The fourth edition electromagnetic compatibility (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 interfering with or being interfered by other equipment in electromagnetic environments in which they are intended to be used. With more electronics in medical equipment and wireless devices expanding in the marketplace, ensuring proper function of 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. The standard requires a test plan, which includes what is to be monitored in the equipment during testing. This edition increases test levels for immunity requirements and lists new immunity requirements for radio frequency (RF) wireless communications equipment effects.
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 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. The power supply provides isolation from the AC utility, and in many cases from ground, so high voltage discharge inside the power supply could disrupt output or cause permanent damage. 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 that the power supply will perform properly under these conditions. Additional component or printed circuit board (PCB) trace spacing or increased insulation may be needed. Additional shielding or RF decoupling may also be necessary.
The following tables list the requirements that are different compared to the third edition.
AC/DC input ports; Coupling ports; signal input/output ports
More detailed investigation of AC mains distribution at different phase angles is added to the fourth edition of IEC 60601-1-2 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. For an external power supply, this applies to the DC output cables as they are connected to the medical device’s DC input port.
The increased ESD requirements can challenge designers as they reduce the product size and spacing between components. What once may have easily passed the third edition requirements may now result in arcing and malfunction or damage to components and circuitry.
The new requirements outline 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 0.2W to 2.0W, depending on the test band. Immunity levels are as high as 28V/m albeit at a 0.3m distance. This new requirement will add significant test and analysis time during product development. The risk management department should determine which services are applicable in the application or device.
The IEC60601-1-2 fourth edition will be required in the U.S. 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 third and fourth 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 and tests are system level requirements. However, the power supply is an important part of the system to achieve compliance.
SL Power Electronics