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ARCHIVE >  September 2013 Issue >  Tech Watch > 

Dealing With A Different Medical Safety Standard

The third edition of the EN60601-1 safety standard for medical devices and systems has been in force in Europe since mid-2012, and has resulted in disharmony with power module manufacturers. This newest version of the medical safety standard was not nearly as uniform as it might have been, and those power module manufacturers have been forced to cope. Standards are developed to provide uniform rules for manufacturers, and the expectations were high regarding the third edition of the EN60601-1 standard. But even after years of preparation, the third edition brought dramatic differences from the first edition of the standard, from 35 years earlier.

Regarding the latest version of the standard, the United States enjoyed an additional year of grace compared to Europe, enforcing the new edition of the UL60601-1 standard on July 1, 2013, while Europe replaced the old second (from 1995) version of the standard with the third version exactly one year earlier. There were differences in application of the standard as well. The new standard applies to all devices launched onto the European market, even new products with old designs. In the US, the new standard only applies to newly developed products. Canada took a middle road with their CAN/CSA standard. It was put into service at the same time as Europe, but applies only to newly developed products as in the US.

Medical devices often linger in product ranges for five to 10 years, so this last point in particular constitutes a costly drawback for European manufacturers — not only because they had to retrofit new components to old designs, but also due to the high additional costs of certifying their new products. This gray zone of longer lasting years is a heavy burden on smaller companies in particular, which often face the decision of taking current products from the market early while their competitors from the US are allowed to keep selling older products.

The situation is even less clear for devices that fall under the EN/UL 60601-2 standard. The third edition is only mandatory for these products once the second edition no longer applies for 60601-2 products, which may indeed come later. Some countries haven't yet enforced the third edition of the standard, and their products are still certified according to the second edition. Medical engineering products will literally be subject to double standards for years to come.

Extended Risk Management Regulations
While virtually nothing has changed in technical specifications for insulation, risk, management has gained focus as a major area of innovation. Medical device manufacturers will be required to document their risk management process as based on the ISO 14971 model. Specific processes will have to be observed and documented, alongside compliance with fundamental technical standards.

As an example, according to the second edition, devices were allowed to break during testing as long as this didn't pose a risk to patient or operator health; the third edition requires that the system maintains its essential functionality. This must be documented in a risk management file (RMF), which will also require far more contact between the manufacturer and testing authority throughout the development process, especially as results from the testing process must be included in the RMF document.

Separating Patients and Operators
Devices which will have contact with a patient must have proper means of patient protection (MOPP). These devices require two isolation barriers for electrical safety, an important requirement in power modules. The first barrier on the supply side has been implemented in a medical power supply unit (PSU). Reinforced isolated DC/DC converters provide the second isolation barrier between the medical electronics and diagnostics tools, such as endoscopes and ECG electrodes, to double the safety for patients.

One key feature of the third edition of the EN60601-1 standard is that it separates operator protection or how electronic devices provide means of operator protection (MOOP). In theory, clearance and creepage distances as defined in the EN60950-1 standard for electronic equipment are enough for devices that will not have patient contact and intended for providing proper MOOP. But the requirements for very low operating current must also be met according to EN60601-1, so electronic manufacturers are generally wise to choose medically isolated converter modules in any devices or products with MOOP requirements.

As a leading DC/DC converter manufacturer, RECOM supplies a broad range of medical converter modules certified according to the third edition of the EN60601-1 standard with double MOPP for direct patient contact such as our RxxP, RxxP2, RV, REC3.5, and REC6 (1, 2, 3.5, and 6 W) lines. Transformer clearance and creepage distances in these reinforced isolated converters must be three times the size as those used in industrial settings. So far, this has been implemented with primary and secondary windings on opposite sides of a toroidal core separated by a partition wall in the middle. That takes care of the isolation issue, but the magnetic fields would not overlap due to the spatial separation between the two windings. An unpleasant side effect would be a decrease in efficiency in the two transformers resulting in increased heat losses.

RECOM's engineers have developed a small transformer with primary and secondary windings interlocked in such a way as to ensure virtually optimal overlapping magnetic fields despite the creepage and clearance distances required for reinforced isolation. The new converters achieve 15 percent to 20 percent more output than earlier designs in the same casing due to quasi-resonant circuit topology, and are also approved for ambient temperatures to +85°C, or around 15°C higher than most transformers with conventional toroidal-core transformers, due to the low heat loss. Depending upon the transformer type, isolation capacitance values were reduced to 1.5 pF, ensuring lower leakage current as required for medical electronics applications.

From this new transformer design, a complete generation of highly isolated converters for medical applications has emerged, useful for such programming devices as pacemakers, blood gas analyzers, and oximeters. The RxxP and RxxP2 series cover the 1 and 2W classes, and are available in SIP7 casings. The 2W version is available as an RV series in DIP24 casings for pin compatibility with legacy designs. The REC3.5 and REC6 series both provide 3.5 and 6 Watts, respectively, and also come in a DIP24 casing. The models quoted are available with isolation voltages to 8 and 10kVDC.

Apart from these reinforced isolated converters, there are many other product lines in the RECOM range approved for medical applications without patient contact (MOOP), including regulated and unregulated SMD converters with power ratings from 0.25 to 2W (the RxS family) as well as a wide variety of different converters to 6W.


Contact: RECOM Electronic GmbH, Otto-Hann-Strasse 60, 63303 Dreieich, Germany +49 (0)6103-30007-0 fax: +49 (0)6103-30007-62 E-mail: info@recom-electronic.com Web:
www.recom-electronic.com

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