Medical Device Link.

Originally Published MEM Fall 2004

EMC REQUIREMENTS

The deadline for compliance with new test standards to qualify equipment for sale in the European Union is November 1, 2004.

Jack Black

The European Union (EU) requirements for selling and marketing electrical and electronic medical devices in Europe are spelled out in the Medical Devices Directive (MDD; 93/42/EEC). This product safety directive is the enforceable law in the EU. Medical devices that fall within the scope of this directive must comply with the standards it establishes.

The latest revision of the MDD has established updated standards that go into effect soon. The directive update greatly changes the requirements pertaining to electromagnetic compatibility (EMC), adding new tests and increasing the severity of existing tests. Also included are changes to user manuals and referenced documentation.

The European marketplace has high expectations with respect to EMC. In general, any electric or electronic device must not emit harmful electromagnetic energy, and any electric or electronic device must continue to operate safely when unwanted electromagnetic energy is present in the vicinity. With the new standards, medical devices will be held to much higher qualifications than before.

A medical electronic device now on the market in the EU may not have been tested to all the updated requirements. Though compliant at the time of being introduced for sale, a device may very possibly be noncompliant when it is eventually sold. It is up to the manufacturer to determine whether the device should be tested to the new standard or withdrawn from the market. No grandfather clause covers these existing devices.

New Standard EN 60601-1-2

The new EMC standards are found in the second edition of EN 60601-1-2, published in 2001, with a deadline of November 1, 2004, for compliance.¹ Medical products and devices that are already in service in the EU, and that are compliant with the old standards, are exempt from the new requirements. Existing products must be in service to qualify for the exemption. Any products put into the market, but not yet purchased and put into service, will be held to the new, higher standards.

Many manufacturers are not certain whether to invest in additional testing, let alone potential redesign of existing models, in order to meet a compliance requirement. Getting detailed analysis from technical experts often is the best way to proceed.

A review of existing test reports, along with a review of the existing design, can determine the optimal test plan and design regimen. In many cases, only a few new tests will need to be performed, rather than the entire suite. A record of marginal results from the previous testing suggests a potential for failure at the more stringent testing level. Design changes made to address the relevant issues can be implemented more effectively and at a lower cost if undertaken at an early review stage.

The determination of a passing test result has changed with the new standard EN 60601-1-2, which also references new interpretations of criteria for acceptable performance. The performance criteria used to determine whether a device is immune to outside electromagnetic phenomena are often referred to as pass-fail parameters. The second edition revision was developed with the shortcomings of the earlier standard in mind—specifically, that the performance criteria had been unclearly and inadequately defined.

In the past, medical devices were considered immune to outside influence so long as the device continued to perform its intended functions as specified by the manufacturer or else failed without creating a safety hazard in the process. The second edition also allows performance degradation so long as it is considered "clinically acceptable." It provides annexes to offer general guidance and to supply a rationale for the new requirements.

The maintenance of clinical utility is the basic performance criterion for all immunity tests. Without a detailed risk analysis in place, the following failure criteria would apply by default:

• Component failures.
• Changes in programmable parameters.
• Reset to factory defaults (i.e., the manufacturer's presets).
• Change of operating mode.
• False alarms.
• Cessation of any intended operation, even if accompanied by an alarm, or initiation of any unintended operation, including unintended or uncontrolled motion, even if accompanied by an alarm.
• Error in a displayed numerical value sufficiently large to affect diagnosis or treatment.
• Noise on a waveform such that the noise is indistinguishable from physiologically produced signals or interferes with interpretation of physiologically produced signals.
• An artifact or distortion in an image such that the artifact is indistinguishable from physiologically produced signals or the distortion interferes with interpretation of physiologically produced signals.
• Failure of automatic diagnosis or treatment equipment and/or systems to diagnose or treat, even if accompanied by an alarm.

EMC Test Requirements; Emissions Testing

Figure 1. An emissions test setup.

The EN 60601-1-2 requirements are specific to two basic electromagnetic phenomena: emissions and immunity. MDD emissions requirements are specific to airborne, or radiated, emissions, and those that are conducted. These tests were specified under the first edition of the directive. Also included in the emissions section under the revision are new tests for line harmonics and voltage fluctuations. A detailed analysis of the requirements is shown in Table I, with the EN 55011 EMC emissions testing standards referenced in the standard for compliance with EN 60601-1-2. Figure 1 shows a setup for emissions testing.

Table I. EN 60601-1-2 conducted (a) and radiated (b) emissions requirements according to EN 55011. (For discontinuous disturbances, see CISPR 14.)

The purpose of testing radiated emissions is to ensure that, while the device is in operation under any operating condition, it does not generate harmful airborne electromagnetic, or radio-frequency (RF), energy that may interfere with the safe operation of any other device located near the device in question. Commonly, many electronic devices are running at the same time in close proximity. Electromagnetic emissions have been known to cause device failures or performance anomalies with the potential to create a hazardous or critical situation.

