Among the many sites and publications I follow (yes, even in print) is Medical Design Briefs, since so much or today’s electronic design (hardware and software) is related to that arena, ranging from personal, wearable medical devices all way up to “big” items such as MRI, CAT scanner, and X-ray systems. (The publication also gives insight into mechanical and materials issues which also critical to overalls system implementation.)
Of course, each class of product has its own unique set of design challenges -- no need to spell them out here, of course -- but all have one thing in common: they must meet a multiplicity of regulatory mandates related to patient safety, user safety, EMC (EMI/RFI), and more. These are all in addition to their basic medical function and objectives. For example, Apple’s Watch Series 4, announced in mid-September, also received FDA clearance for both an atrial fibrillation-detecting algorithm and an ECG function, see “Apple unveils Watch Series 4 with FDA-approved ECG.”
I knew that the regulatory strictures were extensive, but had no idea of how much so until I saw the article, “EMC for Medical Devices: EN/IEC 60601-1-2, 4th Edition.” It’s timely because the identified standard formally goes into effect in Europe and the U.S. on Dec 31, 2018, after several years of preview.
Looking at the article and the issues it raises, my thoughts were along these lines: a) it’s extraordinarily complicated; b) you need a committee of lawyers who are also degreed engineers at every design review; c) you need some major consulting help to understand the requirements; and d) you need some sophisticated test labs and specialists to help you set-up the certification tests and execute them.
All this is necessary, I suppose, for both safety and maintaining the integrity of the broader electromagnetic environment. Still, depending on your perspective, all these mandates can either be a supreme engineering challenge, or a major engineering impediment to getting a product released in reasonable time. It’s especially daunting so since, depending on the product function and classification, almost even most small changes must be fully documented, the effects noted, tested, verified, and so on; often, the entire approval sequence and process must be repeated. The “ripple effect” is significant when doing almost anything other than something “trivial,” such changing the color of the user panel. Even the humble AC power-line cord must meet rigorous standards.
There are also mandates on the power supply, of course. If you have a small, battery-powered device, you’re in a much better position than if you connect to the AC line or use higher DC voltages (even if from a battery stack). That may be one of the incentives pushing designers to low-power operation: they can use batteries at low voltages, which automatically takes away some the more-stringent safety requirements. But you are not home free, as EMC issues never go away. (For a readable introduction to the power aspects, see the application brief “Product Spotlight: Medical Power Supplies - IEC 60601-1” from CUI, Inc.). The design reviews are major exercises and must follow a formal process and documentation path, Figure 1. You’ll see terms such as overall means of protection (MOP) which combines "means of operator protection" (MOOP) and "means of patient protection" (MOPP).
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This is a very high-level overview of the medical-product design-review process but it does not begin to show the intense depth of details and requirements at every step in the product design, manufacturing, and release journey. (Image source: CUI, Inc.)
Reading through these documents as well as others, my takeaway is this: if you are doing an AC-powered product, don’t even think of attempting your own supply design unless you have a lot of experience in the subject, or have truly unique requirements. Instead, look to buy -- an open-frame, brick, module supply, or whatever you need, and just double-check that the product has all the relevant certifications. Doing so will get you part-way to the “total compliance” goal. You are still not fully there on the power-related EMI/RFI side, as the power cables between the certified supply and your electronics can source EMC issues -- but at least you have “bounded” the potential problem area.
As for the rest of those regulatory requirements on the total design, including EMC, I have mixed feelings. On one hand, they are needed for the bigger picture of keeping EMI/RFI issues to a minimum, as these can affect the product itself, as well as nearby system. On the other hand, they really do slow down design, and affect design strategy: do you plan the design from the start with EMC issues in mind (that’s what most of the pundits and the consultants will say, and it does makes sense); or do you do the best design you can, then figure out how to make it EMC-proof (risky but has its virtues); or do you do a little of both, and to what extent?
My other takeaway from reading the detailed summaries of medical-product EMC and power regulations: if I were a new engineer just starting out, I’d think long and hard before becoming involved in their design (despite any other engineering attractiveness). This is because the pace of forward movement looks to be slow and deliberate, and the regulatory constraints can be very suffocating, the “fault and impact” analysis is intensive. But to each his or her own, as they say.
What’s your view of these standards and requirements related to medical-product design? Too much, too little, or just right? And do you ever wonder who actually sits down and writes all these detailed regulations?
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