When every heartbeat counts: EMC in medical applications
01 November 2019
Schaffner_EMC in medical applications
It’s apparent that the medical electronics market continues to grow – and this trend is unlikely to slow down any time soon. Every person who has access to advanced medical care will try to get the best support available and the best treatment possible to increase their quality of life.
This article was originally featured in the November 2019 issue of EPDT magazine [read the digital issue]. Sign up to receive your own copy each month.
Due to changes in demographic and social standards, we expect further increases in demand on medical infrastructure over the next few years. Holger Urban, Product Marketing Manager at EMC & power electronics specialist, Schaffner explains what this means for design engineers working on electronic medical devices.
The ability to design customer centric solutions for home care, wearables for mobility or even robot-aided surgery drives engineering to the edge, and to technologies inconceivable just decades ago. The central challenge for designers of medical devices is to improve health without applying any additional risk to the patient.
Figure 1. Demographic change in Germany
EMC is now considered to be one of the most important design aspects that any new electrical or electronic system design needs to fulfill. It is therefore essential that designers should consider integrating EMC filters as soon as possible in the development phase. Selecting the right EMC filter could save time and prevent additional costs in later stages of the design approval process.
A good example of a medical application with limited space is an automated syringe pump. Such pumps are directly attached to the patient through an insulating plastic hose. The medication delivery must be programmable and repeatable; this means that the control logic has to be reliable. That’s why EMC matters, in order to ensure the pumps continue to operate as intended without interfering with (or being affected by) other pumps or other equipment operating nearby (within a hospital for example). Therefore, relevant EMC and safety standards need to be fulfilled. The medical Standard IEC60601-1 focuses on major safety points; some of these are applicable to the mains power entry, where Schaffner has a range of solutions.
Figure 3. Standard filter with Y-capacitors
Specifying components for fulfillment of IEC60601-1
Here, Schaffner offers a level of product certification which helps designers to meet the safety requirements of both European and US legislations. The approval certificate for Schaffner filters according to IEC60939-3 includes a section where the filters’ compatibility to fulfill the requirements of IEC60601-1 is stated:
“The FN92XX filters (B-types in particular) comply with the requirements of the EN/IEC 60601-1 standard regarding creepage and clearance distances, leakage current and voltage withstand.”
Figure 4. B-version (no added leakage current)
Medical EMC filters also have to be designed to allow design engineers to fulfill MOPP and MOOP (Means of Patient Protection and Means of Operator Protection) for any medical application. Depending on the level of insulation needed, design of a custom filter solution can be considered.
The leakage current definition for electrical medical devices is another important topic, which has the same purpose of reducing the risk to the patient. There are number of different connections to consider. The most severe level within the standard is CF (Class C floating type connection suitable for cardiac application) applied part, which is limited to 10µA in normal condition, and 50µA in a single fault condition. Considering parasitic effects in a system, the filter should not introduce any additional leakage current. However in less critical applications, EMC filters with very low leakage current can be considered as well. Such filters have higher performance compared to filters without any leakage currents. Leakage currents are directly related to the value of capacitors used in filters connected between Lines to Protective Earth (PE) (Y-capacitors or Cy).
Performance levels with reduced leakage current
Figure 5. Schematic of EB-type filter
Schaffner offers standard solutions for different levels of leakage current requirements. In general, the solution for medical applications is the so-called B-type filters. These filters do not have any capacitance to PE and therefore do not add any leakage current to the system. It must be noted that the overall leakage current for the whole system needs to be determined, even with a filter which does not introduce any leakage current.
With removal of (Cy) capacitance to PE, the overall performance of the filter is reduced compared to the standard filter with Cy. Schaffner also offers so-called EB-type filter to compensate some of lost performance as a result of no Cy.
In addition to the performance enhancement, EB-type filters increase immunity to electrical fast transients compared to the B-type. This will help customers comply with the IEC/EN61000-4-4 immunity tests.
Figure 6. Comparison of common mode insertion loss measurement (standard = black; B-type = red; EB-type = green)
Therefore Schaffner EB-Type Filters can be the best performing filters available in its class for a reliable medical electrical design.
To conclude, EMC filters for medical applications should:
• fulfill the most stringent leakage current regulations
Schaffner EMC filter
• offer the best size versus performance
• be designed for typical usage in medical environment
Overall, it’s clear devices should help to increase the health of patient and should not pose any potential risk when applied to a human body. With a Schaffner filter, customers can easily solve their EMC issues and get products certifications without applying any additional risk to the patient. Schaffner not only offers a number of “off the shelf” EMC filtering solutions for medical applications but also works closely with customers who require customised solution.
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