Electromagnetic compatibility (EMC) requirements for medical devices and systems is defined by IEC 60601-1-2. The fourth edition implementation of this EMC standard is on the horizon and is a collateral standard to the IEC 60601-1 medical safety standard. It was issued by the International Electrotechnical Commission (IEC) in February 2014. FDA has deferred compliance for new products from April 1, 2017 to the end of 2018, and the EN 60601-1-2:2007 3rd edition withdrawal date is December 31, 2018. It is expected that the fourth edition EMC standard will be in effect in the EU on or before this date.
There are important changes and additions medical device manufacturers need to know. The category of Risk Management is expanded and the Life Supporting category has been removed. In addition, these new categories have been introduced: Professional Healthcare Facilities, Home Healthcare, and Special Environments. The new edition has significant impact on the medical industry for product design, testing, and documentation. Also, immunity requirements have increased and new requirements added.
This article discusses the significant differences between the third and fourth editions of the EMC standard and how components such as power supplies used in the medical equipment are impacted by the new standard.
The risk management process, now part of the IEC 60601-1-2, 4th edition, requires assessment of “risk resulting from reasonably foreseeable electromagnetic disturbances.” This is an additional entry into the medical device risk management file. The term safety is defined to mean “freedom from unacceptable risk as defined in ISO 14971. Basic safety and essential performance are included within this definition of safety”. 2 The risk management file may need reference to technical rationale, calculations verification plans, and test data. Simply testing at the higher immunity test levels is not sufficient to achieve safety. ISO 14971:2007 includes the following requirements: General requirements for risk management, risk analysis, risk evaluation, risk control, evaluation of overall residual risk acceptability, risk management report, and production and post-production information. The details of these requirements are described in the IEC 60601-1-2, 4th edition standard. Figure 1 shows an outline of how this IEC 60601-1-2, 4th edition standard links to the risk management file.
In discussing the impact and experience of implementing this standard with medical device manufacturers, there is a significant impact in the pretest planning and report generation. There seems to be a consensus that the largest impact is on the initial implementation and setting up the process, plans, and report templates.
This article does not go into detail of this EMC standard, but rather outlines the major changes in the IEC 60601-1-2, 4th edition and provides a comparison to the third edition standard. Although this is a medical device or system level standard, components such as power supplies can play an important role in aiding in system level compliance. Areas where power supplies may be impacted by this standard and the changes to the standard are stressed.
The fourth edition requires clear pass/fail criteria prior to testing. This is linked to the “Essential Performance and Basic Safety” outlined in the risk management file. A test plan is required that includes what is to be monitored in the equipment during testing. There are increased test levels for the immunity requirements. There are new immunity requirements added that take into consideration the effects from radiofrequency (RF) wireless communications equipment as detailed in Table 9 of the standard. These are not all encompassing; medical device manufactures need to take into account other possible sources of interference that may affect their equipment. The electromagnetic immunity requirements are detailed in tables 4 through 9 of the standard.
Immunity Requirement Changes and Comparison to Third Edition. Tables 1, 2, and 3 in this article (tables 4, 5, and 6 in the standard) list only the requirements that are different from the third edition and do not list all of the immunity requirements due to the space limitation for this article. Refer to the standard for the complete listing and details on the note references.
Applicable to all the enclosure ports, the immunity requirements are defined in Table 4 of the standard. The electrostatic discharge (ESD) and RF electric fields’ immunity are the most significant changes, where the input power supply plays a critical role. For ESD, the discharge potential is between the point of application of the ESD and earth ground. This places high voltages across isolation barriers in the power supply, which arc and can cause damage to the power supply or malfunction of the system if not designed properly.
External radiated electromagnetic fields may cause the output voltage to shift or oscillate if not designed for these increased levels of interference. To eliminate the influence of the higher RF EM fields, design changes may be needed. Additional components or PCB trace spacing or increased insulation are often the consequence. Additional shielding or RF decoupling may also be necessary.
Immunity requirements of the device’s AC input ports are defined in Table 5 of the standard. There are some additional requirements for half cycle drop-outs needing to be tested at various phase angles and a full line cycle dropout. There is the deletion of the 40 percent nominal AC mains operations. However, given that the third edition is still used and will continue to be in some countries for years to come, it is advisable to verify whether this condition is needed for the application.
DC output ports changes are listed in Table 6 in the standard. For an external power supply, this applies to the DC output cables as they are connected to the medical device’s DC input port.
Tables 7 and 8 of the standard (not shown, see the standard) apply to patient coupling ports and signal input and output ports. With the higher ESD voltage levels, spacing and insulation requirements also increase to meet this standard. What once passed the third edition requirements may now result in arcing and malfunction or damage to components and circuitry. These changes create increased challenges to reduce product size.
Table 9, not shown here due to its complexity, specifies 15 test frequencies for seven different frequency bands. Significant analysis and test time will be needed during development to verify compliance to these requirements. Also, not all 15 test frequencies apply, but rather are application specific. For that reason, understanding the application will be an important part of this assessment.
The IEC 60601-1-2, 4th edition will be required in the United States by December 31, 2018 as is the EU EN 60601-1-2:2015 implementation. Implementation throughout the globe will occur at different times, so consideration to both third and fourth editions may be necessary. There are significant changes that require testing to verify compliance. Some fourth edition requirements are not backward compatible with the third edition. Tests are system-level requirements. However, the power supply is an important part of the system to achieve compliance. SL Power Electronics has and continues to support medical applications with products designed to meet the new fourth edition requirements.
This article was written by Lorenzo Cividino, Director, Global Applications & Support, for SL Power Electronics (Ventura, CA). For more information, Click Here .