EMC Standards
Stricter EMC Requirements in Store for Electrical Medical Devices
A new electromagnetic compatibility (EMC) standard for electrical medical devices will impose more-stringent requirements on products before being placed on the market.
Dan Hoolihan
The International Electrotechnical Commission (IEC) released a new international standard regarding the EMC characteristics of electrical and electronic products in July 2001. In January 2002, the Association for the Advancement of Medical Instrumentation (AAMI) in conjunction with the American National Standards Institute (ANSI) adopted and published the new international standard in the United States. It is anticipated that the European Union will adopt it in the third quarter of 2002.
IEC 60601-1-2:2001, "Medical Electrical Equipment—Part 1-2: General Requirements for Safety—Collateral Standard—Electromagnetic Compatibility—Requirements and Tests," is the second edition and updates the previous version of the same international document, which was released in 1993. The standard reflects the real-world environment of medical devices, both for emission criteria and for immunity criteria.
This article provides an overview of the changes. Table I shows a comparison of the EMC test requirements for different types of medical equipment.
|
Test
|
Medical
Devices IEC 60601 1-2 (1993)
|
Medical
Devices IEC 60601 1-2 (2001) Non-Life-Supporting
|
Medical
Devices IEC 60601 1-2 (2001) Life Supporting
|
Comments
on Updates
|
| Emissions | ||||
| Emissions | CISPR
11 Class A (high-frequency [HF] apparatus/special cases) Class B (most devices) |
CISPR
11 Class A (HF apparatus/special cases) Class B (most devices) |
CISPR
11 Class A (HF apparatus/special cases) Class B (most devices) |
CISPR 14 may be required if the product uses only simple components (i.e., motors and switches). |
| Harmonic Distortion | Not applicable | IEC/EN
61000-3-2 Applicable per the standard |
IEC/EN
61000-3-2 Applicable per the standard |
New requirement—may impact power supply design. |
| Voltage Fluctuations | Not applicable | IEC/EN
61000-3-3 Applicable per the standard |
IEC/EN
61000-3-2 Applicable per the standard |
New requirement—may impact power supply design. |
| Immunity | ||||
| Electrostatic Discharge (ESD) | IEC
801-2 8 kV air / 3 kV contact |
IEC/EN
61000-4-2 2, 4, and 8 kV air / 2, 4, and 6 kV contact Positive and negative voltages |
IEC/EN
61000-4-2 2, 4, and 8 kV air / 2, 4, and 6 kV contact Positive and negative voltages |
Contact discharge requirement has doubled; may impact cabinet design. |
| Radiated E-Field | IEC
801-3 26 MHz–1 GHz, 3 V/m 80%, 1 kHz or significant signal passband, swept for life-support equipment. ISM frequencies for non-life-support equipment 1 V/m shielded room equipment |
IEC/EN
61000-4-3 80 MHz–2.5 GHz, 3 V/m 80% amplitude modulation; Physiological device: 2 Hz; All other devices: 1 kHz |
IEC/EN
61000-4-3 80 MHz–2.5 GHz, 3 V/m 80% amplitude modulation; Physiological device: 2 Hz; All other devices: 1 kHz |
Frequency range increased from1 GHz to 2.5 GHz. Required field strength has increased for life-supporting equipment. This also may impact shielding and filtering design elements. |
| Electrical Fast Transient/Burst | IEC
801-4 Removable mains plug: 1 kV Permanent mains plug: 2 kV Interconnecting lines > 3 m: 0.5 kV |
IEC/EN
61000-4-4 Ac/dc power ±2 kv Input/output lines: ±1 kV (signal/control lines > 3 m) |
IEC/EN
61000-4-4 Ac/dc power ±2 kv Input/output lines: ±1 kV (signal/control lines > 3 m) |
Amplitude requirement has doubled. This may impact cable shielding and power-line filtering. |
| Surge | IEC
801-5 Differential mode: 1 kV Common mode: 2 kV |
IEC/EN
61000-4-5 Differential mode: ±0.5 kV and ±1 kV Common mode: ±0.5 kV, ±1 kV, and ±2 kV |
IEC/EN
61000-4-5 Differential mode: ±0.5 kV and ±1 kV Common mode: ±0.5 kV, ±1 kV, and ±2 kV |
All voltage steps (levels) must be tested up to the maximum level. |
| Conducted Radio Frequency (RF) | Not applicable | IEC/EN
61000-4-6 0.15–80 MHz, 3 V (rms), 80% amplitude modulation; Physiological device: 2-Hz modulation All other devices: 1-kHz modulation |
IEC/EN
61000-4-6 0.15–80 MHz, 3 V (rms), (outside ISM* bands) 0.15–80 MHz, 10 V (rms), (in ISM* bands) 80% amplitude modulation; Physiological device: 2-Hz modulation All other devices: 1-kHz modulation |
New
requirement—may impact power-line filtering and signal cable shielding
and filtering. *ISM — Industrial, Scientific, and Medical |
| Magnetic-Field Power Frequency (50/60 Hz) | Not applicable | IEC/EN
