs can be coupled into signal lines from nearby power leads.

IEC 61000-4-5 Surge Immunity Test
This standard tests a device’s immunity to high energy/voltage disturbances on power leads. This type of disturbance is usually caused by over voltage transients and lighting strikes on the main power distribution system.

IEC 61000-4-6 Immunity to Conducted RF Disturbances
The standard calls for application of RF stress to the power input lines and interconnecting cables of the medical device over the frequency range from 150kHz to 80MHz. The stress level is based upon the category of the device, such as life-support versus non-life-support.

IEC 61000-4-8 Magnetic Field Immunity
This standard applies a magnetic field to the device at both 50Hz and 60Hz to simulate magnetic fields generated by power lines.

IEC 61000-4-11
IEC 61000-4-11 checks for the product’s immunity to short interrupts and voltage drops of the power distribution system.

Test Levels
The immunity test levels and special conditions of test are specified in IEC 60601-1-2 for the above mentioned basic standards.

Compliance
There are a number of keys to complying with the EMC standards. As with IEC 60601-1, just sending a medical device to a third-party test laboratory for testing is not usually sufficient. The manufacturer must outline the essential performance of the device and address risk management. In addition, IEC 60601-1-2 specifies some compliance conditions that always apply to the basic safety and essential performance of the device. Some of these are no change in operating mode, no resets to factory default conditions, no component failures, and more as outlined below.

ISO 14971: Risk Management and Essential Performance
The manufacturer must perform effective risk management. Outlining essential performance of the medical device is the first step in ISO 14971. Essential performance relates to any feature or function of a medical device that might cause harm or injury to the patient, to others, or to the operator of the equipment. This essential performance is then used in evaluating the device during EMC testing. A medical device is allowed some degradation as long as it does not affect essential performance and safety.

IEC 60601-1-2 also outlines a number of degradations that are prohibited. These are:

Component failure;
Changes in programmable parameters;
Reset to factory defaults or presets;
Change of operating modes;
False alarms;
Cessation or interruption of any intended operation, even if accompanied by an alarm;
Initiation of any unintended operation, including unintended or uncontrolled motion, even if accompanied by an alarm;
Initiation of any unintended operation, including unintended or uncontrolled motion, even if accompanied by an alarm;
Error of a displayed numerical value sufficiently large to affect diagnosis or treatment;
Noise on a waveform that is indistinguishable from physiologically produced signals or noise that interferes with interpretation of physiologically produced signals;
Artifact or distortion in an image in which the artifact is indistinguishable from physiologically produced signals or in which the artifact interferes with interpretation of physiologically produced signals;
Failure of the automatic diagnostic or treatment equipment to diagnose or treat, even if accompanied by an alarm.

Testing
Once the compliance criteria has been established utilizing the above list and the risk management process, testing must be performed on the medical device to verify that the basic safety and essential performance of the medical device are maintained during the above described electromagnetic disturbances.

Labeling and Documents for Use
The final step in the process of complying with 60601-1-2 is to fulfill the extensive labeling and manufacturer’s declarations required by the standard. The following is a list of most of these requirements:

A marking on the outside of the medical device that contains an RF transmitter or that applies RF energy for diagnosis or treatment;
A marking on the outside of the medical device that uses the connector ESD exemption;
A marking on the outside of the medical device that must be used in a shielded location;
A statement that the medical device needs special precaution regarding EMC;
A statement that the medical device can be affected by portable and mobile RF communications equipment;
If the ESD exemptions is used:

The ESD warning symbol;

A warning that pins of the connector should not be touched;

An ESD precautionary procedure;

A recommendation that all staff be trained in the ESD precautionary procedure;

A specification of the minimum contents of the ESD precautionary procedure.

If claimed, a warning that type A professional equipment may cause interference;
In the technical description:

A list of cables, maximum lengths of cables, transducers and other accessories that may affect compliance;

A warning that use of accessories, cables, and transducers other than those specified may result in increased emissions and decreased immunity;

Tables regarding the emissions and immunity of the medical device;

A warning that the medical device should not be used adjacent to or stacked with other equipment;

A list of the product’s essential performance;

Any justifications for lower immunity levels;

A table with safety separation distances for portable and mobile RF transmitters. n

Robert M. Brown is the vice-president of technical operations at QuadTech, Inc., and be reached at rbrown@quadtech.com.

James Conrad is an independent EMC consultant based in Hamilton, MA, and can be reached at http://obcompman.com/conrademc.

Frank O’Brien is the principal of O’Brien Compliance Management, and can be reached at http://obcompman.com .

References

Smith, J., “Updates on the new release of IEC 61000-4-3 Edition 3,” AR Worldwide, Application Note #41, link.
Gensel, Rodger, Immunity Testing for the CE Mark”, AR Worldwide, link.
International Electrotechnical Commission website at www.iec.ch.
Food and Drug Administration website at www.fda.gov.