Philip Lechner, Product Marketing – Power, Avnet Abacus
One of the areas that electronics has been making a significant impact in recent years is in the medical sector. This increase in health and medical services utilizing high tech equipment to monitor, diagnose and treat patients has seen a large increase in new suppliers to the sector. However, the medical sector differs from most other sectors in the stringency of its regulations that are intended to protect both medical staff and patients.
In particular, the Internet of Things (IoT) has been a strong driver of medical innovation. IoT devices can constantly monitor patients and report health statuses back to a central server. In some cases, these devices can also act on the patient. The devices can be found in controlled environments, such as hospitals, or in uncontrolled environments, like patients’ homes.
The regulations concerning medical devices go beyond safety. One area of particular concern is electromagnetic compatibility, as it could be very dangerous if the emissions from one device interfered with the operation of other devices. It is extremely important to ensure that medical devices neither create excessive emissions nor are affected by emissions from other sources.
Governments around the world have taken note of these new trends for connected medical devices and have begun analyzing the situation and formulating standards for manufacturers to follow. Existing legislation, which was intended to focus on specific device categories, is now being replaced with flexible legislation that takes into account the additional complexity of today’s devices that are often intended to perform more than a single function.
One constant in all medical devices is the need for power. Designers of powered medical devices look to IEC 60601 legislation, which is the standard that has set out the rules for medical equipment since it was first introduced in 1977. The legislation has seen three major revisions during that 40-year period, and now the fourth revision is now in progress.
The initial scope of IEC 60601 was to ensure the safety of medical equipment, so that it would not cause electric shocks or short circuit if it stopped working correctly. Later revisions of the legislation concentrated on how defects could affect the “essential performance” of the product and the hazards that could result from that impaired performance.
The third edition of IEC 60601 introduced a major change to the legislation. The standard came into force in the EU on June 1st 2012 and was followed by Canada and the US in April and June 2013 respectively. It required the producer of each complete medical product to undertake a formal risk assessment conforming to that detailed in ISO 14971. The manufacturer must identify any hazard possible through the operation of the device and then appraise the risk and detail the solutions in place to address the risk over every stage of the device’s lifecycle. The risk management of IEC 60601 is intended to cover the device’s safety and essential performance, but it is also required to take into account all the subsystems that make up the product and not only the end product and process. These subsystems obviously include the power supply.
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Figure 2. Bel Power Solutions ABC/MBC41 Series
The third edition of IEC 60601 also contained another major change – the definition of electrical contact with patients and operators. The change was made to help define the ISO 14971 risk assessment process and state the protections required for both patients and operators. In the previous editions of IEC 60601, three different scenarios were laid out to define the different types of interaction of equipment with the patient. Devices that had no electrical contact with the body of the patient were classified Type B (Body). Type BF (Body Floating) was the classification for equipment that did make electrical contact with the patient in all areas except the heart. The third type, CF (Cardiac Floating), was used to designate the equipment that has a floating electrical connection to the heart.
The means of protection (MOP) requirement, as stated in the third edition of IEC 60601, defines the required isolation between electrically charged circuitry, other devices that could come into contact with the device, and any people around it. For power supplies, the level of protection stipulates the specifications required, such as creepage, clearances, insulation and earth connections.
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Figure 3. Murata MVAC400 Series
Each of the two types of MOP has sub-levels. To give a practical example, if the initial risk assessment finds that a system should be classed as level two for means of operator protection (MOOP), then it should be designed with an isolation of 3,000V AC and a creepage distance of 5mm. A system that has been assessed as less dangerous may be classed as level one MOOP and would have an isolation of 1,500V AC and creepage of 2.5mm.
The process of conformance with the third edition of IEC 60601 has increased cooperation between the equipment manufacturers and its subsystem suppliers to ensure the final product conforms to the legislation and offers maximum safety protection to patients and operators.
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Figure 4. MWL MSP-100
The fourth edition of IEC 60601 was published in 2014 and this has caused a further move in design requirements for medical equipment. Later in 2014, the US Food and Drug Administration produced a guidance note for manufacturers of medical equipment to recommend that they start developing medical products in accordance with the fourth edition, as the law is expected to come into practice in the near term. As expected, the fourth edition makes a number of additions to the legislation. The most important of these changes are new EMC immunity requirements and a more comprehensive risk analysis. In addition to the new EMC requirements for radiated and conducted emissions, the new legislation calls for large increases in electrostatic discharge (ESD) protection levels, as well as levels of allowable voltage dips and power interruptions. Another change in the regulation has been made to take into account the higher levels of complex wireless communications found in today’s equipment. The fourth edition tightens the requirements for immunity from RF transmissions, giving medical devices better protection.
The environment in which the equipment will be used is also recognized in the fourth edition. The level of immunity required for devices is dependent on whether it will be used in a protected professional medical location, for example in a hospital, or in another location, such as a home or in an industrial environment. That is not to say that everyone is ready to change over. Regions around the globe are proceeding towards adoption of the fourth edition IEC 60601 regulations at their own pace. However, as the FDA stopped allowing declarations of conformity for the third edition at the start of April this year, the other regions are expected to pick up pace in their own adoption. Many manufacturers will comply with the fourth edition voluntarily to allow products to have access to the widest possible number of customers, and they can only do that by complying with the most stringent regime, which at this time is the US.