New Medical Device EMC Requirements

Implementation of IEC 60601-1-2, 4th edition is on the horizon. This collateral standard to the IEC 60601-1 medical safety standard specifies the electromagnetic compatibility (EMC) requirements for medical devices and systems. The fourth edition was issued by the International Electrotechnical Commission (IEC) in February 2014. The FDA is requiring compliance for new products after April 1, 2017, and in Europe, the EN 60601-1-2:2007 3rd edition withdrawal date is currently set for December 31, 2018. It is expected that the EN 60601-1-2:2015 (4th) edition will be in effect in the EU before that date.

Fig. 1 – Shown is Table 4 Enclosure Port.

Notable in the 4th edition is that risk management is expanded. In addition, the “Life Supporting” category has been removed, and the introduction of “Professional Healthcare Facilities”, “Home Healthcare”, and “Special Environments” have been added. The new edition has significant impact to the medical industry in terms of product design, testing, and documentation. Immunity requirements have increased and new requirements added.

This article does not go into detail about 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 emphasized.

Changes

Fig. 2 – Shown is Table 5 - Input AC Power Port.

The new 4th edition EMC standard better harmonizes with the risk concepts and basic safety. Life-support equipment is no longer referenced; rather, emphasis is made for the Risk Management File (RMF) and the expectation of the medical equipment to provide Basic Safety and Essential Performance without being interfered by or interfering with other equipment in the electromagnetic environments in which they are intended to be used. With more and more electronics in medical equipment and wireless devices expanding in the marketplace, ensuring proper function of devices like infusion pumps, electrocardiograms (ECGs), defibrillators, pacemakers, electrical surgical equipment, and other devices is paramount.

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 which includes what is to be monitored in the equipment during testing. There are increased test levels for the immunity requirements. There are also new immunity requirements that take into consideration the effects from radio frequency (RF) wireless communications equipment as detailed in Table 9 of the standard. These are not all encompassing as the medical device manufacturers 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.

Fig. 3 – Shown is Table 6 - Input DC Power Port.

Immunity Requirement Changes and Comparison to 3rd edition

Tables 4 to 8 of the standard list only the requirements that are different compared to 3rd edition and do not list all the immunity requirements due to the space limitation for this article. Refer to the complete standard for the full listing. Fig. 1 shows Table 4 from the standard and provides the immunity requirements applicable to all the enclosure ports. The most significant changes where the input power supply plays a role are in the Electrostatic discharge (ESD) and RF electric fields immunity. The path to ground from an ESD may be through the power supply. Given that the power supply is to provide isolation from the AC utility, and in many cases from ground, the high voltage discharge can discharge inside the power supply and disrupt the output or even cause permanent damage. The increased RF electromagnetic (EM) fields may cause the output voltage to change or oscillate if not designed for these levels of interference. Design changes may be needed to ensure the power supply will perform properly under these conditions. Additional component or PCB trace spacing or increased insulation may be needed. Additional shielding or RF decoupling may also be necessary.

Fig. 4 – Shown are Table 7 - Patient Coupling Port and Table 8 - Signal Input/Output Parts (SIP/SOPS) Port.

Figure 2 shows Table 5, which focuses on the device’s AC input ports. Here, more detailed investigation of AC mains distribution at different phase angles is added as well as a full line cycle drop out. One area that is less stringent is the omission of the 40% 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 prudent to continue to plan for this condition.

Figure 3, which shows Table 6, addresses changes to the DC input ports. For an external power supply, this applies to the DC output cables as they are connected to the medical device’s DC input port.

Figure 4, showing Tables 7 and 8, apply to patient coupling ports and signal input and output ports. The increased ESD requirements can challenge designers as they reduce the product size and spacing between components. What once may have easily passed the 3rd edition requirements may now result in arcing and malfunction or damage to components and circuitry.

Fig. 5 – Here is an example of external power supplies that adhere to the 4th edition Medical EMC standard and protect home healthcare devices with Class B EMI and Class I & II wide range AC input.

Figure

Table 9, not shown here due to its complexity, specifies 15 test frequencies for seven different frequency bands. The carrier frequency may be pulse modulated or FM modulated and the maximum power level varies from 0.2 watts to 2 watts depending on the test band. Immunity levels are as high as 28 Volts/Meter albeit at a 0.3 meter distance. This new requirement will add significant test time and analysis during product development. The risk management should determine which services are applicable in the application or device.

Summary

The IEC 60601-1-2, 4th edition will be required in the US in the second quarter of 2017 and is expected in the European Union in 2018. Implementation throughout the globe will occur at different times so consideration to both 3rd and 4th edition is needed. There are significant changes which 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. (See Figure 5)

This article was written by Lorenzo Cividino, Director, Field Technical Support, SL Power Electronics, Ventura, CA. For more information, Click Here .