COVER STORY Looking into MOPP


Medical equipment must be designed to meet very stringent technical standards for both patient and operator safety. The mandatory standard for power modules is IEC/EN/UL 60601-1, now in its 3rd edition. Andrew Leake, Dengrove Electronic Components, looks into this further


T


he 3rd edition of 60601-1 introduced many additional requirements, including a new classification system (MOP – Means of Protection). Safety requirements for operators (MOOP – Means of Operator Protection) are less onerous and correspond closely to those laid down in EN 60950-1 "Information technology equipment – Safety". However, more stringent requirements were applied to patient protection (MOPP – Means of Patient Protection), especially in regards to insulation (see table 1). To protect patients against electric shocks, two separate insulation barriers must be implemented (Reinforced Isolation).


Minimum leakage currents Electric currents through the body are dangerous. For a healthy person, currents as low as 40mA can be fatal. For an


The next class is BF (Body Float) with less onerous requirements. It covers applied parts other than CF that are in direct contact with the patient. Such as incubators and diagnostic equipment. Class B (Body) covers applications


where equipment does not come into contact with the patient, such as lasers and lighting systems. Type B applied parts may be connected to earth, while Type BF and CF are 'floating' and must be separated from earth.


Risk management Apart from technical changes, the new standard now demands a formal risk analysis according to ISO 14971. Based on a risk management (RM) matrix, all risks that might potentially arise from the power module must be assessed. The matrix must consider the occurrence,


scheme as the basis for a new European Medical Device Regulation. It is expected that the new regulation will be published this year, with a five year implementation time frame.


EMC regulations tougher In life-support or life-saving devices, even temporary faults and malfunctions caused by electromagnetic interference could be fatal. To prevent such incidents, a revised version of the IEC60601-1-2 "Medical electrical equipment - Part 1-2: General requirements for basic safety and essential performance - Collateral standard: Electromagnetic disturbances - Requirements and tests" was introduced. This is somewhat


magnetic immunity. Equipment must be immune to HF fields up to 2.7GHz, an increase by 0.2GHz. The ESD thresholds have also been increased. For contact discharge, the threshold went up 6kV to 8kV. For air discharge, it has been increased 8kV to 15kV. Table 3 provides an overview of the main changes affecting power modules.


Power modules for medical equipment In order to meet all of the above safety and EMC requirements, a combination of medical grade AC/DC power supplies and DC/DC converters is often the most efficient solution. This approach makes it easier to meet the stringent requirements of operator and


Table 1: Insulation requirements for class up to 250VAC and class up to 43VDC or 30VAC


anaesthetised or ill person this threshold is lower. For adequate protection, medical power supplies must meet tough requirements for leakage and stray currents. The limit values depend on the type and nature of applied part (AP) that is brought into contact with the patient's body. Table 2 shows the applicable limits for normal condition (NC) and single fault condition (SFC).


Medical safety classification - CF, BF and B Type CF (Cardiac Float) is the most stringent classification. It applies to applications where the applied part is in direct conductive contact with the heart, such as heart lung machines and external pacemakers.


probability and impact of the potential risk, based on a rating from 1 to 5 in each category. If the risk index is ≤6 (probability x impact), the risk is deemed acceptably low. If the risk index is higher, suitable measures must be taken to reduce it.


When purchasing power modules, medical equipment integrators must obtain the risk management reports from the power supply manufacturer so that they can perform their own RM analysis. Only if these documents are available is it possible to select a manufacturer which allows certification for the end product. The European Committee for


Electrotechnical Standardisation (CENELEC) has made it clear that it intends to adopt and extend the RM


Table 3: Changes in IEC60601-1-2 relevant to power supplies


confusingly the 4th edition of the EMC standard. So we have 60601-1 third edition and 60601-1-2 4th edition. The old EMC medical standard distinguished between life-supporting and non-life-supporting equipment, this is now gone. For the new standard, only the application environment of the equipment is relevant. It distinguishes between three environments to which different limit values apply: • Healthcare establishments • Domestic environment • Special environments (army, heavy industry)


The EMC 4th edition stipulates more stringent requirements for electro-


Table 2: Limit values for stray currents by device category 8 May 2017 Components in Electronics


patient protection by separating out functional blocks, each with its own MOP system. RECOM offers a broad range of


products certified to 60601-1 3rd edition, 60601-1-2 4th Edition and 60950-1 general safety for use in medical electrical equipment. The medical grade AC/DC power modules are the RACM40, RACM60, RACM100 and RACM150 (40W to 150W respectively), all with 2xMOPP/2xMOOP. For DC/DC applications Recom offers the REM series, in power levels of 1W, 3W, 6W and 10Watts, again with 2xMOPP/250Vac certification.


www.dengrove.com www.cieonline.co.uk


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