The reason for testing for conducted emissions is to ensure that no unwanted or hazardous electromagnetic or RF energy propagates through the power line that could cause another device to operate in an unsafe condition.

All medical equipment is required to be identified as Group 1 or Group 2, Class A or Class B. This necessary identification is based on the location of the equipment while it is in use and on the intended use of the device. It is important to understand that only the manufacturer can make this determination. Manufacturers should review Annex CCC of EN 60601-1-2:2001 to determine how best to classify their devices. European hospitals have long preferred that the more stringent Class B requirements be met.

As mentioned, two new emissions tests have been added to the second edition of EN 60601-1-2. They are EN 61000-3-2 for line harmonics and EN 61000-3-3 for voltage fluctuation, also referred to as flicker.

The main reason for testing in these modes is twofold. One objective is to ensure that the device under test does not send out unwanted excessive harmonic current along the power lead back to source, or to other devices that take power from the same source. These harmonics are a known cause of equipment failure.

The other objective concerns the effect a voltage fluctuation may have on other systems such as lighting. The initial current draw and cycling by a medical device may pull enough power from a circuit to cause room lighting to flicker. This phenomenon has been known to cause epileptic seizures in patients that are sensitive to such flashing light. In some instances, individuals may not know that they are susceptible to such a phenomenon until the reaction occurs.

Immunity Testing

The other basic electromagnetic phenomenon covered by EN 60601-1-2 is immunity. A series of immunity tests has been established that either is more stringent than the testing under the first edition or is newly added to the second edition. A comparison of old and new EMC testing requirements for immunity is presented in Table II.

Figure 2. An ESD test setup according to IEC 61000-4-2.

Electrostatic Discharge (ESD), IEC 61000-4-2. This test replaces the older standard IEC 801-2. The ESD test setup is shown in Figure 2. The specified procedure involves simulating the repetitive voltage strikes that would be generated by human contact, or a charge that builds up on equipment under certain other conditions. This is a cumulation test, reflecting the fact that multiple contact hits over time can cause a failure and an unsafe condition.

The new requirements provide for testing through the application of 10 actual hits, in two polarities, in positive and negative modes. New test requirements are:

• Air discharge: ±2, 4, and 8 kV.
• Contact discharge: ±2, 4, and 6 kV.

The old requirements were:

• Air discharge: ±8 kV.
• Contact discharge: ±3 kV.

Figure 3. The radiated susceptibility test according to IEC 61000-4-3.

Radiated Susceptibility, RF Electromagnetic Fields, IEC 61000-4-3. The setup for this testing sequence, which replaces the old IEC 801-3 standard, is shown in Figure 3. The test simulates the effect of unwanted airborne electromagnetic phenomena that could affect the safe operation of a device, for example, as caused by the use of a cell phone or walkie-talkie close to the device.

The new standard IEC 61000-4-3 increases the high end of the frequency range to 2.5 GHz, up from 1 GHz, and increases the low end of the frequency range from 27 to 80 MHz. Also, it adds a field-strength differentiation between medical devices that are used in life-support applications and those that are not. Life-support devices are now required to meet a 10-V/m field severity level, while devices not used for life support must tolerate a 3-V/m field, as was the case with the old standard.

Any device that is tested under these conditions must continue to operate safely, with its performance essentially unaffected.

Figure 4. The electrical fast transient test setup according to IEC 61000-4-4.

Electrical Fast Transients and Burst, IEC 61000-4-4. This test replaces the old IEC 801-4 requirements. Figure 4 shows the setup. The test simulates the effect of unwanted conducted electromagnetic energy that can come from a variety of sources, such as the electrical arcing of contacts, and could be induced in the power and signal lines of the medical device. It stipulates that the device under test shall continue to operate safely and maintain the essential performance identified by the manufacturer for intended operation and use.

New requirements under IEC 61000-4-4 are the following:

• ±2 kV for ac and dc power lines.
• ±1 kV for signal and interconnecting cables.
• 5-kHz repetition rate.

The old requirements were:

• ±1 kV for a detachable wall power plug.
• ±2 kV for permanently installed equipment.
• ±0.5 kV for input/output (I/O) lines longer than 3 m.

Testing is to be performed at minimum and maximum input voltages.

Figure 5. Testing for voltage surge according to IEC 61000-4-5.

Voltage Surges, IEC 61000-4-5. Replacing IEC 801-5, this test deals with the potential for an indirect lightning strike on the power signal lines. The old requirement had levels of 1 kV differential mode (DM) and 2 kV common mode (CM). No testing was required for I/O cables. The new requirement (see Table II) calls for additional surge testing if surge protection is in place. The test is depicted in Figure 5.

Conducted-RF Immunity, IEC 61000-4-6. This test simulates an RF wave from a transmitter coupling into a product via the power leads or signal leads. It was not required by the original version of standard EN 60601-1-2. The new test establishes the required frequency range of 150 kHz to 80 MHz and provides for two different field severity levels, depending on the application. Medical devices deemed life-support apparatus are required to meet a 10-V-rms standard, while other devices not used in critical situations must meet only a 3-V-rms requirement.

