EMC & Circuit Protection
EMC filters in medical technology - high performance requires optimum design
Holger Urban - product marketing manager, Schaffner Group
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ecause of very high safety standard requirements, medical devices must be equipped with special EMC filters. This inevitably entails performance losses. Selecting the right magnetic components and appropriate filter topologies helps to counteract these effects. Technologisation and digitalisation also
affect medical technology. Not least because the changing demography and increasing demands of our society require continuous expansion of medical care. As the international market leader for EMC filters, Schaffner continuously explores new developments in efficient and powerful solutions for medical technology.
Compliance with safety standards In medical engineering, the focus must be on the trouble-free functioning of devices. Whether life support is concerned or damage to health is to be avoided the devices used must not unintentionally affect the patients and compliance with safety standards is stringently required. One of these global standards is IEC 60601-1 which contains requirements for safety and performance features of medical devices.
In addition, guidelines for the direct handling of medical technology for operators (MOOP - Means of Operator Protection) and patients (MOPP - Means of Patient Protection) must be observed in order to guarantee absolute safety. In addition to these safety standards, it is imperative to comply with standards on electromagnetic compatibility (EMC).
EMC - Electromagnetic compatibility Electromagnetic compatibility deals with different propagation types and the suppression of interferences in an electrical system. The electromagnetic compatibility of a device describes its potential to neither influence an electromagnetic environment
Typical filter attenuation
(source of interference) nor to be influenced by it (load).
Digital technology used in an analogue
environment must not interfere with other devices in the vicinity. In order to counteract malfunctions when operating electronic devices, certain statutory protection requirements must be complied with. Interferences typically occur in the conversion of voltages or in digital “clocked” applications and can spread either in a conducted or radiated manner. In addition, common-mode signals and differential-mode signals are distinguished. In order to protect sensitive electronics against conducted signals, EMC filters are used for interference elimination.
How EMC filters work EMC filters suppress interferences in the conducted spectrum (up to 30MHz). X and Y capacitors are used in devices to improve the interference immunity and to reduce the interference emission. X capacitors are located between the phase and neutral conductor of the filter. Together with the leakage inductance of the magnetic component they prevent differential-mode interferences. Y capacitors filter the common-mode component together with the main inductance of the common-mode choke. These filter topologies, as well as their variations, serve to meet the different application-specific limits of interference emission required. The efficiency of a filter is measured and depicted in a standardised
process. This also provides the opportunity to compare different filters. The result can be expressed by the so-called insertion loss in decibels (dB) against frequency.
Leakage current in medical technology
In medical engineering, the leakage current plays an important role. A high leakage current poses a high risk to the patient. In order not to jeopardise the patient’s, possibly fragile, health even more it should therefore be reduced to a minimum and certain statutory limits must be fulfilled.
path, you must additionally pay attention to the above-mentioned safety insulation requirements (MOOP/MOPP).
EMC filters in practical use The powerful EMC filters by Schaffner find uses in a wide number of medical devices. The high-performance EMC filters find applications, for example, in automated syringe pump systems where they help to ensure a reliable and, above all, uniform supply of medicinal substances to a patient. Dialysis machines also require EMC filters - here they make sure that the
The leakage current values can only be complied with if the Y capacitors in the EMC filter are reduced. However, as already mentioned, the Y capacitors serve to compensate the common-mode interferences. The reduction of this important core component in the EMC filter automatically affects the performance of the medical device’s EMC compatibility.
Compensation by a magnetic component Limiting the effect of the Y capacitor may only be compensated by using a magnetic component. Designers have to be aware that a filter only provides a limited space and there is the risk that magnetic components might saturate at high interference levels. Should this be the case, they no longer work as required. Increasing the impedance of a common-mode choke therefore requires the use of higher-quality magnetic material, as used in Schaffner’s filter families FN9262 and FN9266. Meeting the expectations of the insertion loss in this way, ie. using the filter in the interference
18 September 2019 Components in Electronics
systems work consistently and without failure during the patient’s blood purification treatment which extends over several hours.
Schaffner’s new filter family provides a highly performing solution
Optimised for use in medical technology, the newly developed filter families FN9262 and FN9266 B-types (medical version) , have achieved a differentiated classification according to MOPP1. Furthermore, the filters comply with all filter-specific test requirements required by IEC 60601-1. The high-performance filters have been developed in such a way that they can easily and widely find applications in medical technology. Thanks to a perfect balancing of magnetic components and filter topology, the performance losses expected elsewhere are avoided, while fully complying with the high safety requirements.
schaffner.com
www.cieonline.co.uk
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