61000-4-8 Power frequency: 50 Hz and/or 60 Hz Level 3 A (rms)/m Only applicable to apparatus containing devices susceptible to magnetic fields |
IEC/EN
61000-4-8 Power frequency: 50 Hz and/or 60 Hz Level 3 A (rms)/m Only applicable to apparatus containing devices susceptible to magnetic fields |
New requirement—may impact video display units and shielding design may need to be strengthened. |
| Voltage Dips | Not applicable | IEC/EN
61000-4-11 >95% for 0.5 cycle 60% for 5 cycles 30% for 25 cycles |
IEC/EN
61000-4-11 >95% for 0.5 cycle 60% for 5 cycles 30% for 25 cycles |
New requirement—may impact power supply design. |
| Voltage Interruptions | Not applicable | IEC/EN
61000-4-11 >95% for 5 seconds |
IEC/EN
61000-4-11 >95% for 5 seconds |
New
requirement—may impact power supply design. **Equipment must remain safe during and after the voltage interruption. |
| Immunity Pass-Fail Criteria | Equipment passes if it continues to operate according to manufacturer’s specifications or it fails in a manner that doesn’t create a safety hazard. | A device must maintain its essential performance and remain safe under test conditions. | A device must maintain its essential performance and remain safe under test conditions. | More-stringent pass-fail criteria in 2nd edition of standard. |
| Table I. Comparison of the EMC test requirements for medical device equipment. | ||||
Pass-Fail Determination
One of the key new elements of the standard is the pass-fail determination relative to the immunity tests. The new requirements state that a device should "maintain its essential performance and remain safe" under the applied immunity tests. The standard itself states, " …this second edition of IEC 60601-1-2 departs from the first edition by establishing a minimum baseline of performance in the presence of expected levels of electromagnetic disturbance." The first edition allowed a product to fail, under an applied electromagnetic disturbance, as long as it failed safely (i.e., shut down without injuring the patient). This condition is no longer allowed under the new standard.
Added Immunity Tests
The standard also added immunity tests such as conducted-radio-frequency (RF) immunity testing, magnetic-field immunity testing, and voltage-variation immunity testing.
The conducted-RF immunity testing is based on the IEC 61000-4-6 EMC standard, "EMC—Part 4—Testing and Measurement Techniques—Section 6: Immunity to Conducted Disturbances Induced by Radio-Frequency Fields." This test couples either a 10- or a 3-V rms signal to all cables (with some selected exceptions) entering the equipment. The 10-V rms level is applied for life-supporting equipment in the industrial, scientific, and medical (ISM) frequency bands, and the 3-V rms level is applied to non-life-supporting equipment and all non-ISM frequencies for life-supporting equipment. The signals are also modulated with an 80% amplitude modulation (AM) at an appropriate modulation frequency (usually 2 Hz or 1 kHz), which increases the severity of the test. In general, the RF frequencies are swept from 150 kHz to 80 MHz, although the starting frequency may vary with some special products.
The magnetic-field immunity test is intended to check the immunity of products to power-line-frequency magnetic fields. The fields are applied as a continuous field at a level of 3 A/m. The frequency of the applied magnetic field must be the same as the power-line frequency that energizes the product under test, that is, either 50 or 60 Hz. If the product can be powered by either frequency, it must be tested at both frequencies. Also, if the equipment or system is internally powered or powered from an external direct-current (dc) supply, then it must be tested at both 50 and 60 Hz. The magnetic-field immunity test is based on IEC 61000-4-8, "EMC—Part 4: Testing and Measurement Techniques—Section 8: Power Frequency Magnetic Field Immunity."
The voltage-variation immunity test is called "voltage dips, short interruptions, and voltage variations on power supply input lines." The criteria for this voltage-variation immunity testing apply to all life-supporting equipment and systems as well as non-life-supporting equipment with a rated input power of 1 kVA or less. Non-life-supporting equipment with rated input power >1 kVA has special requirements, which are detailed in the standard. A voltage dip of 95% must be successfully endured for half a period of applied power, a dip of 60% must be endured for 5 periods, and a dip of 30% must be endured for 25 periods.