Figure 6. Testing for conducted RF immunity according to IEC 61000-4-6.

The test setup for conducted-RF immunity testing appears in Figure 6.

Magnetic Field, IEC 61000-4-8. This standard did not exist in the first edition of EN 60601-1-2. The test simulates the effects caused by a magnetic (H) field derived from sources such as power lines, transformers, or motors. The setup for testing is shown in Figure 7. It requires devices, equipment, or systems to be subjected to an H field of 3 A/m at 50 Hz and again at 60 Hz if the device is rated for both frequencies. In the event the device is rated for one frequency only, testing at that frequency only needs to be performed.

Figure 7. Testing for magnetic-field immunity according to IEC 61000-4-8.

This test has turned up failures in equipment that contains magnetically sensitive components such as Hall-effect devices or bimetal switches. Special care must be taken to properly shield such components from magnetic fields. The acceptance criterion for this test is that the device, equipment, or system must maintain an essential performance level and operate safely.

Voltage Dips, Interruptions, or Variations, IEC 61000-4-11. This standard also did not exist in the first edition. It applies to devices, equipment, or systems that have an input-current rating of 16 A per phase or less. The test deals with the ability of the device under test to operate in the event the input voltage is changed or cut off during operation. Testing requirements are itemized in Table II.

Figure 8. Testing for voltage dips, interruptions, or variations according to IEC 61000-4-11.

In the event the device fails during the test, its essential performance must be maintained, and continuing operation must be safe. If the device requires repairs on a malfunctioning component, a fuse for example, requires replacement, the test result would be classified as fail. If the device stops functioning during the test, it must be restorable to pretest conditions through an intervention such as reset switch, or must be able to be turned back on, in either case with no loss of data. The test apparatus for IEC 61000-4-11 is shown in Figure 8.

Additional Requirements

Also identified in the second edition of the standard are new and updated requirements for documentation. The following types of documentation should be reviewed with respect to devices already in the field and updated if necessary, and should be instituted for all new and future products.

• Documentation detailing that equipment accessories, transducers, cables, and cable lengths remain in compliance with emissions and immunity requirements.
• A standardized table showing that the emissions/immunity test plan was carried out.
• For equipment used inside shielded rooms only, a clear definition of emissions characteristics of other equipment that may be allowed in close proximity and a statement of the assumed shielding effectiveness.
• Specific operating parameters of equipment using radio receivers.
• A comprehensive table setting the immunity performance and recommended separation distance for various types of radio transmitters.

A number of standards for medical-related equipment have been published as Part 2 of each of the standards in the IEC/EN 61010 series covering laboratory, measurement, and control equipment harmonized under the Low Voltage Directive (LVD; 73/23/EEC). These contain particular requirements for autoclaves, sterilizers, and steam disinfectors used in the medical, pharmaceutical, and veterinary fields.

Some standards under the MDD are focused on such non-equipment-related requirements as those for quality systems. For example, EN/ISO 13485 and 13488 are replacing the previous EN 46001, 46002, and 46003. Compliance via notified body audit to the appropriate standards, as well as to the appropriate annexes of the MDD, determines the degree of freedom that a manufacturer may exercise in the conformity assessment and certification of equipment for use in Europe.

Not all medical devices are within the scope of the MDD. In vitro diagnostic (IVD) medical devices must comply with the IVD Directive (IVDD; 98/79/EEC). Directive 90/385/EEC covers active implantable medical equipment, such as pacemakers, internal insulin pumps, and implanted drug delivery systems. The latter was the first so-called new-approach directive—that is, one requiring CE marking—applicable to medical devices.

The recently published international standard IEC 61010-2-101 (January 2002) covers IVD equipment. Although an EN equivalent has not yet been released, it is anticipated that this standard will be referenced to the IVDD as well as the LVD.

Conclusion

The general compliance trend for medical products sold in Europe presents manufacturers with a good news–bad news scenario. On one hand, specific requirements for a vast array of medical products and systems are better defined and more flexible than those under the earlier directive published years ago. On the other, these refinements, additional requirements, and a plethora of associated standards make the compliance process more confusing to navigate. This is especially true for companies just entering the CE arena.

Each EU member state is empowered to enforce compliance with the laws deriving from the medical device directives. For medical products to be marketed legally in Europe, all applicable requirements must be met. The addition of new test requirements obliges companies selling new medical devices in EU countries to be aware of the details of the updated directive. Those companies must even determine whether products currently on the market can still be sold without additional testing or, possibly, redesigned to ensure their compliance with the new standards.

Reference

1. IEC 60601-1-2:2001, "Medical Electrical Equipment—Part 1: General Requirements for Safety—Section 2: Collateral Standard—Electromagnetic Compatibility—Requirements and Tests" (Geneva: International Electrotechnical Commission, 2001).

Jack Black is the business development manager at D.L.S. Electronic Systems Inc. (Wheeling, IL). He can be reached at jblack@dlsremc.com.

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