Medical Electronics


Make sure your power supply meets the latest medical EMC requirements


Designing medical electrical equipment can be challenging enough; designing it to meet the required safety standards adds a whole extra layer of complexity. This is especially true when safety standards evolve and new revisions are introduced. While no one would argue with the need to ensure medical equipment does not pose a risk to patients or operator, the time and effort needed to achieve compliance can be a burden for manufacturers. Jeff Schnabel, VP of Global Marketing, CUI Inc, will look at the latest medical standard that deals with electromagnetic compatibility (EMC) requirements in medical environments


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Medical environments impact EMC considerations


one are the days when medical equipment was confined to hospitals and the use of mobile phones within hospital walls was banned. Today’s proliferation of wireless communication devices now includes smart watches, fitness trackers, tablet computers and e- readers, along with longer-established mobile phones and laptop computers. Restricting the use of these in hospital environments is all but impossible, aside from which, many of these same devices are actually deployed by


medical staff to monitor and observe patient information. Consequently, the design of medical electrical equipment now needs to pay attention to the potential issues that can arise due to RF interference from such sources. Equally, equipment should be designed to ensure that it too is not a source of interference. Achieving this reciprocal immunity from interference between medical electrical equipment and other electronic devices operating in the same environment is the primary aim of the revisions contained in the 4th edition of IEC 60601-1 or, more accurately, its collateral standard IEC 60601-1-2.


The collateral standard deals with this by defining three “intended use environments”: the classification professional healthcare facilities includes hospitals, medical treatment centres, and dental offices, or essentially anywhere where professional medical staff are present; home healthcare covers residential locations where equipment will be operated by non-specialist users and where electrical supplies may be less stable; “Special” environments is a category that recognises locations subject to high levels of electromagnetic disturbance, e.g. radio-therapy equipment or in the presence of industrial electrical machinery. Coupled with its more rigorous


treatment of EMC, the 4th edition of IEC 60601-1 further develops the risk management process introduced by the 3rd edition of the standard. This requires manufacturers to engage with test laboratories to ensure that the risk analysis they have undertaken reasonably anticipates potential EMC disturbances, which can be taken account of during compliance testing.


The 4th edition also defines new immunity test procedures and sets more stringent test thresholds, as illustrated by some of the key test criteria detailed in figure 1.


Power supplies are affected by changes to IEC 60601-1 IEC 60601-1 does not directly define specific requirements for the safety and performance of power supplies. However, a power supply is an integral part of medical electrical equipment and thus its operation will have a bearing on the safety and performance of that equipment. Consequently, the design of medical equipment has to embrace the characteristics of the power supply. As noted earlier, the 2nd and 3rd editions of the standard first focused on safe operation of equipment within the vicinity of the patient and then on the means of protecting both patient and operator. Essentially this meant protection from potentially hazardous voltages by way of electrical isolation and creepage limits, and methods of insulation. Correctly understanding which of


these requirements must be met is vital. No one wants to over-engineer their design as this will almost certainly lead to additional costs. On the other hand, having to remedy a design that subsequently fails qualification will result in similar engineering costs and the potential losses incurred from any delay in getting the product to market. The tougher EMC immunity


Figure 1: Changes in key immunity test levels between the 3rd and 4th editions of IEC 60601-1 32 December 2017/January 2018 Components in Electronics


requirements dictated by the 4th edition of IEC 60601-1 poses a similar predicament; over-engineer and get it right first time, or take longer to fine-


tune the design accepting this may require extra test-qualification cycles. This is where an equipment maker may simply want to acknowledge that its system designers are not power supply experts and that the better option would be to procure power supplies that have been specifically developed to meet IEC 60601-1 edition 3.1 safety requirements and 4th edition EMC criteria to simplify the qualification process.


Preparing for compliance with IEC 60601-1 4th edition The adoption of IEC 60601-1 through its various editions has not been uniform around the globe. While the 3rd edition applies in most regions (with edition 3.1 current in the US, Canada and Brazil), there are some countries, notably China, which still only enforce the 2nd edition. For the 4th edition, the US, Canada and Europe have agreed to the common date of January 1, 2019 for its introduction. Other countries will inevitably follow suit but any manufacturer in those countries wishing to export medical electrical equipment to the US, Canada and Europe will also need to align their production to the January 2019 timeline.


Summary


Compliance with product standards is an inevitable consequence of the increasing globalisation and a greater focus on safety. Keeping up with these requirements is a continuing challenge, not just in ensuring new designs meet the latest criteria but also ensuring that existing equipment designs are kept up-to-date or phased out at the appropriate time Standards like IEC 60601-1, which applies to the safety and performance of medical electrical equipment, are complex and affect many aspects of an equipment’s design, not least its power supply. Adopting a pre-certified power supply does not excuse a manufacturer from equipment compliance testing but it will alleviate many potential sources of problems affecting both basic safety and performance, as defined by earlier editions of the standard and the latest EMC immunity requirements.


The embedded and external medical power supplies offered by CUI range from 6 watts to 300 watts. These fully comply with IEC 60601-1, achieving the two MOPP performance required by edition 3.1 and the EMC requirements specified in the 4th edition’s 60601-1-2 collateral standard. This makes these medical grade power supplies from CUI an ideal solution for simplifying the compliance process of medical device design.


www.cui.com www.cieonline.co.uk


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