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Understanding EMC principles saves medical compliance testing costs

Tue, 06/19/2012 - 9:57am
Donald L. Sweeney
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Fred is a well respected engineer in the medical industry. He has worked hard designing a new IV Pump and proudly presents it to a test lab for its final compliance testing. But to his dismay it utterly fails its EN 60601-1-2 EMC testing.

Fred can take his product back to his company and re-design it, guessing at what might be the cause of the failure, then make changes, and bring it back for re-testing. This often results in costly over design because unnecessary fixes are added due to lack of understanding the cause of the problem. This technique often requires multiple cycles before compliance is achieved, thereby delaying the product.

In order to save time and have an expert’s assistance, Fred can instead work with an EMC engineer at the test lab to discover what went wrong and to develop specific solutions to bring the device into compliance. This approach generally costs less because the solutions are more fitting to the problem.

However, both scenarios often result in costly fixes such as adding large power line filters, ferrites, shielding, inductors/choke, or even totally redesigning the product. To get Fred’s IV Pump into compliance, it is discovered that he will need to add a $10 low leakage power line filter. Assuming that the filter will not be physically too large to be accommodated in the present design, the filter would then need to be added to every IV Pump already manufactured in anticipation of regulatory compliance, as well as in all future manufactured IV Pumps. If Fred’s company plans to manufacture a total of 1,000 pumps, the added filter will cost them $10,000. Add to that the cost to install the filters, the cost of the extra time spent problem solving and retesting, and the delay in getting Fred’s product to market. These changes may also affect safety compliance which could add even more time to market and increased cost. More than likely Fred’s company plans on selling more than a thousand pumps. Imagine the added expense if they planned to manufacture 100,000 or even a million pumps.

So what went wrong with Fred’s design?
Will the same thing happen to Fred on his next project?
For years EMC (Electromagnetic Compatibility) has been considered black magic. Design engineers could not understand why their system worked in the lab, but failed in the field. Yet, once designers learn the concepts of EMC and how these concepts apply to real life circuits, they can understand what they can do at the beginning of a project to minimize the impact of EMI/RFI. They learn to design their product to be Electromagnetic Compatible. Having EMC knowledge up front would have allowed Fred to design his product such that it may not have needed the commercial filter or allowed him to design it to simply use capacitors or inductors/chokes instead of an entire filter.

If Fred had takes a three-day design seminar before he designed his product, when he discovered the EMI problem during the design stage, he would have had an unlimited number of options to fix the problem and the cost to implement the many options at that time would have been much less. However, once a product has been designed, built and is at the test lab for compliance testing, the options to fix any design flaws are greatly reduced and the cost to implement any fixes is dramatically increased.

By taking an EMC design seminar, Fred would have learned the fundamentals of electromagnetic compatibility, including understanding the many EMC regulatory requirements, such as the Medical EMC Standard EN 60601-1-2. He would have learned the methods of minimizing EMC problems, starting with the design process through final testing and approval, all of which would have been brought to life through hands-on practical application to real life products. He would also have learned how an electronic circuit becomes a radio transmitter, how the physics of even the simplest components such as capacitors, inductors and shielding material can help or hinder compliance and how to control the design to minimize emissions. For example, when designing medical equipment, the leakage current at the power entry is very limited, reducing or eliminating the amount of line-to-ground capacitance that can be used. Fred needed to think this point through very carefully.

Fred would also have been introduced to noise paths; grounding; cabling, shielding, pig tails and cross talk; electric and magnetic fields and how to predict them; digital circuit layout; filter design; and shielding and cabinet design. He would have been lead step-by-step through sample calculations, be introduced to take-home proprietary software, and be led through trouble shooting a product that does not meet the requirements. In addition, after Fred learned to understand EMC design, he would have been given an exclusive, hands-on personal consultation to apply what he had learned to his IV Pump, possibly saving him tens or hundreds of thousands of dollars. One student explained the value of this personalized consultation well when during his product review he exclaimed, “I would not have even understood what you are talking about had I not just taken the class. Now I see what we have been doing wrong!”

Donald L. Sweeney, senior EMC Engineer, is President of D.L.S. Electronic Systems, Inc. He is a graduate of the Department of Electrical Engineering, University of Illinois at Urbana and has over 44 years experience in the EMC and electrical engineering fields. Don specializes in EMC, RFI and EMI consulting and testing. He has taught at the University of Wisconsin and Oakton College. Don has served as a special consultant to the Lawrence Livermore National Laboratory and the Nuclear Regulatory Commission and also consults for companies worldwide. He is founding chairman of U.S. Council of EMC Laboratories (USCEL), has served on the board of directors of the IEEE EMC Society for 13 years, is a member of the IEEE EMC Standards Development Committees, serves as "angel" for several standards and is an iNARTE certified EMC Engineer.Under Don’s direction, D.L.S. Electronic Systems, Inc. provides EMC and product safety testing and consulting services to Medical as well as other types of industries. D.L.S. is a NVLAP accredited test facility, capable of testing electronic equipment to today's high frequency requirements. Its 14 Test chambers and 2 Open Area Test Sites can perform full scan Immunity and Emission testing at frequencies up to 40 GHz.

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