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EMC IN MEDICAL APPLICATIONS

Posted by Holger Urban

When every heartbeat counts

It is apparent that the medical electronics market continues to grow and that 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. Due to changes in demographic and social standards, we expect further increases in demand on medical infrastructure within the next few years.

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Figure 1 - Demographic change in Germany

The ability to design customer centric solutions for home care or even robot-aided surgery drives engineering to the edge and to technologies inconceivable just decades ago. The central challenge to designers is to improve health without applying any additional risk to the patient.

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 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 and equipment operating nearby (within a hospital for example). Therefore relevant EMC and safety standards need to be fulfilled. The medical Standard IEC60601-1 focusses on major safety points; some of these are applicable to the mains power entry where Schaffner has a range of solutions.

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Figure 2 - Modern operating room
 

Specifying components for fulfillment of IEC60601-1

Here Schaffner offers a level of product certification which helps designers to meet the safety requirements of European and U.S. 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.”

Medical EMC filters also have to be designed to allow the customer to fulfill MOPP and MOOP (Means of patient 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 an 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

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.

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Figure 3 - Standard Filter with Y-Capacitors

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Figure 4 - B-Version (no added Leakage Current)

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Figure 5 - Schematic of EB-Type Filter

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Figure 6 - Comparison of common mode insertion loss measurement (Standard = black; B-type = red; EB-type = green)

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.

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
  • offer the best size vs performance
  • be designed for typical usage in medical environment

Overall its 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 customized solution.

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