In addition, a voltage interruption of greater than 95% must be successfully overcome for a duration of 5 seconds. The standard does allow a deviation from some of the standard compliance criteria for the voltage interruption provided the equipment remains safe, the equipment experiences no component failures, and the equipment is restorable to the pretest state with operator intervention.
Life-supporting equipment that uses this deviation allowance must provide an alarm to notify personnel that the intended function has ceased. This series of voltage-variation tests is extracted from the basic EMC standard, IEC 61000-4-11, "EMC—Part 4: Testing and Measurement Techniques—Section 11: Voltage Dips, Short Interruptions, and Voltage Variations Immunity Tests."
More-Stringent Immunity Requirements
The second edition of the medical device EMC standard adds requirements to the electrostatic discharge test. The contact discharge criteria changed from a two-step routine (2 and 3 kV) to a three-step test of 2, 4, and 6 kV. This was changed to reflect a more real-life environment of electrostatic discharges. It is interesting to note that the air-discharge levels remained at the same high levels of 2, 4, and 8 kV. All voltage levels are tested at plus and minus values of the indicated amplitude.
In addition, increased test levels and a changed frequency range were added to the radiated-RF electromagnetic fields test. For non-life-supporting equipment, the requirement for field strength remains the same at 3 V/m; however, the frequency range changed from the previous 26–1000 MHz to the revised range of 80–2500 MHz. The 26–80 MHz range was deleted because of the addition of the conducted-RF test described previously. The frequency range 1000–2500 MHz was added to reflect the growing use of that frequency range by wireless communications devices, including cell phones and plug-in cards for personal computers using wireless-fidelity (Wi-Fi) technologies.
Life-supporting equipment must comply with a level of 10 V/m over the new frequency range of 80–2500 MHz. For both types of equipment, the applied signals are AM with either a 2-Hz or a 1-kHz modulation frequency.
The electrical-fast-transient test requirements have also changed from the first edition; the standard now requires devices to meet a ±2-kV transient on all power lines rather than the earlier and lower value of ±1 kV. Signal and interconnection cables are tested to ±1 kV, which is twice the amplitude allowed in the earlier edition of this standard. Signal and interconnecting cables less than 3 m in length and all patient-connected cables are not tested directly.
Added Emissions Requirements
The second edition of the standard applies harmonic distortion criteria and voltage fluctuations to the emissions criteria for the first time. The harmonic distortion is based on IEC 61000-3-2, "Limits for Harmonic Current Emissions (Equipment Input Current <16 Amps Per Phase)."
The voltage fluctuations criteria will be based on IEC 61000-3-3, "Limitation of Voltage Fluctuations and Flicker in Low-Voltage Supply Systems for Equipment with Rated Current <16 Amps Per Phase." Both of these added requirements might necessitate some changes to existing power-supply configurations in medical electrical equipment.
Some Requirements Unchanged
The voltage-surge immunity requirements stayed the same in the new standard; however, the revised standard clearly points out that the lower voltage-surge levels (at both plus and minus values of the voltage) must be tested in addition to the maximum voltage level. The conducted- and radiated-emission requirements stayed the same, and they continue to reference CISPR 11, "Limits and Methods of Measurement of Radio Disturbance Characteristics of Industrial, Scientific, and Medical (ISM) Radio-Frequency Equipment" for the basic emission criteria.
Conclusion
IEC 60601-1-2, the second edition of the international standard on EMC requirements for medical devices was released in mid-year 2001. In the United States, the Food and Drug Administration will accept test results to the new standard to show compliance with EMC engineering criteria. It is anticipated that the European Union will adopt this standard in the third quarter of 2002.
The standard, which imposes new requirements on electro-medical devices, will affect the design and testing of new products. It will also force manufacturers to review existing designs to determine whether they will continue to market their present products in the EU after the adoption date of the new standard.
This article covers only the highlights of the new standard. For further details on the standard and its detailed criteria, it is critical for manufacturers to read the nearly 100-page document in its entirety or, at the very least, read the selected portions focusing on a given project.
Dan Hoolihan authored this article on behalf of TÜV America (New Brighton, MN). He was formerly vice president for TÜV America. For more information, contact Mark Romanowski at 978-739-7015.
Copyright © 2002 Medical Electronics Manufacturing
